Inverse Effects of Cooling Rates on the Interfacial Shear Strength of Carbon Fiber/PEEK Composites with and without Presence of Transcrystal Layers

The crystallization behavior of polyetheretherketone (PEEK) is essential for the interfacial properties of its carbon fiber (CF) reinforced composites. It has already been well known that the transcrystalline (TC) layer at the CF/matrix interface is beneficial of improving the interfacial shear strength (IFSS). However, not all CF can induce the formation of TC layers in the PEEK matrix. This study aims to compare the effects of cooling rates on the IFSS of CF/PEEK composites with and without existence of the TC layer. In comparison to the original PEEK matrix (PEEK-O), we applied both physical (PEEK-A) and chemical (PAEK) modifications to increase the nucleation ability of the matrices. As a result, obvious TC layer was only observed in CF/PEEK-O composite. We further found that the effects of cooling rates on the IFSS of CF composites were opposite for samples with and without the TC layer. For CF/PEEK-O composite which contains the TC layer, the fast-cooling sample showed a smaller IFSS than the slow-cooling sample. This work reveals the key role of crystallization behavior at the interface in modulating the effects of cooling rates on IFSS, which is beneficial for the customized manufacturing and processing of different CF/PEEK composites.