Uso da técnica de emissão acústica na investigação do comportamento mecânico do polipropileno fotoestabilizado e envelhecido artificialmente.

Abstract

This work aims to investigate the mechanical behavior of polypropylene (PP) photostabilized and artificially aged by using acoustic emission techniques. Injection molded tensile specimens containing UV absorber, sterically hindered amines (HALS) and HALS/UV absorber at concentrations of 0.5; 0.5 and 0.25/0.25 mass%, respectively, were exposed to ultraviolet (UV) radiation in the laboratory for different periods of exposure. The monitoring by acoustic emission of samples not exposed and exposed to UV radiation was carried out during the tensile tests. The results showed that pure PP exhibited a highly fragile behavior with exposure time increase, whereas the PP/absorber, PP/HALS and PP/HALS/absorber showed low elongation values until rupture and practically the same tensile strength when compared to non-exposed materials. Comparing the results obtained by Fourier transform infrared spectroscopy (FTIR), optical microscopy and mechanical properties, it was observed that the degradation profile was one of the factors responsible for the better mechanical performance of the PP containing the photostabilizing additives. From the acoustic emission technique it was possible to detect shear bands, cracking, nucleation and crack propagation and their location as well as material failure, showing a promising way to monitor PP changes due to exposure to UV radiation. In general, light stabilizers and the HALS/absorber mixture were effective in stabilizing the mechanical properties of PP, and the acoustic emission technique has shown to be a very promising in the monitoring of PP changes due to exposure to UV radiation.