Thermal behavior of crystalline and amorphous HDPE phase in the process of necking at creep deformation

Thermodynamic aspect plays an important role in the structural processes in the neck of partially crystalline polymers under tension. Method of deformation calorimetry, simultaneously recording thermal and mechanical effects allows quantitative determination of entropic and energy effects during deformation. Evaluation of such parameters in combination with structural analysis provides important information for the analysis of the deformation mechanism of various polymer systems. It was revealed that the change in internal energy is due to the contributions of several processes: the destruction of the initial lamellar structure, the formation of a "neck" (lamellae-fibrillae transition), and the formation and deformation of fibrilae. The stretching of partially crystalline polymers in an amorphous state promotes crystallization. The chains in the formed crystallites are oriented along the axis of action of the applied force. The growth of crystallites is accompanied by straightening of the folded sections of the chains, which causes stress relaxation or rapid elongation of the sample when tested for creep.