The contribution of various network knots during the deformation of ethylene copolymers and nanocomposites based on them

Abstract

An analysis of the deformation mechanism and changes in mechanical parameters of low-crystallinity ethylene–octene copolymers of various densities and modified with detonation nanodiamonds is performed through the use of models based on the statistical theory of rubber-like elasticity. Experimental data were processed in terms of the Haward model with allowance for the non-Gaussian statistics of macromolecules at high strain and limited extensibility and the so-called “slip-link” model, which considers the density of labile knots and permanent entanglements. Despite obvious simplifications, both models attribute the discovered extrema of the concentration dependences of mechanical properties at low concentrations of nanodiamonds to the change in the number of segments between network knots and the following change in elastic modulus (Haward model) or to the number of labile and permanent knots (“slip-link” model), a circumstance that verifies the nucleating effect of nanodiamonds. It was found that the relative increase in density of each type of knot significantly depends on the degree of crystallinity of the matrix and the concentration of the modifier. Deformation calorimetry showed that tensile and cyclic loading of the investigated systems are followed by changes in internal energy. The roles of its intramolecular and intermolecular components at the various stages of deformation and the causes of their changes were estimated. The correlation between energy effects and the transformation of the structuring and parameters of the used models was determined.