Crystallization Behavior and Dielectric Response of Melt Crystallized PLLA/TiO2 Bio Nanocomposites

Abstract

In this work, melt crystallized PLLA / TiO 2 bionanocomposites, with concentration of TiO 2 ranging from 1-10%wt, are produced via twin-screw extrusion melt blending. Their crystalline structure and crystallization behavior are studied by means of X-rays Diffraction (XRD) and Polarizing Optical Microscopy (POM) and their dielectric response via Broadband Dielectric Spectroscopy (BDS). XRD results suggest transformation of the α΄-crystal form of PLLA into the more stable α-form at elevated crystallization temperatures. According to POM observations all samples are fully crystallized for crystallization times of 1h. The growth size of PLLA spherulites increases linearly with time, while the growth rate is essentially independent of nanofiller content. BDS analyses reveal the presence of three relaxation processes in PLLA/TiO 2 nanocomposites, at temperatures ranging from 20°C to 140°C. These mechanisms are attributed to α–relaxation of the polylactide matrix, the Maxwell–Wagner–Sillars (MWS) interfacial polarization effect and the dc conductivity effect (CR), in terms of increasing temperature. The dynamics of all three relaxation mechanisms and the fragility index of the PLLA matrix appear independent of filler loading.