Biodegradable cationic waterborne polyurethanes from poly(caprolactone)diol and trimethylol propane monooleate

Abstract Biodegradable cationic waterborne polyurethanes (WPUs) were successfully prepared using poly(caprolactone) diol as the soft segment. To improve the mechanical performance, adhesive strength and water resistance of the WPU films, different amounts of trimethylol propane monooleate (TMPM) containing biodegradable long‐branched aliphatic chains were incorporated in the PU structure. The T‐peel strength of WPU‐3 reached 42.8 N/25 mm, which was about 324% higher than that of WPU (10.1 N/25 mm) without TMPM. On the other hand, the elongation at break of WPU‐5 was 811%. On enhancing the TMPM content from 0 to 7.8 wt %, the surface tension decreased from 53.6 to 41.5 mN/m and the water contact angle of the WPU films increased from 52.4 to 81.0°, whereas the water absorption was observed to decrease from 15.6% to 9.6%. The fracture mechanism of the WPU films transformed from the brittle failure to the ductile fracture. The experiment results showed the cationic WPU modified by TMPM displayed excellent film‐forming property flexibility and adhesion, the surface tension of WPU dispersion and crystallinity of the resulting film were significantly reduced. For the first time, a biodegradable cationic WPU has been prepared by modification with TMPM, which can be employed for constructing the eco‐friendly biodegradable cationic WPUs.