Grafting polymerization of l-lactide on the surface of hydroxyapatite nano-crystals

Abstract

A novel method of grafting ring-opening polymerization of l-lactide (LLA) onto the surface of hydroxyapatite nano-particles ( n-HAP) was developed. PLLA was directly connected onto the HAP surface through a chemical linkage. The PLLA- g-HAP particles could be stably dispersed in organic solvent such as chloroform for several weeks. The n-HAP particles still retained the original dimension and shape after the grafting of PLLA. Compared with the 31P MAS-NMR spectrum of pure HAP powders, there appeared a downfield displacement of 1.2 ppm in the spectrum of PLLA- g-HAP. Fourier transformation infrared (FT-IR) spectra further confirmed the existence of PLLA on the surface of PLLA- g-HAP. The amount of grafted polymer determined by thermal gravimetric analysis (TGA) was about 6% in weight. The tensile strength and elongation at break of the PLLA/PLLA- g-HAP composite containing 8 wt% of PLLA- g-HAP were 55 MPa and about 10–13%, respectively, while those of the PLLA/ n-HAP composites were 40 MPa and 3–5%, respectively.