Progress of bio-based coatings in waterborne system: Synthesis routes and monomers from renewable resources

Bio-based coatings are becoming more relevant today due to depleting fossil resources as well as the adverse environmental impacts from the wide usage of petrochemicals in coating formulations. The growing interest in this research area is evident from the increasing volume of reports on the innovation of new coating binders derived from various renewable resources such as plant oil, fatty acids, cellulose, cardanol, etc. Although this is a positive development, many of the bio-based coatings are however still formulated as solvent-borne coatings, and the vapour emitted during curing of such coatings is known to be one of the major pollutants from the coating industry. To maximize the environmental benefits of bio-based coatings, it is necessary to adopt a curing mechanism or formulation which eliminates the use of organic solvents. The current review paper details the recent progress of bio-based coatings in waterborne systems, with specific focus on synthetic route and the selection of monomers derived from renewable resources used to develop such coating. The scope of this review paper includes waterborne bio-based polyurethane coatings, waterborne bio-based polyester and alkyd coatings, and waterborne bio-based epoxy coatings. Detailed discussion on the modifications adopted to induce specific properties in some of the coatings to serve as flame retardant, antimicrobial and anticorrosion coatings were elaborated as well.