Hemp Hurd and Alfalfa as Particle Filler to Improve the Thermo-Mechanical and Fire Retardant Properties of Poly(3-Hydroxybutyrate-Co-3-Hydroxyhexanoate)

The poor thermo-mechanical and flame-retardant properties of biopolymers are currently limiting their application and potential exploitation as sustainable polymers. The use of agricultural by-products as a functional filler for biopolymers is here presented to address the production of environmentally friendly and economically sustainable biocomposites. To this aim, hemp hurd and alfalfa particles were melt-blended with a poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB) co-polymer. The 30 wt% of filler achieves an improvement of 150% in stiffness. The same composites show an increase in the heat deflection temperature over 100°C. Flameretardant properties were also evaluated evidencing strong reductions in flame spread rates (−40%) and combustion kinetics (−30%). The achieved performances are compared with those reported in the literature for PHB composites pointing out how these completely renewable materials can compete with other currently studied solutions. The new presented composites show an opportunity for the production of functional and sustainable materials through the valorization of agricultural by-products.