Co-authors​ :

 Irene BAVASSO (ITALY), Alessia PANTALEONI (ITALY), Claudia SERGI (ITALY), Maria Paola BRACCIALE (ITALY), Jacopo TIRILLÒ , Fabrizio SARASINI  

Biopolymers and biodegradable materials are gaining attention as alternatives to petroleum-based polymers, aligning with the EU Green Deal and Zero Pollution Action Plan. However, widespread use is hindered by limited thermo-mechanical properties and cost competition with petroleum-based counterparts. To address the thermo-mechanical limitations, one potential solution involves blending two or more biodegradable polymers. For instance, the ductility and processability of the rigid polylactic acid (PLA) can be enhanced by blending it with the flexible poly(butylene adipate-co-terephthalate) (PBAT). Similarly, it is possible to use poly(hydroxybutyrate-co-valerate) (PHBV), which exhibits properties similar to polypropylene, to promote the mechanical strength of PBAT. While blending contributes to a balance of properties rather than a synergistic effect, introducing a reinforcing agent can potentially lead to superior properties in the resulting composites. Importantly, the composites are expected to be biodegradable because both components are inherently biodegradable. Natural fibers, particularly flax, represent a viable and eco-friendly option as biodegradable reinforcing agent. Flax possesses good specific stiffness, making it well-suited as reinforcing materials and the cost-effectiveness of flax contributes to reduce the final cost of the composites for the partial substitution of the high-cost polymer matrix. In this study, the research focused on exploring the reinforcing effect of varying amounts of short flax fibers (from 10 wt.% to 20 wt.%) in a ternary blend consisting of PLA/PBAT/PHBV (12 wt.%/48 wt.%/40 wt.%). The composites were manufactured through melt extrusion and injection molding processes. A comprehensive material characterization was conducted, evaluating mechanical properties through tensile and 3-point bending tests, Charpy impact tests, and thermal properties through thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis. The results revealed that the incorporation of 20 wt.% of flax fibers led to notable enhancements in tensile and bending strengths (20% and 73%, respectively) and moduli (99% and over 100%) compared to the neat polymer blend. However, there was a slight reduction in thermal stability. It was observed that the inclusion of flax fibers had an effect on the mobility of polymer molecules, evident from a significant decrease of about 66% in the melt mass flow rate (MFR). This reduction in MFR raised concerns about the material's suitability for 3D printing filament production. To address this limitation, surface modifications of flax fibers were explored as a strategy to modify the flow properties of the biocomposites and biodegradable chemicals, such as citric acid and epoxidized soybean oil, were considered. These modifications effectively increased MFR, opening up possibilities for 3D printing applications.