Enhanced transverse and longitudinal compressive strength of micro-/nano- aramid pulp interleaved unidirectional CF/PEEK composite laminates

Carbon fiber-reinforced polyetheretherketone (CF/PEEK) thermoplastic composites are increasingly used in biomedical implants and are attracting attention as potential alternatives to carbon fiber-reinforced epoxy (CF/epoxy) thermosets due to their superior toughness and biocompatibility. However, delamination in CF/PEEK composite laminates, arising from the absence of fiber reinforcement in resin-rich regions, remains a critical limitation. This study demonstrates the interfacial toughening effect of micro-/nano- aramid pulp (AP) interleaving in unidirectional CF/PEEK laminates, as well as comparing the AP interleaving effect in CF/epoxy counterparts. AP-interfacial toughening led to notable improvements in CF/PEEK composites, with up to 21% higher longitudinal compressive strength, 27% higher transverse compressive strength, and 15% higher short-beam shear strength. A comparison further revealed that AP-interfacial toughening exhibits distinct behaviors in CF/PEEK and CF/epoxy under different loading modes. While AP interleaving enhanced compressive strength in both systems, its effect on flexural strength diverged: CF/epoxy benefited due to compression-driven failure, whereas CF/PEEK, governed by tension-driven failure, experienced flexural strength reduction when interlayer thickness exceeded 10 μm. Overall, this work establishes AP-interfacial toughening as an effective strategy to enhance CF/PEEK compressive performance by promoting fiber bridging in resin-rich layers and reducing delamination between carbon fiber plies.