Thermoplastic Blends Based on Poly(Butylene Succinate-co-Adipate) and Different Collagen Hydrolysates from Tanning Industry—II: Aerobic Biodegradation in Composting Medium

Two different raw hydrolyzed collagens (HCs), by-products of the Tannery industry, were investigated in blends with a bioplastic, as poly(butylene succinate-co-adipate) (PBSA), for the production of thermoplastic items for possible applications in agriculture. Chemical characterization of selected PBSA/HC blends and phytotoxicity assays on garden cress seeds (Lepidium sativum L.), used as spy species, were carried out; in addition, biodegradation and disintegration of specimens were assessed under controlled composting conditions at different temperature (58 and 25 °C). Although one of the HC investigated released sodium chloride in the aqueous extract, all PBSA/HC blends, up to 20 wt.% HC, resulted no-phytotoxic and showed considerable amounts of macro- and micro- nutrients for plants (mainly nitrogen). Regardless the amount added, HCs enhanced the biodegradation rate of PBSA/HC blends in compost at 58 °C compared to pure PBSA; lowering the temperature at 25 °C, as expected, biodegradation rate slightly lowered using the same compost. Most disintegration tests, performed on dog bone samples, corroborated the results of the biodegradation tests, thus suggesting that plastic mixtures could reasonably end their life cycle in a composting facility without decreasing the quality and the safety of the resulting compost. The outcomes achieved encourage the use of raw collagen hydrolysates from tanning industry in the production of PBSA-based thermoplastic blends to produce compostable items (mulching films and/or plant pots) for more sustainable uses in agriculture and/or plant nurseries. In addition, the use of these low-cost by-products can lower the cost of final product and give it fertilizing properties for plants given the presence of organic nitrogen in the hydrolysates.