THERMODYNAMICS OF SMALL DEFORMATIONS OF HIGHLY ORIENTED SINGLE-CRYSTAL MATS OF POLYETHYLENE

Deformation calorimetry was utilized to study small deformations of single crystal mats of ultra-high-molecular-mass polyethylene oriented to various extension ratios. The results of deformation calorimetry, coupled with X-ray data obtained earlier, allowed us to resolve the elastic and viscoelastic components of the deformation. It was established that the internal energy of the samples changed irreversibly in the loading-unloading cycle. The decrease in the internal energy is due the ''curing'' of conformational defects, and the increase in the internal energy with the deformation is determined by the process of the accumulation of defects in crystalline regions and by the loss of continuity of the material.