Compatibilization of highly sustainable polylactide/almond shell flour composites by reactive extrusion with maleinized linseed oil

Highly sustainable composites were produced by melt compounding polylactide (PLA) with almond shell flour (ASF), a processed by-product of the food industry, at a constant weight content of 30 wt.-%. However, due to the lack of miscibility between PLA and ASF, both being raw materials obtained from crops, resultant green composite presented poor ductility and low thermal stability. To overcome this limitation, maleinized linseed oil (MLO), a multi-functionalized plant-derived additive, was originally incorporated as a reactive compatibilizer during the extrusion process. Both chemical and physical characterizations showed that 1–5 parts per hundred resin (phr) of MLO successfully serve to obtain PLA/ASF composites with improved mechanical, thermal, and thermomechanical properties. The enhancement achieved was particularly related to a dual compatibilizing effect of plasticization in combination with melt grafting. The latter process was specifically ascribed to the formation of new carboxylic ester bonds through the reaction of the multiple maleic anhydride functionalities present in MLO with the hydroxyl groups of both the PLA terminal chains and cellulose on the ASF surface. The fully bio-based and biodegradable composites described herein give an efficient sustainable solution to upgrade agro-food wastes as well as contributing to reducing the cost of PLA-based materials.