Effect of molecular weight and concentration of polyethylene glycol on physicochemical properties and stability of shellac film.

The effects of molecular weight and concentration of plasticizer on physicochemical properties and stability of shellac films were investigated. Type of plasticizer was previously reported to have some effects on the stability of shellac films, and polyethylene glycol (PEG) was the plasticizer of choice for plasticizing shellac films. In this study, different molecular weights of PEG (200, 400 and 4000) were chosen at a concentration of 10% w/w of shellac films. Shellac in alcohol was prepared in a free film. The stability of shellac film was then performed at 75% RH, 40 °C for 3 months. The comparison was made between the film with and without plasticizer. Shellac films were then determined for acid value, insoluble solid, mechanical properties and water vapor permeability coefficient. It was reported that different molecular weights of PEG had some influence on physicochemical properties of the shellac films. Among different molecular weights of PEG, PEG 400 showed a suitable molecular weight that could protect the shellac chain at the carboxylic and hydroxyl groups. Therefore, the molecular weight of plasticizer played a crucial role for the protective ability at active sites. Further study was performed to investigate the effect of concentrations of PEG 400 on the stability. The results demonstrated that PEG 400 at a concentration of 10% (w/w) could prevent the polymerization process for only 4 months and a significant change of all parameters was then reported. However, a higher concentration, 20% (w/w) of PEG 400, could prolong the stability of shellac for 6 months of study. Therefore, the drawback of shellac as a natural polymer in pharmaceutical and food industries could be tackled by the appropriate size and concentration of plasticizer.