Effect of nanoparticle SiO2 grafted poly (methyl methacrylate) on poly(l-lactic) acid crystallization

For practical applications of poly(l-lactic acid) (PLLA), PLLA crystallization with keeping transparency is preferable. As one method to keep transparency without inhibiting crystallization, we prepared SiO2 nanoparticles which were modified with poly (methyl methacrylate) (PMMA-g-SiO2). FT-IR and TG–DTA measurement indicated that PMMA was grafted on SiO2 surface successfully. TG–DTA and GPC measurement of free PMMA cleaved from PMMA-g-SiO2 determined graft density of PMMA as 0.039 chains/nm2. The effect of PMMA-g-SiO2 on PLLA crystallization was characterized by DSC measurement and POM observation. Although PMMA-g-SiO2 could not promote PLLA crystallization significantly like commercial crystal nuclear agents, it did not inhibit PLLA crystallization. By UV measurement and Haze meter, it was indicated that crystallized PLLA with PMMA-g-SiO2 generated 3.5–5.3 times higher transparency than crystallized PLLA with/without commercial nucleating agent. TEM observation indicated that the aggregation size of PMMA-g-SiO2 was 21.7 ± 13.9 nm which was smaller than visible wavelength. Transparency improvement likely resulted from size-reduced aggregation of PMMA-g-SiO2 in PLLA matrix. On the other hand, PMMA-g-SiO2 made size of generated spherulite smaller but increased its number in PLLA matrix, which inhibited transparency improvement.