Synthesis of a fully bio-based self-catalyzed hyperbranched waterborne polyurethane as a sizing agent for enhancing the interfacial properties of CF/PA6 composites

The scientific community has dedicated the past decade to integrate its resources in pursuit of “sustainable development”, aiming to pave the way for a perpetually eco-friendly and sustainable future. As a part of this collective effort, traditional petroleum-based polyurethanes have been progressively substituted by environmentally friendly alternatives. In this study, a conservation-minded approach was implemented using a green solvent, γ-valerolactone, along with fully biogenic-derived reagents: epoxidized soybean oil, tartaric acid and L-lysine diisocyanate to develop a hyperbranched waterborne polyurethane (HWPU) sizing agent. Meanwhile, tertiary amine was integrated into the polyol structure, facilitating the self-catalytic process en route to polyurethane, thereby eliminating the need for highly toxic catalysts. The meticulously developed fully bio-based sizing agent notably enhanced the interfacial properties between the carbon fiber (CF) and nylon 6 resin matrix. Comprehensive mechanical property evaluations of the modified composites revealed 49.4% and 49.6% improvements in flexural strength and interlaminar shear strength, respectively, compared with pristine CF composites. Additionally, interfacial shear strength tests demonstrated a substantial increase of 66.1%. This work presents an attractive avenue for the prospective industrial production and application of a green HWPU sizing agent.