Use of acoustic emission in the analysis of polypropylene failure caused by photodegradation

Abstract

ABSTRACTPhotodegradation is among the most frequent causes for the low performance of polypropylene (PP) products during service. This type of failure has been investigated extensively throughout the years using conventional methods including infrared spectroscopy and molar mass measurements. The use of acoustic emission, conversely, is not a common technique to evaluate polymer behavior, even though showed to be very useful to detect and locate damage during loading, contributing to the understanding and, hence, to the prevention of failure. In this investigation, injection molded tensile bars were exposed to the ultraviolet radiation in the laboratory for periods of up to 35 weeks and then characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, tensile properties, and scanning electron microscopy. During tensile testing, the acoustic emission technique was applied to monitor parameters like intensity of hits, events, and energy released during deformation. The results confirmed the high efficiency of hindered amines light stabilizers to inhibit chemical degradation of PP and the high sensitivity of the neat polymer toward UV exposure. The several steps of polymer failure were detected by acoustic emission, being a very important tool to understand the differences in mechanical behavior of the types of samples under investigation. It showed the beginning of the failure process as well as significant events that occurred during the test, such as the formation of shear bands, cracking, and material fracture. These observations, combined with the traditional degradation monitoring procedures, allowed a good understanding of the effect of UV radiation on PP failure mechanism. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46943.