Investigation of Degradation Effects on Crystallization of Thermoplastic Composites

Abstract

Thermoplastic composites such as PEKK or PEEK reinforced with carbon fibers go through heating and consolidation steps during processing. Upon heating and subsequent cooldown, a semi-crystalline structure nucleates and grows in the molten polymer. However, thermal degradation or partial oxidation of thermoplastics may severely affect this process and impact their mechanical properties as well as chemical resistance to common solvents. This also affects the recyclability of the material, as well as available repair-time or time to bring large-scale parts to melt. This paper presents a novel approach to investigate and quantify degradation effects in thermoplastic composites using a combination of polarizing light microscopy (PLM), Fourier transform infrared (FTIR) spectroscopy, and machine learning (ML) analysis. While PLM is used for in-situ investigation of the effect of degradation on crystallization, FTIR and ML are used for in-vitro analysis of degradation effects on chemical signature of the material. The results can be used to potentially develop robust manufacturing processes to optimize performance while minimizing degradation.