Effect of crystallinity and morphology on the mechanical properties of CF/PEKK composites manufactured under compression moulding and automated tape placement

Abstract

The present work aims to establish to what extent crystallisation morphology and kinetics affect the matrix-dominated properties of CF/PEKK composites, two factors which have been minimally investigated together in existing literature. Different compression-moulding cycles and automated tape placement (ATP) were used as the processing routes. Their effects on void content, crystallinity development, morphology and mechanical performance were investigated. Results showed that all compression-moulded laminates undergoing different isothermal crystallisation conditions achieved similar levels of consolidation and crystallinity, although the spherulitic development varied considerably. The effect of different crystalline structures was not evident on the properties investigated, as all compression-moulded laminates performed similarly. However, ATP laminates displayed a higher void content and low crystallinity, resulting in a lower performance across the investigated mechanical properties. While the modification of some ATP parameters resulted in slight improvements in performance in some testing, the results indicated that a thorough understanding of the correlation between processing conditions and development of crystalline structures in PEKK is needed in order to produce good-quality CF/PEKK parts under very rapid processing conditions and ensure the repeatability of this.