Exploiting the neutralizer to optimize amide content in bio-based waterborne polyurethane sizing agent for enhancing the interfacial properties of CF/PA6 composites

Within the context of optimizing the composition and structure of waterborne polyurethanes (WPU), neutralizer—a key component of ionic WPU that neutralize weak electrolytes in ionic segments to facilitate the formation of stable polyurethane dispersions often receives inadequate attention. Despite extensive research efforts aimed at understanding the effects of polyols, isocyanates and chain extenders on the properties of WPU, the specific impact of neutralizers on WPU performance remains notably understudied. In this research, a series of biogenic-derived reagents, including gallic acid, tartaric acid, as well as the L-Lysine diisocyanate were utilized to design a WPU sizing agent. Additionally, incorporation of aminoethylpiperazine as a neutralizer furnished plenty of amide bonds into polyurethane backbones upon heating treatment, thereby further improve the interfacial adhesion performance between carbon fibers and nylon 6 resin. Assessments of mechanical characteristics demonstrated notable improvements: 55.9% increase in flexural strength, 56.6% enhancement in interlaminar shear strength in comparison with unsized CF composites and a significant 70.1% boost in interfacial shear strength. This study offers a promising avenue for the formulation and utilization of high-amide-content WPU sizing agents in various applications.