Influence of peroxide addition on the morphology and properties of polypropylene - multiwalled carbon nanotube nanocomposites
The incorporation of peroxide as a reactive additive during the processing of polypropylene (PP) with multiwalled carbon nanotubes (MWCNTs) is investigated for its influence on the morphology, rheology, electrical, mechanical and thermal properties of the composites. PP is compounded with 2. wt.% of MWCNT in a twin-screw extruder with screw speeds of 500 and 1100. rpm. Additionally, PP modified with 1. wt.% peroxide is processed at 500. rpm with 1 and 2. wt.% MWCNT. Morphological investigations indicate better MWCNT dispersion in the composites at considerably lower specific mechanical energy (SME) input on peroxide addition. The decrease in complex melt viscosity on peroxide addition to PP is substantially compensated in the composites by the simultaneous enhancement in MWCNT dispersion. Electrical properties of the composites shaped by compression molding show at least three orders of magnitude higher conductivity than those obtained by injection molding. To detect el ectrical percolation, the composite granules from the compounding process were diluted to lower MWCNT contents using a small-scale melt mixer resulting in a threshold on compression molded plates at around 0.4. wt.%. Elastic modulus, tensile strength and notched impact strength of PP of the injection molded samples were slightly enhanced with MWCNT incorporation, but the effect of peroxide addition on these composite properties was rather negligible or negative. Thermal stability of PP was considerably enhanced on MWCNT addition and the composite with 1. wt.% MWCNT composite on peroxide addition showed thermal stability similar to that of the 2. wt.% MWCNT composite without peroxide. The finding that electrical and thermal properties achievable with 2. wt.% MWCNT incorporation in a widely used polyolefin like PP could be achieved with the combined effect of 1. wt.% MWCNT and peroxide at much lower SME highlights the significance of this investigation.