No abstract

The present paper aims to investigate a hydrolytic method, feasible to be applied at industrial level, to turn into useful products the Chamois leather wastes, mainly the buffing dust. The efficacy of acid treatments with 0.3, 0.5 and 1.0 % HCl solutions, by autoclaving at 105 °C, for reaction times of 6, 10 and 14 hours, was determined in an attempt to optimize the hydrolysis parameters. Based on the mass balance of performed experiments, the yields of hydrolysis processes were calculated for two of the products that were separated from the final mixture: collagen hydrolysates and fats. Optimal working parameters were: a concentration of 0.5 % HCl, and a duration of 10 hours, by simply boiling in autoclave, at 105 °C. The resulted polypeptides mixture was characterized by chemical (total nitrogen content) and physical-chemical methods (FTIR spectra, EDAX). The recovered greasy matters were purified by water-solvent partition, and the specific physical-chemical indicators were determined. The main advantage of the polypeptide mixtures obtained by Chamois wastes hydrolysis consists in the fact that they are chromium-free, and can be used for a large range of industrial (foaming agents, waste water treatment, chemical auxiliaries, fillers, adhesives, blends with synthetic polymers, concrete mixtures etc.) and agricultural applications (nitrogen and sulfur slow release fertilizers, animal feeding). The grease fraction can be used in leather wet finishing, or can be further chemically modified to produce surfactants. The small amounts of solid residues which resist to the acidic hydrolysis can be used, after neutralization, as additives of concrete mixtures, in producing decorative bricks.

The present paper aims to synthesize and test a pretanning agent based on isocyanatefunctionalized collagen hydrolysates of low molecular mass (0.9 ÷ 3.6 kDa; polypeptides that include 8 to 32 amino acids), obtained starting from hides wet wastes, and used without further purification. Raw colloidal suspension resulted after hydrolysis was centrifuged to separate insoluble particles, and then was repeatedly filtered to retain coarse particulate and fatty maters. The clarified solution was concentrated by vaporization up to 35 % w/v dry matter, mixed with 10 % v/v dimethyl sulfoxide (DMSO), and maturated overnight under efficient mixing, in a hermetically closed reaction vessel, at ambient temperature. Using a solution of diisocyanate in DMSO, the molecular mass of the product was further increased by cross-linking, in parallel with the functionalization in the virtue of a small amount of free isocyanate groups that remain unreacted. The functionalized collagen hydrolysate was characterized by chemical (total nitrogen content, the amount of free carboxyl, amino, and isocyanate groups) and instrumental methods (infrared spectroscopy). The fraction of increased molecular mass after cross-linking was determined by comparative dialysis through membranes with 3.5 and 12 kDa. Pretanning ability of the functionalized hydrolysates was estimated by gelatin precipitation, and tested on sheep pelts. An increase of 6 ºC was measured for the shrinkage temperature. Pretanned pelts were gradually dehydrated (preventing the local drying) and drum-tumbled, and then was treated once again with the same functionalized product, in a short concentrated float. A supplemental increase of shrinkage temperature with 8 ºC was measured.