Effects of Poly(Ether Ketone Ketone) Thermal Degradation on the Processability of Carbon Fiber‐Reinforced Composites

Poly(ether ketone ketone) (PEKK) is a high‐performance semi‐crystalline aromatic polymer, widely used in applications requiring excellent thermal and mechanical stability. However, thermal degradation occurring at elevated temperatures during composite manufacturing processes, such as compression molding or stamp forming, can have detrimental effects, particularly on the mechanical properties of PEKK composites. Therefore, elucidating the degradation mechanism of PEKK is crucial for manufacturing continuous carbon fiber‐reinforced PEKK (CF/PEKK) composites. In this study, the effects of thermal degradation of PEKK on the processability of CF/PEKK composites were investigated by revealing changes in rheological behavior, crystallization kinetics, chemical structure, and physical appearance of PEKK. The thermal degradation studies were conducted at four different degradation temperatures of 370°C, 380°C, 390°C, and 400°C for 90 min for all analyses. At elevated temperatures, PEKK undergoes degradation reactions, with initial backbone scission followed by thermally activated crosslinking, resulting in a more rigid, brittle structure. Moreover, thermally degraded samples require a longer induction time to initiate crystallization, and their crystallization proceeds more slowly, as evidenced by the reduced slope of the curves. Certain structural changes hinder the ability of PEKK chains to reorganize into ordered crystalline domains, thereby delaying both nucleation and crystal growth. The viscoelastic behavior of CF/PEKK composites was also consistent with the degradation mechanism of PEKK.