Biodegradable packing materials based on waste collagen hydrolysate cured with dialdehyde starch

Hydrogels of collagen hydrolysate (H) of mean M-w 15-30 kDa obtained from waste collagen from meat casings manufacture, cross-linked with 15% (based on H) polymeric dialdehyde starch (DAS), have a marked tendency to ageing, which shows in hydrogel gradually increasing rigidity and decreasing thermo- reversibility. Methods of thermal analysis (DSC, TG) proved that ageing of hydrogels is not related with a non-equilibrium state of the cross-linking reaction but is rather given by increasing density of inter-chain hydrogen bonds between polypeptide segments of H. Plasticizing effect of DAS on H is not too pronounced but the difference between glass transition temperature of dry xerogel T-g=189.5 +/- 2.5 degrees C and temperature of starting degradation (DAS component) 241.4 +/- 12.7 degrees C offers certain space for processing these xerogels into biodegradable (edible) packaging material by usual plastics technologies. Films obtained from the reaction mixture by casting and drying at room temperature after thermal processing (105 degrees C for 4 h) dissolve at room temperature only after 350 h. This effect can be employed for time-controlled releasing of active substances from such biodegradable (edible) packages.