Spherulitic morphology of the matrix of thermoplastic PEEK/carbon fibre aromatic polymer composites

PEEK/carbon fibre composites (derived from APC-2) have been examined with a permanganic etching technique in order to reveal the crystalline, spherulitic morphology of the thermoplastic PEEK polymer matrix. The locations of the nucleation sites for spherulite growth have been categorized. Nucleation can occur both within the matrix and from the carbon fibres. Crystallization at lower temperatures favours matrix nucleation. Nucleation from fibres is dominated by sites associated with fibre-fibre contact. There is no evidence of “transcrystalline” growth. The study also identifies two types of crystal orientation effect in the polymer matrix. The first is a slight orientation that can occur in standard mouldings and is the result of the fibres constraining the shape of the volume into which spherulite growth can occur. The second effect produces abnormally high crystal orientation and is the result of improper processing at too low a melt temperature. Such conditions cause self-seeding during consolidation of laminates which, coupled with flow-induced orientation, can lead to directionally arranged spherulite precursors in different stages of morphological development.