Analytical interpretations of structural and mechanical response of high density polyethylene/hydroxyapatite bio-composites

Hydroxyapatite (Hap) filled high density polyethylene (HDPE) composites were fabricated by extrusion mixing followed by injection molding. The onset-to-degradation temperature remained unaffected indicating the absence of any structural interaction, which is also supported by infrared spectroscopy. Differential scanning calorimetry (DSC) has revealed inappreciable changes in Tg and increase in crystallinity due to Hap. Wide-angle X-ray diffraction (WAXD) plots indicated the retention of characteristic structural attributes of HDPE and Hap in spite of the two-stepped processing approach. The tensile and flexural properties increased whereas impact strength decreased linearly with Hap content though the yield stress remained unaffected. Dynamic mechanical analysis (DMA) revealed an increase in storage and loss component indicating enhanced recoverable and non-recoverable energy dissipation with Hap content. Theoretical models were used to analyze Young’s modulus and yield strength data for the estimation of various phase-adhesion parameters indicating the mechanical interlocking and polymer–filler interaction aspects. The failure-mode of the composites has been found to undergo a switch-over from matrix-controlled shear deformation to filler-controlled quasi-brittle modes above a hydroxyapatite loading of 10 wt.% in the composites.