Producing toughened PP/HA-LLDPE ternary bio-composite using a two-step blending method

The mechanical and morphological properties of polypropylene/hydroxyapatite/linear low density polyethylene ternary bio-composites which were produced by blending of polypropylene (PP), hydroxyapatite, modified and unmodified linear low density polyethylene (LLDPE) were studied. In this research, effects of LLDPE weight percent, modification of PP/LLDPE interface by a high crystallizable high density polyethylene, and the method of blending on tensile strength, Young’s modulus and impact absorbed energy of composites were investigated. Results of mechanical tests showed that by adding LLDPE to these composites, ultimate tensile strength and Young’s modulus of the composites dropped slightly, while their impact strength was increased significantly. Mechanical properties of composites were improved by modification of PP/LLDPE interface and changing from one-step blending to two-step blending. However, for the composites produced by two-step blending, by adding modified LLDPE (15 wt.%), the impact strength was 90% more than that of pure PP/HA composites. Fractography of the surface fractures of the impact samples for both types of composites were performed using a scanning electron microscope (SEM). Two different toughening mechanisms of these composites were distinguished by drawing a schematic sketch of the mechanisms.