The environmental performance of biodegradable materials has attracted attention from the academic and the industrial research over the recent years. Currently, degradation behavior and possible recyclability features, as well as actual recycling paths of such systems, are crucial to give them both durability and eco-sustainability. This paper presents a review of the degradation behaviour of biodegradable polymers and related composites, with particular concern for multi-layer films. The processing of biodegradable polymeric films and the manufacturing and properties of multilayer films based on biodegradable polymers will be discussed. The results and data collected show that: poly-lactic acid (PLA), poly-butylene adipate-co-terephthalate (PBAT) and poly-caprolactone (PCL) are the most used biodegradable polymers, but are prone to hydrolytic degradation during processing; environmental degradation is favored by enzymes, and can take place within weeks, while in water it can take from months to years; thermal degradation during recycling basically follows a hydrolytic path, due to moisture and high temperatures (β-scissions and transesterification) which may compromise processing and recycling; ultraviolet (UV) and thermal stabilization can be adequately performed using suitable stabilizers.

Anything that is not recycled and/or recovered from waste represents a loss of raw materials. Recycling plastics can help to reduce this loss and to reduce greenhouse gases, improving the goal of the decarbonization of plastic. While the recycling of single polymers is well assessed, the recycling of mixed plastics is very difficult because of the strong incompatibility among the different polymers usually present in urban waste. In this work, heterogeneous mixed polymers, i.e., polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyethylenetherephthalate (PET) were processed using a laboratory mixer under different conditions of temperature, rotational speed and time to evaluate the effect of the above parameters on morphology, viscosity and mechanical properties of the final blends. Morphological analysis shows a strong incompatibility between the polyethylene matrix and the other dispersed polymers. The blends show, of course, a brittle behavior, but this behavior slightly improves with decreasing temperature and increasing rotational speed. A brittle-ductile transition was observed only at a high level of mechanical stress obtained by increasing rotational speed and decreasing temperature and processing time. This behavior has been attributed to both a decrease in the dimensions of the particles of the dispersed phase and to the formation of a small amount of copolymers that act as adhesion promoters between matrix and dispersed phases.

Three dimensional-printability of green composites is recently growing in importance and interest, especially in the view of feasibility to valorize agricultural and marine waste to attain green fillers capable of reducing bioplastic costs, without compromising their processability and performance from an environmental and mechanical standpoint. In this work, two lignocellulosic fillers, obtained from Opuntia ficus indica and Posidonia oceanica, were added to PLA and processed by FDM. Among the 3D printed biocomposites investigated, slight differences could be found in terms of PLA molecular weight and filler aspect ratio. It was shown that it is possible to replace up to 20% of bioplastic with low cost and ecofriendly natural fillers, without significantly modifying the processability and the mechanical performance of the neat matrix; at the same time, an increase of surface hydrophilicity was found, with possible positive influence on the biodegradability of such materials after disposal.

The formulation of polymeric films endowed with the abilities of controlled release of antimicrobials and biodegradability is the latest trend of food packaging. Biodegradable polymer (Bio-Flex^®)-based nanocomposites containing carvacrol as an antimicrobial agent, and a nanoclay as a filler, were processed into blown films. The presence of such hybrid loading, while not affecting the overall filmability of the neat matrix, led to enhanced mechanical properties, with relative increments up to +70% and +200% in terms of elastic modulus and elongation at break. FTIR/ATR analysis and release tests pointed out that the presence of nanoclay allowed higher carvacrol loading efficiency, reasonably hindering its volatilization during processing. Furthermore, it also mitigated the burst delivery, thereby enabling a more controlled release of the antimicrobial agent. The results of mass loss tests indicated that all the formulations showed a rather fast degradation with mass losses ranging from 37.5% to 57.5% after 876 h. The presence of clay and carvacrol accelerated the mass loss rate of Bio-Flex^®, especially when added simultaneously, thus indicating an increased biodegradability. Such ternary systems could be, therefore, particularly suitable as green materials for food packaging applications, and for antimicrobial wrapping applications.

The addition of natural scraps to biodegradable polymers has gained particular interest in recent years, allowing reducing environmental pollution related to traditional plastic. In this work, new composites were fabricated by adding 10% or 20% of Hedysarum coronarium (HC) flour to Poly (lactic acid) (PLA). The two formulations were first produced by twin screw extrusion and the obtained filaments were then employed for the fabrication of composites, either for compression molding (CM) or by fused deposition modeling (FDM), and characterized from a morphological and mechanical point of view. Through FDM it was possible to achieve dense structures with good wettability of the filler that, on the contrary, cannot be obtained by CM. The results indicate that the filler effectively acts as reinforcement, especially for FDM composites. The most remarkable enhancement was found in the flexural properties (+100% of modulus and ultimate strength), followed by tensile resistance and stiffness (+60%) and impact strength (+50%), whereas a moderate loss in tensile deformability was observed, especially at the highest loading. By adding HC to the polymeric matrix, it was possible to obtain a green, high-performance, and cost-effective composite, which could find applications for the fabrication of panels for furniture or the automotive industry.