Study On Structure And Properties Of Modified Carbon Nanotubes Filled PVDF/PC Composites

In this study,using multi-walled carbon nanotube(MWNTs)as fillers,polycarbonate(PC)and Poly(vinylidene fluoride)(PVDF)as matrix,conductive composites were produced by a torque rheometer,and then hot compression-molding into a sheet.The effects of contents,morphology and surface treatment of fillers on micro-structure and electrical conductivity properties were investigated.An in-situ method was used to study the kinetics of conductive network formation of the composites by recording the variation of electrical resistivity with time during the isothermal treatment.Particular attentions has been paid on the effect of fillers structures,surface characters and synergistic effect of MWNT and CB on conductive network formation of the composites,and a thermodynamic percolation model was proposed to fit the kinetics of the conductive network formation in electric field.The volume resistivity of MWNT,MWNT-COOH and MWNT-HBPE(HBPE,hyperbranched polyethylene)filled PVDF composites showed percolation clearly.The percolation threshold of PVDF/MWNT,PVDF/MWNT-COOH,PVDF/MWNT-HBPE were 1.7Phr?2.5Phr and 5.8Phr,respectively,due to the surface modification of MWNT resulting in enhancing the interacion among the molecular chains.The room temperature electrical properties of the PVDF/MWNT and PVDF/MWNT-HBPE system were higher than that of the PVDF/MWNT-COOH system.An in-situ method,named as dynamic percolation,was used to study the kinetics of conductive formation of the composites in the non-electric field conditions The results showed that the percolation time,characterized at a certain annealing time when the electrical resistivity started to decrease drastically,decreased with the increase of both the fillers concentration and the annealing temperature.The activation energy of conductive network formation(Ec)for PVDF/MWNT,PVDF/MWNT-COOH and PVDF/MWNT-HBPE was 107,126 and 83kJ/mol,respectively.The E,was related to the structure and the interfacial interaction of MWNT-polymer.Furthemore,a modified thermodynamic percolation model was proposed to predict the percolation time in the carbon nanotubes filled polymer system.The predicted data fitted the experimental results very well.For MWNT,treated by the coupling agent KH550,filled PC system,the activation energy of the formation of the conductive network increases with the coupling agent,after the ratio of MWNT to KH550 was 100/6,further increase the coupling agent content did not lead to higher activation energy of conductive network.the percolation time was firstly extened with the increase of coupling agent,then coupling agent has little effection.Using multi-walled carbon nanotubes(MWNT)and carbon black(CB)as fillers,polycarbonate(PC)as a matrix,conductive polymer composite was prepared.The kinetics of conductive networks formation in the composite was investigated by in-situ tracing the time dependence of electrical resistivity when the samples were isothermally treated above the melting temperature.It was found that when the electric field and fillers concentration was low,the percolation time of PC/MWNT/CB(for the weight ratio of MWNT/CB as 8/2)system was shorter than that of the MWNT system because of the synergistic effect of MWNT and CB.But with the increase of fillers concentration,synergy effect was weaked.Under high electric field,the synergistic effect which was significant under low electric field was weaked.