BRAN OR HAZELNUT SHELL POWDER REINFORCED COMPOSITES PROCESSING AND RECYCLING BY BIOBASED CHAIN EXTENSION

The valorization of agro-food waste in biobased and biodegradable materials is a strategy to apply circularity concepts and at the same time to boost the use of biopolymers in applications with a short life cycle. Wheat bran is an abundant waste of the cereal food chain, representing the external part of wheat grain. The powder obtained by grinding hazelnut shells is another underutilized waste of the food industry. Wheat bran was added to polylactic acid (PLA)/poly(butylene succinate-co-adipate) (PBSA) blends to produce biobased and biodegradable composites by twin screw extrusion, but an evident chain scission of biopolyesters occurred. This was detrimental for both processing and recycling of this material. Thus, biobased chain extenders were developed for this composite using dicarboxylic acids coming from fruits and epoxidized vegetable oils. This biobased chain extender system could work well only in a specific range of composition and showed inferior performances with respect to commercial fossil-based chain extenders. Similar composites were produced by using as reinforcing filler the hazelnut shell powder. Two different dimensions of the powder were considered. In this case it was found that only a limited chain scission occurred. Results of this study evidenced a modest increase in melt viscosity due to biobased chain extension system, but only for the hazelnut shell powder with the lower dimension. The observed differences can be tentatively ascribed to the different compositions of the two fillers.