Study on distribution of hydroxyapatite (HA) in twin screw extruded cum injection moulded polylactic acid (PLA) composites and their effect on mechanical property

Hydroxyapatite (HA) reinforced polylactic acid (PLA) composite is the most investigated material for biodegradable implant applications such as screws and plates. The objective of this work is to test hypothesis of distribution of HA in PLA composite influence on the variations in the properties of the composites. Investigation was done for the distribution of HA in PLA injection mould (IM) composites for the various concentrations (2 to 8 wt.%) and their effect on mechanical properties such as flexural and tensile test. Proportionate quantity of HA was introduced at fixed intervals in a twin screw extruder for the preparation of PLA composites pellets containing in various wt.% of HA. The distribution of HA in IM PLA composite specimens was analysed by elemental mapping using scanning electron microscope (SEM) and also by estimation of residue (HA) after burn out test of sampling of specimens. Differential scanning calorimetry (DSC) was used for the study of effect of HA in PLA composites. The value of standard deviations of mechanical properties, taken as a rudimentary measure of reliability of IM PLA-HA composites, was found to have influence from the distributions of HA. Among the composites studied, PLA-HA composite with 4 and 5 HA wt.% found exhibiting reliable mechanical property due to crystallinity of 31.83% and a comparatively better homogenous dispersion of HA in PLA. A case study of distribution of HA in a product, namely, bone screw, promulgated the issues of IM PLA-HA composites for biomedical applications.