Study of thermal behaviour of lac resin using specular reflectance spectroscopy

Abstract

Purpose

To determine molecular level changes occurring in lac resin, due to the effect of thermal stress at different levels of temperature and baking times.

Design/methodology/approach

Films of lac resin were applied on tin panels and baked at 100 and 200°C for different time intervals. The baked films were examined by specular reflectance spectroscopy, as they were otherwise difficult to examine through conventional IR techniques, using KBr pellet method. The results obtained were compared and correlated with work reported by earlier authors using wet chemical methods.

Findings

No significant spectroscopic change was observed on heating lac resin films at 100°C for different time intervals, as compared to air‐dried (parent) lac films. However, it was observed that when the films were baked at 200°C, the spectroscopic data indicated anhydride formation in the oligomers, due to heating effects.

Research limitations/implications

Chemical researches on lac resin have been typically limited by lack of modern tools, due to the difficult and unique nature of the material. The present method to determine molecular level changes in lac due to heating effects, using state‐of‐art instrumentation and computational technique opens a new vista in this field of research.

Practical implications

Lac resin still has a significant place in the surface coating industry, typically in food applications, insulating vanishes, etc. The results obtained indicate that lac‐based baking compositions, when baked at 200°C, exhibit improved characteristics, in terms of adhesion, scratch hardness and even acid resistance. Such an improvement can be attributed unequivocally to the formation of anhydride linkage as evident from spectroscopic data.

Originality/value

As of now, there is no report of specular reflectance data on lac resin and its derivatives. This paper represents the first attempt to obtain and correlate reflectance data on lac. It also highlights the convenience of the method and the scope of sophisticated data analysis, using computational methods.

Citation

Bhatia, D., Sarkar, P.C. and Alam, M. (2006), "Study of thermal behaviour of lac resin using specular reflectance spectroscopy", Pigment & Resin Technology, Vol. 35 No. 1, pp. 36-44. https://doi.org/10.1108/03699420610638030