Lap shear properties of CF/PEKK composites through nanoparticle-enhanced adhesive joints

Abstract

This study investigates the effects of incorporating halloysite nanotubes (HNTs) into polyetherimide (PEI) adhesive for carbon fiber/polyetherketoneketone (CF/PEKK) composite joints. The CF/PEKK substrate is fabricated through an oven consolidation process, while PEI adhesive films with varying HNTs loadings (0.5, 1 and 3[Formula: see text]wt.%) are prepared using solvent casting with [Formula: see text]-butyrolactone. Homogeneous dispersion of HNTs in PEI is achieved through magnetic stirring and IR heating. The resulting film is hot pressed to form a 100[Formula: see text][Formula: see text]m thick film, and adhesive lap shear joint specimens are manufactured through oven consolidation. Morphology and dispersion of HNTs in PEI are analyzed using SEM and EDS, revealing favorable dispersion at 0.5[Formula: see text]wt.% HNTs and aggregation at higher loadings. Differential scanning calorimetry (DSC) is employed to study the glass transition temperature (Tg) of PEI, showing decreased Tg for solvent-cast PEI and increased Tg with HNTs incorporation. This increase is attributed to the constrained mobility of polymer chains due to HNTs’ influence. Lap shear strength (LSS) is evaluated, demonstrating enhancement with HNTs incorporation: 0.5[Formula: see text]wt.% HNTs (+12.5%) > 1[Formula: see text]wt.% HNTs (+8.33%) > Pure PEI > 3[Formula: see text]wt.% HNTs (−12.5%). The study attributes this enhancement to HNTs’ reinforcement and chemical interactions with PEKK. Aggregation tendencies at 3[Formula: see text]wt.% HNTs lead to decreased LSS. SEM-EDS analysis of fractured specimens indicates a multifaceted bonding joint interface involving PEKK, PEI and HNTs. CF/PEKK composites show adhesive, cohesive and adherend failure modes, with adherend failure being dominant. Notably, fabric-like textures and plastic deformations in PEI with 0.5[Formula: see text]wt.% HNTs contribute to enhanced LSS, while higher HNTs content leads to cohesive failure due to aggregation. This study provides insights into optimizing composite adhesive systems by harnessing nanotube reinforcement and controlling dispersion, thereby influencing interfacial strength.