Recyclability of biodegradable polymer blends and biocomposites through reprocessing tests

In Europe post-consumer plastics packaging amounted in 2020 at about 18 Mt. Its management consists mainly of energy recovery (42%), recycling (35%) and landfill. The necessity of producing carbon neutral goods is addressing packaging companies towards biobased materials. In particular, biobased and compostable packaging is strategic because it provides the possibility of using carbon neutral materials that can be managed by composting (organic recycling) as they turn into waste. The european BIONTOP project (https://biontop.eu/) has developed home-compostable blends including biopolyesters and composites including bran, an underutilized agro-food by-product. Prototypes of trays, films and textiles developed during the project are currently under validation in the involved industries. Recycling these materials in the same or other applications can be relevant, because their life duration can be increased and the final composting postponed. To investigate their recyclability by grinding and melt processing, the materials were reprocessed several times by injection moulding and they were characterized in terms of melt index, thermo-mechanical properties and colour as a function of injection moulding cycles number. Thanks to the full analysis it was possible to assess the number of injection moulding cycles that materials could undergo without significant detrimental effect onto their properties. Hence, it can be deducted that biobased and biodegradable films could be ground and recycled for the same film production before being composted. On the other hand, biocomposites containing wheat bran are more susceptible to polymer degradation. Thus, they could be recycled only with a “downcycling” approach or adopting chain extenders as reactive additives to counterbalance the biopolyesters decrease in molecular weight.