Rigid filler toughening in PLA-Calcium Carbonate composites: Effect of particle surface treatment and matrix plasticization

In recent years the plastics market is moving towards biopolymers and the increasing demand of not oil derived products has led to the development of new composites deriving from renewable resources. Undoubtedly the most studied biopolymer is poly(lactic acid) (PLA). This work is focused on the use of rigid inorganic fillers as toughening agents, in order to obtain a rigid and tough PLA composite and enlarge the range of applications for PLA. The rigid filler toughening mechanism has been studied and, as toughening agent, commercial calcium carbonate particles with and without surface treatment have been compared. Because of the PLA intrinsic fragility, a plasticization of the matrix was necessary to favor the plastic deformation and consequently the stretching of interparticle ligaments. In particular, in this work, the effect of both the plasticizer and the particles surface treatment with stearic acid were analyzed. It has been observed that the surface treatment alone is not able to provide a significant increase in the PLA toughness. In fact, the particle surface coating favors the particles dispersion and reduces the adhesion with the matrix, favoring debonding, but the plastic deformation of the matrix around the voids is not significant without a plasticizer addition. Moreover, the best impact performance and ductility were achieved with the surface treated calcium carbonate, in agreement with a more controlled growth of voids formation during material solicitation, as resulting from tensile dilatometric tests.