**2. Analytical model**

In this section, we briefly discuss the important nonlinear effects in SOAs, mathematical formulation of modified nonlinear Schrödinger equation (MNLSE), finite-difference beam propagation method (FD-BPM) that is used in the simulation, and nonlinear propagation characteristics of solitary optical pulses in SOAs.

#### **2.1. Important nonlinear effects in SOAs**

86 Optical Communication

Kawaguchi & Inoue, 1996b).

(Das *et al.,* 2007).

**2. Analytical model**

although they may include waveform distortion and additional chirp. If the demultiplexed signal obtained as the FWM signal has optical phase-conjugate characteristics, the demultiplexed signal can be compressed using a dispersive medium. However, such optical phase-conjugate characteristics of FWM signals have not yet been reported to the best of author's knowledge. Another advantage of FWM with short duration optical pump pulses is the high conversion efficiency. In conventional systems, the FWM conversion efficiency in an SOA is limited due to gain saturation. However, high FWM conversion efficiency can be achieved with short duration optical pump and probe pulses as it is possible to reduce gain saturation and hence increase FWM conversion efficiency in an SOA by applying strong pump intensity (Shtaif & Eisenstein, 1995; Shtaif *et al.,* 1995; Kawaguchi & Inoue, 1996a;

In this chapter, we present the detail numerical simulation results of optical phase-conjugate characteristics of picosecond FWM signal pulses generated in SOAs using the FD-BMP (Das *et al.,* 2000; Razaghi *et al.,* 2009). These simulations are based on the nonlinear propagation equation considering the group velocity dispersion, self-phase modulation (SPM), and twophoton absorption (TPA), with the dependencies on the carrier depletion (CD), carrier heating (CH), spectral-hole burning (SHB), and their dispersions, including the recovery times in SOAs (Hong *et al.,* 1996). The main purpose of our simulations is to provide answers to the following questions: 1) how is the nature of the optical phase-conjugate maintained for a short FWM signal pulse? 2) how does the chirp observed in the FWM signals affect the nature of the optical phase-conjugate? For this reason, we have analyzed the system in which the Fourier transform-limited Gaussian optical pulse is linearly chirped by transmission through a fiber (Fiber I) and then injected into an SOA as a probe pulse, together with a pump pulse that has a 1 ~ 10 ps pulsewidth. The FWM signal is generated by the mixing of the pump pulse and the probe pulse, and is selected by an optical narrow band-pass filter. The FWM signal is then transmitted through another fiber (Fiber II) that has the same group velocity dispersion (GVD) as Fiber I and an appropriate length. The simulations are based on the nonlinear propagation equation considering the GVD, SPM, and TPA, with dependencies on CD, CH, SHB, and

The FD-BPM is useful to obtain the propagation characteristics of single pulse or miltipulses using the modified nonlinear Schrödinger equation (MNLSE) (Hong *et al.,* 1996 & Das *et al.,* 2000), simply by changing only the combination of input optical pulses. These are: (1) single pulse propagation (Das *et al.,* 2008), (2) FWM characteristics using two input pulses (Das *et al.,* 2000), (3) optical DENUX using several input pulses (Das *et al.,* 2001), (4) optical phase-conjugation using two input pulses with chirp (Das *et al.,* 2001) and (5) optimum time-delayed FWM characteristics between the two input pump and probe pulses

In this section, we briefly discuss the important nonlinear effects in SOAs, mathematical formulation of modified nonlinear Schrödinger equation (MNLSE), finite-difference beam

dispersion of those properties (Das *et al.,* 2000; Hong *et al.,* 1996).

There are several types of "nonlinear effects" occurs in SOAs. Among them, the important four types of "nonlinear effects" are shown in Fig. 1. These are namely: (i) spectral holeburning (SHB), (ii) carrier heating (CH), (iii) carrier depletion (CD) and (iv) two-photon absorption (TPA).

**Figure 1.**

Figure 1 shows the time-development of the population density in the conduction band after excitation (Das, 2000). The arrow (pump) shown in Fig. 1 is the excitation laser energy. When the life time is less than 100 fs (i.e., < 100 fs), the SHB effect is dominant. The SHB occurs when a narrow-band strong pump beam excites the SOA, which has an inhomogeneous broadening. The SHB arises due to the finite value of intraband carriercarrier scattering time (~ 50 – 100 fs), which sets the time scale on which a quasi-equilibrium Fermi distribution is established among the carriers in a band. After the life time ~ 1 ps, the SHB effect is relaxed and the CH effect becomes dominant. The process tends to increase the temperature of the carriers beyond the lattice's temperature. The main causes of heating the carriers are (1) the stimulated emission, since it involves the removal of "cold" carriers close to the band edge and (2) the free-carrier absorption, which transfers carriers to high energies within the bands. The "hot"-carriers relax to the lattice temperature through the emission of optical phonons with a relaxation time of ~ 0.5 – 1 ps. The effect of CD remains for about 1 ns. The stimulated electron-hole recombination depletes the carriers, thus reducing the optical gain. The band-to-band relaxation also causes CD, with a relaxation time of ~ 0.2 – 1 ns. For ultrashort optical pumping, the TPA effect also becomes important. An atom makes a transition from its ground state to the excited state by the simultaneous absorption of two laser photons. All these nonlinear effects (mechanisms) are taken into account in the

modeling/ simulation and the mathematical formulation of modified nonlinear Schrödinger equation (MNLSE).


*3.1. Participants*

Between 11 January 2017 and 12 April 2018, 150 children and adolescents (mean age 11.8 ± 4.1 years, median 11.25, range 5.1–20.8; 80% boys) entered the trial. The ASD symptoms were 'severe' in 78.7% per ADOS-2 (comparison score = 8–10) [31] and the adaptive levels were 'low' (composite score ≤ 70) in 88%, as per the Vineland Behavior Scales [32].

The participant's characteristics are provided in Table 1. Fifty participants were randomly assigned to each of the three treatments in Period 1 and 44 participants per group completed the study (Figure 2).

Among the 150 participants who underwent randomization, 131 (87%) submitted valid questionnaires at the onset and end of the first treatment period (Figure 2), enabling a between-subject analysis in this period (i.e., to compare the change in sleep parameters between the participants who received cannabinoids and the participants who received the placebo). In total, 107 participants (71%) submitted valid questionnaires at the onset and the end of both the first and second treatment period, enabling a within-subject analysis (i.e., to compare the change in sleep parameters while receiving cannabinoids, while receiving the placebo, and in participants who received both treatments).

The participants' baseline characteristics, including sleep disturbances, as indicated by the CSHQ total and sub scores, were similar in the three treatment arms (Table 1).

Overall, 18 participants (12%) withdrew from the trial for the following reasons: 13 for reasons unrelated to treatment, three due to adverse events, and two due to ineffectiveness. In total, 131 participants (87%) had valid CSHQ scores before and after the treatment in the first treatment period. In total, 107 participants (71%) had valid pre-and post-treatment scores in both treatment periods, allowing a within-subject comparison.

#### *3.2.  Higher CSHQ scores (indicating more prominent sleep disorder symptoms) at the baseline were correlated with a younger age (Pearson correlation r = −0.288, *p* < 0.001) and with higher SRS total scores, indicating more severe core autistic traits (r = 0.175, *p* = 0.036). The CSHQ scores were not associated with sex or adaptive behavior, as indicated by the VABS composite scores.

Notably, the baseline characteristics were not different between the participants included in the per-protocol analysis and the participants who were excluded due to withdrawal or missing data, including age (*p* = 0.83); sex (*p* = 0.86); the severity of sleep disorders, as reflected by the CSHQ total score (*p* = 0.63); adaptive behavior, as evaluated by the VABS Composite scores (*p* = 0.57); and the severity of the core autistic symptoms, as assessed by the ADOS-2 (*p* = 0.58), CARS (*p* = 0.75), and the SRS (*p* = 0.25).

#### *3.3. Impact of Cannabinoid Treatment on Sleep*

The impact of the cannabinoid treatment on sleep disturbances was assessed using the CSHQ. In total, 131 participants had valid CSHQ scores, both pre-treatment and post-treatment, in the first 12-week treatment period. Among these 131 participants, 44 received a whole-plant extract (BOL-DP-O-01-W, CBD:THC ratio = 20:1), 42 received pure cannabinoids (BOL-DP-O-01, CBD, and THC at a 20:1 ratio), and 45 received a placebo. The CSHQ total scores and the subscale scores did not differ significantly between the participants who received cannabinoids and the participants who received the placebo

(Table 2). None of these measures differed significantly between the participants who received the whole-plant extract versus the pure cannabinoids (Table 2).

**Table 2.** Impact of cannabinoid treatment on sleep. Comparison of treatment effects in the 1st 12-week period.

Between-subject analyses of the change in the CSHQ scores following treatment in the first treatment period. CSHQ—Children's Sleep Habits Questionnaire. Positive change (increment of CSHQ scores) indicates worsening of the sleep disorder. Change in the CSHQ scores from baseline following treatment is compared between the 3 treatment arms. ˆ One-way ANOVA for influence of treatments between study groups. Notably, the difference between cannabinoid treatment and placebo was not statistically significant, even when combining the two cannabinoid treatments into one group, compared to placebo (data not shown).

Similar negative results were found in the second treatment period (Table S2) and when comparing the two treatments that each participant received, using a within-participant analysis (Table S3).

#### *3.4. Longitudinal Associations between Sleep, Behavior, and Autistic Core Symptoms*

Regardless of the treatment, improvements in the sleep disturbances, as indicated by a decline in the CSHQ total score, were associated with improvements in the autistic core symptoms, as well as the associated disruptive behaviors in both treatment periods.

The autistic core symptoms were assessed using the SRS total score (higher scores indicate higher severity of symptoms). Changes in the SRS total score correlated with changes in the CSHQ total score in Period 1 (Pearson correlation: r = 0.266, *p* = 0.008) and Period 2 (r = 0.309, *p* = 0.004).

Improvements in the ASD-associated disruptive behaviors were evaluated by the Clinical Global Impression–Improvement rate (CGI-I: lower rates indicate improvement). The CGI-I rate was associated with a change in the CSHQ total score in Period 1 (one-way ANOVA: f = 4.5, *p* = 0.013) and Period 2 (f = 3.36, *p* = 0.038).


**3. Data resources**

#### **3.1 Wind pressure data resources**

Pressure measurement testing was carried out on a rectangular tall building, of cross-Section 180 mm � 60 mm (Breadth�Depth) and height of H = 600 mm. The pressure distribution on the 1:400 scaled building model was measured using a DSM3400 synchronous multi-pressure sensing system (SMPSS). **Figure 1** shows arrangement details of the pressure taps and experimental setup. Pressure taps were arranged in 14 rows �12 columns on the windward/leeward surfaces and in 14 rows �4 columns on side surfaces. The sampling frequency and duration were 330 Hz and 90 s respectively. In this study, the approaching wind perpendicularly attacking the relatively wider and narrower surface of the building correspond to two different working conditions, i.e., angle of attack (AOA) of 0 degree and 90 degrees respectively.

The three targeted wind profiles have similar distributions of velocity and turbulence but different twisted angle profiles. Specifically, the wind speed and turbulence intensity profiles follow power-law functions with exponents of 0.11 and � 0.24. The maximum twisted angles are 0°, 15° and 30°, thus the profiles are respectively labeled CWP, TWP15 and TWP30. It should be noted that variation of twisted angles with height for TWP15 and TWP30 conforms with the negative power curve expressed in Eqs. (7) and (8), and as given in [22].

$$\theta\_{15}(z) = \mathbf{15} \times \exp\left(-0.0976 \times (z/25)\right) \tag{7}$$

*Mode Interpretation of Aerodynamic Characteristics of Tall Buildings Subject to Twisted… DOI: http://dx.doi.org/10.5772/intechopen.103757*

$$\theta\_{\text{30}}(z) = \mathbf{30} \times \exp\left(-0.106 \times (z/25)\right) \tag{8}$$

where *θi*ð Þ*z* represents the twisted angle measured at the height z; the subscript i denotes the maximum twisted angle of TWP, herein, i = 15 and 30.

Three types of wind fields (CWP, TWP15 and TWP30), were generated in a wind tunnel by using passive simulating facilities. As shown in **Figure 2(b)** and **(c)**, to replicate the twisted wind, the wooden vane system was placed 5 m upstream away from the central axis of the building model, and the windward ends of the single wooden vane were isolated 1 m from each other. It should be noted that the wooden vane employed in this study was adjustable, indicating that the wooden strip at a certain height could be offset at any desired angle. Moreover, to compensate for the dissipation near the wind tunnel ground, three rows of roughness elements were rotated at a certain angle are set in a stagger arrangement and placed between the wooden vane

#### **Figure 2.**

*Experimental setup and details: (a) distribution of pressure taps on building model; (b) TWP test arrangement in wind tunnel; (c) section plan of the experimental setup.*

system and the building model. To determine the region with uniform twisted flow properties, a grid measurement system constituted by blue dash lines was utilized to monitor the flow features at each grid point. After trial and error, it turned out that the targeted twisted wind can maintain consistent flow properties within a rectangular region (shaded in orange) with dimensions of 1.5 m � 2.0 m (width �length) around the turntable center. *zref* indicates the reference height which is located at the building roof (z = 0.6 m); *Uref* denotes the reference velocity and equals 6.2 m/s; *Iref* represents the reference turbulence intensity and equals 6.9%. According to the reference wind speed *Uref* and building breath *B*, the Reynolds number is calculated as *Re* = 2.55 � 104 .

#### **3.2 Flow field data resources**

#### *3.2.1 Inflow turbulence generation*

Appropriately replicating the inflow turbulence features is a requisite for obtaining accurate LES simulation results. In this study, the narrowband synthesis random flow generator (NSRFG) technique is utilized to simulate inflow turbulence by generating time history series of the fluctuating velocity. Turbulence integral scales (see Eqs.(9)– (11)) conform to those in wind codes (AIJ, 2004; ESDU 85020, 2001), which are also identical to the setting given in [7]; the velocity distribution in the frequency domain corresponds to the von Karman spectrum (see Eqs. (12)–(14)), which can reflect typical spectral features of the turbulent ABL flow in a wind tunnel. The superimposition of the zero-mean fluctuating component and the mean wind profile formulate the initial inflow boundary condition. For specific implement procedures, one can refer to the work of [23]. Note that the profiles of wind speed, turbulence intensity and twisted angle are consistent with the setting in the wind tunnel.

$$L\_{\rm u}(\mathbf{z}) = \mathbf{100} \cdot \lambda\_L \cdot \left(\frac{z}{\mathbf{30}\lambda\_L}\right)^{0.5} \tag{9}$$

$$L\_v(\mathbf{z}) = \mathbf{0}.5 \frac{\left(\sigma\_v\right)^3}{\sigma\_u} L\_u(\mathbf{z}) \tag{10}$$

$$L\_w(\mathbf{z}) = \mathbf{0}.5 \left(\frac{\sigma\_w}{\sigma\_u}\right)^3 L\_u(\mathbf{z}) \tag{11}$$

$$\mathcal{S}\_{\boldsymbol{u}}(\mathbf{f}) = \frac{4(I\_{\boldsymbol{u}}\boldsymbol{U})^{2}(L\_{\boldsymbol{u}}/\boldsymbol{U})}{\left[\mathbf{1} + \text{70.8}\left(\boldsymbol{f}L\_{\boldsymbol{u}}/\boldsymbol{U}\right)^{2}\right]^{5/6}}\tag{12}$$

$$\mathcal{S}\_{\boldsymbol{v}}(\mathbf{f}) = \frac{4(I\_{\boldsymbol{v}}\boldsymbol{U})^{2}(L\_{\boldsymbol{v}}/\boldsymbol{U})\left[\mathbf{1} + \mathbf{1}\mathbf{8}\mathbf{8}.4\left(\mathbf{2}\mathbf{f}L\_{\boldsymbol{v}}/\boldsymbol{U}\right)^{2}\right]}{\left[\mathbf{1} + \mathbf{7}\mathbf{0}.\mathbf{8}\left(\mathbf{2}\mathbf{f}L\_{\boldsymbol{v}}/\boldsymbol{U}\right)^{2}\right]^{11/6}}\tag{13}$$

$$\mathbf{S}\_{w}(\mathbf{f}) = \frac{4(I\_{w}U)^{2}(L\_{w}/U)\left[1 + \mathbf{188.4}\left(2\mathfrak{f}L\_{w}/U\right)^{2}\right]}{\left[1 + \mathbf{70.8}\left(2\mathfrak{f}L\_{w}/U\right)^{2}\right]^{11/6}}\tag{14}$$

where *λL* is the scaled ratio; *L*(*z*), *I*(*z*) and *S*(*z*) are the turbulence integral scale, turbulence intensity and power spectral respectively. The subscripts *u*, *v* and *w* denote *Mode Interpretation of Aerodynamic Characteristics of Tall Buildings Subject to Twisted… DOI: http://dx.doi.org/10.5772/intechopen.103757*

the components of the physical quantities in the along-wind, crosswind, and torsional directions respectively; *f* is the frequency.


# **Biocultural Restoration in Hawaiʻi**

Edited by Kawika B. Winter, Kevin Chang and Noa Kekuewa Lincoln Printed Edition of the Special Issue Published in *Sustainability*

www.mdpi.com/journal/sustainability


**1. Introduction**

Austenitic stainless steels (ASSs) that generally have excellent corrosion resistance, good plasticity, and a high strain hardening coefficient are widely used in food, petrochemicals, and the nuclear industry. However, their low yield strength limits their application in structural engineering and automotive industry [1,2]. The development of high strength-high ductility ASSs is considered an attractive approach to expanding their use and has been extensively studied.

There are various methods to improve the strength of ASSs, including cold deformation strengthening, bake hardening strengthening, grain size strengthening, et cetera. [3]. Due to the high strain hardening coefficient of ASSs, cold deformation strengthening with a simpler and easier process is considered an effective method and more suitable for industrial application [4,5]. The high yield strengths of 570–926 MPa and 554–735 MPa with reasonable elongations of ~43–22% and ~35–19% were achieved in 304 [6] and 316 L [7] ASSs through 10–30% cold rolling, respectively. However, the plastic straining induced ductility loss was more pronounced than the strength increase for the ASSs as the cold rolling reduction further increased, exhibiting a typical "banana-shaped" strength-ductility trade-off [8].

The mechanical properties of cold-rolled (CR) ASSs are determined by their deformation microstructures. Normally, the austenite phase in ASSs is not a stable phase and will transform into strain-induced martensite during the plastic deformation process [9]. Martensite phase generally exhibits a higher strength and lower plasticity. According to the mix law described by Huang et al [10] for two phase materials, the strengths of two phase materials are determined by the volume fractions

and the corresponding strengths of the two phases. The transformation from austenite phase into martensite phase will improve the strength of CR ASSs [6,11]. The phase transformation in ASSs is controlled by the stability of austenite that is determined by Md30 temperature (where 50% ά-martensite is present after 30% tensile deformation) [12]. Due to the higher content of alloy elements, some ASSs, like 316 ASSs, have a lower Md30 temperature and higher stability of austenite that inhibit the phase transformation during plastic deformation. Previous studies indicated that only 46–67% of austenite phase in 316 ASSs can be transformed into strain-induced martensite, even after 80–90% cold rolling [13–15]. Interestingly, these steels also exhibited the tendency of significant loss in plastic straining induced ductility [13–15], which cannot be explained by the mix law. Therefore, it is not enough to only consider the effect of volume fraction of the strain-induced martensite on the mechanical properties of ASSs, and the untransformed austenite evolution and its effect on mechanical properties should be considered at the same time. However, the evolution of untransformed austenite phase with increasing cold rolling reduction is less studied. The influence of untransformed austenite in CR ASSs on mechanical properties is not clear and needs in-depth studies.

In this study, the electron backscattered diffraction (EBSD) was chosen to study the evolution of untransformed austenite phase in CR 316LN ASS as the cold reduction increased from 10% to 40%. Evaluating the evolution of untransformed austenite in CR ASSs by using EBSD is rarely reported and is the innovation of this paper. Furthermore, transmission electron microscopy (TEM) was used to study the evolution of the deformation microstructures as the cold rolling reduction increased. The effect of cold deformation on the mechanical properties of 316LN ASS was studied by analyzing the relationship between deformation microstructures and mechanical properties.

#### **2. Experimental Procedures**

The chemical composition, the stacking fault energy (SFE) based equation of Brofman and Ansell [12], and the Md30 temperature based on Nohara's equation [16] of 3mm-thick 316LN ASS used in this study, are shown in Table 1. The strips were cold rolled in a pilot plant with thickness reductions from 10% to 90% reduction at room temperature. The volume fraction of martensite in CR samples was determined by X-ray diffraction (XRD, Panalytical, Almelo, The Netherlands). The Vickers hardness of samples was determined by measuring more than 20 points in different regions of the samples using a microhardness tester with a 0.5 kg load (HV-1000B, Matsuzawa, Tokyo, Japan). The structures in original 316LN ASS and CR samples were evaluated using an OM (Axioplan2 Imaging Zeiss, Göttingen, Germany). For the CR samples, an etchant of two solutions at a 1:1 ratio was used. The first solution consists of 0.20 g sodium-metabisulfate in 100 mL distilled water and the second consists of 10 mL hydrochloric acid in 100 mL distilled water. The original samples were mechanically polished and then electrochemically etched with 60% nitric acid solution. Microstructures of CR samples were examined by TEM (JEM-2100, JEOL, Tokyo, Japan). Thin foils were prepared by twin-jet electropolishing of 3 mm disks, punched from the specimens using a solution of 10% perchloric acid in acetic acid as the electrolyte. EBSD was utilized to evaluate the microstructures and grain boundary of 0–40% CR samples. For that purpose, the samples were electrochemically etched with 20% perchloric acid alcohol solution operated at 25 ◦C with an applied potential of 15 V. The size of the austenite structure in EBSD micrographs was determined by analyzing grain boundary misorientation over 2◦. The original and CR strips were machined to make tensile samples with a profile of 140 × 20 mm and a gage length of 65 mm. The uniaxial tensile tests were carried out at room temperature at an engineering strain rate of 5 × 10−4 s−1 and each specimen was tested three times to obtain an average value for each mechanical property.

**Table 1.** Chemical compositions, stacking fault energy (SFE), and Md30 of the investigated steel (wt, %).


**Author details**

Michael Hausmann\* and Eberhard Schmitt Kirchhoff-Institute for Physics, Heidelberg University, Heidelberg, Germany

\*Address all correspondence to<EMAIL_ADDRESS>
© 2022 The Author(s). Licensee IntechOpen. 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.

*Combinatorial Oligonucleotide FISH (COMBO-FISH): Computer Designed Probe Sets… DOI: http://dx.doi.org/10.5772/intechopen.108551*


*Driver Assistance Technologies DOI: http://dx.doi.org/10.5772/intechopen.94354*

without the intermediary of a central computer. Or data can be logged internally and analyzed back at base where it can be post-processed and exported in CSV file format (("Comma Separated Values") which is often used to exchange data between differently similar applications).


**3. Part B: fluid atoms in P2P streaming networks**

In P2P live streaming systems every user (peer) maintains connections with other peers and forms an application level *logical network* on top of the *physical network*. The video stream is divided in small pieces called *chunks* which are streamed from the source to the peers and every peer acts as a client as well as a server, forwarding the received video chunks to the next peer after some short buffering. The peers are usually organized in one of the two basic types of logical topologies: *tree* or *mesh*. Hence, the tree topology forms structured network of a single tree as in [22], or multiple multicast trees as in [23], while mesh topology is unstructured and does not form any firm logical construction, but organizes peers in *swarming* or gossiping-like environments, as in [24]. To make greater use of their complementary strengths, some protocols use combination of these two aspects, forming a hybrid network topology, such as [25]. Hence, members are free to join or leave the system at their own free will (*churn*), which leads to a certain user driven dynamics resulting in constant disruptions of the streaming data delivery. This peer churn has high influence on the quality of offered services, especially for P2P systems that offer live video broadcast. Also, P2P network members are heterogeneous in their upload bandwidth capabilities and provide quite different contribution to the overall system performance. Efficient construction of P2P live video streaming network requires data latency reduction as much as possible, in order to disseminate the content in a live manner. This latency is firstly introduced by network infrastructure latency presented as a sum of serialization latency, propagation delay, router processing delay and router queuing delay. The second type of delay is the initial start-up delay required for filling the peer's buffer prior to the start of the video play. The buffer is used for short term storage of video chunks which often arrive out of sequence in manner of order and/or time, and resolving this latency issue requires careful buffer modeling and management. Thus, buffer size requires precise dimensioning because even though larger buffers offer better sequence order or latency compensation, they introduce larger video playback delay. Contrary, small buffers offer smaller playback delay, but the system becomes more error prone. Also, since the connections between participating peers in these P2P logical networks are maintained by the means of control messages exchange, the buffer content (buffer map) is incorporated in these control messages and it is used for missing chunks acquisition. Chunk requesting and forwarding is controlled by a chunk scheduling algorithm, which is responsible for on-time chunk acquisition and delivery among the neighboring peers, which is usually based on the available content and bandwidth of the neighboring peers. A lot of research activities are strictly focused on designing better chunk scheduling algorithms [26,27] that present the great importance of carefully composed scheduling algorithm which can significantly compensate for churn or bandwidth/latency disruptions. Beside the basic coding schemes, in latest years an increasing number of P2P live streaming protocols use *Scalable Video Coding* (SVC) technologies. SVC is an emerging paradigm where the video stream is split in several sub-streams and each sub-stream contributes to one or more characteristics of video content in terms of temporal, spatial and SNR/quality scalability. Mainly, two different concepts of SVC are in greater use: *Layered Video Coding* (LVC) where the video stream is split in several dependently decodable sub-stream called *Layers*, and *Multiple Description Coding* (MDC) where the video stream is split in several independently decodable sub-stream called *Descriptions*. A number of P2P video streaming models use LVC [27] or MDC [23,28] and report promising results.


**Heat sensing Thermoplastic Elastomer Based on Polyolefins for Encapsulation Applications**

Tanya Das and Sunanda Roy

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/61691

## **Abstract**

[28] Rutkowska M, Eisenberg A. Ionomeric blends. IV. Miscibility of urethane elastomers with styrene-styrene sulfonic acid copolymer. Journal of Applied Polymer Science.

[30] Lenz RW. Biodegradable Polymers. In: Advances in Polymer Science. Berlin: Spring‐

[31] Li S, Vert M. Biodegradation of Aliphatic Polyesters. In Degradable Polymers Princi‐ ples and Applications. 2nd ed. UK: Kluwer Academic Publisher; 2002. p. 71-132.

[32] Barrat SR, Ennos AR, Greenhalgh m, Robson GD, Handley PS. Fungi are predomi‐ nant micro-organisms responsible for degradation of soil-buried polyester polyur‐ ethane over a range of soil water holding capacities. Journal of Applied

[33] Zhou L, Liang D, He X, Li J, Tan H, Fu Q, Gu Q. The degradation and biocompatibili‐ ty of pH-sensitive biodegradable polyurethanes for intracellular muntifunctional an‐ titumor drug delivery. Biomaterials. 2012;33:2734-2745. DOI: 10.1016/j.biomaterials.

[34] Khan S. Biodegradation of polyurethane by bacterial consortium. Elixir Bio Technol‐

[29] PN-EN ISO 527-1,2,3:1998, Plastics—Determination of Tensile Properties.

Microbiology. 2003;95:78-85. DOI: 10.1046/j.1365-2672.2003.01961.x.

1984;29:755-762. DOI: 10.1002/app.1980.070290304.

er-Velay; 1993. p. 1-40.

94 Thermoplastic Elastomers - Synthesis and Applications

2011.11.009.

ogy. 2011;37:3767-3772.

DOI: 10.1007/978-94-017-1217-0.

Use of Thermoplastic Elastomers (TPEs) has become a unique pathway to meet the daily requirements of various applications. The ease of using TPEs lies in the fact that they pro‐ vide both the character of the individual properties as they are constructional polymers, which are physically crosslinked materials made up of a thermoplastic and an elastomer. There are several TPE's in market and individual have several outstanding performances. Out of several researches, our aim in this article is to focus on the influence of Polyolefin based TPE's. This paper focusses on the different aspects of TPO's their physical, chemi‐ cal, mechanical, and electrical characteristics, advantages and uses of these materials along with a particular focus on their use in encapsulation application. Factors that could affect the end use are also explained here in details. Heat shrinkability test, cure time, and SEM are some of the characterisations used to demonstrate the exact criteria of polyolefin based TPE's for encapsulation application.

**Keywords:** Thermoplastic elastomer (TPE), Thermoplastic polyolefins (TPO's), Shrinka‐ bility, Encapsulation application

## **1. Introduction**

Elastomers are polymers which have viscoelasticity and weak intra-molecular forces. They can be generally explained by their mechanical response rather than their chemical structure. One of the most versatile and immensely used materials in today's world is the engineered Thermoplastic elastomers (TPE's). The TPE's are a class of polymer which consists materials having both thermoplastic and elastomeric properties. They are novel constructional poly‐ mers, which are physically cross linked materials made up of a thermoplastic and an elastomer. The unique properties of both materials exist because TPE materials are created only by physical mixing of a thermoplastic and an elastomer and no chemical or covalent bonding

© 2015 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.

exists between the two [1]. TPEs are generally low modulus, flexible materials that can be stretched repeatedly to at least twice their original length at room temperature with an ability to return to their approximate original length when stress is released. TPE's offer a wide range of performance attributes including: heat and oil resistance, improved adhesion, tear resist‐ ance, surface appearance and low permeability. In addition, TPE's are colorable and can be specified in a variety of hardness grades. They can be processed with the efficiency and economy of thermoplastics and can be molded with other olefin based materials, such as polypropylene, polyethylene without the use of adhesives. Various mechanical designs were implanted within the parts to ensure tight fit in case of other substrates like polyamides, acrylonitrile butadiene styrene and so on. Rubbery materials have high degree of flexibility in their elongated polymeric chains which binds them into an ordered network structure [1]. Due to this mobility and flexibility the long chains when subjected to external pressure or stress change their configuration. Thus chain allied to a structure gives a solid feature preventing them to flow under pressure. Due this fact, this type of materials may be stretched or pulled up to several times of its original length. Withdrawing external forces, it rapidly restore its nearly original dimensions, with essentially no residual or nonrecoverable strain. TPEs serve a wide range of markets:

One of the major usages of TPE is in encapsulations. By encapsulation we mean covering of an object with some material to protect and to insulate it. Polymeric materials are used extensively as encapsulants for coils, motor windings and micro electronics packaging industry. Use of TPEs speed manufacturing with low cost compared with any other material and technology. TPE gives both the characteristics like thermosets along with the process and design flexibility same as plastics thereby enhancing wide design alternatives and cost reduction facility. TPE's can be processed faster more easily and more efficiently. Apart from these advantages TPE's possess many other additional characteristics like lightweight, elastic recovery properties within a specific temperature range, metal replacement, noise reduction by self lubrication, very good electrical insulation properties, heat resistance with in a specific temperature range, oil resistance, improved adhesion, tear resistant surface, low permeability and colorability [2]. TPE's which have contribution in encapsulation application are Polystyr‐ ene, Polyolefin and Polyurethanes. In this chapter we will concern our focus on Polyolefins.

## **1.1. Compounding of TPE's**

The basic characteristics of thermoplastic elastomer greatly depend on polymers used in their manufacturing process based on their application. These properties can be modified, however, through the appropriate addition of compounding ingredients. Some are added to accelerate cross-linking in order to impart the exact cure time required some improve processability, while others improve the properties of the finished product.

Some ingredients are added to deliver the highest levels of performance in the end product. In some applications, compounding is required to reduce cost, diluents and extenders are sometimes added to minimize the ratio of high valued components within the system. By this, certain compromises in the mechanical and other properties are obtained, but for some specific high end applications it is worthwhile. Some other factors that influence the quality of the resulting material includes the quality of the neat materials, the equipment's used and the quality control in mixing techniques [3]. Processing of the compounded material can also influence the end product properties. The major ingredient that affect the properties of the finished product and which have its own importance while making an end product are classified as:

## *1.1.1. Matrix*

exists between the two [1]. TPEs are generally low modulus, flexible materials that can be stretched repeatedly to at least twice their original length at room temperature with an ability to return to their approximate original length when stress is released. TPE's offer a wide range of performance attributes including: heat and oil resistance, improved adhesion, tear resist‐ ance, surface appearance and low permeability. In addition, TPE's are colorable and can be specified in a variety of hardness grades. They can be processed with the efficiency and economy of thermoplastics and can be molded with other olefin based materials, such as polypropylene, polyethylene without the use of adhesives. Various mechanical designs were implanted within the parts to ensure tight fit in case of other substrates like polyamides, acrylonitrile butadiene styrene and so on. Rubbery materials have high degree of flexibility in their elongated polymeric chains which binds them into an ordered network structure [1]. Due to this mobility and flexibility the long chains when subjected to external pressure or stress change their configuration. Thus chain allied to a structure gives a solid feature preventing them to flow under pressure. Due this fact, this type of materials may be stretched or pulled up to several times of its original length. Withdrawing external forces, it rapidly restore its nearly original dimensions, with essentially no residual or nonrecoverable strain. TPEs serve

One of the major usages of TPE is in encapsulations. By encapsulation we mean covering of an object with some material to protect and to insulate it. Polymeric materials are used extensively as encapsulants for coils, motor windings and micro electronics packaging industry. Use of TPEs speed manufacturing with low cost compared with any other material and technology. TPE gives both the characteristics like thermosets along with the process and design flexibility same as plastics thereby enhancing wide design alternatives and cost reduction facility. TPE's can be processed faster more easily and more efficiently. Apart from these advantages TPE's possess many other additional characteristics like lightweight, elastic recovery properties within a specific temperature range, metal replacement, noise reduction by self lubrication, very good electrical insulation properties, heat resistance with in a specific temperature range, oil resistance, improved adhesion, tear resistant surface, low permeability and colorability [2]. TPE's which have contribution in encapsulation application are Polystyr‐ ene, Polyolefin and Polyurethanes. In this chapter we will concern our focus on Polyolefins.

The basic characteristics of thermoplastic elastomer greatly depend on polymers used in their manufacturing process based on their application. These properties can be modified, however, through the appropriate addition of compounding ingredients. Some are added to accelerate

a wide range of markets:

**•** Agriculture & Off Road Appliance

96 Thermoplastic Elastomers - Synthesis and Applications

**•** Hydraulics & Pneumatics ⋅ Marine

**1.1. Compounding of TPE's**

**•** Medical & Safety Plumbing & Irrigation

**•** Automotive & Transportation ⋅ Consumer

**•** Electrical & Industrial Controls ⋅ Food & Beverage

The neat or raw polymer, is the fundamental or main ingredient in determining the properties of the compound or the end product. It is selected in such a way so as to optimize service life and processing requirements with cost effectiveness as one of the main parameter taken into account. Polymers with high molecular weight can give very tough material as the final product. Again this criterion sometimes becomes a disadvantage for some specific product. So depending on the end use application selection of polymer is yet challenging.

## **1.2. Filler**

The most important part of filler is to provide better reinforcement and secondly to reduce the cost of the end product. Generally we have two basic types of fillers. One is the reinforcing type which can reinforce the system according to need and the other is the diluent type which are generally used for calibrating the physical properties of the system. Carbon Black or Nano silica's basically come under reinforcing fillers and are categorized by their respective particle sizes. They become more reinforcing as the particle size decreases [4]. As mentioned above fillers with high reinforcing character can make a compound very hard and rigid which in turn can result in poor flow behavior. Carbon blacks are generally alkaline in nature and tend to accelerate cure time. Other non-black fillers may be acidic and can retard cure as well as absorb moisture, which can result in blistering problems during the processing stage. Several nanofillers like super-fine clays have a high surface area as compared to their volume and can induce better mechanical behavior. They are more expensive than general fillers, the same weight of material goes further because the particles are so much finer.

## *1.2.1. Accelerators*

These speed up the cure mechanism of the system. Accelerators increase the rate of crosslinking and therefore decrease both production time and cost.Accelerators can help to control the cure speed and cure time and also other material properties. They can be incorporated within the system at any amount and sometimes may be more than one accelerators are used in a single formulation. Some important accelerators include peroxides for curing which plays dual character in the network. They can act like an accelerator as well as a modifier for the physical properties of the system.

## *1.2.2. Flame retardants*

These are compounds added to materials to suppress or delay the flames and prevent fire spreading. Most of the TPEs promote combustion and thus the end by-products can be extremely hazardous and dangerous. Due to this fact manufacturers induce flame retardants to improve their flame resistance. There are several flame retardants that can be added to the compound, either inorganic or organic. These include antimony trioxide, zinc borate, alumi‐ num hydroxide and chlorinated paraffins and so on.

## *1.2.3. Curatives*

Curatives are very crucial for compounding of elastomers. They are the crosslinking agents generally used to connect separate neat polymers. The type of curative used varies upon the elastomer selected. Like in sulfur-cured, sulfur donors give better heat stability as they tend to give single sulfur crosslinks. Peroxide cures promotes good thermal stability due to the short length of the cross-links between the polymer chains. Fluorocarbons, along with some other polymer types, can have their own specialized cure systems.

## *1.2.4. Plasticizers*

Plasticizers help to reduce the hardness with given filler loading and also gives better filler addition and dispersion. They should be compatible with the matrix polymer. Special types of plasticizers can improve the low temperature flexibility of some rubber. Process aids can also assist with filler dispersion, although they are normally added to improve processability.

## **2. General characteristics of elastomers**

## **2.1. Cure characteristics**

The cure characteristic is one of the major properties of an elastomer to study before its application to different areas. As the compound cures within the hot platens it gradually becomes stiffer. This is measured via a strain gauge connected to an oscillating rotor in contact with the elastomer. The resistance to torque or the stiffness of the material is plotted on a graph against time, known as a rheograph. This information shows the behavior of the moulding characteristics, since the rheograph shows the time available to load the press, the time of cure and the final state of cure. The ultimate state of cure is not always a straight line but can also be a slope [5]. For some elastomers the cure continues in a different way which could be explained as the heat is actually breaking the polymer chain rather than the crosslinks formed during the curing stage.

## **2.2. Abrasion resistance**

in a single formulation. Some important accelerators include peroxides for curing which plays dual character in the network. They can act like an accelerator as well as a modifier for the

These are compounds added to materials to suppress or delay the flames and prevent fire spreading. Most of the TPEs promote combustion and thus the end by-products can be extremely hazardous and dangerous. Due to this fact manufacturers induce flame retardants to improve their flame resistance. There are several flame retardants that can be added to the compound, either inorganic or organic. These include antimony trioxide, zinc borate, alumi‐

Curatives are very crucial for compounding of elastomers. They are the crosslinking agents generally used to connect separate neat polymers. The type of curative used varies upon the elastomer selected. Like in sulfur-cured, sulfur donors give better heat stability as they tend to give single sulfur crosslinks. Peroxide cures promotes good thermal stability due to the short length of the cross-links between the polymer chains. Fluorocarbons, along with some other

Plasticizers help to reduce the hardness with given filler loading and also gives better filler addition and dispersion. They should be compatible with the matrix polymer. Special types of plasticizers can improve the low temperature flexibility of some rubber. Process aids can also assist with filler dispersion, although they are normally added to improve processability.

The cure characteristic is one of the major properties of an elastomer to study before its application to different areas. As the compound cures within the hot platens it gradually becomes stiffer. This is measured via a strain gauge connected to an oscillating rotor in contact with the elastomer. The resistance to torque or the stiffness of the material is plotted on a graph against time, known as a rheograph. This information shows the behavior of the moulding characteristics, since the rheograph shows the time available to load the press, the time of cure and the final state of cure. The ultimate state of cure is not always a straight line but can also be a slope [5]. For some elastomers the cure continues in a different way which could be explained as the heat is actually breaking the polymer chain rather than the crosslinks formed

physical properties of the system.

98 Thermoplastic Elastomers - Synthesis and Applications

num hydroxide and chlorinated paraffins and so on.

polymer types, can have their own specialized cure systems.

**2. General characteristics of elastomers**

*1.2.2. Flame retardants*

*1.2.3. Curatives*

*1.2.4. Plasticizers*

**2.1. Cure characteristics**

during the curing stage.

Abrasion resistance is important where friction, rough surface, industrial use is a key factor. Hard TPOs have good abrasion resistance. Abrasion damage can occur when there is dynamic motion against an abrasive surface. Standard abrasion tests depend on producing relative motion between a rubber sample and an abrasive surface, pressed together by a fixed force. These tests do not correlate particularly well with application experience. It is sometimes believed that tensile strength is related to abrasion resistance, higher the tensile strength higher is the abrasion resistant property while a high tensile strength compound can have good abrasion resistance. Abrasion resistance is mainly related more to the polymer taken and the nature of compounding ingredient used [6]. Abrasion resistant elastomers must therefore be specifically developed. Polyolefin based TPEs show good abrasion resistant character.

## **2.3. Tear strength**

Tear strength is a measure of the resistance of an elastomer to tearing. It is measured using a tensile test machine operating at a constant rate of traverse until the test piece breaks. Various types of test pieces can be used, and depending on the method employed the maximum or median force achieved is used to calculate the tear strength.

## **2.4. Adhesion and bondability**

Parameters affecting the adhesion and bond ability: The application of elastomers at high temperature is generally determined by their chemical structure and stability and varies depending on the elastomers being used. In course of developing high temperature product, these elastomers can be attacked by several chemical species like hydrogen, oxygen, and other groups which results in some chemical reaction and as a result the effectiveness or power increases at high temperature. Another parameter responsible for affecting the adhesion and bond ability is the degradative chemical reactions. It may hamper the product in two specific ways. 1. Breaking the molecular chains or cross-links, thus softening the rubber because they weaken the network. 2. Additional cross-linking, hardening the rubber, often characterized by a hard, cracked and degraded skin occuring on the elastomer component [7]. One more important criterion responsible for adhesion and bond ability is the perfect selection of the materials based on the end product needed. For example elastomers significantly weaken at high temperatures so in the case of seals, can result in a significant reduction in extrusion resistance. For applications involving elevated temperatures, especially at high pressures, antiextrusion elements may also need to be used, either incorporated into the seal design or added as an additional component when manufacturing the seal.

## **2.5. Low temperature applications**

Elastomers when cooled to sufficiently low temperatures show the characteristics of glass, including hardness, stiffness and brittleness, and do not behave in the readily deformable manner usually associated with elastomers. As the temperatures rises, the segments of the polymer chain gain sufficient energy to rotate and vibrate. At high temperatures full segmental rotation is possible and the material behaves in the rubbery way. The usefulness of an elastomer at low temperatures is dependent on whether the material is above its glass transition temperature (Tg), where it will still behave elastically, or below its Tg, where the material will be hard and relatively brittle.

## **3. Polyolefins (POEs)**

Polyolefins also named as poly alkenes are simple long chain hydrocarbon. They are prepared by the reaction of an alkene as a monmer with general formula CnH2n. The most commonly used Polyolefins are low and high density polyethylene copolymer, polypropylene copolymer and polymethyl pentene. Polyethylene and polypropylene are produced by long chain polymerization of olefins ethylene and propylene respectively

**Sheme 1.** Structure of Polyolefins

## **3.1. Chemistry and manufacturing process**

The metallocene catalyst helps to instigate polymerization of the ethylene and co-monomer sequences and while further increasing the co-monomer content will produce polymers with higher elasticity due to the fact that the co-monomer incorporation disrupts the polyethylene crystallinity. The molecular weight of the copolymer will help determine its processing characteristics and end-use performance properties. Higher in molecular weights higher is the polymer toughness. Hence depending on the end use application one can choose the appro‐ priate copolymer with molecular weight according to the requirement. POEs are produced using refined metallocene catalyst. These catalysts have a constrained transition metal such as Ti, Zr, sandwiched between one or more cyclopentadienyl ring structures to form a sterically hindered polymerization site. The catalyst is usually first mixed with an activator or cocatalyst, which can significantly enhance the polymerization efficiency rate to beyond a million units of polymer per unit of catalyst [8-9]. The molecular weight build-up with the polymeri‐ zation of ethylene and comonomer at the catalyst site until restricted by catalyst deactivation or chain termination with hydrogen introduction to the reactor. The polymerization process is exothermic in nature and requires efficient heat removal from the transport media of gas or solvent. Post-reactor processes involve additives addition and isolation of the polymer from the transporting media. The final product is then packaged as per manufacturer demand or end-user need.

**Polyolefin Preparation Process**

**Sheme 2.** Polyolefin Preparation Process

rotation is possible and the material behaves in the rubbery way. The usefulness of an elastomer at low temperatures is dependent on whether the material is above its glass transition temperature (Tg), where it will still behave elastically, or below its Tg, where the

Polyolefins also named as poly alkenes are simple long chain hydrocarbon. They are prepared by the reaction of an alkene as a monmer with general formula CnH2n. The most commonly used Polyolefins are low and high density polyethylene copolymer, polypropylene copolymer and polymethyl pentene. Polyethylene and polypropylene are produced by long chain

The metallocene catalyst helps to instigate polymerization of the ethylene and co-monomer sequences and while further increasing the co-monomer content will produce polymers with higher elasticity due to the fact that the co-monomer incorporation disrupts the polyethylene crystallinity. The molecular weight of the copolymer will help determine its processing characteristics and end-use performance properties. Higher in molecular weights higher is the polymer toughness. Hence depending on the end use application one can choose the appro‐ priate copolymer with molecular weight according to the requirement. POEs are produced using refined metallocene catalyst. These catalysts have a constrained transition metal such as

material will be hard and relatively brittle.

100 Thermoplastic Elastomers - Synthesis and Applications

polymerization of olefins ethylene and propylene respectively

**3. Polyolefins (POEs)**

**Sheme 1.** Structure of Polyolefins

**3.1. Chemistry and manufacturing process**

## **4. Thermoplastic Polyolefins (TPOs) blends**

These are a class of plastic used in a wide range of markets and applications – mainly in transportation sector, including automotive exterior and interior parts. TPOs are generally produced by the blending of polypropylene (PP) with elastic ethylene copolymers (polyolefin elastomers or POEs), and the addition of other fillers and additives. Thermoplastic olefin (TPO) elastomers are obtainable in several grades in the market, having room-temperature hardness starting from 60 Shore A to 60 Shore D. These polyolefin elastomers have the lowest specific gravities of all thermoplastic elastomers available in the market. They are uncured or have low levels of crosslinking. These elastomers are flexible at around -60°F and are not brittle at -90°F. They can be used at service life at temperatures as high as 275°F in air. The TPOs have good resistance to some acids, most bases, butyl alcohol, many organic materials, formaldehyde, ethyl acetate and nitrobenzene. They are affected by chlorinated hydrocarbon solvents [10]. The specific blending amounts are dependent upon the properties needed to meet the desired end product application. TPO system generally include:

Rigid TPOs are normally made up of polypropylene or polyethylene component in majority, with other component to attain an overall balance of properties. Efficient rigid TPO develop‐ ment starts by optimizing an appropriate polymer, and adjusting the optimum modifier level to achieve acceptable ductility, while maintaining rigidity as high as possible. In contrast, flexible TPOs contain a majority phase of elastomer with polymer added for improved temperature stability.

TPO's as one of the fastest growing synthetic polymers can be substituted for a number of generic polymers including ethylene styrene-block copolymers (SBCs), propylene rubbers (EPR or EPDM), ethylene vinyl acetate (EVA), and poly vinyl chloride (PVC). TPO's are wellmatched with most of the olefinic materials, are an excellent impact modifier for plastics, and offer unique performance application for compounded products [11]. These compounds are easily colored, possess soft-touch molding and extrusion applications. They are generally resistant to acids and bases and are available in UV-resistant grades for outdoor applications. The main advantages are excellent abrasion resistance, high heat stability, wide use tempera‐ ture, low-temperature flexibility and so on. Recently, TPO's has established itself as a leading material for automotive exterior and interior applications like extruded and molded goods, wire and cable, film applications, medical goods, adhesives, footwear, and foams. The advantage of using Polyolefins with other materials is that they have wide hardness range, excellent flex fatigue and impact resistance, good retention of properties etc. They are solvent resistant. The typical glass transition temperature can exceed 140C. They are also used to make lenses for cameras, projectors and copiers, LCD monitors, contact lenses for eye and reinforced tubes or pipes for medical use. TPO's provide an economical alternative to traditional thermoset rubbers and more costly thermoplastic elastomers [12]. Thermoplastic polyolefin elastomers provide an excellent balance of performance and price. Their service temperature range is from -60 to 275°F (-50 to 135° C); hardness ranges from 35 Shore A to 50 Shore D.TPO ingredients generally have a polymer (homopolymer, copolymer) which provides the rigidity and thermal stability, along with elastomers which gives the flexibility. It also includes mineral fillers which gives dimensional stability to the system. Other additive includes additives (antioxidants, plasticizers, and so on) depending on the application of the end use.

**Sheme 3.** Car Bumper made out of TPO material, (Source Google)

elastomers are obtainable in several grades in the market, having room-temperature hardness starting from 60 Shore A to 60 Shore D. These polyolefin elastomers have the lowest specific gravities of all thermoplastic elastomers available in the market. They are uncured or have low levels of crosslinking. These elastomers are flexible at around -60°F and are not brittle at -90°F. They can be used at service life at temperatures as high as 275°F in air. The TPOs have good resistance to some acids, most bases, butyl alcohol, many organic materials, formaldehyde, ethyl acetate and nitrobenzene. They are affected by chlorinated hydrocarbon solvents [10]. The specific blending amounts are dependent upon the properties needed to meet the desired

**•** Filler (like minerals or talc), imparts higher stiffness and dimensional stability of the body **•** Other additives (plasticizers, antioxidants, and additives for ignition resistance, scratch

Rigid TPOs are normally made up of polypropylene or polyethylene component in majority, with other component to attain an overall balance of properties. Efficient rigid TPO develop‐ ment starts by optimizing an appropriate polymer, and adjusting the optimum modifier level to achieve acceptable ductility, while maintaining rigidity as high as possible. In contrast, flexible TPOs contain a majority phase of elastomer with polymer added for improved

TPO's as one of the fastest growing synthetic polymers can be substituted for a number of generic polymers including ethylene styrene-block copolymers (SBCs), propylene rubbers (EPR or EPDM), ethylene vinyl acetate (EVA), and poly vinyl chloride (PVC). TPO's are wellmatched with most of the olefinic materials, are an excellent impact modifier for plastics, and offer unique performance application for compounded products [11]. These compounds are easily colored, possess soft-touch molding and extrusion applications. They are generally resistant to acids and bases and are available in UV-resistant grades for outdoor applications. The main advantages are excellent abrasion resistance, high heat stability, wide use tempera‐ ture, low-temperature flexibility and so on. Recently, TPO's has established itself as a leading material for automotive exterior and interior applications like extruded and molded goods, wire and cable, film applications, medical goods, adhesives, footwear, and foams. The advantage of using Polyolefins with other materials is that they have wide hardness range, excellent flex fatigue and impact resistance, good retention of properties etc. They are solvent resistant. The typical glass transition temperature can exceed 140C. They are also used to make lenses for cameras, projectors and copiers, LCD monitors, contact lenses for eye and reinforced tubes or pipes for medical use. TPO's provide an economical alternative to traditional thermoset rubbers and more costly thermoplastic elastomers [12]. Thermoplastic polyolefin elastomers provide an excellent balance of performance and price. Their service temperature range is from -60 to 275°F (-50 to 135° C); hardness ranges from 35 Shore A to 50 Shore D.TPO ingredients generally have a polymer (homopolymer, copolymer) which provides the rigidity and thermal stability, along with elastomers which gives the flexibility. It also includes mineral

end product application. TPO system generally include:

102 Thermoplastic Elastomers - Synthesis and Applications

temperature stability.

**•** Polymer., (provides rigidity and temperature stability to the body)

resistance) for improving end-use performance and shelf life.

**•** Elastomers, which gives movability and impact strength to the system

## **4.1. Heat sensing property of TP0's based materials**

When a polymeric materials is subjected to stretch either at room temperature or at elevated temperature, the molecules of the materials are oriented towards the stretching direction and the material freezes in its elongated or extended form. Stretching decreases the entropy of the system. If we heat the stretched sample without applying mechanical force the material shrinks. Such heat shrinkable polymers are recently getting tremendous application in the packaging industry, cable industry and heat shrinkable tube production. As a flexible material elastomers do not provide the same level of tolerance as rigid materials do. Shrinkage is highly dependent on tolerance which again varies with the type of elastomers and other factors like hardness, stiffness and so on. Soft elastomers generally shrink more than harder elastomers. Shrinkage is also affected by other parameters like cure time, pressure, temperature, post-cure time, etc[13]. Most materials like metals, plastics or fabric have their own percentage tolerances. However, when designing inserts for moulding to elastomers, other factors need to be considered such as, the location of the inserts with respect to other shapes, fit in the mould cavities, proper spacing to match with mould pins, and the fact that inserts at room tempera‐ ture should fit into a heated mould.

## **4.2. Electrical property of TPO's**

With increasing demand for insulating materials researchers have paid attention towards materials that can provide the best according to the requirement. Various factors depend on to which materials can suit the best. Among them the most important criteria of a material as electrical insulation is determined by its dielectric breakdown strength. This in turn depends on some other properties like voltage applied, frequency, temperature, partial discharges, impurities in that material, dielectric constant, thickness and layers of insulation, and volume resistivity[14-15]. A material should fulfill some of the criteria to become useful in electrical insulation application. These properties include low specific weight, good mechanical, chemical and thermal strength, and good surface leakage resistance, ability to maintain good surface hydrophobicity, easy processing and production [4]. TPO gives a package of these combinations of properties and thus makes it most suitable to use in encapsulation applica‐ tion.. These materials are recently used widely for medium to high voltage cable encapsula‐ tions. They are also used in encapsulation of coils.

## **5. Experimental**

## **5.1. Heat shrinkability test**

For R-T stretched samples the samples were stretched at room temperature at a stretching rate of 50 mm/min. Samples were allowed to shrink at 80 °C for 10 min in a hot air oven. The percentage shrinkability was measured by the following equation..

$$\mathbf{S}\_{\rm h} = \left(\mathbf{L}\_{\rm str} \cdot \mathbf{L}\_{\rm shr}\right) / \mathbf{L}\_{\rm str} \times 100\,\mathrm{J}$$

where Sh is the percentage of shrinkability, Lstr is the length of the sample after stretching, and Lshr is the length of the shrunk sample.

Uncoiling of the polymer chains occurs when a polymer sample is stretched above the glass transition temperature, which in turn is frozen into the structure when the samples are cooled down. Although sufficient drop of entropy is witnessed during the uncoiling process the obtained stretched polymers are stabilized by a cohesive force received from the semicrystal‐ line region of the polymers. Stretching also has some properties of its own. It causes unrecov‐ erable viscous flow, which gradually increases with the increased stretching temperature and are not recoverable in any circumstances. Crosslinked points also known as permanent point strongly contribute in the shrinkage process. The molecules in the flexible amorphous phase shrink easily due to their mobility as compared to those in the crystalline zone. The observed shrinkability is a composite effect of the above mentioned factors. All samples were stretched at room temperature. The viscous flow is same in all cases.

## **5.2. Effect of cure time on heat sensing property of TPO**

Some experiments were performed with different types of TPO's to study the heat sensing property. The parameter on which the heat sensing character depends gives a vast knowledge to the industries as well as other fields which deals especially with this parameter of TPO's. Polymers taken are LLDE, LDPE, HPDE and the curing agents are mostly CSM, DCP, sulfur etc. The formulations are given in Table 1 and 2.

**Table 1.** Formulation of TPO with curing agents

chemical and thermal strength, and good surface leakage resistance, ability to maintain good surface hydrophobicity, easy processing and production [4]. TPO gives a package of these combinations of properties and thus makes it most suitable to use in encapsulation applica‐ tion.. These materials are recently used widely for medium to high voltage cable encapsula‐

**b.** Above materials were given stretching at ambient and at 150°C and then the shrinkage of

**c.** Above materials were stretched at 150C and cured under stretching conditions and then

For R-T stretched samples the samples were stretched at room temperature at a stretching rate of 50 mm/min. Samples were allowed to shrink at 80 °C for 10 min in a hot air oven. The

S = L -L /L 100 h str shr str ( ) ´

where Sh is the percentage of shrinkability, Lstr is the length of the sample after stretching, and

Uncoiling of the polymer chains occurs when a polymer sample is stretched above the glass transition temperature, which in turn is frozen into the structure when the samples are cooled down. Although sufficient drop of entropy is witnessed during the uncoiling process the obtained stretched polymers are stabilized by a cohesive force received from the semicrystal‐ line region of the polymers. Stretching also has some properties of its own. It causes unrecov‐ erable viscous flow, which gradually increases with the increased stretching temperature and are not recoverable in any circumstances. Crosslinked points also known as permanent point strongly contribute in the shrinkage process. The molecules in the flexible amorphous phase shrink easily due to their mobility as compared to those in the crystalline zone. The observed shrinkability is a composite effect of the above mentioned factors. All samples were stretched

Some experiments were performed with different types of TPO's to study the heat sensing property. The parameter on which the heat sensing character depends gives a vast knowledge to the industries as well as other fields which deals especially with this parameter of TPO's.

tions. They are also used in encapsulation of coils.

104 Thermoplastic Elastomers - Synthesis and Applications

**a.** Shrinkage was measured at 150°C for above materials.

shrinkage was measured also at 150°C.

Lshr is the length of the shrunk sample.

the stretched samples was measured at the same temperature.

percentage shrinkability was measured by the following equation..

at room temperature. The viscous flow is same in all cases.

**5.2. Effect of cure time on heat sensing property of TPO**

**5. Experimental**

**5.1. Heat shrinkability test**

**Table 2.** Formulation of TPO with curing agents

Figure 1. elaborates that with increasing the cure time the shrinkability of the blends increases for all the systems. From the graph it could be observed that the LLDPE/CSM blends show the highest shrinkability degree both for Room Temperature and High Temperature stretched sample as compared to LDPE/CSM and HDPE CSM blends. H-T stretching is accompanied by high shrinkage rather than R-T stretched samples. Increase in cure time accelerates the shrinkability. This may be due to more crosslinking of the elastometric phase. In case of Figure 2. we notice the same trend as above. Shrinkability of all blends increases with increase in cure time. Here two types of curing agent were applied a) DCM b) sulfur. From both the figures it is apparent that rate of increase in shrinkability is much higher in case of DCP than sulfur as curing agent.

LLDPE/BB blends show the highest degree of shrinkability with increase with cure time for both the systems either with sulfur or DCP as the curing agent. But the extent of increase in shrinkability is even sharper in case of DCP as curing agent. This may be due to the fact that DCP attacks both polymer chains to generate active sites leading to more efficient crosslinking which results in higher degree of shrinkability whereas the sulfur only gives a bridging agent between the elastomers. Higher shrinkability of H-T stretched samples than the R-T stretched samples may be due to more crosslinking of elastomeric phase at elevated temperature to deposit curatives to crosslink further strongly which is not possible in case of room tempera‐ ture stretched samples. Increase in cure time allows the elastomer phase to crosslink for longer duration resulting in sufficient crosslinking thereby increasing the shrinkability of the system.

## **5.3. Effect of flame retardant on shrinkability**

Flame retardant pays an important role in shrinkability. It can be observed that with incorpo‐ ration of some amount of flame retardants the shrinkability of the system is changed to some extent. For blends having high elastomer ratio the reduction in shrinkage occurs to a very small

samples may be due to more crosslinking of elastomeric phase at elevated temperature to deposit curatives to crosslink further strongly which is not possible in case of room temperature stretched samples. Increase in cure time allows the elastomer phase to crosslink for longer duration

resulting in sufficient crosslinking thereby increasing the shrinkability of the system.

**Figure 1.** Study of shrinkability over cure time i) LLDBE/CSM, ii) LDPE/CSM, iii) HDPE/CSM

**Figure 2.** Study of shrinkability over cure time 2A) H-T stretched samples and 2B) R-T stretched samples of the blends of HDPE, LDPE, LLDBE with sulfur and DCP as curing agents. **Figure 2.** Study of shrinkability over cure time 2A) H-T stretched samples and 2B) R-T stretched samples of the blends of HDPE, LDPE, LLDBE with sulfur and DCP as curing agents.

extent in case of H-T stretched samples but for the low elastomer ration the shrinkability value is scarified to larger extent. The stretch ability of the H-T stretched blends again decreases to some extent with the addition of flame retardants. This may be the result of lower compatibility of flame retardants in the polyolefin phase at its higher level, suggesting the efficiency of flame retardants. The observed flame retardancy may be due to the fact that formation of some groups; entrap the flame propagating radicals like H, OH, O etc. and does not allow the flame to propagate. One more reason may be due to the fact that polymer structure after addition of flame retardants, is modified in such a way that char formation is facilitated thereby resisting the flame. **5.3. Effect of flame retardant on shrinkability:**

## **6. Encapsulation applications**

Thermoplastic elastomeric encapsulation is used in many applications that require some special manufacturing techniques and materials of encapsulation. These include solenoids, sensors, self-supporting coils, transformers, motors, and electronic components of various types.

Various heat recoverable materials, which possess sufficient rigidity to hold out the elastomeric layer, may be used for the heat recoverable layer. Thermoplastic polymers are generally suitable heat recoverable materials either being crosslinked, or possessing the property of heat recoverability. Examples of such desirable TPEs that are crosslinked or which inherently possess the property of heat recoverability are polyolefins, such as ethylene-vinyl acetate copolymer, polyethylene, ethylene-ethyl acrylate copolymer or other ethylene copolymers, polyvinyl chloride, polyvinylidine difluoride, etc. Apart from that, other flexible polymers possessing necessary crystallinity such as trans-polybutadiene, ethylene-propylene-diene terpolymers, and trans-polyisoprene may also be used [16-18]. In addition, various commer‐ cially available elastomer-thermoplastic blends such as nitrile rubber-PVC and nitrile rubber-ABS may be taken into consideration. The only necessary property of the said thermoplastic material, used in place of the heat-recoverable material, should have sufficient rigidity at storage temperatures to seize the elastomeric sleeve. Such a material could be bonded to the elastomeric sleeve on either sides, by molding it in place or by placing concentric sleeves of thermoplastic material and relaxed elastomeric material in contact with each other and bonding them together at the interface.

In case of the elastomeric layer, any chosen material possessing elastomeric properties may be used. Suitable elastomers include rubber or rubber-like material such as natural rubber, styrene-butadiene rubber (SBR), cis-polyisoprene, cis-polybutadiene, butadieneacrylonitrile rubber, Neoprene Rubber, butyl rubber, (BB), silicone rubber, polysulfide, urethane rubber, polyacrylate, propylene oxide rubber, fluorosilicone rubber, chlorosulfonated polyethylene, chlorinated polyethylene, fluorohydrocarbon rubber, and so on.

It is generally desirable that the two layers be bonded to each other. If the inner layer is the heat recoverable layer the external rubber layer may stick or adhere tightly enough to it by virtue of its tendency to contract down onto the heat recoverable layer. In cases for some other applications where the elastomeric material is the inner layer, a stronger bond may be desired. A bond can be developed by several means. Any suitable adhesive can be used to bond the heat recoverable and elastomeric layers together. Examples of such adhesives are laminating adhesives, such as polyesters, polyurethanes. Peroxides, either organic or silyl, which form crosslinks between the two layers; structural adhesives such as epoxies, nitrile rubber, phenolics,, hot melt adhesives of suitable bond strength and softening temperatures, such as polyamides and various rubber-based adhesives such as those based on silicone nitrile and neoprene [19].It may be desired to bond or weld both the layers together without using an adhesive. Such bonding may be achieved simply by heating the layers to a high enough temperature at their interface so that they become soft and flow able and then applying sufficient pressure to achieve a bonding or welding of the layers [20-22].

extent in case of H-T stretched samples but for the low elastomer ration the shrinkability value is scarified to larger extent. The stretch ability of the H-T stretched blends again decreases to some extent with the addition of flame retardants. This may be the result of lower compatibility of flame retardants in the polyolefin phase at its higher level, suggesting the efficiency of flame retardants. The observed flame retardancy may be due to the fact that formation of some groups; entrap the flame propagating radicals like H, OH, O etc. and does not allow the flame to propagate. One more reason may be due to the fact that polymer structure after addition of flame retardants, is modified in such a way that char formation is facilitated thereby resisting

**Figure 2.** Study of shrinkability over cure time 2A) H-T stretched samples and 2B) R-T stretched samples of the blends

**Figure 2.** Study of shrinkability over cure time 2A) H-T stretched samples and 2B) R-T stretched samples of the blends of HDPE, LDPE, LLDBE with sulfur and DCP as curing agents.

**Figure 1.** Study of shrinkability over cure time i) LLDBE/CSM, ii) LDPE/CSM, iii) HDPE/CSM

samples may be due to more crosslinking of elastomeric phase at elevated temperature to deposit curatives to crosslink further strongly which is not possible in case of room temperature stretched samples. Increase in cure time allows the elastomer phase to crosslink for longer duration

**Figure 1.** Study of shrinkability over cure time i) LLDBE/CSM, ii) LDPE/CSM, iii) HDPE/CSM

resulting in sufficient crosslinking thereby increasing the shrinkability of the system.

Thermoplastic elastomeric encapsulation is used in many applications that require some special manufacturing techniques and materials of encapsulation. These include solenoids,

the flame.

**6. Encapsulation applications**

**5.3. Effect of flame retardant on shrinkability:**

of HDPE, LDPE, LLDBE with sulfur and DCP as curing agents.

106 Thermoplastic Elastomers - Synthesis and Applications

General applications of heat-shrinkable items are caps, sleeves, pipes, tubes, multi-way cable breakouts etc. In order to achieve the best quality the materials need to undergo certain specifications during the manufacturing process and application stages. Therefore there is also a great requirement to develop new materials tailored or manufactured exactly to specific applications. But developing such tailored products requires overcoming certain challenges like dispersibility, processability, exact mechanical properties (expandability, shrink ratio and temperature, flexibility, tensile properties, hardness), continuous operating temperature, chemical resistance, flame retardancy, electrical and dielectrical properties, and crack resist‐ ance. These are some of the criteria's that should be taken into consideration during the process of development of new materials for heat-shrinkable items [23]. As a result the process need several materials some times more than 10 ingredients and there is the possibility of unwanted interactions between them [24]. The aim of this paper was to focus on some selected topics of technological importance, related with the research and development of work dedicated to modern materials for production of heat-shrinkable items.

## **6.1. Application of encapsulated TPO's**

**•** TPO heat shrink tubing is used to protect wires, for better abrasion resistance as well as environmental protection for solid wire conductors, connections, joints and terminals used in several industrial and domestic fields. It also has application to modify or repair the insulation on wires or to bundle them together, to protect wires or small parts from minor abrasion, offering environmental sealing protection. The tubing provides good electrical insulation protection from dust, solvents and other foreign materials, and is mechanically held in place by its tight fit [25-27].

**Sheme 4.** TPO heat shrinkage tube

Some types of heat shrink tube contain a layer of thermoplastic adhesive on the inside to help provide a good seal and better adhesion, while others rely on friction between the closely conforming materials.

The manufacturing process of these types of tubes generally follows certain simple steps. The raw material is chosen based on its properties and end use application. The material are always manufactured along with many additives like certain stabilizers, colorants based on the application concerned. It can be briefly discussed for better understanding. At first the tube is extruded from the raw or neat material. Then the tube is subjected to a separate process where it is cross-linked. The material is often cross-linked through the use of electron beams, peroxides, or moisture. The main objective for cross-linking is to create a memory in the tube so that it is able to shrink back to its original extruded dimensions upon heating. Then the tube is heated just above the polymer's crystalline melting point and expanded in diameter, often by placing it in a vacuum chamber [28-29]. After this step, in its expanded form a rapid cooling is applied. Later, when heated (above the crystalline melting point of the material), the tubing shrinks back to its original extruded size. For external use, heat shrink tubing often has a UV stabilizer added.

**•** PO tubes, are the most widely and commonly used tubes in some major field in military, aerospace industries. It has maximum continuous-use temperatures from -55 to 135 °C. The main advantage of using PO tubes are their flexibility and fast-shrinking property, and they are manufactured in a wide range of colors (including clear), which can be used for colorcoding wires also. Black color PO tubes tend to have lower resistance to ultraviolet light; accordingly, and are only recommended for outdoor applications. A common shrink ratio is 2:1, but high-grade polyolefin heat shrink is also available with a 3:1 ratio [30].

There are several other materials that offers resistance to diesel and aviation fuels, and also some woven fabric, providing increased abrasion resistance in harsh environments.

Heat shrink tubing is also available in a wide variety of colors for color-coding of wires and connections. Since long heat shrink tubing has been used for PC to tidy up the interior of computers and provide an appearance considered pleasing. In response to this opening market manufacturers have started producing heat shrink tubing in luminous and UV reactive varieties.

Although heat shrink is usually used for insulation, heat shrink tubing with a conductive lining is available, for use particularly on joints that are not soldered. Heat shrink end caps, closed at one end, are used to insulate the exposed cut ends of insulated wires.

**Sheme 5.** Heat shrink insulated wires

applications. But developing such tailored products requires overcoming certain challenges like dispersibility, processability, exact mechanical properties (expandability, shrink ratio and temperature, flexibility, tensile properties, hardness), continuous operating temperature, chemical resistance, flame retardancy, electrical and dielectrical properties, and crack resist‐ ance. These are some of the criteria's that should be taken into consideration during the process of development of new materials for heat-shrinkable items [23]. As a result the process need several materials some times more than 10 ingredients and there is the possibility of unwanted interactions between them [24]. The aim of this paper was to focus on some selected topics of technological importance, related with the research and development of work dedicated to

**•** TPO heat shrink tubing is used to protect wires, for better abrasion resistance as well as environmental protection for solid wire conductors, connections, joints and terminals used in several industrial and domestic fields. It also has application to modify or repair the insulation on wires or to bundle them together, to protect wires or small parts from minor abrasion, offering environmental sealing protection. The tubing provides good electrical insulation protection from dust, solvents and other foreign materials, and is mechanically

Some types of heat shrink tube contain a layer of thermoplastic adhesive on the inside to help provide a good seal and better adhesion, while others rely on friction between the closely

The manufacturing process of these types of tubes generally follows certain simple steps. The raw material is chosen based on its properties and end use application. The material are always manufactured along with many additives like certain stabilizers, colorants based on the application concerned. It can be briefly discussed for better understanding. At first the tube is

modern materials for production of heat-shrinkable items.

**6.1. Application of encapsulated TPO's**

108 Thermoplastic Elastomers - Synthesis and Applications

held in place by its tight fit [25-27].

**Sheme 4.** TPO heat shrinkage tube

conforming materials.

Cross linked polyolefin heat shrink flame retardant sleeving with an adhesive lining. Designed to provide a permanent encapsulation for protection against moisture in a wide variety of applications once heated.Operating temperature -55°C to +125°C.(Source Google)

**Sheme 6.** Cross linked polyolefin heat shrink flame retardant sleeving

Heat shrinkable Polyolefin tubing with an integrally bonded adhesive inner lining, designed to provide a permanent encapsulation for protection against moisture in a wide variety of applications such as electrical wire splices, cable jackets, wire breakouts, strain reliefs and protection boots for electrical components. (Source Google)

## **7. Conclusion**

Use of TPEs is increasing for wide range of applications. Encapsulation is one of the areas where TPEs are hugely used. About 85% of plastic products in the modern world are made up of TPEmaterials of which a huge percentage is occupied by TPO's as they provide compara‐ tively high price performance as compared to other natural rubbers. The selection of a TPO material for any particular end application requires a special focus on its physical, chemi‐ cal,mechanical and electrical properties. Polyolefin elastomers (TPO's) have proven their viability in flexible plastics applications and use in a variety of industries. Further advances in application development, product design, and manufacturing capabilities will provide increasing opportunities for years to come. TPO's has proven to be the best material used for outdoor encapsulation application. One of the major criteria for TPO's suitability in this sector is the heat sensing ability. There is a direct relation between the processing parameters and the shrinkability of the TPO polymer blends. With increase in crosslinking and the cure time the shrinkability increases. The shrinkability also depends on the curing agent taken into consideration. Addition of flame retardant decreases the stretchability of the material.

## **Author details**

Cross linked polyolefin heat shrink flame retardant sleeving with an adhesive lining. Designed to provide a permanent encapsulation for protection against moisture in a wide variety of

Heat shrinkable Polyolefin tubing with an integrally bonded adhesive inner lining, designed to provide a permanent encapsulation for protection against moisture in a wide variety of applications such as electrical wire splices, cable jackets, wire breakouts, strain reliefs and

Use of TPEs is increasing for wide range of applications. Encapsulation is one of the areas where TPEs are hugely used. About 85% of plastic products in the modern world are made up of TPEmaterials of which a huge percentage is occupied by TPO's as they provide compara‐ tively high price performance as compared to other natural rubbers. The selection of a TPO material for any particular end application requires a special focus on its physical, chemi‐ cal,mechanical and electrical properties. Polyolefin elastomers (TPO's) have proven their viability in flexible plastics applications and use in a variety of industries. Further advances in application development, product design, and manufacturing capabilities will provide increasing opportunities for years to come. TPO's has proven to be the best material used for outdoor encapsulation application. One of the major criteria for TPO's suitability in this sector is the heat sensing ability. There is a direct relation between the processing parameters and

applications once heated.Operating temperature -55°C to +125°C.(Source Google)

**Sheme 6.** Cross linked polyolefin heat shrink flame retardant sleeving

110 Thermoplastic Elastomers - Synthesis and Applications

protection boots for electrical components. (Source Google)

**7. Conclusion**

Tanya Das1\* and Sunanda Roy2

\*Address all correspondence to<EMAIL_ADDRESS>
1 Berkeley Education Alliance for Research in Singapore Ltd, National University, Singapore

2 Materials Science and Engineering, Nanyang Technological University, Singapore

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**Barbara Speranza 1, Arcangelo Liso 2,\* , Vincenzo Russo 3 and Maria Rosaria Corbo 1,\***

Received: 29 November 2019; Accepted: 21 January 2020; Published: 25 January 2020

**Abstract:** This study proposes to exploit the in vivo metabolism of two probiotics (*Bifidobacterium longum* subsp. *infantis* and *Lactobacillus reuteri*) which, upon adhesion on a solid surface, form a biofilm able to control the growth of pathogenic and food spoilage bacteria. The results showed that pathogenic cell loads were always lower in presence of biofilm (6.5–7 log CFU/cm2) compared to those observed in its absence. For *Escherichia coli* O157:H7, a significant decrease (>1–2 logarithmic cycles) was recorded; for *Listeria monocytogenes*, *Staphylococcus aureus,* and *Salmonella enterica*, cell load reductions ranged from 0.5 to 1.5 logarithmic cycles. When tested as active packaging, the biofilm was successfully formed on polypropylene, polyvinyl chloride, greaseproof paper, polyethylene and ceramic; the sessile cellular load ranged from 5.77 log CFU/cm2 (grease-proof paper) to 6.94 log CFU/cm2 (polyethylene, PE). To test the potential for controlling the growth of spoilage microorganisms in food, soft cheeses were produced, inoculated with *L. monocytogenes* and *Pseudomonas fluorescens,* wrapped in PE pellicles with pre-formed biofim, packed both in air and under vacuum, and stored at 4 and 15 ◦C: an effective effect of biofilms in slowing the decay of the microbiological quality was recorded.

**Keywords:** probiotic; biofilm; pathogen; spoilage bacteria; active packaging