Epoxidized Soybean Oil‐Based Phosphorus‐Containing Waterborne Polyurethane Coating for <scp>PET</scp> Rope With Enhanced Flame Retardancy and Mechanical Properties

ABSTRACT Waterborne polyurethane (WPU) is a promising surface finishing agent for polyethylene terephthalate (PET) ropes used in marine operations, industrial lifting, outdoor activities, and agricultural settings. However, WPU exhibits poor flame retardancy, and developing a WPU coating that enhances the flame retardancy of PET ropes while maintaining good mechanical properties remains a challenge. Herein, we report PET ropes coated with flame‐retardant waterborne polyurethane (FRWPU) synthesized from epoxidized soybean oil‐based phosphorus‐containing polyol and poly(propylene glycol). The breaking strength of FRWPU coated PET rope (PET–FRWPU) reaches 8092 N, which is more than twice that of pristine PET rope; the elongation at break reaches 82.30%, nearly twice that of pristine PET rope. The PET–FRWPU achieves a V‐0 rating in the UL‐94 test, and the time required for a vertical flame to burn through the horizontal rope is extended to 90 s, more than twice that of pristine PET rope. In the cone calorimetry test, the PET–FRWPU inhibits heat release and smoke release more effectively compared to the pristine PET rope. Moreover, the FRWPU coating can withstand 800 cycles of abrasion and bending tests. This study provides insights into the design and manufacture of flame‐retardant coatings for PET ropes.