New sustainable green composites based on polylactide (PLA) and cotton industry byproducts were successfully manufactured by extrusion, and subsequently by conventional injection molding. Cottonseed flour was used as reinforcement filler and modified cottonseed oil (epoxidized and maleinized cottonseed oil, ECSO and MCSO respectively) were used to improve filler-polymer matrix interactions among the interface. Mechanical properties were obtained by standard tensile, flexural, Shore D hardness and impact Charpy tests, while the surface morphology characterization on fractured specimens was carried out by using field emission scanning electron microscopy. Thermal properties were obtained by differential scanning calorimetry and the effect of both cottonseed flour and chemically-modified cottonseed oil was evaluated on dynamic mechanical behavior of the obtained composites. Unlike typical lignocellulosic fillers, 15 wt% cottonseed flour does not lead to more brittle materials due to stress concentration phenomena. In fact, cottonseed flour provides improved toughness and elongation at break (mechanical ductile properties) compared to neat PLA without any other compatibilizer. Addition of both epoxidized and maleinized cottonseed (7.5 wt%) has a positive effect on improving ductile behaviour of composites, thus leading to new green composites with good balance between processability and overall properties. In particular, the impact strength is remarkably improved which plays a key factor in these composites since PLA is, intrinsically, a brittle polymer.
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