| The objective of this research was to characterize compression molded sodium caseinate based films and investigate the effect of water and glycerol ratios on thermal transition and heal sealing properties. Studies were conducted on films from three variations of film-forming mixtures or "resins", derived from US patent 4,076,846 containing sodium caseinate (NaCas), methylcellulose (MC), calcium chloride (CaCl2), glycerol (Gly), and distilled water.Moisture sorption isotherms were used to evaluate the water-protein and water-glycerol interactions in the resins. Sorption isotherms were characteristic of most biopolymer material and showed increasing moisture sorption with increasing amounts of glycerol. In compression molded films containing &ge29% glycerol, visible opaque specks of unincorporated matter were attributed to the high water binding property of glycerol and its interaction with the NaCas, which prevented the NaCas from being able to fully solubilize.Thermal analysis by DSC and TMA showed that all films were amorphous and that water and glycerol were equally effective at lowering Tg within the different water: glycerol ratios that were tested. While water and glycerol were equally effective at lowering Tg, they affected the strength properties and heat seal strengths of the film in different ways. Increasing amounts of glycerol decreased heat seal strengths (maximum load force/width) at higher seal temperatures (195°F) because it interacted with the protein chains, increasing mobility and elongation of the film under tensile stress and interfering with protein entanglements at the seal interface. Less glycerol increased stiffness causing increased film strength and seals with higher breaking stress. |
