Synthesis of palm oil-based bio-polyol by thiol-ene reaction: Preliminary study of its potential as cationic waterborne polyurethane for coating application

Abstract

Thailand has the world's third-largest planting area for oil palm. Palm oil can be chemically modified to obtain bio-polyol instead of petroleum-based polyol. In this research, a new bio-polyol based on modified palm oil (MPO) was successfully synthesized by thiol-ene click reaction using Darocur1173 as a photoinitator. The molar ratios 2-Mercaptoethanol (ME) to carbon‑carbon double bonds for MPO synthesis was studied. The kinetics of the thiol-ene click reaction was investigated by monitoring with 1H NMR technique. The chemical structure of MPO was confirmed by 1HNMR and FTIR spectroscopy. In addition, the average molecular weight (Mn) of a series of MPO was determined by GPC. The influence of N-methyl diethanolamine (NMDEA) content as an internal emulsifier on cationic waterborne polyurethane (cWPU) was investigated. The resulting cWPU based on MPO showed well-dispersed particles with a shelf life of >6 months and the zeta potential increased with increasing NMDEA content ranging from 5.6 % to 9.6 %wt. Moreover, the plywood with cWPU coatings had a shiny gloss surface, with increasing NMDEA content. The cWPU coating with NMDEA content lower than 7.6 %wt protected the plywood surface against QUV accelerated weathering for 48 h without cracking the cWPU film. The cWPU showed a high gloss value, decreased contact angle, and increased water absorption behavior. The hydrophilicity of cWPU film increased with increasing NMDEA content. Also, increasing the NMDEA content led to a higher ratio of hard segment to soft segment in the PU chain which improved the tensile strength and thermal stability. These results demonstrated an efficient synthesis procedure which offers an opportunity to use palm oil as bio-polyol to develop green cWPU that can be used as a binder in coating applications.