Enhancing Electrical Insulation and Interfacial Properties of Polyphenylene Sulfide/Nylon 66/Glass Fiber Composites via Isocyanate Chain Extenders

ABSTRACT This study investigates the effects of isocyanate chain extenders, namely diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI), on the properties of polyphenylene sulfide (PPS)/nylon 66/glass fiber composites. The primary objective was to address the interfacial weakness inherent in these systems to improve electrical insulation performance. Results indicate that the incorporation of isocyanates led to a significant enhancement in key electric properties: volume resistivity increased by 1–2 orders of magnitude, and breakdown voltage was markedly improved. This is attributed to the formation of covalent “molecular bridges” at the interface, which minimized micro‐voids and defects that act as pathways for charge carriers. While tensile strength, flexural strength, comparative tracking index, and limiting oxygen index experienced slight decreases, impact strength and heat deflection temperature showed modest increases. Furthermore, the modified composite containing 0.3 wt% TDI maintained a UL‐94 V0 flame‐retardancy rating. The study demonstrates that isocyanate modification, particularly with 0.3 wt% TDI and 0.1 wt% MDI, offers a highly effective strategy for tailoring PPS‐based composites for high‐performance insulation applications, such as in electric vehicles and high‐voltage connectors, where superior dielectric strength is paramount.