Preparation and Properties of Polylactic Acid (PLA)/Silica Nanocomposites

Surface-modified silica was incorporated into bio-based polylactic acid (PLA) to improve its performance. The modification by aminosilane on the silica was confirmed through FTIR (Fourier transform infrared) spectra. Following the aminosilane modification, polyethylene glycol methyl ether (PEGME) was grafted, via the aminosilane, on the silica to form the desired surface-modified silica (PEGME-silica). The grafting percentage of polyethylene glycol methyl ether was about 6.9wt%. Unmodified silica, having underwent a similar treatment to maintain the same thermal history but without adding silane and PEGME, was also prepared. The PEGME-silica system had slightly higher tensile strength than the unmodified silica system, with a rheological study showing an enhanced polymer matrix-dispersed silica interaction and better dispersion in morphology observations being proposed as the cause. The dynamic storage modulus in the terminal zone was reduced for large amounts of highly dispersed surface-modified silica in comparison with unmodified silica. Tan decreased significantly with increasing unmodified silica contents in the low frequency region, resulting in solid-like behaviors. On the other hand, there was only a limited decrement for modified silica-filled samples in the corresponding ranges, especially for low dosages of the modified silica. The shear thinning phenomenon appeared to be more pronounced for unmodified silica at high silica content, but not for modified silica. To the best of our knowledge, this is the first report of the effect of polyethylene glycol methyl ether (PEGME)-modified nanosilica on the properties of PLA/silica nanocomposites prepared under a melt mixing process to illustrate the significance of surface modification via Cole-Cole plots.