Thermomechanical and optical properties of biodegradable poly(L‐lactide)/silica nanocomposites by melt compounding

Poly( L ‐lactide) (PLA)/silica (SiO 2 ) nanocomposites containing 1, 3, 5, 7, and 10 wt % SiO 2 nanoparticles were prepared by melt compounding in a Haake mixer. The phase morphology, thermomechanical properties, and optical transparency were investigated and compared to those of neat PLA. Scanning electron microscopy results show that the SiO 2 nanoparticles were uniformly distributed in the PLA matrix for filler contents below 5 wt %, whereas some aggregates were detected with further increasing filler concentration. Differential scanning calorimetry analysis revealed that the addition of SiO 2 nanoparticles not only remarkably accelerated the crystallization speed but also largely improved the crystallinity of PLA. An initial increase followed by a decrease with higher filler loadings for the storage modulus and glass‐transition temperature were observed according to dynamic mechanical analysis results. Hydrogen bonding interaction involving CO of PLA with SiOH of SiO 2 was evidenced by Fourier transform infrared analysis for the first time. From the mechanical tests, we found that the tensile strength and modulus values of the nanocomposites were greatly enhanced by the incorporation of inorganic SiO 2 nanoparticles, and the elongation at break and impact strength were slightly improved. The optical transparency of the nanocomposites was excellent, and it seemed independent of the SiO 2 concentration; this was mainly attributed to the closed refractive indices between the PLA matrix and nanofillers.