Fabrication and characterization of graphite reinforced poly (lactic acid) composites

Abstract

Biocomposites of poly(lactic acid) (PLA) and micro-size graphite (GP) flake powder with 0 ‒ 30 wt% GP contents have been prepared using extrusion molding followed by compression molding method. The pure PLA and PLA-GP composites (PGC) have been examined by the Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy (RS), X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), transmission electron microscopy (TEM), mechanical test, micromechanical test, differential thermal analysis (DTA) and thermogravimetric analysis (TGA). Almost all the peaks of FTIR spectra for composites resemble to those of neat PLA except C-O stretching vibration at 1130cm -1 and another peak at 1160cm -1. The shifting of these two peaks may correspond to some kind of adhesion of graphite with PLA. The Raman spectra reveals that PLA is poorly crystalline. The intensity ratio of D and G bands increases with the increase of graphite, indicating fewer defect structure in the composites. XRD shows broader peak that signifies poorly crystalline structure of PLA. Inclusion of filler affects to decrease both crystalline structure and crystallinity. SEM and TEM exhibit a clear dispersion of graphite particles in PLA matrix at lower loading and aggregates at higher loading. The tensile strength(TS) for pure PLA is 55MPa and that for composites gradually decreases to 4MPa for 30wt% graphite content. In contrast, Young Modulus(Y) for composites gradually increases and show the maximum of 2.31GPa for 30 Wt% graphite content. A theoretical model proposed by Guth-Smallwood fits well with the Y increase. The change of flexural strength and tangent modulus resemble to that of TS and Y. Microhardness is found to decrease from 220MPa for pure PLA to 143MPa for 30 wt% graphite loaded composites. The onset of thermal degradation ocurs at 3340C for PLA and at 3560C for 30wt% loaded composite. On the other hand the degradation temperature for pure PLA is 3630C and that 30wt% composite is 3830C.