Effect of salts and plasticizers on stability of shellac film

The aim of this study was to increase the stability of shellac because of the polymerization. A few approaches have been applied in this study. Shellac film was prepared in two salt forms, that is, ammonium and 2-methyl-2-amino 1-propanol salts, and a comparison was made with shellac film in free acid form. The other approach was by the application of plasticizers. These plasticizers were diethyl phathalate, triacetin, and polyethylene glycol 400 (PEG 400). Plasticized shellac and unplasticized shellac films in free acid form were then compared. All shellac films were kept in stability chamber at 40 degrees C, 75% RH for a period of 3 months. The studied parameters such as insoluble solid, acid value, mechanical properties, and water vapor permeability were detected every month. Analysis of variance (ANOVA) technique was used to analyze data. The applications of salt forms proved statistically significant (p < 0.01) to reduce the polymerization process whereas certain plasticizers could enhance the stability. PEG 400 was the only plasticizer that could show the increase in stability. The improvement of stability might be a result of the interference of a larger molecule of PEG 400 causing the difficulty in interaction among carboxyl or hydroxyl groups of shellac and the effect of lower loss of plasticizer.