Twin-screw extrusion is a promising method for the direct incorporation of carbon micro- and nanomaterials into a polymer matrix using a dry procedure. The aim of the study was to determine the influence of the parameters of the twin-screw extruder plasticizing system on the dispersion homogeneity and distribution of graphite filler in the PLA polymer matrix and overall quality of the composite. As a filler, a graphite micropowder with a 5 μm lateral size of plates was used at concentration of 1 wt. %.

Three configurations of screws with different mixing intensity and various types of mixing segments were considered in the modelling of mixing process and extrusion experiments. Morphology and chemical structure of the obtained composites were examined using scanning electron microscopy (SEM) and FTIR spectroscopy. Differential scanning calorimetry (DSC) and melting flow index (MFI) measurements were used to asses thermal and rheological properties of composites. Samples of the PLA / graphite composites were also subjected to mechanical tests.

The results show that the selection of the mechanical parameters of twin-screw extruder plasticizing system plays a key role in the preparation of the homogeneous PLA / graphite composites. Incorrect selection of the screw geometry results in poor mixing quality and a significant deterioration of the mechanical and thermal properties of the composites. Optimized mixing and extrusion parameters can be the starting point for the design of efficient twin-screw extruder plasticizing system for fabrication of PLA composites with carbon nanotube and graphene fillers.