The crystallization behaviors and mechanical properties of poly(l-lactic acid)/magnesium oxide nanoparticle composites

Abstract

Nanocomposites of biodegradable PLLA and magnesium oxide composite (PLLA/MgO-NPs) and surface modified magnesium oxide composite (PLLA/m-MgO-NPs) were prepared using a solution casting method. Effects of the MgO-NPs and m-MgO-NPs on the crystallization behavior and mechanical properties of the PLLA are investigated systematically. Differential scanning calorimetry (DSC) was used to characterize the melting behavior and isothermal crystallization kinetics of pure PLLA and PLLA nanocomposite samples at varying isothermal crystallization temperatures. The Avrami equation was used to calculate the half crystallization time (t_1/2) and shown that the m-MgO-NPs is a kind of better nucleating agents than MgO-NPs because it enhanced crystallization rate significantly. Polarized optical microscopy (POM) results showed the density of spherulites increased and their size decreased in PLLA/MgO-NPs and PLLA/m-MgO-NPs samples. While the large amount (1.5 wt%) of MgO-NPs could hinder the crystallization of the PLLA. α′-PLLA emerged more easily than α-PLLA. The nucleation mechanism and geometry of crystal growth of neat PLLA and PLLA nanocomposite materials were determined to be similar. Mechanical property analysis showed both MgO-NPs and m-MgO-NPs could improve greatly the tensile strength, Young's modulus and elongation at break. Especially in the case of PLLA/m-MgO-NPs, the elongation at break was increased by 8.2 times. Uniform dispersion of m-MgO-NPs, and strong interaction and binding force between m-MgO-NPs and the PLLA matrix are favorable for the large enhancement in mechanical properties of the PLLA.