The changes in tensile strength and elongation at break of films after biodegradation with selected fungi are shown in Figure 1. It has been reported that the changes in tensile strength and elongation loss are excellent indicators of degradation (Reddy et al., 2008).

Fig. 1. Mechanical properties of films after biodegradation

Although little weight loss of polyethylene was observed after 84 days of biodegradation, a marked reduction in tensile strength imply that both *Penicillium funiculosum* and mixed fungi population excrete enzymes able to cleave macromolecules of LDPE. Slight increase in the elongation at break in samples incubated with mixed population of fungi, could be tentatively attributed to a sort of plasticisation effect exerted by low molecular weight fractions produced in the first stage of the biodegradation of the polymer matrix (Chiellini et al., 2003). After 84 days of biodegradation, the tensile strength of film containing 30% Bionolle® decreased by about 20%. At this time, elongation at break changed by about 74% and 52% after incubation with *Penicillium funiculosum* and mixed fungi population, respectively. Far-advanced decomposition of 40/60 blend, prevented determination of its mechanical properties.

Data obtained from FTIR spectra (spectra are presented elsewhere (Łabużek et al.) of examined films showed an increase in carbonyl and double bond indices, except for LDPE (decrease in carbonyl index by 57%), incubated with mixed population of fungi (Łabużek et al., 2006a). Increase in the internal double bond index is in accordance with the biodegradation mechanism suggested by Albertsson et al. who reported on the formation of terminal double bonds as a result of exposure to biotic environment (Albertsson et al., 1987). This can be attributed to biotic dehydrogenation (Chiellini et al., 2003). However, in contrast

Biodegradation of Pre-Aged Modified Polyethylene Films 653

experiments were conducted in minimal solid medium, it is obvious that solid surface of

b)

 Fig. 3. SEM micrographs of neat LDPE film after biodegradation with a) *Aspergillus niger*

As a result of fungal degradation, peeling and cracking in texture of film containing 15% Bionolle® were visible (Figure 4). The entire surface of film was densely covered with spores belonging to *Aspergillus niger* (Figure 4a) and *Aureobasidium pullulans* (Figure 4b). Scarce hyphae of *Paecilomyces varioti* (Figure 4c), *Penicillium funiculosum* (Figure 4d) and mixed population of fungi (Figure 4f) colonised both the edges and the surface of film. Agglomerations of *Trichoderma viride* conidiophores (Figure 4e) inhabited primarily the

d)

The destructive process of biodegradation was very prominent in film containing 30% Bionolle®. Small holes and cracks, surface irregularities, peeling and exfoliation appeared. *Aspergillus niger* (Figure 5a), *Paecilomyces varioti* (Figure 5c), *Penicillium funiculosum* (Figure 5d) and mixed population of fungi (Figure 5h) produced a well-developed mycelium over the entire surface of the film. Hyphae and conidiophores of *Penicillium ochrochloron* (Figure 5e), *Scopulariopsis brevicaulis* (Figure 5f) and *Trichoderma viride* (Figure 5g) was scattered on the film surface. *Aspergillus terreus* (Figure 5b), almost unable to colonise 85/15 composition, introduced deep cracks and holes, suggesting that the fungi penetrate into the sample

After 84-day incubation with filamentous fungi the most intense changes were found on the surface of 40/60 composition. Hyphae and conidiophores of *Aspergillus niger* (Figure 6a), *Aspergillus terreus* (Figure 6b), *Aureobasidium pullulans* (Figure 6c) and *Trichoderma viride*

b) *Aureobasidium pullulans* c) *Paecilomyces varioti* d) *Penicillium funiculosum*

edges of the sample.

a)

c)

matrix during degradation.

LDPE, at least for some fungi, served as the source of carbon and energy.

with study of Albertsson et al., we found an increase in the amount of carbonyl residues (up to 525%) in LDPE after 84 days of incubation with *Penicillium funiculosum* (Albertsson et al., 1987). Carbonyl residues have been reported as major products formed in the presence oxidoreductases (Sudhakar et al., 2008).

Important aspect during the biodegradation of a material is the sustained growth of microorganisms during the entire process (Abrusci et al., 2011). The changes on the surface of polymers as a result of biodegradation are no less important (Nowak et al., 2011).

Figure 2 shows the micrographs of control films.

Fig. 2. SEM micrographs showing surface of control films a) LDPE b) composition 85/15 c) composition 70/30 d) composition 40/60

The photomicrograph shows that the surface of non-degraded material is smooth, without cracks and holes.

Neat polymer samples after biodegradation with filamentous fungi are presented in Figures 3-6.

*Paecilomyces varioti* (Figure 3c) and *Penicillium funiculosum* (Figure 3d) expanded their colonies over the entire surface of neat LDPE. Apart from hyphae and conidiophores, samples were covered with characteristic spores. *Aspergillus niger* (Figure 3a), *Aspergillus terreus*, *Aureobasidium pullulans* (Figure 3b), *Penicillium ochrochloron*, *Scopulariopsis brevicaulis*, *Trichoderma viride* and mixed fungal population grew less rapidly and primarily on the edges of the sample. Considerable change in mechanical properties (Figure 1) and FTIR spectrum of LDPE proved that growth of fungi cannot be considered only as a result of the surface moistness (Sahebnazar et al., 2010). Moreover, knowing that the biodegradation

with study of Albertsson et al., we found an increase in the amount of carbonyl residues (up to 525%) in LDPE after 84 days of incubation with *Penicillium funiculosum* (Albertsson et al., 1987). Carbonyl residues have been reported as major products formed in the presence

Important aspect during the biodegradation of a material is the sustained growth of microorganisms during the entire process (Abrusci et al., 2011). The changes on the surface

of polymers as a result of biodegradation are no less important (Nowak et al., 2011).

b)

 Fig. 2. SEM micrographs showing surface of control films a) LDPE b) composition 85/15 c)

The photomicrograph shows that the surface of non-degraded material is smooth, without

d)

Neat polymer samples after biodegradation with filamentous fungi are presented in Figures

*Paecilomyces varioti* (Figure 3c) and *Penicillium funiculosum* (Figure 3d) expanded their colonies over the entire surface of neat LDPE. Apart from hyphae and conidiophores, samples were covered with characteristic spores. *Aspergillus niger* (Figure 3a), *Aspergillus terreus*, *Aureobasidium pullulans* (Figure 3b), *Penicillium ochrochloron*, *Scopulariopsis brevicaulis*, *Trichoderma viride* and mixed fungal population grew less rapidly and primarily on the edges of the sample. Considerable change in mechanical properties (Figure 1) and FTIR spectrum of LDPE proved that growth of fungi cannot be considered only as a result of the surface moistness (Sahebnazar et al., 2010). Moreover, knowing that the biodegradation

oxidoreductases (Sudhakar et al., 2008).

composition 70/30 d) composition 40/60

cracks and holes.

3-6.

c)

a)

Figure 2 shows the micrographs of control films.

experiments were conducted in minimal solid medium, it is obvious that solid surface of LDPE, at least for some fungi, served as the source of carbon and energy.

Fig. 3. SEM micrographs of neat LDPE film after biodegradation with a) *Aspergillus niger* b) *Aureobasidium pullulans* c) *Paecilomyces varioti* d) *Penicillium funiculosum*

As a result of fungal degradation, peeling and cracking in texture of film containing 15% Bionolle® were visible (Figure 4). The entire surface of film was densely covered with spores belonging to *Aspergillus niger* (Figure 4a) and *Aureobasidium pullulans* (Figure 4b). Scarce hyphae of *Paecilomyces varioti* (Figure 4c), *Penicillium funiculosum* (Figure 4d) and mixed population of fungi (Figure 4f) colonised both the edges and the surface of film. Agglomerations of *Trichoderma viride* conidiophores (Figure 4e) inhabited primarily the edges of the sample.

The destructive process of biodegradation was very prominent in film containing 30% Bionolle®. Small holes and cracks, surface irregularities, peeling and exfoliation appeared. *Aspergillus niger* (Figure 5a), *Paecilomyces varioti* (Figure 5c), *Penicillium funiculosum* (Figure 5d) and mixed population of fungi (Figure 5h) produced a well-developed mycelium over the entire surface of the film. Hyphae and conidiophores of *Penicillium ochrochloron* (Figure 5e), *Scopulariopsis brevicaulis* (Figure 5f) and *Trichoderma viride* (Figure 5g) was scattered on the film surface. *Aspergillus terreus* (Figure 5b), almost unable to colonise 85/15 composition, introduced deep cracks and holes, suggesting that the fungi penetrate into the sample matrix during degradation.

After 84-day incubation with filamentous fungi the most intense changes were found on the surface of 40/60 composition. Hyphae and conidiophores of *Aspergillus niger* (Figure 6a), *Aspergillus terreus* (Figure 6b), *Aureobasidium pullulans* (Figure 6c) and *Trichoderma viride*

Biodegradation of Pre-Aged Modified Polyethylene Films 655

b)

d)

e) f)

g) h)

Fig. 5. SEM micrographs of neat 70/30 composition after biodegradation with a) *Aspergillus niger* b) *Aspergillus terreus* c) *Paecilomyces varioti* d) *Penicillium funiculosum* e) *Penicillium ochrochloron* f) *Scopulariopsis brevicaulis* g) *Trichoderma viride* h) mixed fungal

population

a)

c)

(Figure 6g) grew out directly from the polymer sample. However, changes induced by the action of these microorganisms deep and distinct. Dense network of fractures was particularly visible after incubation with *Aspergillus terreus*. *Aspergillus niger* and *Aureobasidium pullulans* caused massive exfoliation of the plastic edges. Although *Penicillium ochrochloron* (Figure 6e) and *Scopulariopsis brevicaulis* (Figure 6f) created mycelium, a considerable part of the film surface was found to be unaffected. Loss of integrity of film resulted into fragile surface entirely covered by dense mycelia of *Penicillium funiculosum* (Figure 6d) and mixed population of fungi (Figure 6h).

Fig. 4. SEM micrographs of neat 85/15 composition after biodegradation with a) *Aspergillus niger* b) *Aureobasidium pullulans* c) *Paecilomyces varioti* d) *Penicillium funiculosum* e) *Trichoderma viride* f) mixed fungal population

(Figure 6g) grew out directly from the polymer sample. However, changes induced by the action of these microorganisms deep and distinct. Dense network of fractures was particularly visible after incubation with *Aspergillus terreus*. *Aspergillus niger* and *Aureobasidium pullulans* caused massive exfoliation of the plastic edges. Although *Penicillium ochrochloron* (Figure 6e) and *Scopulariopsis brevicaulis* (Figure 6f) created mycelium, a considerable part of the film surface was found to be unaffected. Loss of integrity of film resulted into fragile surface entirely covered by dense mycelia of *Penicillium funiculosum*

b)

d)

*niger* b) *Aureobasidium pullulans* c) *Paecilomyces varioti* d) *Penicillium funiculosum*

e) *Trichoderma viride* f) mixed fungal population

e) f)

Fig. 4. SEM micrographs of neat 85/15 composition after biodegradation with a) *Aspergillus*

(Figure 6d) and mixed population of fungi (Figure 6h).

a)

c)

Fig. 5. SEM micrographs of neat 70/30 composition after biodegradation with a) *Aspergillus niger* b) *Aspergillus terreus* c) *Paecilomyces varioti* d) *Penicillium funiculosum* e) *Penicillium ochrochloron* f) *Scopulariopsis brevicaulis* g) *Trichoderma viride* h) mixed fungal population

Biodegradation of Pre-Aged Modified Polyethylene Films 657

Weight variations of LDPE film and LDPE/Bionolle® compositions recorded after exposing

Photodegradation 0,06 0,05 0,07 0,06 Thermodegradation 0,02 0,03 0,13 0,1 Photo- and thermodegradation 0,03 0,04 0,09 0,26 Hydrolysis 0 0,04 0,07 0,38 Photodegradation and hydrolysis 0,02 0,05 0,07 0,27 Thermodegradation and hydrolysis 0,02 0,03 0,08 0,34 Photo- thermodegradation and hydrolysis 0 0,04 0,09 0,31

Regardless of the type and combination of abiotic aging factors, there were no significant differences in weight loss observed for LDPE and its compositions containing up to 30% Bionolle®. More significant decrease of the weight in film containing 60% polyester was recorded not till then it was subjected to hydrolysis or when more than one aging factor was used during degradation experiments. Oxidative aging of films did not accelerate their loss of mass, most likely due to the presence of crosslinks evolved under the action of radiation and/or heat (Ojeda et al., 2011). It is often reported that, in LDPE films, crosslinking competes with the chain scission mechanism depending on the oxygen concentration at the

Changes in some mechanical properties of films after abiotic degradation are presented in

Values obtained by measuring elongation at break of polyethylene after photodegradation, thermodegradation and photothermodegradation slightly increased. As it was reported above, due to the formation of cross-linking bonds between the polyethylene chains. However, reduction in the mechanical properties after hydrolysis was observed. This decrease can be attributed to the chain scission of the polymer which, in this case, most intensively proceeded in films exposed earlier to both UV radiation and heat. This macromolecular chain scission is the cause of embrittlement of films (Abrusci et al., 2011). Amongst modified films, sensitivity toward abiotic treatment in terms of loss in the mechanical properties can be arranged as follows: 40/60>85/15>70/30. It seems that the exposure of the films containing 15% and 30% polyester to abiotic oxidation has accelerated their subsequent hydrolysis. On the contrary, in film consisted in most part of polyester, the most significant decrease in tensile strength by about 81% and elongation at break reduced by 99% was observed in samples subjected only to hydrolysis. From the above results it can be concluded that the samples with low content of Bionolle® behaved more like polyethylene while 40/60 composition more like polyester. It is known, that in hydrolytic degradation of biodegradable polyesters, elongation at break is the most sensitive property

LDPE/Bionolle® film compositions 100/0 85/15 70/30 40/60 Weight loss, %

**3.2 Abiotic degradation**

to abiotic treatment are shown in Table 3.

Table 3. Weight loss of films after abiotic aging

reaction site (Feuilloley et al., 2005).

among the tensile properties (Tsuji et al., 2006).

Figure 7.

**Abiotic degradation processes**

Fig. 6. SEM micrographs of neat 40/60 composition after biodegradation with a) *Aspergillus niger* b) *Aspergillus terreus* c) *Aureobasidium pullulans* d) *Penicillium funiculosum* e) *Penicillium ochrochloron* f) *Scopulariopsis brevicaulis* g) *Trichoderma viride* h) mixed fungal population

## **3.2 Abiotic degradation**

656 Scanning Electron Microscopy

b)

d)

e) f)

g) h)

*Aspergillus niger* b) *Aspergillus terreus* c) *Aureobasidium pullulans* d) *Penicillium funiculosum* e) *Penicillium ochrochloron* f) *Scopulariopsis brevicaulis* g) *Trichoderma viride* h) mixed fungal

Fig. 6. SEM micrographs of neat 40/60 composition after biodegradation with a)

population

a)

c)

Weight variations of LDPE film and LDPE/Bionolle® compositions recorded after exposing to abiotic treatment are shown in Table 3.

Table 3. Weight loss of films after abiotic aging

Regardless of the type and combination of abiotic aging factors, there were no significant differences in weight loss observed for LDPE and its compositions containing up to 30% Bionolle®. More significant decrease of the weight in film containing 60% polyester was recorded not till then it was subjected to hydrolysis or when more than one aging factor was used during degradation experiments. Oxidative aging of films did not accelerate their loss of mass, most likely due to the presence of crosslinks evolved under the action of radiation and/or heat (Ojeda et al., 2011). It is often reported that, in LDPE films, crosslinking competes with the chain scission mechanism depending on the oxygen concentration at the reaction site (Feuilloley et al., 2005).

Changes in some mechanical properties of films after abiotic degradation are presented in Figure 7.

Values obtained by measuring elongation at break of polyethylene after photodegradation, thermodegradation and photothermodegradation slightly increased. As it was reported above, due to the formation of cross-linking bonds between the polyethylene chains. However, reduction in the mechanical properties after hydrolysis was observed. This decrease can be attributed to the chain scission of the polymer which, in this case, most intensively proceeded in films exposed earlier to both UV radiation and heat. This macromolecular chain scission is the cause of embrittlement of films (Abrusci et al., 2011). Amongst modified films, sensitivity toward abiotic treatment in terms of loss in the mechanical properties can be arranged as follows: 40/60>85/15>70/30. It seems that the exposure of the films containing 15% and 30% polyester to abiotic oxidation has accelerated their subsequent hydrolysis. On the contrary, in film consisted in most part of polyester, the most significant decrease in tensile strength by about 81% and elongation at break reduced by 99% was observed in samples subjected only to hydrolysis. From the above results it can be concluded that the samples with low content of Bionolle® behaved more like polyethylene while 40/60 composition more like polyester. It is known, that in hydrolytic degradation of biodegradable polyesters, elongation at break is the most sensitive property among the tensile properties (Tsuji et al., 2006).

Biodegradation of Pre-Aged Modified Polyethylene Films 659

Fig. 8. FTIR spectra of films before and after degradation with selected abiotic and biotic

factors a) LDPE b) 70/30 composition c) 40/60 composition

Fig. 7. Changes in some mechanical properties of films after abiotic degradation A) and B) LDPE C) and D) 85/15 blend E) and F) 70/30 blend G) and H) 40/60 blend

Figure 8 shows FTIR spectra of samples before and after exposing to selected abiotic and biotic factors.

Fig. 7. Changes in some mechanical properties of films after abiotic degradation A) and

Figure 8 shows FTIR spectra of samples before and after exposing to selected abiotic and

B) LDPE C) and D) 85/15 blend E) and F) 70/30 blend G) and H) 40/60 blend

biotic factors.

Fig. 8. FTIR spectra of films before and after degradation with selected abiotic and biotic factors a) LDPE b) 70/30 composition c) 40/60 composition

Biodegradation of Pre-Aged Modified Polyethylene Films 661

Compared to the smooth control film (Figure 2), only some irregularities were visible on the surface of 70/30 composition exposed to UV radiation (Figure 9a). After thermodegradation numerous and well distributed oval cavities with a diameter 1-8 mm were seen all over the surface (Figure 9b). Observations of changes resulting from the individual oxidative processes (photo- and thermodegradation) were helpful in interpreting the data obtained after simultaneous action of UV radiation and heat (Figure 9c). It is evident that both processes act antagonistically. This observation confirms the results obtained by other methods. The smallest weight loss and negligible increase in carbonyl index, probably resulted from the fact that sites of potential chain oxidation (macro radicals) were involved in the crosslinks formation (H-S. Kim & H-J Kim, 2008). Hence, observed reinforcement of plastics after photothermodegradation. However, the most pronounced changes were observed after hydrolysis of the film (Figure 9d). Holes on the surface were less in number but bigger in size than cavities observed after thermodegradation. Studies conducted by other researchers suggest that hydrolysis, in contrast to the photodegradation, occured mainly in the amorphous region of polymer (Bikiaris et al., 2006; Tsuji et al., 2006). Judging by the size, shape and distribution of holes, identical to that observed after thermodegradation, it can be concluded, that during the heat-treatment, the amorphous phase breaks down in the first place. This is due to the fact that, under the impact of warmth, the mobility of macromolecules within amorphous region increases more

significantly, therefore they become more prone to degradation.

a)

c)

b)

There were no visible changes of film texture after photo- and photothermodegradation (Figure 10a and c). Again, after another analysis of 40/60 composition, it could be stated that the behaviour of the composition under the influence of different factors is affected mainly by a large quantity of polyester in polyethylene. These findings are in agreement with our previous study on photodegradation of PBSA (Łabużek et al., 2006b). Thermodegradation of

d)

Fig. 10. SEM micrographs of 40/60 composition after a) photodegradation

b) thermodegradation c) photothermodegradation d) hydrolysis

The data showed that the area corresponding to the carbonyl region has grown after abiotic degradation of all films indicating the formation of low molecular weight carbonyl compounds as a result of oxidation and/or hydrolysis. Carbonyl index of LDPE was increased by 25%(photothermodegradation)-650%(thermodegradation). As for polyethylene, the greatest impact on the oxidation of 70/30 composition had thermodegradation (230%) while the smallest - photothermodegradation (196%). Similar correlations were also observed for internal double bond index, which after thermodegradation of polyethylene and 70/30 composition increased by 167% and 316%, respectively. For film containing 60% Bionolle®, the largest increase in carbonyl index, amounting 50%, was found after hydrolysis. Such low degree of oxidation resulted probably from the fact that low-molecular fractions of polymer diffused out of the polymer matrix during the hydrolysis of film (Göpferich, 1996). The above findings suggest that single processes, especially thermo-oxidation, are more efficient in polymer degradation than simultaneous action of UV radiation and heat. These findings are in agreement with (Ram et al., 1980) who claims that the presence of oxygen in conjunction with high temperatures, plays more significant role in the increase of carbonyl concentration than when combined with UV exposure. Moreover, the air temperature as a critical factor increases the rate of various chemical reactions associated with degradation (Briassoulis et al., 2004). Additionally, as mentioned earlier, thermodegradation occurs throughout the bulk of polymer, not only on its surface.

Micrographs of films exposed to selected abiotic factors are presented in Figures 9 and 10.

Fig. 9. SEM micrographs of 70/30 composition after a) photodegradation b) thermodegradation c) photothermodegradation d) hydrolysis

The data showed that the area corresponding to the carbonyl region has grown after abiotic degradation of all films indicating the formation of low molecular weight carbonyl compounds as a result of oxidation and/or hydrolysis. Carbonyl index of LDPE was increased by 25%(photothermodegradation)-650%(thermodegradation). As for polyethylene, the greatest impact on the oxidation of 70/30 composition had thermodegradation (230%) while the smallest - photothermodegradation (196%). Similar correlations were also observed for internal double bond index, which after thermodegradation of polyethylene and 70/30 composition increased by 167% and 316%, respectively. For film containing 60% Bionolle®, the largest increase in carbonyl index, amounting 50%, was found after hydrolysis. Such low degree of oxidation resulted probably from the fact that low-molecular fractions of polymer diffused out of the polymer matrix during the hydrolysis of film (Göpferich, 1996). The above findings suggest that single processes, especially thermo-oxidation, are more efficient in polymer degradation than simultaneous action of UV radiation and heat. These findings are in agreement with (Ram et al., 1980) who claims that the presence of oxygen in conjunction with high temperatures, plays more significant role in the increase of carbonyl concentration than when combined with UV exposure. Moreover, the air temperature as a critical factor increases the rate of various chemical reactions associated with degradation (Briassoulis et al., 2004). Additionally, as mentioned earlier, thermodegradation occurs throughout the bulk of

Micrographs of films exposed to selected abiotic factors are presented in Figures 9 and 10.

b)

d)

Fig. 9. SEM micrographs of 70/30 composition after a) photodegradation

b) thermodegradation c) photothermodegradation d) hydrolysis

polymer, not only on its surface.

a)

c)

Compared to the smooth control film (Figure 2), only some irregularities were visible on the surface of 70/30 composition exposed to UV radiation (Figure 9a). After thermodegradation numerous and well distributed oval cavities with a diameter 1-8 mm were seen all over the surface (Figure 9b). Observations of changes resulting from the individual oxidative processes (photo- and thermodegradation) were helpful in interpreting the data obtained after simultaneous action of UV radiation and heat (Figure 9c). It is evident that both processes act antagonistically. This observation confirms the results obtained by other methods. The smallest weight loss and negligible increase in carbonyl index, probably resulted from the fact that sites of potential chain oxidation (macro radicals) were involved in the crosslinks formation (H-S. Kim & H-J Kim, 2008). Hence, observed reinforcement of plastics after photothermodegradation. However, the most pronounced changes were observed after hydrolysis of the film (Figure 9d). Holes on the surface were less in number but bigger in size than cavities observed after thermodegradation. Studies conducted by other researchers suggest that hydrolysis, in contrast to the photodegradation, occured mainly in the amorphous region of polymer (Bikiaris et al., 2006; Tsuji et al., 2006). Judging by the size, shape and distribution of holes, identical to that observed after thermodegradation, it can be concluded, that during the heat-treatment, the amorphous phase breaks down in the first place. This is due to the fact that, under the impact of warmth, the mobility of macromolecules within amorphous region increases more significantly, therefore they become more prone to degradation.

Fig. 10. SEM micrographs of 40/60 composition after a) photodegradation b) thermodegradation c) photothermodegradation d) hydrolysis

There were no visible changes of film texture after photo- and photothermodegradation (Figure 10a and c). Again, after another analysis of 40/60 composition, it could be stated that the behaviour of the composition under the influence of different factors is affected mainly by a large quantity of polyester in polyethylene. These findings are in agreement with our previous study on photodegradation of PBSA (Łabużek et al., 2006b). Thermodegradation of

Biodegradation of Pre-Aged Modified Polyethylene Films 663

Changes in some mechanical properties of film samples after the abiotic degradation and

A B

C D

E F

 Photodegradation and biodegradation Thermodegradation and biodegradation Photothermodegradation and biodegradation Hydrolysis and biodegradation

Fig. 11. Changes in some mechanical properties of films after abiotic and biotic degradation

A significant increase in elongation of LDPE after thermo-, photo-thermo- and biodegradation with both *Penicillium funiculosum* and mixed populations of fungi was noted. These values were significantly higher than observed after biodegradation of neat polyethylene. The highest impact of abiotic pretreatment on the subsequent biodegradability was observed for 85/15 composition which elongation decreased by 9,26%- 16,82% as compared to 3,09%-8,49% for the film subjected only to biodegradation. As seen from Figure 11 there is a difference concerning the influence of abiotic aging to biodegradation of modified films between mixed fungi population and *Penicillium*

A) and B) LDPE C) and D) 85/15 blend E) and F) 70/30 blend.

Control *Penicillium funiculosum* Mixed fungal population

biodegradation are shown in Figure 11.

film containing 60% Bionolle® resulted in the formation of regular holes in small quantities (Figure 10b). The most significant surface fragmentation was observed after hydrolysis of the film (Figure 10d). As is evident from SEM, amorphous regions are preferably hydrolysed, revealing the crystalline ones which in turn affects the mechanical properties. It is postulated that mechanical properties, especially elongation at break (see Figure 7G and H), depend more on changes occurring in the amorphous phase (Briassoulis et al., 2004).

## **3.3 Influence of abiotic degradation on the rate of biodegradation**

*Penicillium funiculosum* and mixed population of fungi were used in studies on biodegradation of abiotically aged films, since, in previous stage of experiments, they exhibited the greatest ability to degrade examined plastics.

Table 4 shows the percentage weight loss of pre-aged LDPE film and LDPE/Bionolle® compositions after biodegradation with *Penicillium funiculosum* and mixed fungal population.

Table 4. Weight loss of pre-aged films after biodegradation

Based on material weight loss it cannot be clearly determined what impact have abiotic processes had on subsequent biodegradation of the material. Contrary to LDPE, photodegradation, thermodegradation and photothermodegradation of modified polyethylene films accelerated their biodegradation. Percentage weight loss of LDPE films modified with 30% Bionolle® after biodegradation with *Penicillium funiculosum* and mixed population of fungi increased by 15% and 13%; 19% and 28%; 17% and 4% in comparison to weight loss of neat films, respectively. The biodegradative propensity of abiotically degraded 40/60 composition was also markedly affected. The pre-treated film after being exposed to *Penicillium funiculosum* and mixed population of fungi exhibit a mass loss of 15- 19% and 4-28% higher than observed for control film. However, the biggest mass loss was observed after hydrolytic aging and biodegradation with *Penicillium funiculosum*. Biodegradation of films containing 15%, 30% and 60% polyester after prior hydrolysis increased by 104.5%, 75.8% and 24%, respectively. Considering percentage weight loss after hydrolysis and biodegradation of 40/60 composition, we have to remark, that any amount greater than 60% meant the degradation of polyethylene.

film containing 60% Bionolle® resulted in the formation of regular holes in small quantities (Figure 10b). The most significant surface fragmentation was observed after hydrolysis of the film (Figure 10d). As is evident from SEM, amorphous regions are preferably hydrolysed, revealing the crystalline ones which in turn affects the mechanical properties. It is postulated that mechanical properties, especially elongation at break (see Figure 7G and H), depend more on changes occurring in the amorphous phase (Briassoulis et al., 2004).

*Penicillium funiculosum* and mixed population of fungi were used in studies on biodegradation of abiotically aged films, since, in previous stage of experiments, they

Table 4 shows the percentage weight loss of pre-aged LDPE film and LDPE/Bionolle® compositions after biodegradation with *Penicillium funiculosum* and mixed fungal

Based on material weight loss it cannot be clearly determined what impact have abiotic processes had on subsequent biodegradation of the material. Contrary to LDPE, photodegradation, thermodegradation and photothermodegradation of modified polyethylene films accelerated their biodegradation. Percentage weight loss of LDPE films modified with 30% Bionolle® after biodegradation with *Penicillium funiculosum* and mixed population of fungi increased by 15% and 13%; 19% and 28%; 17% and 4% in comparison to weight loss of neat films, respectively. The biodegradative propensity of abiotically degraded 40/60 composition was also markedly affected. The pre-treated film after being exposed to *Penicillium funiculosum* and mixed population of fungi exhibit a mass loss of 15- 19% and 4-28% higher than observed for control film. However, the biggest mass loss was observed after hydrolytic aging and biodegradation with *Penicillium funiculosum*. Biodegradation of films containing 15%, 30% and 60% polyester after prior hydrolysis increased by 104.5%, 75.8% and 24%, respectively. Considering percentage weight loss after hydrolysis and biodegradation of 40/60 composition, we have to remark, that any amount

LDPE/Bionolle® film compositions 100/0 85/15 70/30 40/60 Weight loss, %

*P. funiculosum* 0,13 0,26 1,43 69,19 Mixed fungal population 0,07 0,18 1,38 65,61

*P. funiculosum* 0,28 0,28 1,48 71,61 Mixed fungal population 0,04 0,23 1,56 74,14

*P. funiculosum* 0,08 0,14 1,45 70,16

*P. funiculosum* 0,17 0,45 2,18 74,62 Mixed fungal population 0,13 0,32 1,86 59,32

Mixed fungal population 0,12 0,15 1,27 60,38

**3.3 Influence of abiotic degradation on the rate of biodegradation**

exhibited the greatest ability to degrade examined plastics.

Table 4. Weight loss of pre-aged films after biodegradation

greater than 60% meant the degradation of polyethylene.

Process Fungi

population.

Photodegradation and biodegradation

Thermodegradation and

thermodegradation and

biodegradation

biodegradation

Hydrolysis and biodegradation

Photo- and

Changes in some mechanical properties of film samples after the abiotic degradation and biodegradation are shown in Figure 11.

Fig. 11. Changes in some mechanical properties of films after abiotic and biotic degradation A) and B) LDPE C) and D) 85/15 blend E) and F) 70/30 blend.

A significant increase in elongation of LDPE after thermo-, photo-thermo- and biodegradation with both *Penicillium funiculosum* and mixed populations of fungi was noted. These values were significantly higher than observed after biodegradation of neat polyethylene. The highest impact of abiotic pretreatment on the subsequent biodegradability was observed for 85/15 composition which elongation decreased by 9,26%- 16,82% as compared to 3,09%-8,49% for the film subjected only to biodegradation. As seen from Figure 11 there is a difference concerning the influence of abiotic aging to biodegradation of modified films between mixed fungi population and *Penicillium*

Biodegradation of Pre-Aged Modified Polyethylene Films 665

b)

 Fig. 12. SEM micrographs of films after exposing to different abiotic factors and subsequent biodegradation with mixed fungal population a) LDPE after thermo- and biodegradation b) 85/15 composition after photo- and biodegradation c) 70/30 composition after photothermo- and biodegradation d) 40/60 composition after hydrolysis and biodegradation

d)

Massive erosion (holes with diameter about 200 mm) of film 70/30 and dense network of fungal hyphae indicated that, after abiotic degradation, surface of film become at least as

It was impossible to separate fungal hyphae from the residual 40/60 composition after 84 days of hydrolysis and subsequent biodegradation. As revealed earlier (Table 4), weight loss of film exposed to both factors increased slightly compared to film subjected only to biodegradation. In order to describe the possible mechanism of degradation of this material, it is essential that a few facts should be given. Firstly, hydrolytic degradation (abiotic or biotic) of the polymer occurs predominantly in the amorphous regions (H-S. Kim & H-J Kim, 2008) Secondly, hydrolysis of the crystalline material is slow, because of the limited water diffusion rates into the crystalline domains and stereochemical limitations (Bikiaris et al., 2006). In our study, after inoculation of the composition with fungi, developing hyphae at first assimilated low-molecular products of polymer hydrolysis then attacked its crystalline region (Tserki et al., 2006)). Moreover, by taking into account the weight loss of the composition (59-75%), it can be assumed that fungi (long before the end of the experiment) completely assimilated polyester. Remaining LDPE fibres are clearly visible in the micrographs. Hence, decrease in the rate of biodegradation could be the result of (i) slow biodegradation of crystalline phase of polyester (ii) complex biodegradation of LDPE and

available to microorganism as unaged 40/60 blend.

a)

c)

(iii) penetration of fungi into the depths of the polymer matrix.

*funiculosum*. Contrary to mixed fungal population, assimilation of products of polymer oxidation during incubation with *Penicillium funiculosum* occurred less efficiently than depolymerisation of long LDPE chains. Far-advanced decomposition of 40/60 blend, prevented determination of its mechanical properties.

The amount of carbonyl groups, resulting from thermodegradation, decreased by 83% as a consequence of the assimilation of the degradation products by *Penicillium funiculosum*. Similar mechanism of biodegradation of abiotically aged polymers is repeatedly reported. Also Albertsson et al. (1987) found a synergistic effect between photooxidation and the biodegradation of polyethylene. Carbonyl residues completely disappeared after the incubation of the polymer samples in the presence of *Arthrobacter paraffineus*. Decrease of carbonyl index by 30-35% with respect to the starting materials was described for LDPE film samples containing pro-oxidant additives exposed to thermal- and biological degradation (Chiellini et al., 2007). The spectroscopic investigations led by Roy et al. revealed that the bacterial consortium consisted of *Bacillus pumilus*, *Bacillus halodenitrificans* and *Bacillus cereus* preferentially consumed the oxygenated products, thus leading to a decrease in the carbonyl index from 1,29 to 0,31 (Roy et al., 2008). In our study, internal double bonds also proved to be equally easily digested, since their amount after thermo- and biodegradation decreased by 92%. Interestingly, our study also shown that the number of carbonyl residues was about 80% lower than that observed during the biodegradation alone. The amount of carbonyl groups in the film with 30% content of polyester after thermo- and biodegradation compared to control film increased by 96%, while in relation to the film after thermodegradation decreased by 41%. As shown on Figure 8 carbonyl index of aged 40/60 composition after hydrolysis and subsequent biodegradation was lower by 40%, 93% and 60% than the value obtained for the control, after biodegradation and after hydrolysis, respectively.

These results implies that the filamentous fungi having at their disposal oxidised degradation products of polyethylene become less effective in degradation of macromolecules. Decrease in both indices (carbonyl and internal double bond) is a clear evidence that microorganisms use other set of enzymes during biodegradation of aged films than when they grow on high-molecular neat LDPE and polyester. Another conclusion is that the main enzymes involved in degradation of polymers are not constitutive proteins, expressed and secreted by microorganism independently of the substrate. On the contrary, the difference in mechanism of biodegradation clearly indicates the participation of inducible enzymes expressed only under specific conditions.

Micrographs of films exposed to selected abiotic factors and subsequent biodegradation are presented in Figure 12.

Compared to the film exposed only to biodegradation, observations of LDPE after thermoand biodegradation revealed filamentous fungi growing over the entire surface of the film (Figure 12a). Rough, peeling surface of the material was seen at higher magnification. It is likely that the fungi inhabiting film, used the degradation products of LDPE as a carbon and energy source. This surveillance was supported by a decrease of carbonyl index (Figure 8) and elongation at break (Figure 11) indicating fungal assimilation of low-molecular weight fractions.

SEM micrographs of 85/15 composition revealed deep cracks and holes with diameter 5-50 mm. The cavities on the surface suggested that microorganisms penetrated the polymer matrix during the degradation process.

*funiculosum*. Contrary to mixed fungal population, assimilation of products of polymer oxidation during incubation with *Penicillium funiculosum* occurred less efficiently than depolymerisation of long LDPE chains. Far-advanced decomposition of 40/60 blend,

The amount of carbonyl groups, resulting from thermodegradation, decreased by 83% as a consequence of the assimilation of the degradation products by *Penicillium funiculosum*. Similar mechanism of biodegradation of abiotically aged polymers is repeatedly reported. Also Albertsson et al. (1987) found a synergistic effect between photooxidation and the biodegradation of polyethylene. Carbonyl residues completely disappeared after the incubation of the polymer samples in the presence of *Arthrobacter paraffineus*. Decrease of carbonyl index by 30-35% with respect to the starting materials was described for LDPE film samples containing pro-oxidant additives exposed to thermal- and biological degradation (Chiellini et al., 2007). The spectroscopic investigations led by Roy et al. revealed that the bacterial consortium consisted of *Bacillus pumilus*, *Bacillus halodenitrificans* and *Bacillus cereus* preferentially consumed the oxygenated products, thus leading to a decrease in the carbonyl index from 1,29 to 0,31 (Roy et al., 2008). In our study, internal double bonds also proved to be equally easily digested, since their amount after thermo- and biodegradation decreased by 92%. Interestingly, our study also shown that the number of carbonyl residues was about 80% lower than that observed during the biodegradation alone. The amount of carbonyl groups in the film with 30% content of polyester after thermo- and biodegradation compared to control film increased by 96%, while in relation to the film after thermodegradation decreased by 41%. As shown on Figure 8 carbonyl index of aged 40/60 composition after hydrolysis and subsequent biodegradation was lower by 40%, 93% and 60% than the value obtained for the

These results implies that the filamentous fungi having at their disposal oxidised degradation products of polyethylene become less effective in degradation of macromolecules. Decrease in both indices (carbonyl and internal double bond) is a clear evidence that microorganisms use other set of enzymes during biodegradation of aged films than when they grow on high-molecular neat LDPE and polyester. Another conclusion is that the main enzymes involved in degradation of polymers are not constitutive proteins, expressed and secreted by microorganism independently of the substrate. On the contrary, the difference in mechanism of biodegradation clearly indicates the participation of

Micrographs of films exposed to selected abiotic factors and subsequent biodegradation are

Compared to the film exposed only to biodegradation, observations of LDPE after thermoand biodegradation revealed filamentous fungi growing over the entire surface of the film (Figure 12a). Rough, peeling surface of the material was seen at higher magnification. It is likely that the fungi inhabiting film, used the degradation products of LDPE as a carbon and energy source. This surveillance was supported by a decrease of carbonyl index (Figure 8) and elongation at break (Figure 11) indicating fungal assimilation of low-molecular weight

SEM micrographs of 85/15 composition revealed deep cracks and holes with diameter 5-50 mm. The cavities on the surface suggested that microorganisms penetrated the polymer

prevented determination of its mechanical properties.

control, after biodegradation and after hydrolysis, respectively.

inducible enzymes expressed only under specific conditions.

presented in Figure 12.

matrix during the degradation process.

fractions.

Fig. 12. SEM micrographs of films after exposing to different abiotic factors and subsequent biodegradation with mixed fungal population a) LDPE after thermo- and biodegradation b) 85/15 composition after photo- and biodegradation c) 70/30 composition after photothermo- and biodegradation d) 40/60 composition after hydrolysis and biodegradation

Massive erosion (holes with diameter about 200 mm) of film 70/30 and dense network of fungal hyphae indicated that, after abiotic degradation, surface of film become at least as available to microorganism as unaged 40/60 blend.

It was impossible to separate fungal hyphae from the residual 40/60 composition after 84 days of hydrolysis and subsequent biodegradation. As revealed earlier (Table 4), weight loss of film exposed to both factors increased slightly compared to film subjected only to biodegradation. In order to describe the possible mechanism of degradation of this material, it is essential that a few facts should be given. Firstly, hydrolytic degradation (abiotic or biotic) of the polymer occurs predominantly in the amorphous regions (H-S. Kim & H-J Kim, 2008) Secondly, hydrolysis of the crystalline material is slow, because of the limited water diffusion rates into the crystalline domains and stereochemical limitations (Bikiaris et al., 2006). In our study, after inoculation of the composition with fungi, developing hyphae at first assimilated low-molecular products of polymer hydrolysis then attacked its crystalline region (Tserki et al., 2006)). Moreover, by taking into account the weight loss of the composition (59-75%), it can be assumed that fungi (long before the end of the experiment) completely assimilated polyester. Remaining LDPE fibres are clearly visible in the micrographs. Hence, decrease in the rate of biodegradation could be the result of (i) slow biodegradation of crystalline phase of polyester (ii) complex biodegradation of LDPE and (iii) penetration of fungi into the depths of the polymer matrix.

Biodegradation of Pre-Aged Modified Polyethylene Films 667

Bikiaris, D.N.; Papageorgiou, G.Z. & Achilias, D.S. (2006). Synthesis and comparative

Bonhomme, S.; Cuer, A.; Delort, A-M.; Lemaire, J.; Sancelme, M. & Scott, G. (2003).

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## **4. Conclusion**

In the environment plastics decompose under the influence of different abiotic and biotic factors. The abiotic factors such as radiation, temperature, humidity, chemical pollution and wind can act synergistically or antagonistically causing various types of structural and chemical changes in the polymer. Microorganisms, especially bacteria or fungi, play a crucial role in biological degradation of polymers.

Scanning electron microscopy (SEM) is an invaluable tool for polymer analysis, since it is extensively used to study changes in the texture and composition of biodegradable polymer materials exposed to various environmental factors. It allows for the exploration of large surfaces with excellent resolution of topographic features.

Especially the new generation of SEM technology, known as ultra-high resolution field emission SEM (UHR FE-SEM) presents a promising technique for polymer morphological characterization, and provides complementary data to other microscopic methods.

One of the possible ways to accelerate the degradation of so-called "stable polymers" in the environment is their blending with polymers containing ester, ether, carboxyl and hydroxyl groups that are susceptible to hydrolytic attack of microorganisms. The chapter describes studies on biodegradation of LDPE/Bionolle® blends. It was shown that the addition of polyester significantly accelerated biodegradation of material.

Another way to sensitize the polymer is to expose it to the abiotic aging (action of abiotic factors) followed by the action of microbes. Abiotically modified surface of plastics promotes growth of microorganisms thus accelerates biodegradation.

Indeed, examined films underwent rapid biodegradation, but the course of the process was significantly different from that seen earlier. Further investigation on the mechanism of biodegradation revealed that fungi secreted different sets of enzymes depending on molecular weight of substrate. Unlike some other researchers, we have shown that filamentous fungi used in our study, were capable of efficient oxidation and degradation of the high-molecular weight LDPE. However, when pre-degraded, low-molecular weight chains of polyethylene served as a source of carbon and energy, microorganisms assimilated only short oligomers resulted from prior abiotic degradation. They did not show strong oxidising activity.

In our opinion, LDPE/Bionolle® blends can be used in the production of environmentally degradable packagings. Particularly noteworthy is composition containing 60% Bionolle®, which decompose several dozen percent within 84 days.

## **5. References**

In the environment plastics decompose under the influence of different abiotic and biotic factors. The abiotic factors such as radiation, temperature, humidity, chemical pollution and wind can act synergistically or antagonistically causing various types of structural and chemical changes in the polymer. Microorganisms, especially bacteria or fungi, play a

Scanning electron microscopy (SEM) is an invaluable tool for polymer analysis, since it is extensively used to study changes in the texture and composition of biodegradable polymer materials exposed to various environmental factors. It allows for the exploration of large

Especially the new generation of SEM technology, known as ultra-high resolution field emission SEM (UHR FE-SEM) presents a promising technique for polymer morphological

One of the possible ways to accelerate the degradation of so-called "stable polymers" in the environment is their blending with polymers containing ester, ether, carboxyl and hydroxyl groups that are susceptible to hydrolytic attack of microorganisms. The chapter describes studies on biodegradation of LDPE/Bionolle® blends. It was shown that the addition of

Another way to sensitize the polymer is to expose it to the abiotic aging (action of abiotic factors) followed by the action of microbes. Abiotically modified surface of plastics

Indeed, examined films underwent rapid biodegradation, but the course of the process was significantly different from that seen earlier. Further investigation on the mechanism of biodegradation revealed that fungi secreted different sets of enzymes depending on molecular weight of substrate. Unlike some other researchers, we have shown that filamentous fungi used in our study, were capable of efficient oxidation and degradation of the high-molecular weight LDPE. However, when pre-degraded, low-molecular weight chains of polyethylene served as a source of carbon and energy, microorganisms assimilated only short oligomers resulted from prior abiotic degradation. They did not show strong

In our opinion, LDPE/Bionolle® blends can be used in the production of environmentally degradable packagings. Particularly noteworthy is composition containing 60% Bionolle®,

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characterization, and provides complementary data to other microscopic methods.

**4. Conclusion**

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**33**

*1Singapore 2,3India*

**Surface Analysis Studies**

**on Polymer Electrolyte Membranes**

**and Atomic Force Microscope**

M. Ulaganathan1,2,\*, R. Nithya3 and S. Rajendran1,\*

*3Dept. of Physics, Shanmuganathan Engineering College,*

*Arasampatti, Pudukkottai, Tamil Nadu,*

*2School of Physics, Alagappa University, Karaikudi, Tamil Nadu,*

**Using Scanning Electron Microscope**

*1Energy Research Institute @ NTU, Nanyang Technological University, Singapore*

A battery generally consists of three important parts namely, anode, cathode and electrolyte. The batteries further classified into primary and secondary batteries. Among the different kinds of batteries, Li-ion batteries are plays a very important role in the development of modern technologies especially in the portable electronic device industries and in heavy electrical vehicles because of its advantages such as high theoretical capacity, improved safety, lower material costs, ease of fabrication into flexible geometries, and the absence of electrolyte leakage. In the battery system different kinds of electrolytes were used for promoting the ions from anode to cathode (during charge) and cathode to anode (during discharge). For this purpose, liquid electrolyte is identified as suitable electrolytes which facilitate higher ionic conductivity (10-2 Scm-1) than other electrolyte systems. However, it has several disadvantages namely gas formation during the operation, leakage, difficult to utilise for portable applications and etc. To overcome these difficulties, many attempts were made on solid polymer electrolyte systems. The main objective of the researchers is to improve the ambient temperature ionic conductivity, mechanical stability, thermal and interfacial stability of the electrolytes. However, it is difficult task for the researchers, inorder to improve these basic requirements of the electrolytes simultaneously because the ionic conductivity and mechanical strength of a polymer electrolyte are disparate to each

other, i.e., mechanical strength of the electrolyte decreases as conductivity increases.

In recent years, Polymer electrolytes have been attracted scientific and technological importance because of their potential applications in many areas such as Li-ion polymer batteries, super capacitor, electro chromic devices and etc. The idea of preparation of

**1. Introduction**

 \*

Corresponding Authors

## **Surface Analysis Studies on Polymer Electrolyte Membranes Using Scanning Electron Microscope and Atomic Force Microscope**

M. Ulaganathan1,2,\*, R. Nithya3 and S. Rajendran1,\*

*1Energy Research Institute @ NTU, Nanyang Technological University, Singapore 2School of Physics, Alagappa University, Karaikudi, Tamil Nadu, 3Dept. of Physics, Shanmuganathan Engineering College, Arasampatti, Pudukkottai, Tamil Nadu, 1Singapore 2,3India*

#### **1. Introduction**

670 Scanning Electron Microscopy

Sivan, A. (2011). New perspectives in plastic biodegradation*. Current Opinion in Biotechnology*, Vol.22, No.3, (June 2011), pp. 422-426, ISSN 0958-1669 Soni, R.; Kapri, A.; Zaidi, M.G.H. & Goel, R. (2009). Comparative Biodegradation Studies of

Sudhakar, M.; Doble, M.; Murthy, P.S. & Venkatesan, R. (2008). Marine microbe-mediated

Tserki, V.; Matzinos, P.; Pavlidou, E.; Vachliotis, D. & Panayiotou, C. (2006). Biodegradable

Tsuji, H.; Echizen, Y. & Nishimura, Y. (2006). Photodegradation of biodegradable polyesters:

Wojcieszyńska, D.; Hupert-Kocurek, K.; Greń, I. & Guzik, U. (2011). High activity catechol

*Polymer*, Vol.36, No.9, (April 1995), pp.1761-1779, ISSN 0032-3861

*& Biodegradation*, Vol.61, No.3, (April 2008), pp. 203-213, ISSN 0964-8305 Thompson, R.C.; Swan, S.H.; Moore, C.J. & vom Saal, F. (2009). Our plastic age. *Philosophical*

ISSN 1566-2543

1973-1976, ISSN 1471-2970

pp. 853-858, ISSN 0964-8305

(February 2006), pp.367-376, ISSN 0141-3910

Non-poronized and Poronized LDPE Using Indigenous Microbial Consortium. *Journal of Polymers and the Environment*, Vol.17, No.4, (December 2009), pp. 233-239,

biodegradation of low- and high-density polyethylenes. *International Biodeterioration*

*Transactions of the Royal Society Biological Sciences*, Vol.364, No.1526, (July 2009), pp.

aliphatic polyesters. Part I. Properties and biodegradation of poly(butylene succinate-*co*-butylene adipate). *Polymer Degradation and Stability*, Vol.91, No.2,

A comprehensive study on poly(L-lactide) and poly(ε-caprolactone). *Polymer Degradation and Stability*, Vol.91, No.5, (May 2006), pp.1128-1137, ISSN 0141-3910 Viezie, D.L.; Thomas, E.L. & Adams, W.W. (1995). Low-voltage, high-resolution scanning

electron microscopy: a new characterization technique for polymer morphology.

2,3-dioxygenase from the cresols – Degrading *Stenotrophomonas maltophilia* strain KB2. *International Biodeterioration & Biodegradation*, Vol.65, No.6, (September 2011), A battery generally consists of three important parts namely, anode, cathode and electrolyte. The batteries further classified into primary and secondary batteries. Among the different kinds of batteries, Li-ion batteries are plays a very important role in the development of modern technologies especially in the portable electronic device industries and in heavy electrical vehicles because of its advantages such as high theoretical capacity, improved safety, lower material costs, ease of fabrication into flexible geometries, and the absence of electrolyte leakage. In the battery system different kinds of electrolytes were used for promoting the ions from anode to cathode (during charge) and cathode to anode (during discharge). For this purpose, liquid electrolyte is identified as suitable electrolytes which facilitate higher ionic conductivity (10-2 Scm-1) than other electrolyte systems. However, it has several disadvantages namely gas formation during the operation, leakage, difficult to utilise for portable applications and etc. To overcome these difficulties, many attempts were made on solid polymer electrolyte systems. The main objective of the researchers is to improve the ambient temperature ionic conductivity, mechanical stability, thermal and interfacial stability of the electrolytes. However, it is difficult task for the researchers, inorder to improve these basic requirements of the electrolytes simultaneously because the ionic conductivity and mechanical strength of a polymer electrolyte are disparate to each other, i.e., mechanical strength of the electrolyte decreases as conductivity increases.

In recent years, Polymer electrolytes have been attracted scientific and technological importance because of their potential applications in many areas such as Li-ion polymer batteries, super capacitor, electro chromic devices and etc. The idea of preparation of

<sup>\*</sup> Corresponding Authors

Surface Analysis Studies on Polymer Electrolyte

**1.2.3 Solvent free polymer electrolytes**

electrolytes iii) Composite polymer electrolytes.

batteries to be constructed [Quartarone et al., 1998].

al., 1994 and Slane & Salomon et al., 1995].

*c) Composite polymer electrolytes*

*a) Solid polymer electrolytes*

*b) Gel polymer electrolytes*

Membranes Using Scanning Electron Microscope and Atomic Force Microscope 673

The polymer –salt complexes are formed by complexes between salts of alkali metals and polymer containing solvating heteroatoms such as O, N, S, etc. The most common examples are complexation between poly (ethylene oxide) (PEO) and alkali metal salts. The polymer salt complexes are further classified into: i) Solid polymer electrolytes ii) Blend polymer electrolytes iii) Gel polymer electrolytes iv) Composite polymer electrolytes. Among the various polymer electrolytes which are used in Li-ion batteries, solvent free polymer electrolytes are the most favourable for device fabrications. The solvent free polymer salt complexes are further classified into: i) Solid polymer electrolytes ii) Gel polymer

Solid polymer electrolytes (SPEs) have an ionic conductivity when modified by dissolving alkali salts in suitable polymer matrix. SPEs are typically thin films, which have a wide range of electrochemical applications such as batteries and electrochromic devices. They have several advantages when used in a battery and can be formed into thin films of large surface area giving high power levels. The flexibility of the films allows space-efficient

Plasticizers incorporated polymer- salt complex is called gel polymer electrolytes. The addition of plasticizers into the polymer matrix softens the polymers and they increase free volumes which are used for ion migration. Addition of plasticizer also increases the chain flexibility, reduces crystallinity, decreases the glass transition temperature and hence increases the ionic conductivity. The conductivity of PEO: LiBF4 is of the order of x10-6 Scm-1 which has been increased to the order of x10-4Scm-1 when the complex is plasticized at 25ºC [Chiodelli et al., 1988] this is mainly due to the specific nature of the plasticizers and the prepared gels has both the cohesive properties of solids and the diffusive property of liquids. Even though the gel polymer electrolyte exhibits high ionic conductivity, its thermal and mechanical stability are poor and it has higher reactivity towards the electrode. Gel electrolytes may undergo solvent exudation upon long storage, especially under open atmosphere conditions. This phenomenon is known as 'Synerisis effect', and has been encountered in many systems such as PAN: EC: PC: LiClO4, PAN: EC: PC: LiAsF6 [Groce et

This is another approach in which both the ionic conductivity and the mechanical stability of the electrolytes were considerably enhanced simultaneously. Composite polymer electrolytes are prepared by the addition of high surface inorganic fillers such as Al2O3, SiO2, MgO, LiAlO2, TiO2, BaTiO3 and Zeolite powders. The mechanical strength and stiffness of the complex systems were improved appreciably when the fillers are incorporated into the polymer matrix. However the main advantages of the composite electrolyte is the enhancement of room temperature ionic conductivity and an improved stability at the electrode electrolyte interface. The inert fillers due to its large surface area prevent the local chain reorganization with the result of locking in at ambient temperature, a high degree of disorder characteristic of the amorphous phase, which is more favour for the high ionic

polymer electrolytes was first proposed by Wright and Fenton et.al in 1973 [wright et al., 1973] but their technological significances are fulfilled and appreciated by Armand et.al few years later [Armand et al., 1998]. Poly (ethylene oxide) was the first solvating polymer to be proposed and studied in solid polymer electrolyte (SPE) Li-rechargeable batteries. Most of the solid polymer electrolytes (SPEs) are prepared by dissolving lithium salts in a solvating polymer using common solvent or by diffusion in the solid (or) molten state. An effort is also made to fix or immobilize the anion on the polymer matrix by covalent bonding (or) another chemical or physical process.

In general, Polymer electrolytes are plastic materials that can be modified and processed by conventional techniques. If the polymer chains are helped for a charge transport of the ionic type, often called "polymer electrolyte". Solid polymer electrolytes (SPEs) afford two important roles in Li-ion battery. 1) It is used as a separator in the battery system because of it rigid structure, at the same time to avoid the electrical contact between the anode and the cathode; 2) it is the medium in which the ions are transported between the anode and cathode during the cell operations. As a result, the polymer electrolyte should act as good electrical insulator but at the same time it should has high ionic conductivity.

## **1.1 Classification of polymer electrolyte systems**

The polymer electrolyte systems could be classified into three categories, namely, i) Polyelectrolyte, ii) Solvent swollen polymer electrolyte and iii) solvent free polymer electrolytes.

## **1.2.1 Polyelectrolyte's**

Polyelectrolytes are polymers which have their own ion-generating groups chemically bound to the macromolecular chain and the presence of a counter-ion maintains the electroneutrality of the salt. This class of materials either positively or negatively charged ions covalently attached to the polymer backbone and therefore only the unattached counter ion has long range mobility. The conductivity of these polymers is very low (10-10-10-15 Scm-1) in dry conditions but hydrated polyelectrolytes achieve high conductivity in the presence of high dielectric constant solvent (e.g. Water). In hydrated polyelectrolytes, ionic transport takes place through the aqueous medium in which the polymer is dispersed. Slade et.al. [Slade et al., 1983] reported high ambient temperature conductivity of 10-2 Scm-1 in hydrated Nafion.

## **1.2.2 Solvent swollen polymer electrolytes**

In solvent swollen polymers, solvents (aqueous/non-aqueous) swell the basic polymer host [like poly(vinyl alcohol) or poly(vinyl pyrrolidone)]. The dopant ionic solutes like H3PO4 are accommodated in the swollen lattice which permits the ionic motion in solvent rich swollen region of the polymer host. These materials are, in general, unstable and their conductivity depends on the concentration of the solvent in the swollen region. The properties of such polymers depend on the pre-treatment, structure of the sample, temperature, relative humidity, etc.

Examples: Nafian, complexes of poly(vinyl alcohol) (PVA) with H3PO4 [Polak et al., 1986] poly (silamine) with H3PO4[Rekukawa et al.,, 1996], PEI with H3SO4 [Daniel et al., 1988].

#### **1.2.3 Solvent free polymer electrolytes**

The polymer –salt complexes are formed by complexes between salts of alkali metals and polymer containing solvating heteroatoms such as O, N, S, etc. The most common examples are complexation between poly (ethylene oxide) (PEO) and alkali metal salts. The polymer salt complexes are further classified into: i) Solid polymer electrolytes ii) Blend polymer electrolytes iii) Gel polymer electrolytes iv) Composite polymer electrolytes. Among the various polymer electrolytes which are used in Li-ion batteries, solvent free polymer electrolytes are the most favourable for device fabrications. The solvent free polymer salt complexes are further classified into: i) Solid polymer electrolytes ii) Gel polymer electrolytes iii) Composite polymer electrolytes.

#### *a) Solid polymer electrolytes*

672 Scanning Electron Microscopy

polymer electrolytes was first proposed by Wright and Fenton et.al in 1973 [wright et al., 1973] but their technological significances are fulfilled and appreciated by Armand et.al few years later [Armand et al., 1998]. Poly (ethylene oxide) was the first solvating polymer to be proposed and studied in solid polymer electrolyte (SPE) Li-rechargeable batteries. Most of the solid polymer electrolytes (SPEs) are prepared by dissolving lithium salts in a solvating polymer using common solvent or by diffusion in the solid (or) molten state. An effort is also made to fix or immobilize the anion on the polymer matrix by covalent bonding (or)

In general, Polymer electrolytes are plastic materials that can be modified and processed by conventional techniques. If the polymer chains are helped for a charge transport of the ionic type, often called "polymer electrolyte". Solid polymer electrolytes (SPEs) afford two important roles in Li-ion battery. 1) It is used as a separator in the battery system because of it rigid structure, at the same time to avoid the electrical contact between the anode and the cathode; 2) it is the medium in which the ions are transported between the anode and cathode during the cell operations. As a result, the polymer electrolyte should act as good

The polymer electrolyte systems could be classified into three categories, namely, i) Polyelectrolyte, ii) Solvent swollen polymer electrolyte and iii) solvent free polymer

Polyelectrolytes are polymers which have their own ion-generating groups chemically bound to the macromolecular chain and the presence of a counter-ion maintains the electroneutrality of the salt. This class of materials either positively or negatively charged ions covalently attached to the polymer backbone and therefore only the unattached counter ion has long range mobility. The conductivity of these polymers is very low (10-10-10-15 Scm-1) in dry conditions but hydrated polyelectrolytes achieve high conductivity in the presence of high dielectric constant solvent (e.g. Water). In hydrated polyelectrolytes, ionic transport takes place through the aqueous medium in which the polymer is dispersed. Slade et.al. [Slade et al., 1983]

In solvent swollen polymers, solvents (aqueous/non-aqueous) swell the basic polymer host [like poly(vinyl alcohol) or poly(vinyl pyrrolidone)]. The dopant ionic solutes like H3PO4 are accommodated in the swollen lattice which permits the ionic motion in solvent rich swollen region of the polymer host. These materials are, in general, unstable and their conductivity depends on the concentration of the solvent in the swollen region. The properties of such polymers depend on the pre-treatment, structure of the sample, temperature, relative

Examples: Nafian, complexes of poly(vinyl alcohol) (PVA) with H3PO4 [Polak et al., 1986] poly (silamine) with H3PO4[Rekukawa et al.,, 1996], PEI with H3SO4 [Daniel et al., 1988].

reported high ambient temperature conductivity of 10-2 Scm-1 in hydrated Nafion.

electrical insulator but at the same time it should has high ionic conductivity.

**1.1 Classification of polymer electrolyte systems**

**1.2.2 Solvent swollen polymer electrolytes**

another chemical or physical process.

electrolytes.

humidity, etc.

**1.2.1 Polyelectrolyte's**

Solid polymer electrolytes (SPEs) have an ionic conductivity when modified by dissolving alkali salts in suitable polymer matrix. SPEs are typically thin films, which have a wide range of electrochemical applications such as batteries and electrochromic devices. They have several advantages when used in a battery and can be formed into thin films of large surface area giving high power levels. The flexibility of the films allows space-efficient batteries to be constructed [Quartarone et al., 1998].

#### *b) Gel polymer electrolytes*

Plasticizers incorporated polymer- salt complex is called gel polymer electrolytes. The addition of plasticizers into the polymer matrix softens the polymers and they increase free volumes which are used for ion migration. Addition of plasticizer also increases the chain flexibility, reduces crystallinity, decreases the glass transition temperature and hence increases the ionic conductivity. The conductivity of PEO: LiBF4 is of the order of x10-6 Scm-1 which has been increased to the order of x10-4Scm-1 when the complex is plasticized at 25ºC [Chiodelli et al., 1988] this is mainly due to the specific nature of the plasticizers and the prepared gels has both the cohesive properties of solids and the diffusive property of liquids. Even though the gel polymer electrolyte exhibits high ionic conductivity, its thermal and mechanical stability are poor and it has higher reactivity towards the electrode. Gel electrolytes may undergo solvent exudation upon long storage, especially under open atmosphere conditions. This phenomenon is known as 'Synerisis effect', and has been encountered in many systems such as PAN: EC: PC: LiClO4, PAN: EC: PC: LiAsF6 [Groce et al., 1994 and Slane & Salomon et al., 1995].

#### *c) Composite polymer electrolytes*

This is another approach in which both the ionic conductivity and the mechanical stability of the electrolytes were considerably enhanced simultaneously. Composite polymer electrolytes are prepared by the addition of high surface inorganic fillers such as Al2O3, SiO2, MgO, LiAlO2, TiO2, BaTiO3 and Zeolite powders. The mechanical strength and stiffness of the complex systems were improved appreciably when the fillers are incorporated into the polymer matrix. However the main advantages of the composite electrolyte is the enhancement of room temperature ionic conductivity and an improved stability at the electrode electrolyte interface. The inert fillers due to its large surface area prevent the local chain reorganization with the result of locking in at ambient temperature, a high degree of disorder characteristic of the amorphous phase, which is more favour for the high ionic

Surface Analysis Studies on Polymer Electrolyte

and cyclic voltametry.

analysis.

**1.4.2 PVC based electrolytes**

**1.4.3 PAN based polymer electrolytes**

Membranes Using Scanning Electron Microscope and Atomic Force Microscope 675

the composite polymer electrolytes using poly(ethylene oxide)/ poly(triethylene glycol) benzoate, BaTiO3 and lithium imides. They estimated the ionic conductivity value as 1.6x10-3 Scm-1 at 80ºC and the electrochemical stability window as 4.0V. The membrane was also characterized by TG/DTA and it is thermally stable upto 307ºC. Novel effect of organic acids such as malonic, maleic and carboxylic acids on PEO/LiClO4/Al2O3 complexes was studied by Park et al. [Park et al., 2006]. It was noted that the ionic conductivity of the film consisting of PEO/LiClO4: Citric acid (99.95:0.05 wt%) was 3.25x10-4Scm-1 at 30ºC and it was further improved to 3.1x10-3 Scm-1 at 20ºC by adding 20wt% of Al2O3 filler. The prepared membranes were also characterized by Brewster Angle Microscopy (BAM), thermal analysis

PVdF/PVC blend composite polymer electrolyte was prepared by Aravindhan et al. [Aravindhan et al., 2007] incorporating lithium bis(oxalate) borate and ZrO2. All the prepared membranes were subjected to SEM, XRD and ac impedance studies. The maximum ionic conductivity (1.53x10-3 Scm-1) was obtained for 2.5wt% of ZrO2 at 343K. The ionic conductivity and FTIR studies on plasticized polymer electrolyte based on PVC and PMMA as host polymer were studied by Manuel Stephan et al. It was found that LiBF4 based PVC/PMMA/EC/PC complexes exhibited higher ionic conductivity compared to that with LiClO4. The thermal stability of the films was also ascertained using TG/DTA

Kim et.al [Kim,D.W. Sun,Y.K. 2001] prepared highly porous polymer electrolyte employing P(VdF-co-HFP) and PAN with a view to attain high ionic conductivity and good mechanical strength. Lithium-ion polymer battery using these gel polymer electrolytes was assembled, and its charge-discharge characteristics were also reported. Panero et al. [Panero et al., 2002] studied the characteristics and the properties of a polymer electrolyte formed by trapping LiPF6-PC solution in a poly(acrylonitrile) matrix with the addition of Al2O3. They reported the ionic conductivity value as 0.8x10-2Scm-1 at 25ºC. The performances of the electrolyte were found to be promising in terms of cycle life and basic energy density content. Very recently, Moreno et.al [Moreno et al., 2010] reported a series of composite electrolytes basically constituted by poly(acrylonitrile), Clay and montmorillonite as filler. The structural and complex formations of the CPEs were also studied. However, the composite

based on PAN system showed poor ionic conductivity of the order of x10-6 Scm-1.

Tsutsumi and Kitagawa [Tsutsumi and Kitagawa et al., 2010] synthesized a new type polymer electrolyte films based on poly(acrylonitrile), and Cyanoethylated poly(vinyl alcohol) (CN-PVA) and its conductivity behaviour was also investigated. They found the ionic conductivity value as 14.6x10-3Scm-1 at 30ºC for PAN (10)-CN-PVA (10) - LiClO4 (8)-PC (4) complex system. The interactions of Li+-ion and nitrile groups of PAN in the matrix were confirmed by FTIR analysis. The ionic conductivity and FTIR studies were carried out on PAN based gel electrolytes with EC: PC and EC: DMC mixtures as plasticizers, LiClO4 or LiBF4 as the salt by Amaral et al [Amaral et al., 2007]. The high ionic conductivity (1.47x10-3 Scm-1) was estimated for 20:28:45:7 molar ratio of PAN-PVA: EC: DMC: LiBF4 system.

transport [G. Nagasubramanian and S. Di Stefano, 1990, Peter P Chu,P.P. Reddy, M.J., 2003]. The nano sized BaTiO3 incorporated PEO composite electrolytes exhibits ionic conductivity of the order of x10-3 Scm-1 and good electrochemical stability (4.0V).

## **1.3 Blend polymer electrolytes**

Blend is a mixture of two or more polymers. Mixing of two polymers is a well established strategy for the purpose of obtaining materials with combined superior properties or avoiding the need to synthesize novel structures constitutes an attractive research area. As many emerging applications are of limited volume and require specific property profiles not suitable for broad application utility, polymer blend technology is often the only viable method to deliver the desired material. These polymer blends have some unique properties that are different from the basic polymers from which these have been produced. To improve the processing behaviour for end use, one polymer blending with another polymer is a common practice. The exploitation of certain unique set of properties of individual polymer for the benefit of the overall properties of a multi component system forms the basis of polymer blending. Hence blending of polymers has resulted in the development of polymeric materials with desirable combination of properties. Polymer blend electrolytes are developed in such a way that they remain structurally stable during manufacturing, cell assembling, storage and usages as well as to prevent leakage from the cell container or without the cell.

### **1.4 Some commonly available polymer electrolytes for lithium ion batteries**

#### **1.4.1 PEO based electrolytes**

PEO is a crystalline polymer. The oxygen in PEO acts as a donor for the cation and the anion generally of large dimension stabilizes the PEO alkali salt complex.

The polymer electrolytes composed of a blend of poly (ethylene oxide) (PEO) and poly (vinylidenefluoride-hexa fluoropropylene) as a host polymer, mixture of EC and PC as plasticizer and LiClO4 as a salt were prepared by Fan et al. [Fan et al., 2002]. The ionic conductivity of various compositions of blend polymers was found to be in the order of x10- 4 Scm-1 at 30ºC. On increasing the PEO content in the matrix, the conductivity decreased due to its high crystalline nature. The mechanical strength of the polymer electrolytes was measured from stress-strain tests. The electrolytes were also characterized by SEM, XRD and thermal analysis techniques. Xi et al. [Xi., 2006] aimed to improve ionic conductivity with a novel approach using PEO and PVdF as host polymers by phase inversion technique. The room temperature conductivity was measured as a function of PEO content. As the weight ratio of PEO was increased from 40 to 50%, the ionic conductivity increased more than one magnitude from 0.15 to 1.96 x10-1Scm-1 which is mainly due to the increasing of pore connectivity. This is very important for the transport of charge carriers in microporous polymer membrane. The plasticizer effect on PEO-salt complex was studied by Fan et al [Fan et al., 2008] using succinitrile (SN) as a plasticizer, LiClO4, LiPF6 and LiCF3SO3 as lithium salts. They found that the addition of plasticizer was responsible for high ionic conductivity which could be attributed to the high polarity and diffusivity of succinitrile. This, in turn, decreased the crystallinity of PEO polymer. Activation energy of the electrolytes was also estimated from Arrhenius plot. Itoh et al. [Itoh et al., 2003] prepared the composite polymer electrolytes using poly(ethylene oxide)/ poly(triethylene glycol) benzoate, BaTiO3 and lithium imides. They estimated the ionic conductivity value as 1.6x10-3 Scm-1 at 80ºC and the electrochemical stability window as 4.0V. The membrane was also characterized by TG/DTA and it is thermally stable upto 307ºC. Novel effect of organic acids such as malonic, maleic and carboxylic acids on PEO/LiClO4/Al2O3 complexes was studied by Park et al. [Park et al., 2006]. It was noted that the ionic conductivity of the film consisting of PEO/LiClO4: Citric acid (99.95:0.05 wt%) was 3.25x10-4Scm-1 at 30ºC and it was further improved to 3.1x10-3 Scm-1 at 20ºC by adding 20wt% of Al2O3 filler. The prepared membranes were also characterized by Brewster Angle Microscopy (BAM), thermal analysis and cyclic voltametry.

## **1.4.2 PVC based electrolytes**

674 Scanning Electron Microscopy

transport [G. Nagasubramanian and S. Di Stefano, 1990, Peter P Chu,P.P. Reddy, M.J., 2003]. The nano sized BaTiO3 incorporated PEO composite electrolytes exhibits ionic conductivity

Blend is a mixture of two or more polymers. Mixing of two polymers is a well established strategy for the purpose of obtaining materials with combined superior properties or avoiding the need to synthesize novel structures constitutes an attractive research area. As many emerging applications are of limited volume and require specific property profiles not suitable for broad application utility, polymer blend technology is often the only viable method to deliver the desired material. These polymer blends have some unique properties that are different from the basic polymers from which these have been produced. To improve the processing behaviour for end use, one polymer blending with another polymer is a common practice. The exploitation of certain unique set of properties of individual polymer for the benefit of the overall properties of a multi component system forms the basis of polymer blending. Hence blending of polymers has resulted in the development of polymeric materials with desirable combination of properties. Polymer blend electrolytes are developed in such a way that they remain structurally stable during manufacturing, cell assembling, storage and usages as well as to prevent leakage from the cell container or

**1.4 Some commonly available polymer electrolytes for lithium ion batteries**

generally of large dimension stabilizes the PEO alkali salt complex.

PEO is a crystalline polymer. The oxygen in PEO acts as a donor for the cation and the anion

The polymer electrolytes composed of a blend of poly (ethylene oxide) (PEO) and poly (vinylidenefluoride-hexa fluoropropylene) as a host polymer, mixture of EC and PC as plasticizer and LiClO4 as a salt were prepared by Fan et al. [Fan et al., 2002]. The ionic conductivity of various compositions of blend polymers was found to be in the order of x10- 4 Scm-1 at 30ºC. On increasing the PEO content in the matrix, the conductivity decreased due to its high crystalline nature. The mechanical strength of the polymer electrolytes was measured from stress-strain tests. The electrolytes were also characterized by SEM, XRD and thermal analysis techniques. Xi et al. [Xi., 2006] aimed to improve ionic conductivity with a novel approach using PEO and PVdF as host polymers by phase inversion technique. The room temperature conductivity was measured as a function of PEO content. As the weight ratio of PEO was increased from 40 to 50%, the ionic conductivity increased more than one magnitude from 0.15 to 1.96 x10-1Scm-1 which is mainly due to the increasing of pore connectivity. This is very important for the transport of charge carriers in microporous polymer membrane. The plasticizer effect on PEO-salt complex was studied by Fan et al [Fan et al., 2008] using succinitrile (SN) as a plasticizer, LiClO4, LiPF6 and LiCF3SO3 as lithium salts. They found that the addition of plasticizer was responsible for high ionic conductivity which could be attributed to the high polarity and diffusivity of succinitrile. This, in turn, decreased the crystallinity of PEO polymer. Activation energy of the electrolytes was also estimated from Arrhenius plot. Itoh et al. [Itoh et al., 2003] prepared

of the order of x10-3 Scm-1 and good electrochemical stability (4.0V).

**1.3 Blend polymer electrolytes**

without the cell.

**1.4.1 PEO based electrolytes**

PVdF/PVC blend composite polymer electrolyte was prepared by Aravindhan et al. [Aravindhan et al., 2007] incorporating lithium bis(oxalate) borate and ZrO2. All the prepared membranes were subjected to SEM, XRD and ac impedance studies. The maximum ionic conductivity (1.53x10-3 Scm-1) was obtained for 2.5wt% of ZrO2 at 343K. The ionic conductivity and FTIR studies on plasticized polymer electrolyte based on PVC and PMMA as host polymer were studied by Manuel Stephan et al. It was found that LiBF4 based PVC/PMMA/EC/PC complexes exhibited higher ionic conductivity compared to that with LiClO4. The thermal stability of the films was also ascertained using TG/DTA analysis.

### **1.4.3 PAN based polymer electrolytes**

Kim et.al [Kim,D.W. Sun,Y.K. 2001] prepared highly porous polymer electrolyte employing P(VdF-co-HFP) and PAN with a view to attain high ionic conductivity and good mechanical strength. Lithium-ion polymer battery using these gel polymer electrolytes was assembled, and its charge-discharge characteristics were also reported. Panero et al. [Panero et al., 2002] studied the characteristics and the properties of a polymer electrolyte formed by trapping LiPF6-PC solution in a poly(acrylonitrile) matrix with the addition of Al2O3. They reported the ionic conductivity value as 0.8x10-2Scm-1 at 25ºC. The performances of the electrolyte were found to be promising in terms of cycle life and basic energy density content. Very recently, Moreno et.al [Moreno et al., 2010] reported a series of composite electrolytes basically constituted by poly(acrylonitrile), Clay and montmorillonite as filler. The structural and complex formations of the CPEs were also studied. However, the composite based on PAN system showed poor ionic conductivity of the order of x10-6 Scm-1.

Tsutsumi and Kitagawa [Tsutsumi and Kitagawa et al., 2010] synthesized a new type polymer electrolyte films based on poly(acrylonitrile), and Cyanoethylated poly(vinyl alcohol) (CN-PVA) and its conductivity behaviour was also investigated. They found the ionic conductivity value as 14.6x10-3Scm-1 at 30ºC for PAN (10)-CN-PVA (10) - LiClO4 (8)-PC (4) complex system. The interactions of Li+-ion and nitrile groups of PAN in the matrix were confirmed by FTIR analysis. The ionic conductivity and FTIR studies were carried out on PAN based gel electrolytes with EC: PC and EC: DMC mixtures as plasticizers, LiClO4 or LiBF4 as the salt by Amaral et al [Amaral et al., 2007]. The high ionic conductivity (1.47x10-3 Scm-1) was estimated for 20:28:45:7 molar ratio of PAN-PVA: EC: DMC: LiBF4 system.

Surface Analysis Studies on Polymer Electrolyte

1 for upto 20 cycles at different current densities.

**1.4.7 PVAc based polymer electrolytes**

was confirmed by XRD and SEM analysis.

performance.

Membranes Using Scanning Electron Microscope and Atomic Force Microscope 677

polymer PVdF-co-HFP/ PC/ DEC/ LiClO4 and PVdF/ PC/ DEC/ LiClO4 separately. The co-polymer complex showed higher ionic conductivity and transport number compared to PVdF system. The higher conductivity of the polymer electrolyte based on copolymer was attributed to its higher amorphousity. Wang et.al [Wang et al, 2004] reported that the polymer electrolyte composed of poly(methyl methacrylate-co-acrylonitrile-co-lithium methacrylate) (PMAML) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) exhibited high ionic conductivity and good electrochemical stability. The ionic conductivity was about 2*.*6×10-3 Scm−1 at ambient temperature and the electrochemical window of the polymer electrolyte was about 4.6V. Charge –discharge test results revealed that lithium ion batteries with these gel polymer electrolytes have good electrochemical

Manuel Stephan et.al [Manuel Stephan et al., 2006] prepared the composite polymer electrolyte membranes, comprising Poly(vinylidene fluoride–hexafluoropropylene), Aluminum Oxyhydroxide of two different sizes 7nm/14 nm and LiN(C2F5SO2)2 as lithium salt and they found that the incorporation of the inert filler not only reduces the crystallinity of the polymer host but also acts as 'solid plasticizer' capable of enhancing the transport properties and also provides a better interfacial property towards lithium metal anode. Nam-Soon Choi et.al [Choi et al., 2001] reported that the interfacial stability between the polymer electrolyte and the lithium electrode was enhanced by blending PVAc with P(VdFco-HFP)(Kynar 2801). The ionic conductivity of the polymer electrolyte based on the Kynar 2801: PVAc (7:3, w:w) blend was 2.3×10-3 S cm-1 at 25°C. Kim et.al [Kim et al., 2005] prepared and characterized gel polymer electrolytes consisting 25wt% PVdF-co-HFP/65 (EC+PC)/10 wt% LiN(CF3SO2)2.They reported the ionic conductivity value as 1.2x10-3Scm-1. The electrochemical stability window of the membrane was obtained at around 4.8V Vs Li/Li+ using linear sweep voltametry technique. The Charge – discharge behaviour of the membrane was also studied and they estimated the specific discharge capacity as 140 mAhg-

Though variety of polymer electrolytes were characterized for the fast four decades, a limited number of studies were made on PVAc based polymer electrolytes. PVAc polymer has a large dipole moment and high relaxation time. Baskaran et al [Baskaran et al., 2006] prepared the polymer electrolyte comprising of PVAc-PMMA and reported the conductivity value as 1.76x10-3Scm-1 at 303K. The DSC thermograms of the blend electrolytes showed two Tg's and they decreased with an increase of LiClO4 concentration. The structural and complex formations of the electrolytes were confirmed by X-ray diffraction analysis. They established that the optimized blend ratio of PVAc: PMMA: LiClO4 is suitable for lithium battery applications. Structural, thermal and transport properties of PVAc-LiClO4 base complexes were studied by Baskaran et al [Baskaran et al., 2007]. The bulk conductivity of PVAc: LiClO4 system was found to vary between 7.6x10-7Scm and 6.2x10-5 Scm-1 at 303K with an increase in the salt concentration. The amorphous nature of the polymer complexes

Surface morphology and ionic conductivity of the membrane based on P(EO)/PVAc /LiClO4 were studied by Animitsa et al [Animitsa et al., 1998]. They reported the conductivity value as 10-5 Scm-1 for lower concentration of PVAc at 25ºC. Baskaran et al.

Charge/discharge performance of the maximum ionic conductivity complex was also studied. The practical performance and thermal stability of Li-ion polymer batteries with LiNi0.8Co0.2O2, mesocarbon microbead-based graphite, and poly (acrylonitrile) (PAN) based gel electrolytes were reported by Akashi et al. [Akashi et al., 2002].

## **1.4.4 PVdF based polymer electrolytes**

PVdF is a semicrystalline polymer and the electrolytes based on PVdF are expected to have high anodic stabilities due to strong electron withdrawing functional groups (-C-F). It also has high permittivity, relatively low dissipation factor and high dielectric constant (ε=8.4) which assist in high ionization of lithium salts, providing a high concentration of charge carriers. Choe et al. [Cheo et al., 1995] reported that the PVdF based electrolytes plasticized with a solution of LiN(SO2CF3)2 in PC had a conductivity of 1.74x10-3 Scm-1 at 30ºC and has a oxidatively stable potential limits between 3.9 and 4.3V vs Li+/Li. Nicotera et al. [Nicotera et al., 2006] measured the ionic conductivity and the lithium salt diffusion coefficient of PMMA/PVdF based blend electrolytes with EC/PC as plasticizers and lithium perchlorate as salt by the PFG-NMR method, which revealed maximum lithium mobility for the composition PMMA 60%-PVdF 40%. Raman spectroscopic study confirmed the change of interaction between the lithium cations and the plasticizer molecules for different PMMA/PVdF ratios. Wang et al. [Wang et al., 2007] prepared the nanocomposite polymer electrolytes comprising of poly (vinylidene fluoride) (PVdF) as a host polymer, lithium perchlorate (LiClO4) as salt and TiO2 used as a filler by solvent-casting technique. The prepared films were characterized by XRD, DSC and SEM. The conductivity value was found to be of the order of 10-3 Scm-1 for the sample with 10% TiO2.

#### **1.4.5 PMMA based electrolytes**

Ali et al. [Ali et al., 2007] reported the electrical properties of polymer electrolytes comprising PMMA, PC, EC as plasticizer and different lithium salts LiCF3SO3 and LiN(CF3SO2)2. The polymer electrolytes exhibited high ionic conductivity at room temperature in the range of 10-6 to 10-4 Scm-1. The temperature dependence studies confirmed that the conduction in electrolyte is only by ions and seemed to obey the VTF rule. FTIR spectroscopy studies confirmed the polymer-salt interactions. FTIR spectroscopic investigations coupled with ionic conductivity and viscosity measurements on lithium imide LiN(CF3SO2)2–propylene carbonate (PC)–poly(methyl methacrylate) (PMMA) based liquid and gel electrolytes over a wide range of salt (0.025–3 M) and polymer (5–25 wt.%) concentration were reported by Deepa et al. [Deepa et al., 2004] and found that the high ionic conductivity occurs at salt concentrations ≥1.25 M.

#### **1.4.6 PVdF-co-HFP based polymer electrolytes**

In recent years, the studies on PVdF-co-HFP based systems are electrochemically stable and indispensable for the electrode properties. The PVdF-co-HFP based electrolyte system shows high electrochemical stability in the range 4V. Fan et al. [Fan et al., 2002] studied the thermal, electrical and mechanical properties of EC/PC/LiClO4 based PEO/P(VdF-co-HFP) blends. They concluded that the polymers have good compatibility and PVdF-HFP hinders the crystallinity of PEO. Saika and Kumar [Saika and Kumar, 2004] made systematic studies on the ionic conductivity and transport properties of polymer electrolytes comprising of co-

Charge/discharge performance of the maximum ionic conductivity complex was also studied. The practical performance and thermal stability of Li-ion polymer batteries with LiNi0.8Co0.2O2, mesocarbon microbead-based graphite, and poly (acrylonitrile) (PAN) based

PVdF is a semicrystalline polymer and the electrolytes based on PVdF are expected to have high anodic stabilities due to strong electron withdrawing functional groups (-C-F). It also has high permittivity, relatively low dissipation factor and high dielectric constant (ε=8.4) which assist in high ionization of lithium salts, providing a high concentration of charge carriers. Choe et al. [Cheo et al., 1995] reported that the PVdF based electrolytes plasticized with a solution of LiN(SO2CF3)2 in PC had a conductivity of 1.74x10-3 Scm-1 at 30ºC and has a oxidatively stable potential limits between 3.9 and 4.3V vs Li+/Li. Nicotera et al. [Nicotera et al., 2006] measured the ionic conductivity and the lithium salt diffusion coefficient of PMMA/PVdF based blend electrolytes with EC/PC as plasticizers and lithium perchlorate as salt by the PFG-NMR method, which revealed maximum lithium mobility for the composition PMMA 60%-PVdF 40%. Raman spectroscopic study confirmed the change of interaction between the lithium cations and the plasticizer molecules for different PMMA/PVdF ratios. Wang et al. [Wang et al., 2007] prepared the nanocomposite polymer electrolytes comprising of poly (vinylidene fluoride) (PVdF) as a host polymer, lithium perchlorate (LiClO4) as salt and TiO2 used as a filler by solvent-casting technique. The prepared films were characterized by XRD, DSC and SEM. The conductivity value was

Ali et al. [Ali et al., 2007] reported the electrical properties of polymer electrolytes comprising PMMA, PC, EC as plasticizer and different lithium salts LiCF3SO3 and LiN(CF3SO2)2. The polymer electrolytes exhibited high ionic conductivity at room temperature in the range of 10-6 to 10-4 Scm-1. The temperature dependence studies confirmed that the conduction in electrolyte is only by ions and seemed to obey the VTF rule. FTIR spectroscopy studies confirmed the polymer-salt interactions. FTIR spectroscopic investigations coupled with ionic conductivity and viscosity measurements on lithium imide LiN(CF3SO2)2–propylene carbonate (PC)–poly(methyl methacrylate) (PMMA) based liquid and gel electrolytes over a wide range of salt (0.025–3 M) and polymer (5–25 wt.%) concentration were reported by Deepa et al. [Deepa et al., 2004] and found that the high

In recent years, the studies on PVdF-co-HFP based systems are electrochemically stable and indispensable for the electrode properties. The PVdF-co-HFP based electrolyte system shows high electrochemical stability in the range 4V. Fan et al. [Fan et al., 2002] studied the thermal, electrical and mechanical properties of EC/PC/LiClO4 based PEO/P(VdF-co-HFP) blends. They concluded that the polymers have good compatibility and PVdF-HFP hinders the crystallinity of PEO. Saika and Kumar [Saika and Kumar, 2004] made systematic studies on the ionic conductivity and transport properties of polymer electrolytes comprising of co-

gel electrolytes were reported by Akashi et al. [Akashi et al., 2002].

found to be of the order of 10-3 Scm-1 for the sample with 10% TiO2.

ionic conductivity occurs at salt concentrations ≥1.25 M.

**1.4.6 PVdF-co-HFP based polymer electrolytes**

**1.4.4 PVdF based polymer electrolytes**

**1.4.5 PMMA based electrolytes**

polymer PVdF-co-HFP/ PC/ DEC/ LiClO4 and PVdF/ PC/ DEC/ LiClO4 separately. The co-polymer complex showed higher ionic conductivity and transport number compared to PVdF system. The higher conductivity of the polymer electrolyte based on copolymer was attributed to its higher amorphousity. Wang et.al [Wang et al, 2004] reported that the polymer electrolyte composed of poly(methyl methacrylate-co-acrylonitrile-co-lithium methacrylate) (PMAML) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) exhibited high ionic conductivity and good electrochemical stability. The ionic conductivity was about 2*.*6×10-3 Scm−1 at ambient temperature and the electrochemical window of the polymer electrolyte was about 4.6V. Charge –discharge test results revealed that lithium ion batteries with these gel polymer electrolytes have good electrochemical performance.

Manuel Stephan et.al [Manuel Stephan et al., 2006] prepared the composite polymer electrolyte membranes, comprising Poly(vinylidene fluoride–hexafluoropropylene), Aluminum Oxyhydroxide of two different sizes 7nm/14 nm and LiN(C2F5SO2)2 as lithium salt and they found that the incorporation of the inert filler not only reduces the crystallinity of the polymer host but also acts as 'solid plasticizer' capable of enhancing the transport properties and also provides a better interfacial property towards lithium metal anode. Nam-Soon Choi et.al [Choi et al., 2001] reported that the interfacial stability between the polymer electrolyte and the lithium electrode was enhanced by blending PVAc with P(VdFco-HFP)(Kynar 2801). The ionic conductivity of the polymer electrolyte based on the Kynar 2801: PVAc (7:3, w:w) blend was 2.3×10-3 S cm-1 at 25°C. Kim et.al [Kim et al., 2005] prepared and characterized gel polymer electrolytes consisting 25wt% PVdF-co-HFP/65 (EC+PC)/10 wt% LiN(CF3SO2)2.They reported the ionic conductivity value as 1.2x10-3Scm-1. The electrochemical stability window of the membrane was obtained at around 4.8V Vs Li/Li+ using linear sweep voltametry technique. The Charge – discharge behaviour of the membrane was also studied and they estimated the specific discharge capacity as 140 mAhg-1 for upto 20 cycles at different current densities.

## **1.4.7 PVAc based polymer electrolytes**

Though variety of polymer electrolytes were characterized for the fast four decades, a limited number of studies were made on PVAc based polymer electrolytes. PVAc polymer has a large dipole moment and high relaxation time. Baskaran et al [Baskaran et al., 2006] prepared the polymer electrolyte comprising of PVAc-PMMA and reported the conductivity value as 1.76x10-3Scm-1 at 303K. The DSC thermograms of the blend electrolytes showed two Tg's and they decreased with an increase of LiClO4 concentration. The structural and complex formations of the electrolytes were confirmed by X-ray diffraction analysis. They established that the optimized blend ratio of PVAc: PMMA: LiClO4 is suitable for lithium battery applications. Structural, thermal and transport properties of PVAc-LiClO4 base complexes were studied by Baskaran et al [Baskaran et al., 2007]. The bulk conductivity of PVAc: LiClO4 system was found to vary between 7.6x10-7Scm and 6.2x10-5 Scm-1 at 303K with an increase in the salt concentration. The amorphous nature of the polymer complexes was confirmed by XRD and SEM analysis.

Surface morphology and ionic conductivity of the membrane based on P(EO)/PVAc /LiClO4 were studied by Animitsa et al [Animitsa et al., 1998]. They reported the conductivity value as 10-5 Scm-1 for lower concentration of PVAc at 25ºC. Baskaran et al.

Surface Analysis Studies on Polymer Electrolyte

Fig. 1. Preparation of Polymer electrolyte

(Fig.1.).

Membranes Using Scanning Electron Microscope and Atomic Force Microscope 679

own advantages and disadvantages. Among the various method of preparation solvent costing is the cost effective one and easier to control the moistures during the preparation of electrolytes as well as in the cell assembling. However, when assembling the cells, these membranes show poor cyclic behaviour. As a result many research groups have been mainly focused on phase inversion method for preparing the suitable electrolytes. Preparation of polymer electrolyte system is explained using the following flow chart

In the present study, all the electrolytes were prepared using solvent casting technique. The polymers PVAc, PVdF-co-HFP, and the salt LiClO4 were dissolved in a common solvent (tetrahydrofuran) separately. All three solutions were mixed together and starrier continuously using magnetic stirrer until got a homogeneous mixture. The low molecular weight plasticizer and the inorganic fillers were added into the matrix inorder to get the gel and composite polymer electrolytes systems. In the present study, ethylene carbonate(EC) and barium titanate (BaTiO3) were used a plasticizer and fillers respectively. Thus the obtained homogenous slurry was degassed to remove air bubbles for about five minutes and the slurry was poured on a well cleaned glass plate. The casted slurry was allowed to evaporate the solution at room temperature about 5h followed by the electrolyte membranes were heated using hot air oven at a temperature of 60 ºC for 6h in order to removing the

[Baskaran et al., 2006] studied the ac impedance and dielectric properties of PVdF/PVAc blend electrolytes. They reported that the blend ratio (75:25) of PVAc/PVdF exhibited a maximum ionic conductivity value of the order of 6.4x10-4Scm-1 at 343K. The ionic transference number of mobile ions was also estimated by Wagner's polarization method. The complex formation and thermal behaviour of the electrolytes were also studied by FTIR and DSC analysis respectively.

## **2. Basic requirements of polymers and the salt for polymer electrolytes**

Atoms or groups of atoms with sufficient electron donor power to form coordinate bonds with cations.

#### **Electron pair donicity (DN)**

DN measures the ability of the solvent to donate electrons to solvate the cations considered as a Lewis acid. So the polymer host should have high DN number.

#### **Acceptor number (AN)**

The acceptor number quantifies the possibility of anion salvation. It should be less for an inorganic salt so that cationic salvation is high compared to anionic salvation.

#### **Entropy term**

The entropy term depends on the optimal spatial disposition of the solvating units which should be high for the polymer host.

#### **2.1 Importance of Li<sup>+</sup> cation**

Last four decades, many alkali salts consisting Li+, Na+, K+, Ag+, Mg+, NH4 + cations were mixed with the polymers (PEO), (PPO) etc in the preparation of polymer electrolytes. Among the various cations in the periodic table, Li+ is the most electropositive. Lithium easily gives up electrons to form a positive Li+ which has small ionic radii (0.6Å). Lithium is promising candidate for high energy density batteries because of its high specific capacity of 3860 Ah/Kg, its light weight and high electrochemical reduction potential [Scrosati et al., 1994; Abraham et al., 1993; Dell, 2000].

#### **2.2 Preparation of polymer blend electrolytes**

Polymer blend electrolytes have been prepared using various approaches namely, Phase inversion method, Hot pressed method, Solvent casting method and etc. Each method has

[Baskaran et al., 2006] studied the ac impedance and dielectric properties of PVdF/PVAc blend electrolytes. They reported that the blend ratio (75:25) of PVAc/PVdF exhibited a maximum ionic conductivity value of the order of 6.4x10-4Scm-1 at 343K. The ionic transference number of mobile ions was also estimated by Wagner's polarization method. The complex formation and thermal behaviour of the electrolytes were also studied by FTIR

**2. Basic requirements of polymers and the salt for polymer electrolytes**

intrapolymers ion bonds appears to be important

movement and yields high ionic conductivity. • The lattice energy of the salt should be low. • High electrochemical reduction potential

• Low glass transition temperature to increase the segmental motion.

as a Lewis acid. So the polymer host should have high DN number.

inorganic salt so that cationic salvation is high compared to anionic salvation.

Atoms or groups of atoms with sufficient electron donor power to form coordinate bonds

• Low barriers to bond rotation so that segmental motion of the polymer chain can take

• A suitable distance between coordinating centres for the formation of multiple

• The polymer should have amorphous phase which lowers the barrier for ionic

DN measures the ability of the solvent to donate electrons to solvate the cations considered

The acceptor number quantifies the possibility of anion salvation. It should be less for an

The entropy term depends on the optimal spatial disposition of the solvating units which

Last four decades, many alkali salts consisting Li+, Na+, K+, Ag+, Mg+, NH4+ cations were mixed with the polymers (PEO), (PPO) etc in the preparation of polymer electrolytes. Among the various cations in the periodic table, Li+ is the most electropositive. Lithium easily gives up electrons to form a positive Li+ which has small ionic radii (0.6Å). Lithium is promising candidate for high energy density batteries because of its high specific capacity of 3860 Ah/Kg, its light weight and high electrochemical reduction potential [Scrosati et al.,

Polymer blend electrolytes have been prepared using various approaches namely, Phase inversion method, Hot pressed method, Solvent casting method and etc. Each method has

and DSC analysis respectively.

with cations.

place readily.

**Electron pair donicity (DN)**

**Acceptor number (AN)**

**2.1 Importance of Li<sup>+</sup>**

should be high for the polymer host.

1994; Abraham et al., 1993; Dell, 2000].

**2.2 Preparation of polymer blend electrolytes**

 **cation**

**Entropy term**

own advantages and disadvantages. Among the various method of preparation solvent costing is the cost effective one and easier to control the moistures during the preparation of electrolytes as well as in the cell assembling. However, when assembling the cells, these membranes show poor cyclic behaviour. As a result many research groups have been mainly focused on phase inversion method for preparing the suitable electrolytes. Preparation of polymer electrolyte system is explained using the following flow chart (Fig.1.).

Fig. 1. Preparation of Polymer electrolyte

In the present study, all the electrolytes were prepared using solvent casting technique. The polymers PVAc, PVdF-co-HFP, and the salt LiClO4 were dissolved in a common solvent (tetrahydrofuran) separately. All three solutions were mixed together and starrier continuously using magnetic stirrer until got a homogeneous mixture. The low molecular weight plasticizer and the inorganic fillers were added into the matrix inorder to get the gel and composite polymer electrolytes systems. In the present study, ethylene carbonate(EC) and barium titanate (BaTiO3) were used a plasticizer and fillers respectively. Thus the obtained homogenous slurry was degassed to remove air bubbles for about five minutes and the slurry was poured on a well cleaned glass plate. The casted slurry was allowed to evaporate the solution at room temperature about 5h followed by the electrolyte membranes were heated using hot air oven at a temperature of 60 ºC for 6h in order to removing the

Surface Analysis Studies on Polymer Electrolyte

and lithium salt.

stretching vibration modes of blend electrolytes.

Membranes Using Scanning Electron Microscope and Atomic Force Microscope 681

all the blends, some peaks are found above 3000 cm-1, which correspond to the C-H

In addition, some new peaks are present and some of them are absent in the blend electrolytes. Thus the spectral analysis confirms the complexation of these two polymers

Fig. 2. FTIR analysis of LiClO4, PVAc, PVdF-co-HFP and their complexes

XRD patterns of LiClO4, PVdF-co-HFP, PVAc and their complexes A, B, C are shown in Fig. 3. The presence of characteristic peaks corresponding to the lithium salt reveals the high crystalline nature of the salt. Three peaks found at 2θ = 17.3, 18.59 and 38.78° for PVdF-co-

**3.2 X-ray diffraction analysis**

residual solvent present in the electrolyte films. Finally, the harvested electrolyte films were stored in highly evacuated desiccators to avoid the moistures absorption.

## **3. Characterization of polymer blend electrolytes**

Ac impedance analysis was carried out with the help of stainless steel blocking electrodes by using a computer controlled micro auto lab type III Potentiostat/Galvanostat of frequency range 1 Hz–300 KHz in the temperature range 303–373 K. The XRD equipment used in this study was X'pert PRO PANlytical X-ray diffractometer. FTIR spectroscopy studies were carried out using SPECTRA RXI, Perkin Elmer spectro-photometer in the range 400–4000 cm−1. FTIR spectroscopy studies were carried out for confirming the complex formation using SPECTRA RXI, Perkin-Elmer spectro-photometer in the range 400–4000 cm−1. TG/DTA thermal analysis of the film having maximum ionic conductivity was studied using PYRIS DIAMOND under air atmosphere with the scan rate of 10 ◦C min−1. The electrolyte film having maximum ionic conductivity was subjected to atomic force microscopy [model Veeco-diCP-II]. The pore size and the root mean square (rms) roughness of the film were measured from the topography image. Secondary electron images of the sample were examined by using JEOL, JSM-840A scanning electron microscope

## **3.1 FTIR analysis**

Infrared spectral (IR) analysis is a powerful tool for identifying the nature of bonding and different functional groups present in a sample by monitoring the vibrational energy levels of the molecules, which are essentially the fingerprint of different molecules [Nagatomo et al., 1987]. Fig.2. depicts the FTIR transmittance spectra in the range 400-4000 cm-1 for polymers, the LiClO4 salt, the blend electrolyte with the incorporation of plasticizer ethylene carbonate and the filler BaTiO3.

The vibrational bands observed at 2933 cm-1 and 2465 cm-1 are ascribed to –CH3 asymmetric and symmetric stretching vibrations of PVAc respectively. The strong absorbance at 1734 cm-1 represents the C=O stretching vibration mode of PVAc polymer. The existence of C-O band has been confirmed by the strong absorbance band at around 1033 cm-1. The strong band at 1373 cm-1 is ascribed to -CH3 symmetric bending vibration of pure PVAc. The band at 1243 cm-1 is assigned to C-O-C symmetric stretching mode of vibration. The peak at 947 cm-1 is ascribed to CH bending vibration and the peak at 609 cm-1 is assumed to be linked with CH3 (C-O) group. The C-H wagging mode of vibration has been confirmed by the presence of a band at 799 cm-1 [Baskaran et al., 2004]. The vibrational peaks at 502 and 416 cm-1 are assigned to bending and wagging vibrations of –CF2 of PVdF-co-HFP polymer respectively. Crystalline phase of the PVdF-co-HFP polymer is identified by the vibrational bands at 985, 763, and 608 cm-1 and the amorphous phase of the co-polymer is confirmed by the presence of vibrational band at 872 cm-1 [Rajendran et al., 2002].

The strong absorption peak appeared at 1173 cm-1 is assigned to the symmetrical stretching of –CF2 group. The peak appeared at 1390 cm-1 is assigned to the CH2 groups [Rajendran et al., 2002; Singh Missan et al., 2006]. Table.1. shows the comparison of band spectra of pure polymers and their blends with different blend ratios. From the table, it is clear that the band assignments of FTIR spectra of blend samples are shifted from their pure spectra. For

residual solvent present in the electrolyte films. Finally, the harvested electrolyte films were

Ac impedance analysis was carried out with the help of stainless steel blocking electrodes by using a computer controlled micro auto lab type III Potentiostat/Galvanostat of frequency range 1 Hz–300 KHz in the temperature range 303–373 K. The XRD equipment used in this study was X'pert PRO PANlytical X-ray diffractometer. FTIR spectroscopy studies were carried out using SPECTRA RXI, Perkin Elmer spectro-photometer in the range 400–4000 cm−1. FTIR spectroscopy studies were carried out for confirming the complex formation using SPECTRA RXI, Perkin-Elmer spectro-photometer in the range 400–4000 cm−1. TG/DTA thermal analysis of the film having maximum ionic conductivity was studied using PYRIS DIAMOND under air atmosphere with the scan rate of 10 ◦C min−1. The electrolyte film having maximum ionic conductivity was subjected to atomic force microscopy [model Veeco-diCP-II]. The pore size and the root mean square (rms) roughness of the film were measured from the topography image. Secondary electron images of the

stored in highly evacuated desiccators to avoid the moistures absorption.

sample were examined by using JEOL, JSM-840A scanning electron microscope

the presence of vibrational band at 872 cm-1 [Rajendran et al., 2002].

Infrared spectral (IR) analysis is a powerful tool for identifying the nature of bonding and different functional groups present in a sample by monitoring the vibrational energy levels of the molecules, which are essentially the fingerprint of different molecules [Nagatomo et al., 1987]. Fig.2. depicts the FTIR transmittance spectra in the range 400-4000 cm-1 for polymers, the LiClO4 salt, the blend electrolyte with the incorporation of plasticizer ethylene

The vibrational bands observed at 2933 cm-1 and 2465 cm-1 are ascribed to –CH3 asymmetric and symmetric stretching vibrations of PVAc respectively. The strong absorbance at 1734 cm-1 represents the C=O stretching vibration mode of PVAc polymer. The existence of C-O band has been confirmed by the strong absorbance band at around 1033 cm-1. The strong band at 1373 cm-1 is ascribed to -CH3 symmetric bending vibration of pure PVAc. The band at 1243 cm-1 is assigned to C-O-C symmetric stretching mode of vibration. The peak at 947 cm-1 is ascribed to CH bending vibration and the peak at 609 cm-1 is assumed to be linked with CH3 (C-O) group. The C-H wagging mode of vibration has been confirmed by the presence of a band at 799 cm-1 [Baskaran et al., 2004]. The vibrational peaks at 502 and 416 cm-1 are assigned to bending and wagging vibrations of –CF2 of PVdF-co-HFP polymer respectively. Crystalline phase of the PVdF-co-HFP polymer is identified by the vibrational bands at 985, 763, and 608 cm-1 and the amorphous phase of the co-polymer is confirmed by

The strong absorption peak appeared at 1173 cm-1 is assigned to the symmetrical stretching of –CF2 group. The peak appeared at 1390 cm-1 is assigned to the CH2 groups [Rajendran et al., 2002; Singh Missan et al., 2006]. Table.1. shows the comparison of band spectra of pure polymers and their blends with different blend ratios. From the table, it is clear that the band assignments of FTIR spectra of blend samples are shifted from their pure spectra. For

**3. Characterization of polymer blend electrolytes**

**3.1 FTIR analysis**

carbonate and the filler BaTiO3.

all the blends, some peaks are found above 3000 cm-1, which correspond to the C-H stretching vibration modes of blend electrolytes.

In addition, some new peaks are present and some of them are absent in the blend electrolytes. Thus the spectral analysis confirms the complexation of these two polymers and lithium salt.

Fig. 2. FTIR analysis of LiClO4, PVAc, PVdF-co-HFP and their complexes

#### **3.2 X-ray diffraction analysis**