The influence of multi-walled carbon nanotubes on the properties of polypropylene nanocomposite. The enhancement of dispersion and alignment of multiwalled carbon nanotube in polypropylene nanocomposite and its effect on the mechanical, thermal, rheological and electrical properties.

摘要

Carbon nanotubes are known as ideal fillers for polymer systems; the main advantage ofudcarbon nanotubes over other nano-reinforcing particles is the combination of superiorudstrength and stiffness with large aspect ratio. Carbon nanotubes may improve theudmechanical, electrical and thermal properties of polymers, but to realise their potentialudin polymer systems uniform dispersion, strong interfacial adhesion and alignment ofudnanotubes within the polymer matrix are necessary. These properties are not easy toudachieve and they are key challenges in producing CNT/Polymer system. This researchudwas carried out in an attempt to understand how the properties of CNT/Polymerudcomposite can be optimised by manipulation of additives, compounding and postcompoundingudconditions.udPolypropylene/Multi-Walled Carbon Nanotube (PP/MCNT) composites were preparedudby conventional twin screw extrusion. Dispersants and compatibilisers were used toudestablish good interaction between filler and polymer. Several different extruder screwudconfigurations were designed and the properties of PP/MCNT composite prepared byudeach configuration investigated. The results indicated that the addition of carbonudnanotubes without additives enhanced mechanical, electrical and thermal properties ofudpolypropylene polymer. Incorporation of compatibilisers into PP/MCNT improved theudstiffness but decreased the strength of the nanocomposite, whilst addition of dispersantsuddecreased the mechanical properties of the nanocomposite. Addition of both additives atudhigh concentration improved electrical conductivity and induced electrical percolationudin the nanocomposite.udExtruder screw configuration was found to have significant effect on the electricaludconductivity whilst only slightly affecting mechanical properties of the nanocomposite, possibly due to the competition between dispersion and degradation of polymer chainsudand possible reduction of carbon nanotube length by intensive shear duringudcompounding. The use of screw configuration with high mixing intensity promoted theuddispersion of nanotubes and favoured the conduction process in the nanocomposite.udFinally in an attempt to improve dispersion and alignment of carbon nanotubes,udcompounded PP/MCNT composite was subjected to micromoulding, fibre spinning andudbiaxial stretching processes and the resultant properties investigated. Application ofudpost-compounding process was found to have significant effect on mechanical andudrheological properties of the nanocomposite. Stiffness and strength of theudnanocomposites treated by post-compounding processes were found to increase by up toud160% and 300%, respectively. The reinforcement effect of carbon nanotubes in theudstretched nanocomposites was found to be the greatest. Rheological analysis suggestedudthat the application of post-compounding processes enhanced dispersion of carbonudnanotubes within the nanocomposite.udOverall, this finding of this research has shown that carbon nanotubes can beudincorporated into polypropylene using conventional equipment to provide significantudimprovement in properties. By careful choices of additives, compounding and postcompoundingudconditions, specific properties can be further enhanced.