LAUSR

The present article reports a new method for the synthesis of ‘artificial urushi’ using cardanol, a major ingredient of cashew nutshell liquid, as the starting monomer. Natural urushi sap is polymerized in a water-in-urushiol (w/o) emulsion system; here, we mimic this system for the polymerization of cardanol. The combination of a weak amine base and a weak carboxylic acid functions as efficient emulsifier. The polymerization of cardanol is carried out in a water-in-cardanol (w/o) emulsion to produce a prepolymer emulsion, which is further cured by crosslinking, resulting in the biomimetic polymerization of cardanol. The prepolymer emulsion is stable for storage. The films were prepared from the prepolymer emulsion; the curing of these films was achieved by thermal annealing or by cobalt naphthenate-catalyzed crosslinking in air to generate ‘artificial urushi’. The rheological properties of the cardanol monomer and the prepolymer emulsions resulted in excellent film formation on the substrate. Physical property examinations of the cured films showed sufficient hardness for use as a coating layer. Cardanol is a renewable resource, and no organic solvent was used, and thus, this polymerization is a green chemical process. A green method for the synthesis of ‘artificial urushi’ has been developed using cardanol, a main ingredient of cashew nutshell liquid, as the monomer via a reaction mimicking that of natural urushi. A water-in-cardanol (w/o) emulsion was developed by identifying a novel emulsifier, and polymerization of the cardanol emulsion generated prepolymer films, leading to polycardanol (artificial urushi) after curing with mechanical properties that are approximate to those of natural urushi coatings.