In-depth study from gluten/PCL-based food packaging films obtained under reactive extrusion conditions using chrome octanoate as a potential food grade catalyst

Single-use food packaging derived from petroleum is causing serious environmental problems, and food hydrocolloids have been suggested as raw materials to replace these non-biodegradable materials. However, food hydrocolloid-based food packaging materials have some challenges that must be overcome to achieve their manufacture on a large scale. Keeping this in view, three thermoplastic gluten (TPG)-based film systems were developed in this study under reactive extrusion (REx) conditions followed by thermo-molding: TPG, TPG/poly (epsilon-caprolactone) (PCL) and TPG/PCL plus chrome octanoate as a potential food grade catalyst (TPG/PCL + Cat). An in-depth analysis in terms of the structural, thermal, crystalline, physicochemical, microstructural, rheological, mechanical and environmental properties was carried out here. The films prepared from the TPG/PCL blend showed a clear phase separation: a TPG-rich phase (hard section) and another PCL-rich phase (soft section). Despite this, mechanical compatibility was observed in these systems. In addition, TPG/PCL and TPG/PCL + Cat films were recommended as potential shape memory food packaging materials. In particular, the addition of the Cat caused the crosslinking of the TPG and PCL chains via Schiff's base reactions, resulting in a more hydrophobic material, which showed to be kinetically less biodegradable than the other developed film systems. It should be noted, however, that all the materials were biodegradable after 90 days under vegetable compost conditions, as well as none of them proved to be ecotoxic. All the materials manufactured in this study can thus be well named as compostable materials.