Storage Moduli of in situ Polymerised and Melt Extruded PA6 Graphite (G) Composites

Abstract

Four PA6/graphite (G) composites systems were made. Two in situ polymerisation equivalent in mixing strain and two melt extrusion of equivalent processing strain. The effective modulus of the carbons, room temperature storage modulus and storage modulus at 80 ⁰C were evaluated using Dynamic Mechanical and thermal Analysis (DMTA). Melt processing, was employed to make PA6/carbon composite systems over a range of loadings of Graphite (G) and Graphite Nano Platelets (GNP) fillers. Melt extrusion was carried out using 100/6 processing condition, which indicates an extrusion screw rotation frequency of 100 rpm applied for 6 minutes (min) and 200/3 processing conditions, of 200 rpm for 3 min. For in situ polymerised systems G and GNP dispersion was made using two similar conditions designated as 40/10 and 20/20. Here, 40/10 indicates that sonication amplitude of 40% was applied for 10 min, whereas in the 20/20 conditions, amplitude of 20% was applied for 20 min. For in situ Nano P INP 40/10 systems weak interaction between PA6 and GNP is indicated by the very low modulus enhancement above glass transition temperature (Tg). The modulus behaviour shows that the reinforcement provided by GNP is not significant relative to unfilled PA6, despite the low loading levels. A similar, but less pronounced, behaviour is observed for INP 20/20 system. Effective modulus for the in situ polymerised systems INP 40/10, was 4.8 GPa. Due to the low loading level of GNP used and the better reaction rates, an extrapolated modulus of 22.4 GPa is obtained in the INP 20/20 system. For G200/3 and G100/6 the trend of increasing modulus with GNP loading is not followed exactly. On all levels of loading, the relative modulus values of the INP 20/20 system are higher than those of the 40/10 system, a reflection of retention or improvement in the aspect ratio of the GNP due to less intensive sonication.