Preparation And Performance Research Of Pvc/graphite Conductive Composites Based On Mechanical Milling

PVC is one of the five common resins in the world,the products from which were widely used in chemical production,home appliance decoration,electronic equipment and all kinds of packaging products.The price of PVC was very low and it has the advantages of easy to be processed and unti-acid and base and retardant.While its production and application were limited by its insulating properties.If the conductivity of PVC products could be improved,it could be used to replace the precious metals in integrated circuits,electromechanical shell and aerospace fields,which would greatly enhance its value and development prospects.The modified graphite and PVC would be used as the main raw material in this study.Firstly,the materials would be mixed through method of mechanical milling,and then it would be thermoformed by vulcanizing machine to prepare graphite/PVC conductive composites,the conductivity of which was tested through resistivity.PVC/graphite two-phase conductive composites,PVC/graphite/MWCNTs three-phase conductive composites and PVC/graphite/cassava residue three-phase conductive composites were separately prepared in this experiment.The main contents are as followings:(1)Different coupling agents such as silane,titanate and aluminum acetate were selected to modify the graphite,which was put into the ball mill with PVC.The mixed powder of PVC and graphite was obtained under.Use the vulcanizing machine to make the powder thermoforme under a certain temperature and pressure.The effect of milling speed,time,and amount of coupling on the electrical properties of composites were studied.The optimal process of PVC/graphite two-phase conductive composites were determined by single factor and orthogonal process optimization.It showedthat:the best milling time was 60 min,best milling speed was 150 r·min-1,the optimum amount of silane coupling agent was 2%,titanate coupling agent was 1%,aluminum coupling agent was 3%,and silane coupling agent had a good modification effect of coupling.Under the condition of 165? hot temperature,10 min cold pressed,the conductivity percolation threshold of composites was between 4-6%.When content of graphite increased to 6%,the resistivity of composites was reduced from 1.075 × 106?·cm to 20.138?·cm,whose conductivity was improved 5 magnitude.(2)The conductivity of the composites was tested by the thermal conductivity tester.The results showed that the thermal properties would increase with graphite content.The thermal conductivity of the composites would up to 0.715w·m-1·k-1when the content of graphite was 20%,which was 5 times of pure PVC material.It demonstrated that the PVC/graphite conductive composites not only had good electrical conductivity,but also had a certain thermal conductivity.(3)The mechanical strength of the composites increased firstly and then decreased with the increase of graphite content.The tensile strength and flexural strength respectively reached maximum value 45.81Mpa and 40.04MPa when the graphite content was 4%and 6%.(4)MWCNTs was added to prepare PVC/graphite/MWCNTs three-phase conductivity composites.The conductivity of the composites would be improved with the synergistic effect of graphite and MWCNTs,the resistivity of composites decrease from 1.075 X 106 Q·cm to 4.99?·cm when the graphite content was 4%and MWCNTs 1%.The thermal conductivity of the composites was 0.501 w·m-1·k-1 and the tensile and flexural strength was 49.39MPa and 38.38MPa.(5)With the addition of cassava to the PVC/graphite,a three-phrase WPC conductive composites was prepared.The results showed that:it had little effect to the conductive properties of the composites when the cassava residue content was less than 15%.The conductivity percolation threshold would increase to 6-8%,resistivity would decrease from 2.418 × 107?· cm to 40.283?·cm when the cassava residue content was 15%.Therefore the large number of fibers in cassava residue could improve the mechanical properties of composites effectively.And the tensile strength and flexural strength were up to 50.13MPa and 47.76MPa,it were raised 9.4%and 19.3%than the maximum value 45.81MPa and 40.04MPa of those without cassava residue.(6)From TGA,the thermal decomposition temperature of the pure PVC material was 287.61?,while the thermal decomposition temperature of PVC/graphite conductive composites prepared by mechanical milling was up to 306.71?,which was improved 19? than pure PVC material.The softening point of conductive composites was up to 86.45?,which was improved nearly 4? than the pure PVC material.It showed that the heat resistance of PVC/graphite conductive composites could improve effectively through mechanical milling.(7)From SEM,it showed that the lamellar graphite could be peel arpartly,and the specific surface area and ratio of radial and thickness be increased through mechanical milling,and thus the conductivity of the composites could be improved,in addition,mechanical milling enabled the graphite highly disperse in PVC,and made them parcel together,form which more effective conductive paths would be formed.