On the mechanical and thermal behaviour of PLA, PBAT and PHBV-based ternary blends and the effect of short flax fibers as reinforcing agents

Bioplastics offer environmental benefits but they are costly and exhibit lower mechanical and thermal performance compared to fossil-based counterparts. Poly(butylene adipate-co-terephthalate) (PBAT) exhibits high ductility but relatively low mechanical strength. Despite its biodegradability, it is derived from fossil-based resources. To resolve these concerns, this study aims to develop a ternary poly(lactic acid) (PLA)/PBAT/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) blend, to enhance mechanical strength and thermal stability. The ternary blend was formulated with increasing PHBV concentrations in a commercial binary PLA/PBAT (20/80 wt.%/wt.%) blend. The results showed that the addition of 20 wt.% of PHBV to the binary blend significantly enhanced tensile and flexural strength by approximately 53.7% and 70.6%, respectively. However, these improvements were accompanied by a reduction in ductility and toughness, primarily due to the brittleness of PHBV. In addition, the role of PBAT was to improve the thermal stability of PHBV by forming a protective char layer. Dynamic mechanical analysis and morphology confirmed PBAT/PHBV immiscibility. To further optimize material properties, flax fibers were incorporated into the blend (PLA/PBAT 60 wt.%/ PHBV 40 wt.%). The addition of flax fibers (20 wt.%) resulted in a 19.7% increase in tensile strength, a 112.6% rise in Young's modulus, and a 152.0% improvement in impact strength at room temperature. The combination of PLA, PBAT, and PHBV in ternary blends reinforced with flax fibers emerges as an effective route to develop biobased materials with competitive and tailored mechanical and thermal properties. Despite challenges with fiber-matrix adhesion, these materials show great potential for applications requiring high stiffness and good thermal stability.