THEORETICAL STUDY OF MODIFIED ELASTIC AND HIGH-ELASTIC PARAMETERS OF HIGH DENSITY POLYETHYLENE BASED ON EXPERIMENTAL RELAXATION CURVES

Abstract

The article provides an alternative method of determining the physical and mechanical parameters of the polymer by the preselected law of stress-strain connection. The non-linear generalized Maxwell-Gurevich equation is chosen as the specified law. It contains one elastic parameter - the modulus of elasticity, and three highly elastic: the modulus of elasticity, the modulus of velocity and the coefficient of initial relaxation viscosity. Existing techniques determine the specified parameters of the polymer as a function of one variable, usually temperature. In the article, using the example of relaxation curves of high-density polyethylene (HDPE), an algorithm is given for determining the characteristics of a material with the subsequent construction of the law of their change as a function of two variables: the level of ionizing radiation and the proportion of hydroxyapatite additive. Analysis of the results showed that the irradiation of the sample and the introduction of the additive have a different effect on the elastic and highly elastic parameters of the polymer. With simultaneous irradiation of the material and the introduction of additives, the polymer velocity modulus increases much more than the effects of each factor separately. In turn, the combined effect of radiation and additives leads to a certain decrease in the value of the coefficient of initial relaxation viscosity in comparison with the level achieved in the presence of either ionizing radiation or the introduction of hydroxyapatite. At the end, a model experiment is presented for constructing polymer relaxation curves using the physic and mechanical parameters obtained. The good agreement between the theoretical and experimental curves allows to speak about the reliability of the method used.