Polycaprolactone-collagen hydrolysate thermoplastic blends: Processability and biodegradability/compostability

Thermoplastic blends of polycaprolactone (PCL) and hydrolyzed collagen (HC) derived from the tannery industry were investigated to assess the feasibility of producing by conventional melting-based procedures biodegradable items for applications in agriculture and plant nurseries. The used HC was obtained by alkaline hydrolysis of the shavings of the tanning process. PCL/HC blends, with 10, 20 and 30 wt.% of HC, were processed by extrusion and compression molding, and characterized in terms of thermal, rheological, morphological and mechanical properties. In view of their possible applications in agriculture, phytotoxicity assays were carried out by using cress (Lepidium sativum L.) germination test and growth analyses of lettuce plants (Lactuca sativa L., cv Canasta), used as reference. Small pots were produced by fused deposition modeling (FDM) and their compostability was evaluated by the standard disintegration test UNI EN ISO 14045. The ultimate aerobic biodegradability of the blends was assessed by the standard UNI EN ISO 14855-1. PCL/HC blends were successfully processed by extrusion providing cohesive and flexible filaments suitable for the FMD 3D-printing. A decrease in the melt viscosity was observed with the addition of HC due to its plasticizing effect. The addition of HC led to a clear decrease of the tensile modulus and, with 30 wt.% HC, a break elongation higher than 600% as pure PCL. Despite the release in water of soluble salts, responsible of a moderate phytotoxicity assessed by L. sativum germination test, PCL/HC blends were not phytotoxic to the lettuce growth. Moreover, PCL/HC blends showed very high biodegradation rates in compost, even higher than cellulose. Composting trial performed under real conditions also confirmed the biodegradability of these blends, showing complete disintegration of the produced 3D printed pots in just 30 days.