The tartaric acid (TA)/polyvinyl alcohol (PVA) composite films were prepared with various TA concentrations from 5 to 20 wt%. The crosslinking due to TA improved the tensile characteristics such as tensile strength and the Young's modulus, and thermal stability of the films. The addition of TA in PVA led to a decrease in the crystallinity. Application of prestretching or preliminary deformation resulted in significant changes in both stress–strain behavior and tensile characteristics of both pure PVA and TA/PVA composite films. Although low preextension levels such as 5% strain did not change much the tensile characteristics, higher preextension levels improved the tensile strength but decreased the extensibility of the films. The recovery processes of the stretched films consisted of a fast recovery process for which most of the recoverable elastic deformation is seen took place within almost 30 min and a time‐dependent long‐lasting recovery process continued in time very slowly, which resulted in undesirable residual deformation. It was also observed that increasing TA concentration accelerated the recovery process, hence, improved the recovery properties of PVA. The use of TA in the membrane applications can be considered to improve the mechanical properties and reusability of the membrane technology.

Uniaxially oriented commercial films of isotactic polypropylene were strained with ends keeping fixed and subjected to the heat treatment at temperatures from 50 to 2008C. The rigidity of annealed samples was characterized by the value of tangent modulus, E t , determined graphically at the initial portions of stress-strain curves. The structural changes in the samples were studied with the help of the IR and low-frequency Raman spectroscopies. The smallest E t values were obtained for the low-strained films, while the tangent moduli measured for highly strained samples exceeded the value for the original (untreated) film. The most prominent positive effect was achieved after annealing the samples at 908C.

Single wool fibers were coated with TiO 2 by using the sol-gel method. The uniaxial tensile properties of TiO 2 coated single wool fibers heated at different temperatures from 25 to 200 C were investigated and compared with those of uncoated single wool fibers. It was observed that the shape of the stress-strain curve of TiO 2 coated wool fibers became the same as uncoated wool fibers and showed a similar tendency of change to uncoated wool fibers with increasing temperature. But, the TiO 2 coated wool fibers obtained higher rigidity than uncoated wool fibers and up to their rupture points; they obtained higher stress levels in three deformation regions in the stress-strain curves, which indicates stronger wool fibers. Although the breaking extension of TiO 2 coated wool fibers decreased little by about 8%, the Young's modulus of TiO 2 coated wool fibers increased significantly by 19%, which was caused mostly by an increment in the stiffness of the cuticle layer of the wool fiber, and remained relatively higher than that of uncoated wool fibers after heat treatments. Structural changes in both uncoated and TiO 2 coated single wool fibers due to thermal effect, which caused the changes in the uniaxial tensile properties and the thermal behaviors of these fibers were discussed by using spectroscopic and thermal analysis methods in detail.

The influence of ultraviolet (UV) radiation on the structural and uniaxial tensile characteristics of reduced graphene oxide (rGO)/poly(vinyl alcohol) (PVA) composite films produced by using various contents (0‐10 wt%) of rGO obtained by a microwave‐assisted reduction process was investigated. With increasing rGO content, significant reinforcing effects of the rGO sheets were seen on the tensile characteristics of the unirradiated rGO/PVA composite films, that is, increases in the stiffness and rigidity and decreases in the strain at break values. After UV exposure times from minutes up to 1 hour, for all the rGO contents, the rGO/PVA composite films had improved tensile strength and modulus values as well as considerable improvement in the stress‐strain behavior in spite of great decreases in the strain at break values. The structural changes responsible for the improvement in the tensile strength and Young's modulus of the rGO/PVA composite films were associated with the development of strong intermolecular interactions between the rGO sheets and the PVA polymer chains through the formation of hydrogen bonds. Deterioration of the mechanical characteristics, especially strain at break values, was mainly due to the photodegradation of the structural units induced by UV radiation leading to the formation of some free radicals caused by the chemical bond breakages in the polymer chains as well as the weakening of intermolecular interactions such as hydrogen bonds. Correlation between the changes in the tensile properties and the structure of the rGO/PVA composite films were sought by analyzing tensile testing, fourier transform infrared/attenuated total reflectance (FTIR/ATR), and UV‐visible spectral results.

Mechanical, optical, and film formation properties of titanium dioxide/polyvinyl alcohol (TiO2/PVA) composites were studied. Two identical experimental sets of % TiO2 content were prepared that one set is in the range of 1, 3, 5, 7, 10, 13, and 20 wt% for the film formation and the second set is 5 and 50 wt% for the mechanical measurements. Photon transmission technique (PT) at room temperature was used for the film formation process after annealing for 10 min at the temperatures changing from 100 to 270°C. The increase and decrease in the transmission light intensity (Itr) from the composite films were attributed to void closure and interdiffusion models, respectively. The results were consistent with the data obtained from the film formation processes and mechanical measurements that the addition of TiO2 in PVA had remarkable improvement on mechanical properties, for example, increment in the Young's modulus and the rigidity as TiO2 content increased from 5 to 50 wt%, and it had also good film forming especially above 10 wt% TiO2 for the void closure processes leading to lower the activation energy. It was observed that for the lower content of TiO2 such as 5 wt%, the tensile strength and Young's modulus increased remarkably for heating temperature increased up to 150°C. However, with the increase of TiO2 content, the maximum values of the mechanical strength and modulus were shifted to 180°C for 50 wt% TiO2 from 150°C for 5 wt% TiO2 because of the thermal stability of TiO2.

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This study investigated the influence of UV-radiation on structural and uniaxial tensile properties of tannic acid (TA)/polyvinyl alcohol (PVA) composite films. All the samples were exposed to UV light. It was observed that TA reinforced the structure of PVA and its uniaxial tensile properties, as TA concentration increased thanks to the formation of crosslinking between TA and PVA molecules. From X-ray diffraction (XRD) measurements, it was seen that TA had a better protective effect on ordered structures such as crystallites against UV irradiation than that of PVA films, because the crystallinity of TA/PVA films did not change much. Major degradation effect of UV-radiation was seen on the amorphous flexible PVA chains and structure. As a result of photodegradation process leading to possibly breakage in the polymer chains in especially amorphous structure, the extensibility or strain at break values of both pure PVA and TA/PVA composite films was decreased dramatically.However, because decrease in the strain at break values for 5% and 10% TA content is less than that for 15% and 20% TA content, the 5% and 10% TA content can be regarded as optimum values, when the protective role of TA against UV irradiation was considered in the studied films.

Mechanical properties" are crucial for biodegradable and/or nonbiodegradable materials used in tissue engineering applications. In this study, bio-hybrid films were produced by using both Bifidobacterium animalis subsp. lactis BB-12 probiotic strain and Bifidobacterium infantis in combination with sodium alginate (SA), which demonstrates biocompatibility and facilitated gelation properties. Bio-hybrid films were characterized by using different methods. Based on the spectroscopic and mechanical analysis, it was found that mechanical strength increased in films produced by adding Bifidobacterium infantis in SA while this increase was relatively lower as compared to those containing Bifidobacterium animalis subsp. lactis BB-12 as crosslinking ratio increases. Besides, bacteria contained in bio-hybrid films increased the percentage of amorphous zone of SA in SA/bacteria films, which reduced the crystallinity ratio. This indicated that crystalline chains contained in the structure of SA are degraded by bacteria.