Onar et al. [32] purposed to achieve the production of water‐repellent cotton fabric by sol‐gel process using tridecafluorooctyltriethoxysilane (FTES), hexadecyltrimethoxysilane (HDTMS), glycidyloxypropyltriethoxysilane (GLYE), phenyltriethoxysilane (FES), vinyltrimethoxysi‐ lane (VTEO), 3‐aminopropyl trimethoxysilane (AMMO), titanium (IV) isopropoxide (TIPT), and zirconium (IV) acetylacetonate (ZrAc) as precursors. They found that the treatment with HDTMS under acidic and alkaline conditions or FTES under alkaline conditions led to pro‐ vide superhydrophobicity on cotton fabric. The fabric samples treated with FES, VTEO, TIPT, and GLYE precursors lost their hydrophobic properties after washing process, while the fab‐ rics treated with HDMS, FTES, AMMO, and ZrAc precursors preserved the hydrophobic properties after washing process [32].

Colleoni et al. [33] treated the cotton and polyester fabric with octyltriethoxysilane (OTES) together with melamine‐based crosslinking agent. They revealed that the cotton and polyester fabrics had good hydrophobic properties with, respectively, 130° and 150° of contact angle values [33].

Gao et al. [34] researched the hydrophobic properties of the cotton and polyester fabric treated with TEOS and then HDTMS by sol‐gel process (**Figure 7**). The process imparted highly hydrophobic properties to the cotton (155° CA) and polyester fabric (143° CA) with durability till 30 washing processes and a slight reduction of their tensile strength (<10%) [34].

Teli and Annaldewar [35] studied the water repellency and UV‐protection properties of cotton fabric dip coated with silica nanoparticles prepared by sol‐gel process and subse‐ quently impregnated with zinc nitrate hexahydrate in hexamine and then hydrophobically modified with ethanolic sodium stearate solution. As a result of that, the fabric samples imparted excellent UV protection with +50 UPF and superhydrophobic properties. The fab‐ ric samples had still excellent UV protection and hydrophobic properties after 10 washing cycles [35].

de Ferri et al. [36] coated the silk fabric with nanosols composed of 3‐glycidoxypropyltri‐ methoxysilane (GLYMO) and DynF8815 with acid catalyst by sol‐gel process. The treatment caused the high abrasion resistance to 8500 cycle, high contact angle (nearly 123° CA) to four oils, and hydrophobic properties with 148° of contact angle. The washing durability of oil and water repellency of the fabric samples was also analyzed. It was observed that the fabric had still hydrophobic (130° CA) and oleophobic properties (100° of CA) after, respectively, 15 washing and 5 washing cycles [36].

**Figure 7.** The reaction of cotton fibers with previous TEOS and the HDTMS. Copyright 2009 American Chemical Society [34].

Vasiljević et al. [37] aimed to produce highly oleophobic and superhydrophobic cotton fabric by three‐step sol‐gel process. The first step was the treatment of cotton fabric with silica nanoparticles with different average particle sizes (50 ± 15, 230 ± 20, and 780 ± 30 nm) prepared according to Stöber method based on sol‐gel process; the second step was the application of the *in situ* growth of polysiloxane layer on cotton fabric in basic TEOS solution, and the third step was the padding with a fluoroalkyl functional water‐borne oligosiloxane (FAS, Dynasylan F 8815). They obtained fabric samples with low sliding angle (2°), high oleophobicity (6), and superhydrophobicity durable to 10 washing cycles [37].

#### **2.3. UV protection, self‐cleaning, and soil repellency (photocatalytic effect)**

de Ferri et al. [36] coated the silk fabric with nanosols composed of 3‐glycidoxypropyltri‐ methoxysilane (GLYMO) and DynF8815 with acid catalyst by sol‐gel process. The treatment caused the high abrasion resistance to 8500 cycle, high contact angle (nearly 123° CA) to four oils, and hydrophobic properties with 148° of contact angle. The washing durability of oil and water repellency of the fabric samples was also analyzed. It was observed that the fabric

**Figure 7.** The reaction of cotton fibers with previous TEOS and the HDTMS. Copyright 2009 American Chemical

CA) and oleophobic properties (100° of CA) after, respectively, 15

had still hydrophobic (130°

262 Recent Applications in Sol-Gel Synthesis

Society [34].

washing and 5 washing cycles [36].

Long‐time exposure to UV light may result in early skin aging, allergy, sun burns, or even skin cancer in especially fair‐skinned human. Various chemical agents such as benzophenone derivatives, ortho‐hydroxy phenyl, and diphenyl triazine derivatives as organic UV absorb‐ ers and TiO2 and ZnO particles as inorganic UV absorbers have been used [38]. Alternatively, UV protection can be obtained by sol‐gel method with generally TiO2 and ZnO nanoparticles incorporated to textile materials. TiO2 nanoparticles provide self‐cleaning as well as UV pro‐ tection by means of photocatalytic reaction. Anatase phase of TiO2 nanoparticles, which is one of three phases of TiO2 (anatase, brookite, and rutile), has photocatalytic activity. The formation of anatase phase at low temperature on textile material coated with titania nanosols is a big challenge because textile materials cannot endure high temperature [39]. Researchers are investigating some solutions such as steaming process [40, 41], hydrothermal process [42], or solvothermal process [43] to produce anatase crystals at low temperature so far.

Photocatalytic reaction leads to the decomposition of organic and inorganic pollutants under the ultraviolet light [43]. In addition, organic components such as microorganisms in textile surfaces and dyestuff residues in textile wastewater can also be decomposed by photocatalytic effect. By this way, photocatalytic effect ensures not only UV protection and self‐cleaning but also antibacterial effect and ecological and economical wastewater treat‐ ment [43, 44]. **Figure 8** illustrates the self‐cleaning properties of cotton fabric treated with titania nanosols.

Liu et al. [46] investigated the self‐cleaning and UV‐protection properties of raw wool fabric and Kroy‐process wool fabric (removed scales with chlorination process) treated with polycarboxylic acid such as 1,2,3,4‐butanetetracarboxylic acid (BTCA), citric acid (CA) as crosslinking agent and then nanosols prepared by using titanium (IV) butoxide (TBT) and TEOS as precursors. The self‐cleaning properties of the fabric samples were evaluated by photo‐induced decomposition test of methylene blue. Self‐cleaning properties of raw wool fabric were found to be better than that of Kroy‐process wool fabric, while UPF values of raw material (356) were lower than that of Kroy‐process wool fabric (992) [46].

Dhineshbabu et al. [47] studied the UV‐protection, antibacterial, and flame retardancy prop‐ erties of cotton fabric treated with colloidal sols containing TEOS as precursor and polyethyl‐ ene glycol (PEG) as stabilizer and TiO2 nanoparticles produced by sol‐gel process. They found that UPF values of the fabric samples were greater than 50 UPF corresponding to excellent UV protection after even 10 washing cycles. According to ASTM D1230 standard, their results showed that the total burning time and residual weight after burning of the fabric samples were higher than that of untreated fabric according to the flame test at 45° angle. Thus, their burning performance improved after the treatment and nearly 70% of this performance was preserved after 10 washing cycles. The study revealed that the fabric samples had good anti‐ bacterial activity against *Staphylococcus aureus* and *Escherichia coli* with, respectively, 18 and 15 mm diameter of inhibition zone because of the reactive oxygen species (ROS) generation mechanism of TiO2 nanoparticles [47].

Rilda et al. [48] previously produced TiO2 ‐SiO2 powder by using titanium isopropoxide and TEOS as precursors with different molar ratios, diethanol amine (DEA) as stabilizer, isopro‐ panol as solvent, and chitosan in acetic acid as dispersing agent by sol‐gel process. The fabric samples coated with acrylic acid binder were immersed to TiO2 ‐SiO2 suspension containing the powder, surfactant, and isopropanol and then coated with the suspension to ensure homoge‐ neous coating by spin‐coating machine. Falling at absorbance of methylene blue under UV irra‐ diation for 120 min was attributed to self‐cleaning properties of fabrics treated with TiO2 ‐SiO2 powders with especially 1:2 molar ratios [48]. The discoloration of wine stain on cotton fabric treated with TiO2 ‐SiO2 colloidal solution increased exposure times under solar light simulator for 0, 4, 8, and 24 h [49].

Wang et al. [39] treated the cotton fabric with TiO2 acidic hydrosol prepared with titanium (IV) butoxide as precursor by dip‐pad‐steam process. Photocatalytic activity of TiO2 prepared by low‐temperature steaming process was higher than that of TiO2 dried at 150°C. They stated that the fabric samples had excellent durable self‐cleaning and UV‐protection properties. The crystallinity and photocatalytic activity of TiO2 improved with the increase of the water content in TiO2 hydrosol [39].

**Figure 8.** Self‐cleaning properties of cotton fabric treated with titania nanosols. Copyright 2009 American Chemical Society [45].

Shaban et al. [50] investigated the self‐cleaning properties of cotton fabrics coated with ZnO nanoparticles or ZnO solution containing zinc acetate dihydrate as precursor, 2‐methoxy‐ ethanol as solvent, and monoethanolamine as stabilizer by sol‐gel spin‐coating process. Their results indicated that ZnO nanoparticles had photocatalytic activity especially under UV irra‐ diation due to their high band‐gap energy and the methyl orange dye on cotton fabrics coated with ZnO nanoparticles or ZnO solution degraded under sunlight and 200‐W lamp illumina‐ tion [50].

Noorian et al. [51] prepared precursor solutions based on copper sulfate and/or zinc chlorite containing folic acid, NaOH, and water by in situ synthesis. They immersed the cotton fabric in the solutions, dried and washed. They stated that the combination of ZnO and Cu2 O and the addition of folic acid improved the UV protection and anticrease properties of the fabric samples with, respectively, 87.31% enhanced UVP and 100.75° of crease recovery angle [51].

### **2.4. Antibacterial and antimicrobial activity**

showed that the total burning time and residual weight after burning of the fabric samples were higher than that of untreated fabric according to the flame test at 45° angle. Thus, their burning performance improved after the treatment and nearly 70% of this performance was preserved after 10 washing cycles. The study revealed that the fabric samples had good anti‐ bacterial activity against *Staphylococcus aureus* and *Escherichia coli* with, respectively, 18 and 15 mm diameter of inhibition zone because of the reactive oxygen species (ROS) generation

‐SiO2

TEOS as precursors with different molar ratios, diethanol amine (DEA) as stabilizer, isopro‐ panol as solvent, and chitosan in acetic acid as dispersing agent by sol‐gel process. The fabric

powder, surfactant, and isopropanol and then coated with the suspension to ensure homoge‐ neous coating by spin‐coating machine. Falling at absorbance of methylene blue under UV irra‐ diation for 120 min was attributed to self‐cleaning properties of fabrics treated with TiO2

powders with especially 1:2 molar ratios [48]. The discoloration of wine stain on cotton fabric

that the fabric samples had excellent durable self‐cleaning and UV‐protection properties.

**Figure 8.** Self‐cleaning properties of cotton fabric treated with titania nanosols. Copyright 2009 American Chemical

(IV) butoxide as precursor by dip‐pad‐steam process. Photocatalytic activity of TiO2

powder by using titanium isopropoxide and

acidic hydrosol prepared with titanium

improved with the increase of the water

suspension containing the

dried at 150°C. They stated

‐SiO2

prepared

‐SiO2

colloidal solution increased exposure times under solar light simulator

mechanism of TiO2

264 Recent Applications in Sol-Gel Synthesis

treated with TiO2

content in TiO2

Society [45].

for 0, 4, 8, and 24 h [49].

nanoparticles [47].

samples coated with acrylic acid binder were immersed to TiO2

by low‐temperature steaming process was higher than that of TiO2

Rilda et al. [48] previously produced TiO2

‐SiO2

Wang et al. [39] treated the cotton fabric with TiO2

The crystallinity and photocatalytic activity of TiO2

hydrosol [39].

Antibacterial and antimicrobial activities are important for sport, outdoor, home, automotive, and medical textiles and for garments like hosiery and underwear. For antibacterial and antimicrobial textile finishing, various biocides like silver, triclosan, chitosan, quaternary ammonium salts, N‐halamines, biguanide derivatives, synthetic dyes, and peroxyacids have been applied to textile surfaces [52–58]. Sol‐gel technology as an alternative method can bring advantages like ecological treatment, less chemical use, low‐temperature processing, low toxicity to human health, protection of inherent properties of textile material, and excellent washing and usage durability in this finishing process [52, 55, 59–61].

Different types of sol‐gel systems are known to have antibacterial or antimicrobial effect. These systems are photoactive titania coatings with anatase modification and sol‐gel coatings with embedded colloidal metal or metal compounds like silver, silver salts, copper compounds, zinc, or biocidal quaternary ammonium salts [5, 62–65]. On the other hand, these systems have several disadvantages like high operation temperatures to produce highly photoactive thin films and the use of strong acids to keep aqueous sols in the peptized state that cause destruc‐ tion on textiles. In addition, titania coatings require UV radiation to perform antimicrobial or antibacterial activity [66–69]. Because of harmful effects of strong acids and high temperatures on textiles, in recent methods, organic solvents, for example, alcohol‐based solutions that can be applied at low temperatures, were developed [5, 59, 60]. Simoncic et al. compiled the anti‐ bacterial activity of silver nanoparticles prepared by *in situ* method and colloidal solutions [70].

Poli et al. prepared zinc‐based coatings by sol‐gel method in neutral hydro‐alcoholic medium and applied on cotton fabric to obtain antibacterial activity. They reported that this method was simple, cheap, reproducible, and less harmful when compared to conventional methods [5]. Other than titania‐based sol‐gel coatings, silica‐based coatings are also under examina‐ tion for antibacterial or antimicrobial effectiveness. To enable the antibacterial or antimicro‐ bial effect, polycationic components are incorporated within the silica layer matrix and by this means positively charged polycationic components interact with negatively charged microbial cell membranes and damage their cellular functions [5, 61, 62, 63]. The use of these systems was researched in detail [5, 59–63, 67].

Mahltig et al. reported that the sol‐gel processing exhibited the antimicrobial activity based on controlled release, contact action, or photocatalytic activity [71].

Rivero and Goicoechea presented the detailed review about improving antibacterial proper‐ ties of textiles by sol‐gel process [72].

Zhang et al. classified the application methods on cotton methods for colloidal suspensions of metal nanoparticles and precursor solutions of metal ions, respectively, titled as sol and solu‐ tion to gain antimicrobial properties [52].

Mohamed et al. [73] prepared the colloidal solutions of silver nanoparticles (10–25 nm) syn‐ thesized by chemical reduction process using dextran as stabilizing and reducing agent and modified TEOS using ascorbic acid as scavenging agent and (3‐aminopropyl)triethoxysilane (APTEOS) by using BTCA or vinyltriethoxysilane (VTEOS) and applied it to cotton fabrics by sol‐gel process by dip coating. Silver nanoparticles modified with TEOS and VTEOS were cured with UV irradiation by means of a photoinitiator. They proved that the modified fabrics had antibacterial activity against *S. aureus* and *E. coli* with nearly 90% of bacterial reduction even after 20 washing cycles and thermo‐regulating properties [73].

The combination of antibacterial biopolymers with titania and silica matrix is a different method and this method is observed to give ecological advantage and possessed antibacterial activity both in the presence or absence of light. Arik and Seventekin [55] studied chitosan/titania and chitosan/silica hybrid coatings in terms of antibacterial activity. Sol‐gel method was used to prepare coating solutions and then solutions were applied to cotton fabric. From the study, hybrid coatings were found to have better antibacterial activity and washing durability than only chitosan, only titania, or only silica coatings [55].

#### **2.5. Antiwrinkle, anticrease, durable press or easy‐care effect**

Antiwrinkle, anticrease, durable press, or easy‐care effect has been enabled by the fixation of the crosslinking agents to textile materials. Since dimethyloldihydroxyethylene urea (DMDHEU), which was used commonly in conventional antiwrinkle finishing treatments, releases free formaldehyde that is harmful to human health and environment and causes negative effects due to the acidic catalysts on tensile properties and whiteness index of textile materials, new alternative crosslinking agents and methods have been recently researched. By means of sol‐gel technology, it is possible to enable antiwrinkle effect herewith good tensile and whiteness properties by the use of silane coupling agents [74, 75] like glycidoxy propyl‐ trimethoxysilane as epoxy silanes, vinyltrimethoxysilane as vinyl silanes [76, 77], and tetrae‐ thoxysilane that do not release formaldehyde [78–80].

The main cause of the tensile strength loss and yellowing in conventional antiwrinkle finish‐ ing is the disruptive effect of the acidic catalyst on fibers at high temperatures. But in sol‐gel method, metallic alkoxides and organic solvents are used in mild conditions that provide tensile strength and color retention [78–80].

In antiwrinkle sol‐gel applications, mixed sols with conventional agents can also be applied and different combinations like DMEU/SiO2 (dimethylolethyleneurea/silica), TEOS‐TTB/

DMDHEU (tetra ethoxysilane‐titanium (IV) n‐butoxide/dimethylol dihydroxyethylene urea), BTCA‐MAH/SiO2 (1,2,3,4‐butanetetracarboxylic acid‐maleic anhydride/silica), BTCA‐SHP/ TEOS‐GPTMS (1,2,3,4‐butan tetracarboxylic acid‐sodium hypophosphite/tetraethoxysilane‐ glycidylpropyloxytrimethoxysilane), DMDHEU/TEOS‐GPTMS were evaluated for antiwrin‐ kle finishing and their effects on physical properties of cotton in previous studies [75, 78–81]. These combinations were also found to have advantages in terms of abrasion resistance [75], heat resistance [78], and UV‐light resistance [79] as well as antiwrinkle effect.

Schramm and Rinderer treated the cotton fabric with BTCA and/or nanosol containing GPTMS together with metal alkoxides such as aluminum isopropoxide (AIP), titanium tetra isopropox‐ ide, and zircon tetrabutoxide (ZTB) or hydrophobic trialkoxysilanes such as methyltriethoxysi‐ lane (MTEOS), octyltriethoxysilane (OTEOS), or Dynasylan F8815 (fluoroalkyl functional oligosiloxane) to impart antiwrinkle properties. Treatment only with metal alkoxides led to no improvement of their anticrease properties, while treatment with GPTMS developed their anticrease properties. Moreover, the addition of AIP and OTEOS or MTEOS to GPTMS solution caused the increase of dry‐crease recovery angle (DCRA) of the fabrics treated with the solution, respectively, from 263° to 289°, 290°, and 294°. Tensile properties of fabric treated with GPTMS solution decreased 10% when compared to that of untreated fabric. The addition of AIP solu‐ tion to GPTMS solution brought on further 10% loss of their tensile strength, while the addition of OTEOS and MTEOS solutions to solution containing GPTMS and AIP induced to increasing 10% of the tensile strength with regard to tensile strength of fabrics treated with solution con‐ taining GPTMS and AIP. The treatment with GPTMS solution containing AIP or AIP together with F8815, MTEOS, and OTEOS solutions ensured the enhancement of contact angle values of the fabrics, respectively, from hydrophilic to 112°, 147°, 145°, and 136° corresponds to excel‐ lent hydrophobic properties. They also found that BTCA pretreatment improved the anticrease properties of the fabrics treated with GPTMS solution until 299° of DCRA and led to further loss of tensile strength of the fabric samples treated with GPTMS solution. BTCA pretreatment also did not cause significant change on contact angle values of the fabric samples‐treated GPTMS together with metal alkoxides and/or hydrophobic trialkoxysilanes [22].

#### **2.6. Multifunctional finishing**

Mahltig et al. reported that the sol‐gel processing exhibited the antimicrobial activity based

Rivero and Goicoechea presented the detailed review about improving antibacterial proper‐

Zhang et al. classified the application methods on cotton methods for colloidal suspensions of metal nanoparticles and precursor solutions of metal ions, respectively, titled as sol and solu‐

Mohamed et al. [73] prepared the colloidal solutions of silver nanoparticles (10–25 nm) syn‐ thesized by chemical reduction process using dextran as stabilizing and reducing agent and modified TEOS using ascorbic acid as scavenging agent and (3‐aminopropyl)triethoxysilane (APTEOS) by using BTCA or vinyltriethoxysilane (VTEOS) and applied it to cotton fabrics by sol‐gel process by dip coating. Silver nanoparticles modified with TEOS and VTEOS were cured with UV irradiation by means of a photoinitiator. They proved that the modified fabrics had antibacterial activity against *S. aureus* and *E. coli* with nearly 90% of bacterial reduction

The combination of antibacterial biopolymers with titania and silica matrix is a different method and this method is observed to give ecological advantage and possessed antibacterial activity both in the presence or absence of light. Arik and Seventekin [55] studied chitosan/titania and chitosan/silica hybrid coatings in terms of antibacterial activity. Sol‐gel method was used to prepare coating solutions and then solutions were applied to cotton fabric. From the study, hybrid coatings were found to have better antibacterial activity and washing durability than

Antiwrinkle, anticrease, durable press, or easy‐care effect has been enabled by the fixation of the crosslinking agents to textile materials. Since dimethyloldihydroxyethylene urea (DMDHEU), which was used commonly in conventional antiwrinkle finishing treatments, releases free formaldehyde that is harmful to human health and environment and causes negative effects due to the acidic catalysts on tensile properties and whiteness index of textile materials, new alternative crosslinking agents and methods have been recently researched. By means of sol‐gel technology, it is possible to enable antiwrinkle effect herewith good tensile and whiteness properties by the use of silane coupling agents [74, 75] like glycidoxy propyl‐ trimethoxysilane as epoxy silanes, vinyltrimethoxysilane as vinyl silanes [76, 77], and tetrae‐

The main cause of the tensile strength loss and yellowing in conventional antiwrinkle finish‐ ing is the disruptive effect of the acidic catalyst on fibers at high temperatures. But in sol‐gel method, metallic alkoxides and organic solvents are used in mild conditions that provide

In antiwrinkle sol‐gel applications, mixed sols with conventional agents can also be applied

(dimethylolethyleneurea/silica), TEOS‐TTB/

on controlled release, contact action, or photocatalytic activity [71].

even after 20 washing cycles and thermo‐regulating properties [73].

only chitosan, only titania, or only silica coatings [55].

thoxysilane that do not release formaldehyde [78–80].

tensile strength and color retention [78–80].

and different combinations like DMEU/SiO2

**2.5. Antiwrinkle, anticrease, durable press or easy‐care effect**

ties of textiles by sol‐gel process [72].

266 Recent Applications in Sol-Gel Synthesis

tion to gain antimicrobial properties [52].

It is possible to give various functional properties to textile materials in one step by the combi‐ nation of compatible inorganic precursors, thanks to sol‐gel technology and the finishing like this is called multifunctional finishing. Multifunctional finishing has drawn much attention in the last decades with many studies on this subject. **Table 1** summarized some researches about various functionalities on textile materials treated with *in situ* sol‐gel method and sols with nanoparticles [82–101].

Memon et al. treated polyester fabrics with titania‐doped silica nanosols. It was observed that the antiwrinkle and UV‐protection properties developed, while air permeability and white‐ ness index values decreased only slightly [102].

Onar and Mete developed water‐oil–repellent and flame‐retardant cotton fabrics by sol‐gel method or knife‐over‐roll coating using a one‐step treatment. The nanosol containing TEOS as a precursor, hexadecyltrimethoxysilane as a precursor with water‐repellent properties, and

**Table 1**. (continued).

**Sol preparation**

NP sols NP sols

UPF, hydrophobicity,

Co/Pes (65/35,

TiO

2

NP, ZnONP

Toluene

–

20/80)

antibacterial,

mechanical strength

NP sols

Electroconductive,

Co, CV

AgNO3

Ethanol

–

–

PVP/stabilizer, EG/

[84]

reducing agent,

NaCl/mediating

agent

antibacterial

*In situ* sol‐gel *In situ* sol‐gel *In situ* sol‐gel

Antibacterial,

Co/PES

GPTMS,

Ethanol, water

 HCl

PVA

aluminum

isopropoxide

antifungal, abrasion,

pilling resistance

**Table 1**.

(continued).

UV‐resistance,

UHMWPE

Titanium

Ethanol, water

Acetic acid

–

MPTMS/graft

[86]

polymerization

monomer

Ag/CuNP/

[87]

bioactive additive

butoxide

thermal properties

Antibacterial,

Co

AgNO3

Water

–

Acrylic acid/

NaBH4/reducing

[85]

agent

plasma

polymerization

monomer

self‐cleaning

Anti‐UV, rubbing

Co

TEOS, GPTMS

Ethanol, water

 NH OH 4

Polyacrylate/

Dodecanol/

[82]

nonsurfactant

template

268 Recent Applications in Sol-Gel Synthesis

adhesive,

NM‐5263/

thickening agent

Acrylate‐based

–

[83]

binder

fastness

**Functionality**

**Textile**

**Precursor or NPs**

**Solvent**

**Catalyst**

**NP binding**

**Other chemicals/**

**Ref. no.**

**function**

**Table 1.** Some researches about various functionalities on textile materials treated with *in situ* sol‐gel method and sols with nanoparticles.

PVS: polyvinylsilsesquioxane, VTES: Vinyltriethoxysilane, PLA: poly(lactic acid), HF: Hydrofluoric acid, BF3.OEt2: Boron trifluoride diethyl etherate, MTMS:

methyltrimethoxysilane, MWCNT: Multiwall carbon nanotube.

guanidine phosphate as a flame‐retardant agent were prepared for using at pad‐dry‐cure process. On the other hand, the combination of the nanosols and various polymers such as polyacrylate, polyvinyl acetate (VA), and polyurethane dispersions and fluorocarbon polymer was applied to cotton fabric by knife‐over‐roll process. They found that the fabric coated with nanosols containing VA polymer relatively has good durable water‐oil repellency and flame retardancy properties [103].

Chakrabarti and Banerjee prepared multifunctional cotton fabric that shows enhanced mechanical strength, water and stain repellence, antimicrobial properties, UV‐blocking capacity, and self‐cleaning characteristics by zinc oxide nanoparticles [104].

Ibahim et al. enhanced both the functionality and pigment‐printability of linen/cotton‐blended fabric in a one‐step process by the incorporation of inorganic nanomaterials such as silver (Ag‐ NPs), zinc oxide (ZnO‐NPs), zirconium oxide (ZrO2 ‐NPs), or titanium dioxide (TiO2 ‐NPs) [105].

Mahltig et al. obtained photobactericidal and photochromic textile materials with UV‐protec‐ tive properties by sol‐gel technology and stated that especially epoxysilane‐modified sols led to promising results [106].

Pan et al. prepared superhydrophobic (water contact angle of 146.27°) and UV‐blocking (UPF value of 164.06) cotton fabric by nano‐alumina sol via sol‐gel method [107].

Simoncic et al. compared the sol‐gel application procedures as one step or two steps in terms of multifunctional water‐oil–repellent and antimicrobial properties of cotton and found that one‐step procedure was more effective in the production of coatings with water‐ and oil‐repellent properties, while two‐step procedure provided higher antibacterial activity, as well as better washing fastness [108].

Mahltig and Fischer applied sol‐gel coatings to viscose and polyamide textiles in order to give functional properties like water repellency and antimicrobial activity at the same time and found that textile comfort properties were also preserved [109].

Textor and Mahltig described a sol‐gel–based surface treatment for the preparation of water‐ repellent antistatic textiles and applied it to two types of textiles (100% polyester fabric and 65% polyester and 35% cotton‐blended fabric). They obtained sufficient water repellency and antistatic properties simultaneously and suggested that this concept can be adapted to the alternative multifunctional surface coatings other than combining water repellence with antistatic properties for textile materials [110].

El‐Shafei et al. purposed to develop flame‐retardant and antibacterial cotton fabric by treat‐ ment with BTCA solution containing sodium hypophosphite (SHP) as a catalyst and chitosan phosphate synthesized and then TiO2 nanosols. Increase of TiO2 , SHP and chitosan‐phos‐ phate concentration led to increase of LOI values of the fabric treated with them. The com‐ bination of BTCA and chitosan phosphate causes lower crease recovery angle than that of treatment with only BTCA. The antibacterial activity of the fabrics against *S. aureus, E. coli, Candida albicans* (fungus), and *Aspergillus flavus* (fungus) developed with the increase of TiO2 and chitosan‐phosphate concentration [111].

Rana et al. investigated the water repellency, UV protection, and antibacterial properties of cotton fabric treated with silica nanosols containing dimethyl dimethoxysilane (DMDMS) and TEOS as precursors and AgBr‐TiO2 nanoparticles, which were synthesized by using silver nitrate, potassium bromide, and titanium tetrachloride as precursors, by spray coating process. The treatment with silica nanosols with and without AgBr‐TiO2 particles gave rise to, respec‐ tively, 145.8°, 149.1° and 136° , 144.3° of contact angle values of the fabrics before and after washing process. Nevertheless, the fabrics treated with silica nanosols along with AgBr‐TiO2 particles have excellent UV protection with 41.9 of UPF value and good antibacterial activity with 99.88% bacterial reduction against *E. coli* [112].

guanidine phosphate as a flame‐retardant agent were prepared for using at pad‐dry‐cure process. On the other hand, the combination of the nanosols and various polymers such as polyacrylate, polyvinyl acetate (VA), and polyurethane dispersions and fluorocarbon polymer was applied to cotton fabric by knife‐over‐roll process. They found that the fabric coated with nanosols containing VA polymer relatively has good durable water‐oil repellency and flame

Chakrabarti and Banerjee prepared multifunctional cotton fabric that shows enhanced mechanical strength, water and stain repellence, antimicrobial properties, UV‐blocking

Ibahim et al. enhanced both the functionality and pigment‐printability of linen/cotton‐blended fabric in a one‐step process by the incorporation of inorganic nanomaterials such as silver (Ag‐

Mahltig et al. obtained photobactericidal and photochromic textile materials with UV‐protec‐ tive properties by sol‐gel technology and stated that especially epoxysilane‐modified sols led

Pan et al. prepared superhydrophobic (water contact angle of 146.27°) and UV‐blocking

Simoncic et al. compared the sol‐gel application procedures as one step or two steps in terms of multifunctional water‐oil–repellent and antimicrobial properties of cotton and found that one‐step procedure was more effective in the production of coatings with water‐ and oil‐repellent properties, while two‐step procedure provided higher antibacterial activity, as

Mahltig and Fischer applied sol‐gel coatings to viscose and polyamide textiles in order to give functional properties like water repellency and antimicrobial activity at the same time and

Textor and Mahltig described a sol‐gel–based surface treatment for the preparation of water‐ repellent antistatic textiles and applied it to two types of textiles (100% polyester fabric and 65% polyester and 35% cotton‐blended fabric). They obtained sufficient water repellency and antistatic properties simultaneously and suggested that this concept can be adapted to the alternative multifunctional surface coatings other than combining water repellence with

El‐Shafei et al. purposed to develop flame‐retardant and antibacterial cotton fabric by treat‐ ment with BTCA solution containing sodium hypophosphite (SHP) as a catalyst and chitosan

phate concentration led to increase of LOI values of the fabric treated with them. The com‐ bination of BTCA and chitosan phosphate causes lower crease recovery angle than that of treatment with only BTCA. The antibacterial activity of the fabrics against *S. aureus, E. coli, Candida albicans* (fungus), and *Aspergillus flavus* (fungus) developed with the increase of TiO2

nanosols. Increase of TiO2

(UPF value of 164.06) cotton fabric by nano‐alumina sol via sol‐gel method [107].

found that textile comfort properties were also preserved [109].

‐NPs), or titanium dioxide (TiO2

‐NPs) [105].

, SHP and chitosan‐phos‐

capacity, and self‐cleaning characteristics by zinc oxide nanoparticles [104].

NPs), zinc oxide (ZnO‐NPs), zirconium oxide (ZrO2

retardancy properties [103].

270 Recent Applications in Sol-Gel Synthesis

to promising results [106].

well as better washing fastness [108].

antistatic properties for textile materials [110].

phosphate synthesized and then TiO2

and chitosan‐phosphate concentration [111].

Vasiljević et al. prepared six different solutions containing 1H,1H,2H,2H‐perfluorooctyl‐ triethoxysilane (SiF), 3‐(trimethoxysilyl)‐propyldimethyloctadecyl ammonium chloride (SiQ), and P,P‐diphenyl‐ N‐(3‐(trimethoxysilyl)propyl) phosphinic amide (SiP) together with TEOS or organocyclotetrasiloxane 2,4,6,8‐tetrakis (2‐(diethoxy(methyl)silyl)ethyl)‐2,4,6,8‐ tetramethyl‐cyclotetrasiloxane. Optimization of water, oil repellency, flame‐retardant, and antibacterial properties of the fabric treated were carried out. They revealed that the fabrics treated at optimized conditions have superhydrophobic properties with 161° of contact angle and 4° of sliding angle and good antibacterial properties with 100 and 81.6% bacterial reduc‐ tion against, respectively, *S. aureus* and *E. coli* but not good oil repellency properties (3) [113].

Gu et al. proved the flame retardancy and water repellency properties of cotton fabric treated with phosphorus‐doped silica hydrosol containing hexadecyltrimethoxysilane. They found that the LOI value, residue amount at 600°C, and contact angle of the fabrics increased from, respectively, 18.5, 13.3% and hydrophilic to 29.4, 29.7, and 134.6° when compared to that of untreated fabric. Their onset temperature and pHRR values decreased from, respectively, 320 and 235°C to 217 and 81.46°C [114].

El‐Naggar et al. stated that the cotton fabrics treated with titania nanosols in situ synthesized and then urea nitrate solution by two‐step process possessed excellent antibacterial properties with, respectively, 99.4 and 99.37% bacterial reduction against to *S. aureus* and *E. coli* and excel‐ lent UV‐protection properties with 42.11% UPF value with good durability to washing [115].

Sivakumar et al. studied the antibacterial, UV‐protection, soil release, and self‐cleaning prop‐ erties of the cotton/polyester fabric subjected to TiO2 nanoparticles, which were synthesized using titanium isopropoxide as precursor and then modified with 3‐aminopropyltriethoxysi‐ lane and silicon oil, by pad‐dry‐cure process. The maximum photocatalytic and antibacterial activities were obtained for the fabrics treated with modified TiO2 , while the maximum UPF values were obtained for the fabric treated with unmodified TiO2 [116].

Behzadnia et al. developed the photosonochemical synthesis of N‐Ag/TiO2 on wool fabric using titanium isopropoxide and silver nitrate as precursors and ammonia as nitrogen doping. The effect of pH, sonication, and precursor concentration on antibacterial and photocatalytic prop‐ erties of wool fabrics treated were researched. Ag doping to N‐TiO2 nanocomposites on wool improved self‐cleaning, photocatalytic, and antibacterial properties of N‐doping TiO2 nanocom‐ posites on wool, while sono‐treated samples containing N‐Ag/TiO2 possess higher self‐cleaning and photocatalytic properties when compared to stirred fabrics containing N‐Ag/TiO2 [117].

## **3. Conclusion**

Since 1960s, sol‐gel‐coating method on the substrates like metal, glass, and ceramic has been studied extensively. In the last decades, researches about sol‐gel technology have focused on enabling functional properties to textile materials as an alternative to conventional tex‐ tile finishing treatments. In textile finishing, flame retardancy, water or oil repellency, UV protection, antimicrobial activity, and antiwrinkle effect were already studied by sol‐gel method. In addition, multifunctionality means that two or more of these properties are evaluated in combination and investigated in terms of washing durability, textile comfort, and physical properties. It is an important fact to ensure multifunctional properties in one step, and by nanotechnological sol‐gel method, this problem can be achieved and moreover, eco‐friendly treatments can be applied in textile finishing due to less harmful chemical use. Therefore, sol‐gel technology is expected to be used in plenty of textile finishing processes and promising studies are the starting points for further developments in future.

## **Author details**

Nurhan Onar Camlibel\* and Buket Arik

\*Address all correspondence to<EMAIL_ADDRESS>
Textile Engineering Department, Engineering Faculty, Pamukkale University, Denizli, Turkey

## **References**

[6] Huang KS, Nien YH, Hsiao KC, Chang YS. Application of DMEU/SiO2 gel solution in the antiwrinkle finishing of cotton fabrics. Journal of Applied Polymer Science. 2006;**102(5)**:4136–4143. DOI: 10.1002/app.24246

**3. Conclusion**

272 Recent Applications in Sol-Gel Synthesis

**Author details**

**References**

243–268 p.

10.1007/s10971‐014‐3589‐9

Nurhan Onar Camlibel\* and Buket Arik

\*Address all correspondence to<EMAIL_ADDRESS>
Since 1960s, sol‐gel‐coating method on the substrates like metal, glass, and ceramic has been studied extensively. In the last decades, researches about sol‐gel technology have focused on enabling functional properties to textile materials as an alternative to conventional tex‐ tile finishing treatments. In textile finishing, flame retardancy, water or oil repellency, UV protection, antimicrobial activity, and antiwrinkle effect were already studied by sol‐gel method. In addition, multifunctionality means that two or more of these properties are evaluated in combination and investigated in terms of washing durability, textile comfort, and physical properties. It is an important fact to ensure multifunctional properties in one step, and by nanotechnological sol‐gel method, this problem can be achieved and moreover, eco‐friendly treatments can be applied in textile finishing due to less harmful chemical use. Therefore, sol‐gel technology is expected to be used in plenty of textile finishing processes

and promising studies are the starting points for further developments in future.

Textile Engineering Department, Engineering Faculty, Pamukkale University, Denizli, Turkey

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DOI: 10.1142/S0218625X16500037

## **Sol-Gel Process for Surface Modification of Leather**

Franco Ferrero, Monica Periolatto and Giuseppe Gozzelino

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/67837

#### **Abstract**

Applications in the textile field of sol-gel processes were widely investigated since coatings of fabrics by materials of nanometric size obtained by sol-gel methods represent a functional surface modification attracting even more attention. However, few experiences of the use of nanostructured coatings are reported for leather finishing. In the experiments reported in the present chapter, a nabuk leather was finished by a sol-gel process to confer hydro and oil-repellency. The silica component could act as a protective coating, improving the rubbing performance of the substrate and conferring a certain grade of hydrorepellency, while the oil repellency was due to a fluorocarbon component. The coatings were applied at low add-on of finishing agent with the aim to keep possibly unvaried the esthetic and hand characteristics of the original leather. Contact angle and sorption time measurements of water and oil drops were carried out on the treated samples and compared with the untreated one. A similar comparison was made by testing color fastness to rubbing and change of esthetic appearance. Finally, chemical surface characterization was carried out by Fourier Transform Infrared in Attenuated Total Reflectance (FTIR-ATR) analysis.

**Keywords:** leather, sol-gel, TEOS, FOS, Fluorolink S10, hydrorepellency, oil repellency, contact angle, FTIR-ATR

## **1. Introduction**

Applications in the textile field of sol-gel processes were widely investigated [1–28]. In fact, coatings of fabrics by materials of nanometric size obtained by sol-gel methods represent a functional surface modification attracting even more attention. They have exceptional physical properties and resistances: justification to this behavior comes from the huge area of contact generated when the fillers reach the nanometric size, in combination with a polymer layer of interphase with properties much higher than the matrix ones.

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Materials with repellent properties against water or oil-based soils are of high commercial interest for textiles and leather-containing materials with high demand efforts for washings and cleaning. The finishing agents are often perfluorinated compounds [25–28], while sol-gel systems or functional silanes are used as nonfluorinated chemical alternative, but the oilrepellency can be achieved only by fluorine compounds.

Manufacture of water-resistant leather has attracted dramatic attention in recent years as the increasing demand for waterproof upper, upholstery and garment leathers. In general, a water-resistant leather is prepared by using chemicals that enable to form hydrophobic coatings with low surface free energy on leather surface. These coatings can be polymeric thin films containing silicones, fluorinated, or long-chain hydrocarbons. However, the permeability of air and water vapor of treated leather could be compromised, and the development of new methods for the production of waterproof leather maintaining its natural characteristics is still a challenge [29]. As an alternative, plasma treatments [29–31] or hybrid nanostructured coatings [32–34] have been proposed.

Generally, pure laboratory-grade alkoxysilanes are used as sol-gel precursors. A hybrid framework composite can be obtained by mixing alkoxysilanes with organic precursors, and the final properties of the coating can be tailored on purpose by choosing proper precursors. Tetraethoxysilane (TEOS) is the most widely used precursor in the sol-gel technology [13], nevertheless, it can be partially or totally replaced by fluorinated alkoxysilanes to confer together hydro and oil repellency typical of these compounds [7, 9, 10, 17, 19, 35]. Therefore, the finishing of cotton fabrics was satisfactory experimented by TEOS nanosol modified with 1H,1H,2H,2Hfluorooctyl-triethoxy-silane (FOS) [19] or with Fluorolink S10 (Solvay Solexis), cheaper commercial perfluoropolyether already used with TEOS to prepare hybrid coatings on glass [20, 36].

In the case of leather, a silica-based fluorinated hybrid coating can act as surface protection, improving the rubbing performance of the substrate and conferring a certain grade of hydrorepellency, while the oil repellency can be due to the fluorocarbon component. Moreover, nano- or microstructured coatings can be applied by the sol-gel process, reducing the amount of applied finishing agent to keep possibly unvaried the esthetic and hand characteristics of the original leather. Therefore, in the experiments reported in the present chapter, TEOS, FOS, and Fluorolink S10 were experimented as sol-gel precursors for leather finishing by analogy with the process experimented on cotton fabrics.

Leather is a material resulting from tanning, i.e., the production from animal skin of a chemically and biologically stable material by a process that leaves the original fiber structure more or less intact. A section of the animal skin is reported in **Figure 1** [37].

The most important part of an animal skin is the corium, consisting mainly of collagen, a fibrous protein that is strongly affected by tanning. The basic collagen structure consists of twined triple left-handed helices of peptide chains of different length. The peptide chains within the triple helices are held together by hydrogen bonding as a consequence of the groups belonging to the typical structure of polypeptide, as shown in **Figure 2** [38]. The amino acid composition of collagen is atypical for proteins, particularly with respect to its high hydroxyproline content. The most common motifs in the amino acid sequence of collagen are glycine-proline-X

**Figure 1.** Section of the animal skin.

Materials with repellent properties against water or oil-based soils are of high commercial interest for textiles and leather-containing materials with high demand efforts for washings and cleaning. The finishing agents are often perfluorinated compounds [25–28], while sol-gel systems or functional silanes are used as nonfluorinated chemical alternative, but the oil-

Manufacture of water-resistant leather has attracted dramatic attention in recent years as the increasing demand for waterproof upper, upholstery and garment leathers. In general, a water-resistant leather is prepared by using chemicals that enable to form hydrophobic coatings with low surface free energy on leather surface. These coatings can be polymeric thin films containing silicones, fluorinated, or long-chain hydrocarbons. However, the permeability of air and water vapor of treated leather could be compromised, and the development of new methods for the production of waterproof leather maintaining its natural characteristics is still a challenge [29]. As an alternative, plasma treatments [29–31] or hybrid nanostructured

Generally, pure laboratory-grade alkoxysilanes are used as sol-gel precursors. A hybrid framework composite can be obtained by mixing alkoxysilanes with organic precursors, and the final properties of the coating can be tailored on purpose by choosing proper precursors. Tetraethoxysilane (TEOS) is the most widely used precursor in the sol-gel technology [13], nevertheless, it can be partially or totally replaced by fluorinated alkoxysilanes to confer together hydro and oil repellency typical of these compounds [7, 9, 10, 17, 19, 35]. Therefore, the finishing of cotton fabrics was satisfactory experimented by TEOS nanosol modified with 1H,1H,2H,2Hfluorooctyl-triethoxy-silane (FOS) [19] or with Fluorolink S10 (Solvay Solexis), cheaper commercial perfluoropolyether already used with TEOS to prepare hybrid coatings on glass [20, 36].

In the case of leather, a silica-based fluorinated hybrid coating can act as surface protection, improving the rubbing performance of the substrate and conferring a certain grade of hydrorepellency, while the oil repellency can be due to the fluorocarbon component. Moreover, nano- or microstructured coatings can be applied by the sol-gel process, reducing the amount of applied finishing agent to keep possibly unvaried the esthetic and hand characteristics of the original leather. Therefore, in the experiments reported in the present chapter, TEOS, FOS, and Fluorolink S10 were experimented as sol-gel precursors for leather finishing by analogy

Leather is a material resulting from tanning, i.e., the production from animal skin of a chemically and biologically stable material by a process that leaves the original fiber structure more

The most important part of an animal skin is the corium, consisting mainly of collagen, a fibrous protein that is strongly affected by tanning. The basic collagen structure consists of twined triple left-handed helices of peptide chains of different length. The peptide chains within the triple helices are held together by hydrogen bonding as a consequence of the groups belonging to the typical structure of polypeptide, as shown in **Figure 2** [38]. The amino acid composition of collagen is atypical for proteins, particularly with respect to its high hydroxyproline content. The most common motifs in the amino acid sequence of collagen are glycine-proline-X

repellency can be achieved only by fluorine compounds.

coatings [32–34] have been proposed.

284 Recent Applications in Sol-Gel Synthesis

with the process experimented on cotton fabrics.

or less intact. A section of the animal skin is reported in **Figure 1** [37].

**Figure 2.** Typical molecular structure of polypeptide.

and glycine-X-hydroxyproline, where X is any amino acid other than glycine, proline, or hydroxyproline. The amino acid composition of a leather collagen is about glycine 26.8% of total nitrogen, alanine 8.0%, arginine 15.3%, proline 9.0%, and hydroxyproline 8.0% [38].

The main chemical processes carried out in sequence to transform animal skin into leather are the following:

The chemical modifications induced by these treatments on collagen make many polar groups, such as –OH, –NH–, =CO, available for adsorption through hydrogen bonding, in the case of sol-gel finishing, with the silanol groups yielded by acid-catalyzed hydrolysis of silane groups of the precursors. Moreover, the condensation reactions occurring in the following thermal step can promote grafting of silanols with polar groups of collagen, improving the adhesion of silica nanoparticles on leather. When TEOS is introduced as a coprecursor, –O–Si(OH)3 groups can be bonded on the leather surface and are able to condense with other ≡≡Si–OH or ≡≡Si–O–CH2 –CH3 groups of the fluorinated alkoxysilane precursor.

Fluorolink has a fairly high molecular weight compared with FOS and two silane grafting end groups. These characteristics have been recognized to increase the hydrophobic/oleophobic character of coatings and resistance to mechanical removal from the matrix [39].

## **2. Experimental**

In the experiments, a nabuk leather provided by Foglizzo Leather, Torino, Italy, was finished by a sol-gel process to confer hydro and oil-repellency. Besides the standard preparation, it was dyed with anionic dyes in the presence of auxiliaries to improve dye penetration. Samples of 15 × 4 cm2 were subjected to the treatment.

Tetraethoxysilane (TEOS) and 1H,1H,2H,2H-Fluorooctyltriethoxysilane (FOS), both pure laboratory-grade reagent purchased from Sigma-Aldrich (Italy), and Fluorolink® S10, commercial product from Solvay Solexis (Italy), were used as precursors. In **Figure 3**, the molecular structures are reported; in particular that of Fluorolink was taken from the literature [39], and the molecular weight of the reagent used was in the range of 1750–1950 g/mol.

Finishing nanosols were synthesized via sol-gel method with acid catalysts in ethanol/water solution. TEOS and FOS, TEOS and Fluorolink S10, or the three products alone were used as

**Figure 3.** Molecular structure of (a) Fluorolink S10, (b) FOS, (c) TEOS.

The main chemical processes carried out in sequence to transform animal skin into leather are

The chemical modifications induced by these treatments on collagen make many polar groups, such as –OH, –NH–, =CO, available for adsorption through hydrogen bonding, in the case of sol-gel finishing, with the silanol groups yielded by acid-catalyzed hydrolysis of silane groups of the precursors. Moreover, the condensation reactions occurring in the following thermal step can promote grafting of silanols with polar groups of collagen, improving the adhesion of silica nanoparticles on leather. When TEOS is introduced as a coprecursor,

Fluorolink has a fairly high molecular weight compared with FOS and two silane grafting end groups. These characteristics have been recognized to increase the hydrophobic/oleophobic

In the experiments, a nabuk leather provided by Foglizzo Leather, Torino, Italy, was finished by a sol-gel process to confer hydro and oil-repellency. Besides the standard preparation, it was dyed with anionic dyes in the presence of auxiliaries to improve dye penetration. Samples

Tetraethoxysilane (TEOS) and 1H,1H,2H,2H-Fluorooctyltriethoxysilane (FOS), both pure laboratory-grade reagent purchased from Sigma-Aldrich (Italy), and Fluorolink® S10, commercial product from Solvay Solexis (Italy), were used as precursors. In **Figure 3**, the molecular structures are reported; in particular that of Fluorolink was taken from the literature [39], and

Finishing nanosols were synthesized via sol-gel method with acid catalysts in ethanol/water solution. TEOS and FOS, TEOS and Fluorolink S10, or the three products alone were used as

character of coatings and resistance to mechanical removal from the matrix [39].

the molecular weight of the reagent used was in the range of 1750–1950 g/mol.

groups can be bonded on the leather surface and are able to condense with other

groups of the fluorinated alkoxysilane precursor.

the following:

286 Recent Applications in Sol-Gel Synthesis

–O–Si(OH)3

≡≡Si–OH or ≡≡Si–O–CH2

**2. Experimental**

of 15 × 4 cm2

and removal of unwanted material;

–CH3

were subjected to the treatment.

precursors obtaining different nanosols by magnetic stirring at 25°C for 24 h. Five nanosols were prepared as detailed in **Table 1**.

The nanosol solutions were applied with the spraying technique, widely used at industrial level in dry finishing, which enables an uniform product distribution, but cannot be utilized in the presence of sediments or precipitates. Hence, before the application, the homogeneity of the solutions was tested by a visual check.

The solution amount to be sprayed on each sample was calculated on the basis of the content of dry resin in each solution providing 2, 5, or 10% add-ons. Higher add-ons were not applied to avoid the overhead of the substrate and maintain the nabuk properties unvaried. Since small solution volumes were needed, these were diluted with ethanol to assure a more homogeneous deposition.

In **Table 2**, the composition of the various samples is reported.

After spraying on both the leather surfaces, an impregnation time of 24 h was adopted, and the samples were maintained in sealed test tubes at room temperature. The following step was a thermal treatment in an oven at 120°C for 1 h to promote the solvent evaporation and at the same time the xerogel formation and the grafting reactions on leather.

**Table 1.** Composition, in percent weight, of the prepared nanosols.

**Table 2.** Composition of the samples (F: front; R: reverse).

Contact angle and sorption time measurements were carried out on the treated samples and compared with the untreated leather, as well as the color fastness to rubbing, esthetic, and hand properties. The color fastness to rubbing was tested by a Taber crockmeter mod. 418 according to ISO 11640.

Water and oil repellency were tested by static contact angle and sorption time measurements using HPLC-grade water and paraffin oil (Sigma–Aldrich) with a surface tension of 72 and 31.5 mN/m, respectively. The instrument was a DSA20E Easydrop standard tensiometer (Krüss, Germany) equipped with DSA software. Measuring liquid drops were deposited from a glass syringe on the sample surface by means of the software controlled dosing. The contact angles were the average of three measurements for each sample with a standard deviation of about 2%.

Finally, chemical surface characterization was carried out by FTIR-ATR analysis performed on a Nicolet 5700 instrument equipped with a Smart Orbit ATR single bounce accessory mounting a diamond crystal. A 128 scans at 4 cm−1 resolution in the 4000–500 cm−1 wavelength range were averaged.

## **3. Results and discussion**

#### **3.1. Contact angles and absorption time measurements**

The results of static contact angles with water and paraffin oil as well as the absorption time measurements are reported and compared in **Table 3**.

**Table 3.** Contact angles and absorption times (F: front; R: reverse).

Contact angle and sorption time measurements were carried out on the treated samples and compared with the untreated leather, as well as the color fastness to rubbing, esthetic, and hand properties. The color fastness to rubbing was tested by a Taber crockmeter mod. 418 according to

**F R**

Water and oil repellency were tested by static contact angle and sorption time measurements using HPLC-grade water and paraffin oil (Sigma–Aldrich) with a surface tension of 72 and 31.5 mN/m, respectively. The instrument was a DSA20E Easydrop standard tensiometer (Krüss, Germany) equipped with DSA software. Measuring liquid drops were deposited from a glass syringe on the sample surface by means of the software controlled dosing. The contact angles were the average of three measurements for each sample with a standard deviation of

Finally, chemical surface characterization was carried out by FTIR-ATR analysis performed on a Nicolet 5700 instrument equipped with a Smart Orbit ATR single bounce accessory mounting a diamond crystal. A 128 scans at 4 cm−1 resolution in the 4000–500 cm−1 wavelength

The results of static contact angles with water and paraffin oil as well as the absorption time

ISO 11640.

about 2%.

range were averaged.

**3. Results and discussion**

**Table 2.** Composition of the samples (F: front; R: reverse).

**3.1. Contact angles and absorption time measurements**

**Sample Nanosol type Add-on (% weight)**

288 Recent Applications in Sol-Gel Synthesis

 Untreated – – Nanosol-1 10 10 Nanosol-1 0.5 0.5 Nanosol-2 10 10 Nanosol-2 0.5 0.5 Nanosol-2 0.2 0.2 Nanosol-3 10 10 Nanosol-3 0.5 0.5 Nanosol-4 10 – Nanosol-4 0.5 – Nanosol-5 10 10 Nanosol-5 0.5 0.5

measurements are reported and compared in **Table 3**.

The untreated sample shows intrinsic water repellency (133° and 125° contact angles) due to the reagents used in the wet finishing, in particular in the greasing step. The absorption times of water drop are 30 and 7 min on front and reverse side, respectively, since the more relaxed structure of the latter justifies the faster absorption.

Instead, the untreated leather does not show oil repellency, as it can be deduced from the measurements with paraffin oil. The oil drop is immediately absorbed on both the sides with a persistent and hard to remove halo.

All the treatments on the front side improve the contact angle with water. Except the sample 8F, with the lowest amount of nanosol containing TEOS and Fluorolink, and 9F, with 10% Fluorolink alone, all the others show contact angles around 150°, threshold beyond which they can be defined superhydrophobic. The best results were obtained with the Nanosol-2, based on TEOS alone, and with the Nanosol-5, containing FOS alone; in fact, the samples 4F and 11F showed a contact angle of 160°.

The treatments on the reverse side generally yielded lower contact angles. This is ascribable to the less compact structure of the collagen fibers, which absorb the lyogel, preventing the formation of a homogeneous film. Nevertheless, the treatment with TEOS and Fluorolink and that based on FOS alone enabled to achieve superhydrophobicity in the case of samples 8R, 11R, and 12R.

The tests of oil repellency generally showed the same trend as those with water, but with the same treatment on the same side, the contact angles are obviously lower, due to the difference of surface tension of both test liquids. The Nanosol-1 and Nanosol-2, based on TEOS added by FOS and TEOS alone did not confer oil repellency. This was expectable with the latter nanosol that was lacking in oil repellent component, while with the former, the concentration of fluorocarbon resin added was not enough to give such property. The contact angles of oil on the samples 2R and 3R treated with Nanosol-1, based on TEOS added with FOS, did not attain the threshold of 90°, hence, these samples cannot be defined as oil repellent. The treatment with the Nanosol-5, based on FOS alone, was the most powerful, above all on the front side.

The results are confirmed by the images of drop shapes of water and oil on the Samples 11F and 11R reported in **Figures 4** and **5**.

### **3.2. Color fastness to rubbing**

The resistance test to rubbing is fundamental to evaluate the property of a leather of not giving color release on textiles and at the same time, the color degradation of the leather itself. It is important for any use to simulate contact and friction between the leather and other fabrics, such as a bag on a shirt, an upper on trousers, and a shoe lining on a stocking. It is carried out by a continuous rubbing of wool felts loaded with 500 g, in the case of suede or nabuck, followed by a visual comparison with standard gray scales of the possible color release on the felts together with the color degradation of the leather. The number of cycles is varied according to the intended purpose, usually 100 cycles in dry conditions or 20 in wet.

**Figure 4.** Images of water and oil drops on the Sample 11F.

**Figure 5.** Images of water and oil drops on the Sample 11R.

The values of the standard gray scale for color release range from degree 1 for the maximum release to degree 5 for the minimum. The results of such evaluation on the all samples, in front and reverse sides, after rubbing tests in wet conditions are plotted in **Figure 6**. The color fastness to abrasion was generally improved by the finishing presence with respect to untreated leather (Sample 1), on which just a 1.5 value on gray scale was measured. The best results were obtained with Fluorolink alone (Samples 9 and 10); however, even FOS yielded a good fastness increase (Samples 2 and 11).

#### **3.3. Esthetic aspect**

based on TEOS alone, and with the Nanosol-5, containing FOS alone; in fact, the samples 4F

The treatments on the reverse side generally yielded lower contact angles. This is ascribable to the less compact structure of the collagen fibers, which absorb the lyogel, preventing the formation of a homogeneous film. Nevertheless, the treatment with TEOS and Fluorolink and that based on FOS alone enabled to achieve superhydrophobicity in the case of samples 8R,

The tests of oil repellency generally showed the same trend as those with water, but with the same treatment on the same side, the contact angles are obviously lower, due to the difference of surface tension of both test liquids. The Nanosol-1 and Nanosol-2, based on TEOS added by FOS and TEOS alone did not confer oil repellency. This was expectable with the latter nanosol that was lacking in oil repellent component, while with the former, the concentration of fluorocarbon resin added was not enough to give such property. The contact angles of oil on the samples 2R and 3R treated with Nanosol-1, based on TEOS added with FOS, did not attain the threshold of 90°, hence, these samples cannot be defined as oil repellent. The treatment with the Nanosol-5, based on FOS alone, was the most powerful, above all on the front side. The results are confirmed by the images of drop shapes of water and oil on the Samples 11F

The resistance test to rubbing is fundamental to evaluate the property of a leather of not giving color release on textiles and at the same time, the color degradation of the leather itself. It is important for any use to simulate contact and friction between the leather and other fabrics, such as a bag on a shirt, an upper on trousers, and a shoe lining on a stocking. It is carried out by a continuous rubbing of wool felts loaded with 500 g, in the case of suede or nabuck, followed by a visual comparison with standard gray scales of the possible color release on the felts together with the color degradation of the leather. The number of cycles is varied accord-

ing to the intended purpose, usually 100 cycles in dry conditions or 20 in wet.

and 11F showed a contact angle of 160°.

290 Recent Applications in Sol-Gel Synthesis

and 11R reported in **Figures 4** and **5**.

**Figure 4.** Images of water and oil drops on the Sample 11F.

**3.2. Color fastness to rubbing**

11R, and 12R.

The esthetic aspect should be critical in order to choose an optimal finish treatment for leather articles. In fact, for these products, the functional property, in this case water and oil repellency, is not the only aspect to consider.

**Figure 6.** Color fastness evaluation after wet rubbing.

By comparison between treated samples and reference, four parameters were visually, or to the touch, evaluated by assigning a number decreasing as the difference with respect to the original sample is increasing:

The results are plotted in **Figures 7**–**10** for each aspect. With all the treatments, a worsening of the esthetic characteristics was generally observed, but not all can be considered equally important. An uniform darkening of color, if not excessive, is preferable to other changes, since in the previous dyeing a clearer shade can be conferred in order to obtain, after the solgel process, the desired shade. This is the case, for example, of the Sample 12F, treated with the lowest add-on of FOS alone, which showed only a color shade change of one degree lower with respect to 11F, one of the best samples, treated with the same nanosol, but with a higher add-on (10%).

Some treatments caused a compaction of surface fibers, with consequent worsening of hand properties and comfort; hence, they should be avoided.

The writing effect is considered a marginal aspect, and its change is not critical for a sample evaluation.

**Figure 7.** Shade change evaluation.

#### Sol-Gel Process for Surface Modification of Leather http://dx.doi.org/10.5772/67837 293

**Figure 8.** Stiffness change evaluation.

By comparison between treated samples and reference, four parameters were visually, or to the touch, evaluated by assigning a number decreasing as the difference with respect to the

The results are plotted in **Figures 7**–**10** for each aspect. With all the treatments, a worsening of the esthetic characteristics was generally observed, but not all can be considered equally important. An uniform darkening of color, if not excessive, is preferable to other changes, since in the previous dyeing a clearer shade can be conferred in order to obtain, after the solgel process, the desired shade. This is the case, for example, of the Sample 12F, treated with the lowest add-on of FOS alone, which showed only a color shade change of one degree lower with respect to 11F, one of the best samples, treated with the same nanosol, but with a higher

Some treatments caused a compaction of surface fibers, with consequent worsening of hand

The writing effect is considered a marginal aspect, and its change is not critical for a sample

original sample is increasing:

292 Recent Applications in Sol-Gel Synthesis

to the maximum stiffness;

add-on (10%).

evaluation.

**Figure 7.** Shade change evaluation.

the maximum change toward darker shades;

attributed to maximum compaction of the fibers;

properties and comfort; hence, they should be avoided.

**Figure 9.** Grain evaluation.

**Figure 10.** Writing effect evaluation.

#### **3.4. FTIR-ATR analysis**

All the samples were subjected to FTIR-ATR analysis to investigate the chemical composition of the leather substrate, highlighting the presence of characteristic groups of leather tanned and dyed as well as of finishing agents. In **Figure 11**, the spectra of the Sample 2F, treated with TEOS and FOS, are compared with that of untreated leather, and the peaks assignable to the characteristic groups according to literature data are evidenced.

The wavelength interval useful to reveal the presence of various finishing agents ranges from 1400 to 700 cm−1. In particular, the peaks between 1250 and 1150 cm−1 shown by the finished leather are due to stretching of C-F bond in CF2 e CF3 groups and indicate the presence of fluorinated compounds on the leather surface. The peak at 1088 cm−1, ascribable to Si-O-Si group, shows the presence of silicone nanoparticles on the surface. Such peak is present also with lower absorbance on the untreated sample since it is due to collagen component of the leather.

The spectrum of the Sample 9F, treated with the Nanosol-4, based on Fluorolink alone, shows a strong presence of fluorine and silicon compounds on the surface, as it can be observed in **Figure 12**. In the spectrum of the Sample 11F, treated with the Nanosol-5, based on FOS alone, a peak at about 900 cm−1, ascribable to Si-C bond, also appears, as evidenced in **Figure 13**. Coupling it with the lowering, in comparison with the reference, of peaks related to OH and CH groups, at 3300 and 1600 cm−1, it can be concluded that a grafting of the finishing agent on the leather surface could occur during the thermal treatment. The comparison between the spectra of the samples treated with nanosols containing TEOS and those with nanosols based on FOS or Fluorolink alone shows a decrease of surface concentration of fluorine groups confirming a dilution effect due to TEOS.

**Figure 11.** FTIR-ATR spectra of Sample 2F, treated with TEOS + FOS, and untreated reference (REF).

**Figure 12.** FTIR-ATR spectra of Sample 9F, treated with Fluorolink alone, and untreated reference (REF).

**Figure 13.** FTIR-ATR spectra of Sample 11F, treated with TEOS alone, and untreated reference (REF).

#### **4. Conclusions**

**3.4. FTIR-ATR analysis**

294 Recent Applications in Sol-Gel Synthesis

leather.

All the samples were subjected to FTIR-ATR analysis to investigate the chemical composition of the leather substrate, highlighting the presence of characteristic groups of leather tanned and dyed as well as of finishing agents. In **Figure 11**, the spectra of the Sample 2F, treated with TEOS and FOS, are compared with that of untreated leather, and the peaks assignable to the

The wavelength interval useful to reveal the presence of various finishing agents ranges from 1400 to 700 cm−1. In particular, the peaks between 1250 and 1150 cm−1 shown by the finished

fluorinated compounds on the leather surface. The peak at 1088 cm−1, ascribable to Si-O-Si group, shows the presence of silicone nanoparticles on the surface. Such peak is present also with lower absorbance on the untreated sample since it is due to collagen component of the

The spectrum of the Sample 9F, treated with the Nanosol-4, based on Fluorolink alone, shows a strong presence of fluorine and silicon compounds on the surface, as it can be observed in **Figure 12**. In the spectrum of the Sample 11F, treated with the Nanosol-5, based on FOS alone, a peak at about 900 cm−1, ascribable to Si-C bond, also appears, as evidenced in **Figure 13**. Coupling it with the lowering, in comparison with the reference, of peaks related to OH and CH groups, at 3300 and 1600 cm−1, it can be concluded that a grafting of the finishing agent on the leather surface could occur during the thermal treatment. The comparison between the spectra of the samples treated with nanosols containing TEOS and those with nanosols based on FOS or Fluorolink alone shows a decrease of surface concentration of fluorine groups con-

**Figure 11.** FTIR-ATR spectra of Sample 2F, treated with TEOS + FOS, and untreated reference (REF).

e CF3

groups and indicate the presence of

characteristic groups according to literature data are evidenced.

leather are due to stretching of C-F bond in CF2

firming a dilution effect due to TEOS.

The research work on the leather was aimed to confer water and oil repellency and increase the color fastness to abrasion through a coating able to give the desired properties without unduly damaging the esthetic characteristics of the final product.

The application of a functional finishing on the leather by sol-gel conferred the desired properties, keeping the peculiar properties of the substrate unvaried. In particular for water and oil repellency, FOS-based nanosol at 10% add-on can be considered the best solution.

However, the nanosol based on Fluorolink alone enabled to obtain the best increase of color fastness to abrasion, but satisfactory results of this property were observed also with FOSbased nanosol at 10%, which can be considered as the optimal solution able to couple the two objectives. Moreover, the evaluation of the esthetic properties did not evidence a significant worsening of these with respect to the untreated leather.

Nanosols obtained by TEOS + FOS and TEOS + Fluorolink mixtures showed results generally worse both in terms of performance and esthetic appearance. This was attributed to the dilution effect due to TEOS.

The surface analysis carried out by FTIR-ATR has validated some previous knowledge in the textile field confirming the possibility to successfully apply the sol-gel treatment on a different substrate.

Thanks to the simple involved reactions and process, and the good obtained results, sol-gel can, in conclusion, be indicated as a valid finishing process for leather, opening the way for a future industrial scale up.

## **Acknowledgements**

The authors are grateful to Foglizzo Leather Company for the technical support and to Ing. Danilo Picariello for the experimental work.

## **Author details**

Franco Ferrero\*, Monica Periolatto and Giuseppe Gozzelino

\*Address all correspondence to<EMAIL_ADDRESS>
Department of Applied Science and Technology, Polytechnic of Torino, Torino, Italy

## **References**

[5] Satoh K., Nazakumi H., Morita M. Novel fluorinated inorganic–organic finishing materials for nylon carpeting. Textile Research Journal 2004; 74: 1079–1084. DOI: 10.1177/004051750407401209.

However, the nanosol based on Fluorolink alone enabled to obtain the best increase of color fastness to abrasion, but satisfactory results of this property were observed also with FOSbased nanosol at 10%, which can be considered as the optimal solution able to couple the two objectives. Moreover, the evaluation of the esthetic properties did not evidence a significant

Nanosols obtained by TEOS + FOS and TEOS + Fluorolink mixtures showed results generally worse both in terms of performance and esthetic appearance. This was attributed to the dilu-

The surface analysis carried out by FTIR-ATR has validated some previous knowledge in the textile field confirming the possibility to successfully apply the sol-gel treatment on a different substrate. Thanks to the simple involved reactions and process, and the good obtained results, sol-gel can, in conclusion, be indicated as a valid finishing process for leather, opening the way for a

The authors are grateful to Foglizzo Leather Company for the technical support and to Ing.

Department of Applied Science and Technology, Polytechnic of Torino, Torino, Italy

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296 Recent Applications in Sol-Gel Synthesis

future industrial scale up.

**Acknowledgements**

**Author details**

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298 Recent Applications in Sol-Gel Synthesis

## *Edited by Usha Chandra*

Versatility, extended compositional ranges, better homogeneity, lesser energy consumption, and requirement of nonexpensive equipments have boosted the use of sol-gel process on top of the popularity in the synthesis of nanosystems. The solgel technique has not only revolutionized oxide ceramics industry and/or material science but has also extended widely into multidimensional applications. The book Recent Applications in Sol-Gel Synthesis comprises 14 chapters that deal mainly with the application-oriented aspects of the technique. Sol-gel prepared metal oxide (MO) nanostructures like nanospheres, nanorods, nanoflakes, nanotubes, and nanoribbons have been employed in biomedical applications involving drug deliveries, mimicking of natural bone, and antimicrobial activities. The possibility of controlling grain size in aerogel and preparation of ultrahigh-temperature ceramic (UHTC)-based materials, fluorescent glasses, ultraviolet photosensors, and photocatalysts have been discussed in detail by the experts in the field. The usefulness of sol-gel materials as active GRIN, as textile finisher, and as leather modifier with water-repellent and oil-resistive properties would be an incentive for researchers keen to pursue the field.

Recent Applications in Sol-Gel Synthesis

Recent Applications in

Sol-Gel Synthesis

*Edited by Usha Chandra*

Photo by Rost-9D / iStock


*Edited by*

*Mohammed Naguib Abd El-Ghany Hasaneen*

This book is divided into two sections namely: synthesis and properties of herbicides and herbicidal control of weeds. Chapters 1 to 11 deal with the study of different synthetic pathways of certain herbicides and the physical and chemical properties of other synthesized herbicides. The other 14 chapters (12-25) discussed the different methods by which each herbicide controls specific weed population. The overall purpose of the book, is to show properties and characterization of herbicides, the physical and chemical properties of selected types of herbicides, and the influence of certain herbicides on soil physical and chemical properties on microflora. In addition, an evaluation of the degree of contamination of either soils and/or crops by herbicides is discussed alongside an investigation into the performance and photochemistry of herbicides and the fate of excess herbicides in soils and field crops.

ISBN 978-953-307-803-8

Herbicides - Properties, Synthesis and Control of Weeds

Photo by Brian Brown / iStock


**Treatment and Control of Leishmaniasis Using Photodynamic Therapy**

Debora P. Aureliano, Martha S. Ribeiro, José Angelo Lauletta Lindoso, Fabio C. Pogliani, Fábio P. Sellera, Dennis Song and Mauricio S. Baptista

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/57456


**3. Ghrelin**

#### **3.1. Generalities**

Ghrelin is a peptide hormone produced in the gastrointestinal tract, and it has an important role in regulating the use of energy in human organism. Ghrelin undergoes posttranslational changes resulting in two circulating forms: unacylated ghrelin (UAG) and acylated ghrelin (AG) [51]. This hormone acts directly on hypothalamus and indirectly by increasing the expression of orexigenic peptides such as neuropeptide Y, Agouti-related protein, proopiomelanocortin, and corticotropin-releasing hormone [52].

In addition to its effect on hunger, ghrelin has important effects on glucose homeostasis, energy homeostasis, heart, muscular atrophy, bone metabolism, and tumors [53]. Recent studies emphasize that AG excess is correlated with insulin resistance and metabolic alterations; thereby, the AG/UAG ratio could play a role in the development of MetS [54].

#### **3.2. Ghrelin and metabolic syndrome**

Ghrelin is inversely associated with MetS components, and progressively lower ghrelin levels are being correlated with its severity. Ukkola O et al. emphasized the correlation of low ghrelin levels in obese patients with metabolic syndrome [55]. Also, the positive correlation of ghrelin levels with hypertension, insulin resistance, and obesity has been confirmed by numerous studies. McLaughlin et al. have concluded that ghrelin correlates with MetS mainly based on obesity as well as they identified lower ghrelin levels in patients with MetS and obesity than in non-obese MetS patients [10]. Likewise, many studies confirm the relation between MetS and ghrelin [11–16].