Polyoxymethylene/graphene nanocomposites: thermal, crystallization, melting and rheological behavior

Polyoxymethylene (POM) and graphene nanoplatelets (GNP) nanocomposites were produced and their thermal properties investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Torque rheology was used to evaluate melted nanocomposites behavior. As nanofiller, two commercial GNP grades were used and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), DSC and TGA showing great morphological and structural differences. Nanocomposites thermal stability has increased for additions up to 0.25 wt.% of both nanoparticles. However, for concentrations above 0.50 wt.%, severe matrix degradation was observed. The extent of the effect on the thermal stability of the materials also varied with the grade of GNP used and seems to be related with GNP's extent of oxidation and defect density. The extrusion process was optimized in order to minimize secondary thermal degradation mechanisms, showing that the nanofiller nature is the most relevant factor in POM/GNP based systems. DSC analyzes showed that the addition of GNP interferes with the polymer crystallization process, alters the degree of crystallinity and increases the crystallization temperature, indicating that GNP acts as a nucleating agent for POM. The torque rheology showed that slope and level of the torque curve seems to be related with the stabilization or degradation effect observed in the thermal analysis, allowing immediate qualitative evaluation of degradation effect during extrusion process.