In this study, the mechanical and structural characteristics of wool fibers were examined, and the contributions of the microfibrils and matrix to the deformation processes were analyzed. The experiments were carried out on single wool fibers. To understand the structural changes at different deformation levels, the wool fibers were treated with a complex mechanical regime. One of the most significant results from the mechanical tests was the estimation of the modulus of the matrix, which changed from 0.07 to 1.6 GPa during stretching. This result proves the proposal of the netlike structure of the matrix. On the basis of the obtained experimental data and the structural model, where the microfibrils and matrix play the role of a reinforcing phase and a filler, respectively, the rigidity of the microfibrils in the initial unstretched state was determined to be equal to about 20 GPa. The experimental data obtained from the Fourier transform infrared–attenuated total reflectance spectroscopy method proved the α–β conformational transition both in the yield and postyield regions and revealed the presence of the stable β form, which was not sensitive to stretching. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

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.

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The recovery process in stretched wool fibers at different strain levels ranging from 5% to 40% was investigated at room conditions for a long time, up to one year, and in water. The recovery process in stretched wool fibers is quite slow at room conditions; thus this slow recovery process causes quite high remaining deformation on the wool. The recovery process in the strain (ε) and logarithm time (log t) coordinates has a linear dependence in the wide time range that allows estimating the required time for a complete recovery. In contrast to the rather slow recovery process at room conditions, a complete recovery in water at room temperature was observed within approximately 30 s. Structural changes during the recovery processes at room conditions and in water were analyzed by an FTIR/ATR method. The influences of water content and new formations of hydrogen bonds in the recovery processes were examined. Slow recovery at room conditions was associated with the reorganization of the hydrogen bonds between microfibrills and matrix which results in formation of a new and rather stable structure. The absorption of water by the matrix phase causes the disruption of the strong hydrogen bonds holding the stretched form of the fiber and leads to a rapid recovery.