A novel high adhesion cationic waterborne polyurethane for green coating applications

This report is the first one on a cationic waterborne polyurethane (cWPU) latex based on epoxidized hydroxyl telechelic natural rubber (eHTNR) polyol, providing potential for use as a coating made of renewable resources. A cWPU latex was synthesized by step growth emulsion polymerization from hydroxyl telechelic natural rubber (HTNR with Mn = 3000 g.mol―1) with fixed N-methyl diethanol amine content of 5.6 wt% and 2,4-toluene diisocyanate (NCO index = 100). The effects of proportion of epoxide units on HTNR polyol from 0 to 30 % on preparing cWPU latex were investigated. Chemical structures of HTNR and eHTNR polyol were confirmed by 1H-NMR spectroscopy. The resulting HTNR and eHTNR polyols present a unimodal size exclusion chromatography trace. The viscosity increased with epoxide fraction. The synthesized cWPU latex based on eHTNR was a stable milky-blue emulsion with well-defined size dispersion. All cWPU-eHTNR films showed good wettability, good chemical resistance, and high thermal stability, improving with the proportion of epoxide units. The mechanical properties of cWPU-eHTNR films were studied from their stress-strain curves. Moreover, the electrical properties were investigated. The cWPU-eHTNR films showed relatively low conductivity. Wettability, chemical resistance, adhesion, thermal stability, and electrical properties of cWPU-HTNR films improved with the proportion of epoxide units on the HTNR polyol. These results demonstrate a new synthesis route to develop cWPU latex based on a biosource, for coating applications.