Bioplastics from renewable sources: physical-mechanical characterization and biodegradation in soil

Bioplastic produced from Renewable Sources (RSB) represents a valid alternative to plastic from fossil sources which has been in common use for decades with disposable objects and with all the components present in all industrial sectors, from automotive to biomedical, from electronics to the clothing/fashion sector [1,2]. Bioplastics biodegrade quickly in the soil compared to plastics of fossil origin which require hundreds and thousands of years with the advantage of containing the problem of plastic pollution. Biodegradation, therefore, favors the ecological transition of these materials which are conceived in the spirit of a circular economy and no longer linear as in the past. In addition, the millions of tonnes of agri-food waste (AFW) produced annually represent a major disposal problem due to their cost. In this work, new RSBs were formulated by mixing bioplastics with appropriately pre-treated agri-food waste (AFW) and with appropriate additives, obtaining bio-composites with different chemical compositions and processed with different transformation technologies. Therefore, the production of RSB with AFW represents a good way to reuse waste products and, at the same time, allows the use of less bioplastic. The physical-mechanical characterizations allowed us to define the optimal compositions in terms of weight percentage of the components, studying a variable weight quantity of AFW between 5 wt.% and 45 wt.%. Both surface (roughness, contact angle, shore D hardness) and bulk (torque analysis, and static tensile test) investigations were carried out. It has also been verified that these blends are workable with normal thermoplastic polymer processing technologies, including extrusion and injection molding. The soil biodegradation tests were carried out according to the ASTM D5988-18 standard. Carbon dioxide monitoring, according to ISO 17556:2019, was performed together with a thermo-mechanical characterization and a wettability/roughness analysis of the surfaces during 3-6 months of degradation in soil. The experimental results indicated the best chemical composition of bioplastics to have optimal mechanical performance and their biodegradation time in soil. The first prototypes of bioplastic plant pots, made by extrusion/injection molding, have the right potential to replace the millions of plastic pots currently produced and then biodegrade in the soil in a few months.