Preparation and mechanical properties of nanocomposites of poly(D,L-lactide) with Ca-deficient hydroxyapatite nanocrystals

Nanocomposites of high molecular poly(D,L-lactide) (PLA) with Ca-deficient hydroxyapatite nanocrystals (d-HAP) were successfully prepared through solv ent-cast technique. Such composites are of great importance to make bone-li ke substitutes as d-HAP nanocrystals have similar composition, morphology a nd crystal structure as natural apatite crystals. Of all the PLA solvents s tudied, N,N-dimethylformamide is the best one to disperse d-HAP nanocrystal s. The resultant sol is a blue, stable dispersion that could preserve sever al days with only slight precipitation. The bright-field TEM micrograph sho ws that d-HAP nanocrystals. form homogeneous dispersion in the PLA matrix a t a microscopic level. The tensile modulus for PLA/d-HAP nanocomposites inc reases with d-HAP loading. Theoretical prediction of the modulus has been m ade by assuming the nanocomposites as short fiber filled systems. The calcu lated values based on Halpin-Tsai equations show excellent agreement with t he experimental results. The yield stress for the nanocomposites has not be en undermined by the presence of the nanocrystals. This preservation of str ength for PLA/d-HAP nanocomposites may be due to the homogeneous dispersion of d-HAP nanocrystals in the PLA matrix as well as the good interfacial ad hesion. (C) 2001 Published by Elsevier Science Ltd.