Gels of collagen hydrolysate (H) crosslinked with dialdehyde starch (DAS) are marked by a strong tendency to aging, which
means a certain problem during their processing into biodegradable packaging materials. Applying casting technology and drying
these materials by heating air-dry films and foils for a limited time (1–4 h) at 105 °C may eliminate the aging problem. Solubility
of heat-treated films in an aqueous environment remains preserved, but depending on how long this temperature acts and on
the DAS content in the film, time of film disintegration prolongs from 1–1.5 h to 1300 h (≈54 days). It is probably caused
by the functional groups initially blocked by sorbed water, which get released to produce hydrogen inter-chain crosslinks.
The decrease in glass transition temperature (Tg) of such films varies with content of water sorbed in films in an interval of 90.2–189 °C.
Processing hydrogels of collagen hydrolysate (H) cross-linked with dialdehyde starch (DAS) by dipping or casting into biodegradable
materials for various applications, is complicated by their marked tendency to aging. One-hour action by temperatures at 60–90 °C
reduces sorbed water content in hydrogels by approx. 12%; dependence of the extent of this reduction on temperature (within
the mentioned range) was not detected. Effect of thermal action on duration of their disintegration in an aqueous medium and
on its pH (within limits 4.8–7.4) was not found either, neither on their gel–sol transition temperature. This supports the
view that aging is caused by time-dependent increasing network density of inter-chain hydrogen cross-links. The given temperature
interval is satisfactory for processing hydrogels through technologies currently used in processing synthetic plastics (compression
molding, injection molding).
Authors:F. Langmaier, P. Mokrejs, K. Kolomazník, M. Mládek, and R. Karnas
Differential scanning calorimetry was employed to investigate the reaction of diglycidyl ethers of bisphenol A (DGEBA) of
mean molecular mass 348–480 Da, with collagen hydrolysate of chrome-tanned leather waste in a solvent-free environment. The
reaction leads to biodegradable polymers that might facilitate recycling of plastic parts in products of the automotive and/or
aeronautics industry provided with protective films on this basis. The reaction proceeds in a temperature interval of 205–220°C,
at temperatures approx. 30–40°C below temperature of thermal degradation of collagen hydrolysate. The found value of reaction
enthalpy, 519.19 J g−1 (= 101.24 kJ mol−1 of epoxide groups) corresponds with currently found enthalpy values of the reaction of oxirane ring with amino groups. Reaction
heat depends on the composition of reaction mixture (or on mass fraction of diglycidyl ethers in the reaction mixture); proving
the dependence of kinetic parameters of the reaction (Arrhenius pre-exponential factor A (min−1) and activation energy Ea (kJ mol−1)) did not succeed. Obtained values of kinetic parameters are on a level corresponding to the assumption that reaction kinetics
is determined by diffusion.
Authors:F. Langmaier, M. Mládek, P. Mokrejš, and K. Kolomazník
Hydrogels of collagen hydrolysate (H) of mean Mw 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 Tg = 189.5±2.5°C and temperature of starting degradation (DAS component) 241.4±12.7°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°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.
Authors:P. Mokrejs, F. Langmaier, D. Janacova, M. Mladek, K. Kolomaznik, and V. Vasek
The study deals with the effect of chemical and physical modifications on thermal properties and solubility properties of
films based on amaranth flour starch–protein hydrolysate. Biodegradable and edible films were prepared by casting a 25% (w/w)
solution of hydrolysate containing 20% glycerol and various additions of dialdehyde starch (0, 1 and 5%). After thermal exposure
of films at 65 and 95 °C (for 6 and 48 h), thermal properties of films were studied employing differential scanning calorimetry
and thermogravimetric analysis. Film solubility tests were performed in an aqueous environment at 25 °C. Chemical and physical
modifications of films markedly affect their thermal properties and solubility.