Recycled Polyacrylonitrile Nanofiber Interleaves With Graphene Nanoplatelets for Adhesively Bonded Composite Joints: Lap‐Shear and Opening‐Mode Fracture Performance

ABSTRACT

This study presents a sustainable toughening strategy for adhesively bonded CFRP joints by using electrospun polyacrylonitrile (PAN) nanofiber interleaves produced from virgin PAN (vPAN) and recycled PAN (rPAN) recovered from textile‐waste Orlon. Graphene nanoplatelet (GNP)‐hybridized vPAN and rPAN interleaves were also examined to clarify the combined effect of nanofiber bridging and GNP‐assisted crack resistance. Single‐lap joint tests showed that the lap‐shear strength increased from 10.34 MPa for neat epoxy to 11.80 MPa for vPAN/Ep and 12.40 MPa for rPAN/Ep. The highest strength was obtained for GNP–rPAN/Ep, reaching 13.24 MPa, which corresponds to a 28.08% improvement over neat epoxy. Under Mode‐I DCB loading, the crack‐initiation load increased from 49.39 N for neat epoxy to 77.68 N for GNP–rPAN/Ep, while the critical fracture energy increased from 230.16 to 376.31 J/m ² . Fracture surface observations indicated that nanofiber interleaving changed the damage response from a more interface‐dominated appearance toward a more heterogeneous mixed‐fracture character. SEM observations further supported the activation of nanofiber bridging, pull‐out, crack‐path deviation, and GNP‐assisted pinning/deflection mechanisms. The results show that rPAN nanofiber interleaves have the potential to improve joint strength and fracture resistance and promote the use of circular materials in composite bonding applications.