Abstract
To assess the impact of graphite fillers on the thermal processing of graphite/poly(lactic acid) (PLA) composites, a series of the composite samples with different graphite of industrial grade as fillers was prepared by melt mixing. The average size of the graphite grains ranged between 100 µm and 6 µm. For comparative purposes, one of the carbon fillers was expandable graphite. Composites were examined by SEM, FTIR, and Raman spectroscopy. As revealed by thermogravimetric (TG) analyses, graphite filler slightly lowered the temperature of thermal decomposition of the PLA matrix. Differential scanning calorimetry (DSC) tests showed that the room temperature crystallinity of the polymer matrix is strongly affected by the graphite filler. The crystallinity of the composites determined from the second heating cycle reached values close to 50%, while these values are close to zero for the neat polymer. The addition of graphite to PLA caused a slight reduction in the oxidation induction time (OIT). The melt flow rate (MFR) of the graphite/PLA composites was lower than the original PLA due to an increase in flow resistance associated with the high crystallinity of the polymer matrix. Expandable graphite did not cause changes in the structure of the polymer matrix during thermal treatment. The crystallinity of the composite with this filler did not increase after first heating and was close to the neat PLA MFR value, which was extremely high due to the low crystallinity of the PLA matrix and delamination of the filler at elevated temperature.
Highlights
Poly(lactic acid) produced from renewable resources has currently a principal position on the market of biodegradable polymers [1]
The introduction of graphite fillers into the poly(lactic acid) (PLA) matrix resulted in the modification of the thermal and melt flow properties of the composites
TG analyses of the materials under nitrogen show a slight drop of the thermal decomposition temperature of the PLA matrix mixed with graphite
Summary
Poly(lactic acid) produced from renewable resources has currently a principal position on the market of biodegradable polymers [1]. To tailor its properties to specific engineering applications, such as mechanical and automotive parts, electronic and electrical devices, or electrodes in electrochemical devices, it is necessary to tune its properties by combining the polymer matrix with different dispersed phases [2]. Carbon nanomaterials such as carbon nanotubes and graphene with its superior thermal and electrical properties can be used as a filler that improves some specific properties, such as stiffness, thermal stability, fire retardancy, and lower permeability [3]. Use of the graphene oxide filler resulted in an increase of the degree of crystallinity to the level of
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