Efeito da fotodegradação no comportamento tribológico e propriedades físico-químicas e mecânicas do polipropileno

Abstract

In this work, the impact of photodegradation induced by UV-A radiation on the physical, chemical, mechanical, and tribological properties of polypropylene without and with carbon black, referred to as PP and PPNF, respectively, was investigated. The materials were subjected to accelerated aging under Cycle 1 of the ASTM G154 standard, at intervals of 250, 500, and 1000 hours, in addition to the examination of samples in the as-supplied state. Characterization included microhardness analyses, to evaluate hardness and elastic modulus; DSC, to determine the degree of crystallinity; FTIR, to identify the presence of carbonyl groups; and SEM and white light interferometry, for surface parameter analysis. Microscratch tests were conducted to evaluate tribological behavior, using SEM and interferometry to investigate wear mechanisms and develop a deformation map, correlating aging time with the applied load level. EDS analyses were performed to quantify the oxygen percentage at different depths of the materials, especially at the bottom of the scratches. The results demonstrated that exposure to UV-A radiation significantly alters the mechanical and physicochemical properties of PP and PPNF, with particular emphasis on changes in crystallinity, carbonyl group formation, and variations in mechanical properties such as elastic modulus and microhardness. The addition of carbon black to PP was shown to provide protection against photodegradation, mitigating changes in crystallinity, as well as maintaining mechanical properties close to initial values after aging. The tribological study revealed a complex interaction between microstructural modifications and new mechanical and physicochemical properties, influencing the coefficient of friction and wear represented by the depth of abrasion scratches. This study contributes to the understanding of the interactions between photodegradation and tribology in polymers, shedding valuable light on the protective effect of carbon black and how the changes induced by UV-A radiation influence the tribological behavior of polypropylene over time.