Stress transfer and fracture in nanostructured particulate-reinforced chitosan biopolymer composites: influence of interfacial shear stress and particle slenderness

Abstract

Analytical models have been evaluated for chitosan nanocomposites reinforced by needle-like hydroxyapatite (HA) and globule-like polyhedral oligomeric silsesquioxane (POSS) particles. The particle elastic stress distribution was investigated for the case of high loads with the matrix deforming plastically and the particle pull-out energy during matrix crack propagation was modelled. Model predictions, over a range of reasonable interfacial shear stress values and particle aspect ratios, show contrasting behaviour between the two types of nanoreinforcement. In HA particles, the axial stress is distributed fairly uniformly, whereas, with POSS it is concentrated towards the centre of the particle. The radial stress at the HA particle surface was found to be uniformly distributed, whereas in POSS it increased non-linearly to a high (theoretically infinite) value with distance from the particle centre to the end. For particles bridging a travelling matrix crack, the model predicts that the pull-out energy density for a POSS particle increases with the interfacial shear stress, the particle aspect ratio and the particle size. The present findings offer a robust methodology for engineering chitosan-based composites for biomaterial implants with mechanical properties tailored to the tissue microenvironment.