Friction and dynamic mechanical characteristics of crystalline polymers during melting

This paper describes a study of the temperature dependence of the dynamic characteristic and friction in the melting and crystallization region of linear polyethylene, isotactic polypropylene and their 9: 1, 5: 5 and 1: 9 mixtures. The measurements were made on a Ferry-Fitzgerald type transducer and on a tribometer. The temperature-dependence curves of shear storage and loss moduli, the loss tangent, the friction and the slider-to-polymer contact area of the above materials were plotted. It is suggested that correlation of the dynamic and tribometric characteristics of polymers may be expected when the nominal contact area of the friction body approximates its actual value. Comparison of these characteristics for linear polyethylene in its pre-melting range reveal only a qualitative similarity between the temperature dependence of its shear storage and loss moduli on the one hand, and the ratio of the loads and friction to the slider-to-polymer contact area on the other. Investigation of mixtures of crystalline polymers has made it possible to determine the sequence of melting of the components in the mixture or the formation of a single-phase system at a definite component concentration. After crystallization of both components, two-phase binary systems containing crystallizing polymers have the structure of two interlaced frameworks formed by the polymer crystallites.