A comparison study on effects of polyglycerols on physical properties of alginate films

The water solubility and brittleness of unplasticized sodium alginate (SA) films hinder their widely application. Glycerol (GLY), the most commonly used plasticizer, is compatible with alginate due to the formation of hydrogen bonding owing to the hydroxyl functional groups. However, GLY is a small water-soluble molecule, and the resulting leaching problem may lead to decline in mechanical properties of SA films. Aimed at better plasticizers for alginate (ALG) films, this work focuses on the effects of polymerization degree of polyglycerol on physical properties of ALG films. The cross-sectional morphology, crystallinity, mechanical and thermal properties, water solubility, water content and barrier property of ALG films plasticized with GLY, triglycerol (TG) and decaglycerol (DG) were characterized and discussed. Results illustrated that owing to the long molecular chains of TG and DG and their strong interactions with ALG matrix, the plasticized films possessed better mechanical properties, higher water content and lower water solubility. Moreover, it was worth mentioning that even after water treatment, the mechanical properties of ALG-TG and ALG-DG films were superior than that plasticized with GLY. The results of this study were believed to provide particular insights into the plasticization mechanism and the improvement in performance of SA films in packaging applications.