Enhancing crystallization rate and melt strength of PLLA with four‐arm PLLA grafted silica: The effect of molecular weight of the grafting PLLA chains

To improve the crystallization rate and melt strength of polylactide (PLLA), nano-size amino silica grafted by four-arm PLLA (4A-PLLA) with different molecular weight was synthesized. 1H nuclear magnetic resonance proved that 4A-PLLA had been grafted onto the surface of SiO2 successfully, and the grafting ratios and the degradation behaviors of the grafted SiO2 nanoparticles (g-SiO2) were studied. When the grafted silica was introduced into PLLA matrix, the crystallization rate and melt strength of composites were found to be improved and the length of grafted chain played an important role. The extension rheology indicated that long grafted 4A-PLLA on the surface of SiO2 was more efficient in enhancing the elongational viscosity of PLLA, owing to the stronger interactions between the grafted chains and the matrix. The crystallization behavior of ungrafted silica filled composite was similar to that of neat PLA, while g-SiO2 played a role of nucleating agent. The crystallinities and the crystallization rates of the composites depended on the content of g-SiO2 and the grafted chain length of 4A-PLLA, especially the latter. Longer grafted chain acted as nucleation site in the matrix and significantly improved the crystallization behaviors of PLLA. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45675.