Bio-based waterborne polyurethane coatings with superior seawater intrusion resistance for marine PET ropes

Polyethylene terephthalate (PET) ropes are widely used in deep-sea and offshore mooring systems due to their high strength, excellent fatigue resistance and low creep deformation. However, long-term marine service leads to seawater intrusion-induced degradation and mechanical property deterioration, threatening mooring system safety. Waterborne polyurethane (WPU) is a promising protective coating for PET ropes, and the demand for bio-based WPU has substantially increased owing to growing concerns over environmental issues and petroleum shortages. Herein, we report a bio-based WPU coating for PET ropes, synthesized from castor oil and poly (propylene glycol). The coated PET rope exhibits a seawater absorption of only 9.4 wt% after 120 days, significantly lower than the 47.7 wt% of pristine PET rope within 10 min. Moreover, its breaking strength increases to 6413.2 N (17% higher than pristine PET rope), and it can withstand 500 cycles of abrasion and bending tests. This study offers insights into the design and fabrication of bio-based WPU coatings with superior seawater intrusion resistance for marine PET ropes.