Investigation on interlaminar fracture toughness and failure mechanisms of MWCNTs reinforced thermoplastic composites

<title>Abstract</title> <p> A liquid thermoplastic resin (Elium) and ultra-high-molecular-weight polyethylene (UHMWPE) fibres were employed to fabricate thermoplastic fibre-reinforced composite laminates. Multi-walled carbon nanotubes (MWCNTs) were incorporated to improve fracture toughness, while a non-ionic aromatic surfactant (TNWDIS) was introduced to achieve superior dispersion of MWCNTs within the resin. Laminates were fabricated by vacuum-assisted resin infusion. Mode I and Mode II interlaminar fracture toughness ( <italic>G</italic> _{<italic>IC</italic>} and <italic>G</italic> _{<italic>IIC</italic>} ) were quantitatively evaluated using double cantilever beam and end-notched flexure tests. The influence of MWCNTs content (0.01–0.15 wt%) on interlaminar fracture performance was systematically investigated. The incorporation of MWCNTs significantly increases resistance to interlaminar crack propagation through synergistic mechanisms of crack bridging, crack deflection and matrix plastic deformation, thereby effectively enhancing the interlaminar fracture properties of the laminates. However, in the MWCNT-only systems, increasing the MWCNT content beyond 0.05 wt% resulted in pronounced agglomeration, leading to a non-linear toughening response and reduced reinforcement efficiency. TNWDIS significantly suppresses MWCNTs agglomeration in the resin. At optimised loadings of 0.1 wt% and 0.03 wt% MWCNTs with TNWDIS addition, <italic>G</italic> _{<italic>IC</italic>} and <italic>G</italic> _{<italic>IIC</italic>} were improved by 78.53% and 152.61%, respectively. Moreover, TNWDIS strengthens the interfacial adhesion between MWCNTs and the resin through synergistic mechanisms of π–π stacking adsorption, steric stabilisation and dipole interactions with the Elium matrix. This enhanced adhesion reinforces the fibre–matrix interface and further elevates matrix fracture toughness, providing a robust route for the design of lightweight high-strength composite laminates. </p>