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.
