Lignocellulosic fillers and graphene nanoplatelets as hybrid reinforcement for polylactic acid: Effect on mechanical properties and degradability

This work investigates the effect of adding relatively low amounts of graphene nanoplatelets (GNP) to a bio-composite based on polylactic acid (PLA) and a lignocellulosic filler achieved by grinding Posidonia Oceanica leaves (Posidonia flour, PF). The ternary composites were prepared by melt extrusion and characterized from a morphological and mechanical point of view. Furthermore, hydrolytic degradation tests were performed under acidic, neutral and alkaline environment up to 900 h. Density measurements enabled to assess the degree of intraphase, i.e. the capability of polymer macromolecules to enter the voids of PF and a modified Halpin-Tsai model was presented and used to fit experimental data obtained from tensile tests. The results demonstrate that the hybrid reinforcement constituted by GNP and PF allows improving mechanical properties (up to 155%) and speeding up the degradation kinetics with respect to neat PLA and composites loaded with GNP only. In particular, the relatively fast degradation kinetics observed at pH = 7 and especially at pH = 10 make these hybrid composites very promising in the perspective of marine disposal.