Molecularly Dispersed Hydroxyapatite Polymer Nanocomposites

Abstract

The synthesis of novel hydroxyapatite (HAP)/polymer composites with enhanced load bearing capabilities is a very important goal in the field of orthopedic biomaterials. Three of the main factors that can contribute to improving the mechanical properties of composites are decreased particle size (nanoscale), molecular level dispersion, and improved interfacial bond strength between the polymer matrix and the hydroxyapatite particles. However, these issues have been difficult to address in the synthesis and processing of HAP/polymer composites because the incorporation of nanoscale HAP in polymers at high solids loadings is extremely difficult. In addition, the surface chemistry of HAP makes the selection of suitable interfacial bond strength enhancement agents difficult. In this study, nanophase HAP particles were modified by surface grafting dodecyl alcohol molecules in an attempt to improve the degree of dispersion during mixing with poly(propylene carbonate) (PPC). The surface modified HAP and HAP/PPC composites were characterized via BET N 2 adsorption, transmission electron microscopy (TEM), Fourier transform spectroscopy (FTIR), and thermal gravimetric analysis (TGA). The HAP surface treatment slightly increased the degree of mixing that could be achieved between the HAP and PPC matrix. However, the presence of inhomogeneous regions indicates that the level of mixing must be improved to obtain true molecular dispersion.