Mechanical and thermal properties of polypeptide modified hydroxyapatite/poly(L-lactide) nanocomposites

A new type of polypeptide (poly(γ-benzyl-l-glutamate) (PBLG)) modified hydroxyapatite (HA)/poly(l-lactide) (PLLA) nanocomposites (PBLG-g-HA/PLLA) were prepared by the solvent-mixing method, and their mechanical and thermal properties were investigated. The tensile test showed that the mechanical properties of PBLG-g-HA/PLLA nanocomposites were better than that of PLLA, even a 0.3 wt% content of PBLG-g-HA in the nanocomposites could make the tensile strength 12% higher than that of the neat PLLA sample, and the tensile modulus was about 17% higher than that of the PLLA sample. The thermal gravimetric analysis (TGA) showed that the PBLG-g-HA/PLLA composites have better thermal stability than the PLLA sample. The differential scanning calorimetry (DSC) was used to characterize the effect of PBLG-g-HA on the crystallization of PLLA. The isothermal crystallization behavior showed that the half crystallization time (t1/2) of PBLG-g-HA/PLLA was much shorter than that of the PLLA sample. When the PBLG-g-HA content was 10%, t1/2 was only 18.7 min, while t1/2 of the PLLA sample was 61.4 min. The results showed that the PBLG-g-HA worked as a nucleating agent and enhanced the crystallization speed of PLLA.