Understanding the toughness mechanism prompted by submicron rigid particles in polylactide/barium sulfate composites

Polylactides are extensively employed as bone-fixation devices, due to their degradability and high tensile modulus. As demonstrated in a previous study, the incorporation of barium sulfate submicron particles impressively enhanced toughness with almost no adverse effect on yield strength. It is therefore a promising strategy in the design of radiopaque materials intended for use in safety-critical systems. In the present study, the mechanism that causes high-level plastic deformation in this system is identified through tensile and fracture tests, together with a thorough analysis of the microstructure via transmission and SEM (Scanning Electron Microscopy). The presence of submicron particles was observed to reduce crystallinity and to increase energy dissipation during the plastic deformation of the polymer matrix, inducing crack widening and fibrillated crazing that propagated around the crack opening. The result is a five-fold increase in the energy that is required to fracture the composite with respect to its neat polymer counterpart.