The effect of the grafted chains on the crystallization of PLLA/PLLA-grafted SiO2 nanocomposites

Two types of homemade poly(l-lactide) (PLLA)-grafted SiO2 nanoparticles with totally different topological structures are introduced into PLLA to prepare PLLA nanocomposites with different interface interactions and study the effect of the topology of polymer grafted nanoparticle on crystallization of PLLA. Differential scanning calorimetry (DSC) and polarized optical photomicrographs (POM) results show that the crystallization rate of PLLA has been greatly improved by the introduction of grafted SiO2, due to the improved heterogeneous nucleating effect. The nucleation constant of the two modified nanoparticles is evaluated by Hoffman–Lauritzen analysis; it is suggested that by introducing modified nanoparticles with long grafted chains, the interaction between the nanofiller and PLLA matrix will be enhanced, leading to the improved nucleation effective (the larger nucleation constant Kg), and the changed crystalline morphology, from large spherocrystals to tiny crystals. These observations are explained on the basis of different nucleation mechanism caused by the different surface structures of grafted SiO2, through the application of time-resolved Fourier transform infrared (FTIR) spectroscopy in the molecular level. The special long grafted PLLA chains can be acted as a more efficient nucleating agent for PLLA, and the conformational ordering of PLLA during the crystallization is significantly influenced by the topology of modified nanoparticles.