Preparation And Properties Of PP/Expanded Graphite Thermal Conductive Composites

Since the polymeric materials have lots advantadges, such as easily obtained,low cost, easily process, which make them widely used, but in general thepolymeric materials are the heat insulator, this limits their applications in somefield, such as electronic package, chemical engineering area, therefore, the researchof how to improve the thermal conductivity of polymeric materials have become thefoucs in materials science. In this thesis, we added thermal conductive fillers topolymer matrix in order to prepare high thermal conductive polymeric composites,the main contents are as follows:PP/graphite composites were prepared by melt compounding, the resultsindicated that the impact strength of the composites were dramatically decreasedwith the increased content of graphite, and the tensile strength, flexural strength,modulus were increased, then decreased, used POE-g-MAH to improve thetoughness of PP/graphite composites, when the content of graphite is40%, themechanical properties were the optimal, the tensile strength was36MPa, whileimpact strength was about4.8kJ/m2; The thermal conductivity of the compositeswas studied, when the graphite is in low content, the thermal concuctivity increasedlinearly, while the volume fraction exceeded50%, the thermal conductivityincreased rapidly, the thermal conductivity reached2.12W/m·K for the volumefraction of graphite exceeding60%; Compared with two different size of graphiteson the effect of composites, the result showed that large diameter was morepropitious to improve the thermal conductivity of the composites; The rheologicalproperty was studied, at the same shear rate, the apparent viscosity raised graduallywith the increased content of graphite, at the same temperature, the non-Newtonianindex was also raised gradually, the viscous flow activation energy of thecomposites increased grudally with the addition of graphite; DSC research showedthat graphite played a role of heterogeneous nucleation in the PP crystallizationprocess, caused the increased of Tp, and when the content of graphite was more than10%, the crystallinity of Polypropylene decreased.PP/expanded graphite composites were prepared by in situ melt compounding,the expansible graphite expanded in twin screw extruder, which had a plate shape,small particle size, and large radius-thickness ratio, the shear, exfoliation by screw caused the lattice (002) diffraction intensity decreased, while the diffraction anglealmost the same, indicated that the PP chain can’t intercalate into graphite layers;Compared the two filler on the effect of the composites’ properties, as the graphite,expanded graphite had the same effect on mechanical property of composites, butthe thermal conductive percolation threshold of PP/EG composite was lower thanPP/NG composite, used thermal conductivity equations to predict the thermalconductivity of PP/EG composite, the results showed that Maxwell-Eucken,Bruggeman equations could predict the thermal conductivity at low volume fractionof EG, and Agari equation predict value were higher than experimental data; Therheological property was also studied, PP and composites were all pseudoplasticfluids, at the same shear rate, the apparent viscosity decreased first, then increasedwith the increased content of expanded graphite, while the viscous flow activationenergy declined all the time; At last, the non-isothermal crystallization kinetics ofPP/EG composites were studied, the results showed that the addition of EGincreased the Tp, decreased the crystallization time when the content of EG was lessthan20%, the modified Avrami equation indicated that the crystallization processcontained two-stage: primary and secondary crystallization. Mo equation showedthat the F(T) of PP/EG composites with low content of EG were less than neat PP,while the content of EG was20%, the F(T) of PP/EG composite was higher thanneat PP, the influence of EG to the crystallization activation energy is the samewith above, when the content of EG less than20%, the crystallization activationenergy lower than neat PP.