Coating properties of shellac modified with synthesised epoxidised-novolac resin

Abstract

Purpose – The purpose of this paper is to improve the properties of shellac by blending with epoxidised novolac resin for its use as coating material for metal surfaces. Design/methodology/approach – Epoxidised-novolac resin was synthesised by epoxidation of novolac resin, which in turn was synthesised by reaction of phenol with formaldehyde. The epoxidised-novolac resin was blended with different weight ratios of shellac ranging 10-50 weight per cent with an interval of 10 weight per cent. Films of the blends were studied for different coating properties using standard procedure. Findings – Significant improvement in coating properties of shellac such as gloss, scratch hardness and impact resistance was observed on blending with epoxidised novolac resin. Resistance towards water and alkali increased, while acid resistance decreased, with the increase in concentration of epoxidised novolac resin in the blends. Contact angle measurement revealed that blends showed more resistance towards polar solvent than non-polar ones. Research limitations/implications – Epoxidised-novolac resin used in the study was synthesised of epoxy equivalent of 187. Epoxidised-novolac resin of different epoxy equivalent can also be synthesised and used for blending and studying the properties. Practical implications – Blending of shellac with epoxidised-novolac resin improved the coating properties of shellac, which was further enhanced with the treatment of butylated melamine formaldehyde resin. The formulation can be used as coating material for metal surfaces. Originality/value – Blending of shellac with epoxidised-novolac resin was done for the first time. The formulation can be utilised for developing coating material for metal surfaces.