Application of protein hydrolysate from chrome shavings for polyvinyl alcohol-based biodegradable material

The use of hydrolysate from chrome-tanned wastes for producing biodegradable plastics particularly applicable in agriculture requires management of the breakdown of modified compounds of synthetic polymers. In this work, the additive applied for this purpose was protein hydrolysate produced by enzymatic hydrolysis of chrome-tanned shavings. It was used for modifying polyvinyl alcohol which had been processed into water-soluble films often employed in agriculture. This material, after being deposited in soil, undergoes biological degradation (first of all anaerobic) which is supported to a large extent by the addition of protein hydrolysate in particular. For this reason, anaerobic biodegrability tests were performed (volumetric test determining methanogenic activity) and the corresponding, percentage of degradation was determined based on a balance of produced biogas and inorganic carbon in the aqueous phase. Polyvinyl alcohol is relatively poorly degradable under aerobic conditions while protein hydrolysate, on the contrary, undergoes biodegradation at a fairly fast rate. From a comparison between the attained degradation degree of blow-extruded film and that of mechanically prepared compounds it follows that the limiting factor of degradability, apart from added protein hydrolysate, is also a chemical reaction between polyvinyl alcohol and hydrolysate taking place during the heat processing of film. It was confirmed that protein hydrolysate from chrome shavings markedly increases biodegradation of material (depending on its content in the plastic matrix), reduces the final cost of product and, last but not least, to some extent also exerts a positive influence on mechanical properties of the film.