Crystallization of water in some crosslinked gelatins

Five gelatin samples crosslinked with 1,4-diisocyanatobutane, 1,6-diisocyanatohexane, 1,12-diisocyanatododecane, 1,3-butadiene diepoxide and 1,2,7,8-diepoxyoctane were used to investigate the behavior of the gelatin–water system. The crosslink densities were estimated quantitatively by the values of the molecular weight between crosslinks Mc. Differential scanning calorimetry indicated that the water was only partially crystallizable below 0°C, and the fraction of non-crystallizable water depends on the nature of the crosslinking agent. This fraction tends to zero for high overall water fraction, approaching unity. The overall water weight fraction at which crystallizable water forms was found to be of the order of 0.35 for four of the samples, whereas for the sample crosslinked with 1,3-butadiene diepoxide it is surprisingly high, specifically 0.68.