Effect of temperature on coating properties of shellac-novolac blends

Purpose ‐ The purpose of this paper is to improve the properties of shellac by blending with novolac and to study the thermal behaviour of the blends with an ultimate aim to use as surface coating material. Design/methodology/approach ‐ Novolac was synthesized by reaction of phenol with formaldehyde in a molar ratio of 1:0.8, in acidic condition. Blending of shellac with novolac was done in solution and films of the blends, prepared on glass slides and tin panels, were baked at 150°C for 15 minutes. Properties of the films were studied as per standard procedures. Findings ‐ Films of shellac-novolac blends showed improvement in gloss and impact resistance compared to those of shellac alone. Gloss of blends increased with the increase in concentration of novolac and further increased on baking the films. Scratch hardness of shellac decreased on blending with novolac. Baked films of the blends showed resistance to heat and water. Films of shellac-novolac blends were found to be more resistant to polar solvents compared to non-polar solvents. Research limitations/implications ‐ Shellac, prepared from kusmi seedlac, was used in the study. Besides shellac, dewaxed decolorized lac (DDL), dewaxed lac (DL) and bleached lac (BL) could also be used for study on blending with novolac. Practical implications ‐ Blending of shellac with novolac improved the film properties of shellac. The study suggests that the compositions can be utilised in developing formulations of coating material with improved properties for metal surfaces. Originality/value ‐ The formulations based on modification of shellac with novolac and study of the film properties utilising various instruments are novel. The formulations based on shellac and novolac can find applications in the field of surface coating with desired purposes.