Study On Wear And Thermal Conductivity Of UHMWPE

Ultra High Molecular Weight Polyethylene （UPE） with its excellent mechanical propertiessuch as high impact resistance, wear resistance, self-lubrication, non-toxic and low temperatureresistance and other properties has been used in the fields of medical, mining, oil and gasexploitation, textile chemical and sports equipment, especially in the application of artificial jointsand wear-resistant pipe. However, the liner structure of UPE and frictional heat during the usemake UPE creep weak and the strength fatigue, and then affect the wear property of UPE. So UPEis modified from two aspects:（1） the irradiation sensitizer is added into UPE to form a crosslinkednetwork to change the linear structure of UPE to make UPE difficult to produce plasticdeformation and creep.（2） Improving the thermal conductivity of UPE is used to export frictionalheat to reduce creep caused by elevated temperature. The method consists of three parts: theimprovement of UPE intrinsic thermal conductivity, Preparation of UPE/Al₂O₃, LLDPE/Al₂O₃andEpoxy/Al₂O₃composites; Preparation of UPE/NG, LLDPE/CF and Epoxy/GS composites. Thedetail contents and conclusions are as follows:1UPE/Al₂O₃, LLDPE/Al₂O₃and Epoxy/Al₂O₃compositesTMPTMA and TPGDA are dispersed on the UPE powders by the solution method. UPE,TMPTMA/UPE�'�TPGDA/UPE composites were made by compression-molded and thencrosslinked by EB. The method above can reduce the irradiation dose at the same time to increasethe crosslinking degree of UPE. FTIR, Swelling balance test, DSC, Electronic tensile testingmachine, friction tester, SEM are used to test the structure changes before and after irradiation, thegel content, crosslinking point between molecular weight, degree of crystallinity, mechanicalproperties, friction properties, friction morphology. The main conclusions are as follows:（a） FTIR and gel content show that the crosslink reaction happens in the composite,. The gelcontent of TMPTMA/UPE�'�TPGDA/UPE composites are all higher than that of UPE. The addingof TMPTMA and TPGDA can reduce the irradiation dose at the same time to increase thecrosslinking degree of UPE. （b） The degree of crystallinity of all specimens increases after irradiation. The degree ofcrystallinity of TMPTMA/UPE�'�TPGDA/UPE composites are all higher than that of that of UPE,showing that the adding of TMPTMA and TPGDA are useful to increasing the degree ofcrystallinity.（c） The increasing of the degree of crystallinity and the degree of crosslinking are useful toincreasing the wear resistance of UPE. The wear rate of1%TMPTMA/UPE（100kGy） and1%TPGDA/UPE（100kGy） is1.89×10-7mm3/（N m） and4.28×10-7mm3/（N m）,respectively, about44.2%and100%of the wear rate of UPE（4.28×10-7mm3/（N m））.2UPE intrinsic thermal conductivityThe intrinsic thermal conductivity of the material of the UPE is improved by controlling thecooling process. The melting and recrystallization process of UPE is studied by DSC method.Themain conclusions are as follows:（a） Cooling rate, holding temperature and holding time will affect the degree of crystallinityof UPE. The slower the cooling rate, the holding temperature at125℃and the longer theholding time are useful to improve the degree of crystallinity and crystallization tacticity of UPE.（b） Stochastic cooling is most useful to increase the degree of crystallinity and melting pointof UPE by the DSC method, and also helpful to improve the tensile strength of UPE. Thermalconductivity of UPE （Stochastic cooling） is0.593W/（m K）,17.9%higher than thermalconductivity of UPE（press with water for10min）（0.503W/（m K））.（c） The improvement of thermal conductivity of UPE is due to the connection of the crystalbridge formed by UPE spherulites. The heat conduction mechanism of UPE is the crystal bridgeconduction mechanism. Stochastic cooling manner is equivalent to widening the width of thecrystal bridge, thereby useful to the transmission of the thermal conductivity phonons, so thethermal conductivity is improved.3UPE/Al₂O₃, LLDPE/Al₂O₃and Epoxy/Al₂O₃compositesUPE/Al₂O₃composite is prepared by powder mixing in ethanol and compression-moldedmethods. Then UPE/Al₂O₃composite is thermal treated at200℃. LLDPE/Al₂O₃composite ismade by Huck mixing method. Epoxy/Al₂O₃composite is made by vacuum casting method.Thermal Conductivity between Highly crystalline materials and low-crystalline materials,crystalline materials and amorphous materials, thermal treatment and un-thermal treatment are studied. The dispersion, thermal properties, crystalline or glass transition temperature, thermalconductivity, dielectric properties and resistivity of UPE/Al₂O₃, LLDPE/Al₂O₃and Epoxy/Al₂O₃composites are measured by SEM, TGA, DSC, thermal analyzer, dielectric spectroscopy and highresistance meter. The main conclusions are as follows:（a） If intrinsic thermal conductivity of the polymer matrix is high, thermal conductivity of theforming composite is also high. The degree of crystallization order is LLDPE <UPE <UPE（thermal treatment）, thermal conductivity order of the composites is: LLDPE/Al₂O₃<UPE/Al₂O₃<UPE/Al₂O₃（thermal treatment）.（b） Thermal treatment can increase the degree of crystallinity and the crystalline regularity ofthe crystalline of the composite, at the same time can improve the thermal conductivity of thematerial. After thermal treatment, the heat of fusion and the melting point are18.5%,3.8℃higher than that of UPE/Al₂O₃（100phr） composite before thermal treatment, respectively. Thermalconductivity of UPE/Al₂O₃（100phr） after thermal treatment is1.960W/（m K）,35.4%higherthan that of UPE/Al₂O₃（100phr） before thermal treatment （1.554W/（m K））.（c） Thermal conductivity of Epoxy（Amorphous polymer） is lower than thermal conductivityof PE（crystalline polymer）. After adding the same content of Al₂O₃filler, thermal conductivityincreasing proportion of Epoxy composite is also lower than that of PE composite. Thermalconductivity of UPE/Al₂O₃（12.0vol%）、LLDPE/Al₂O₃（12.0vol%） and Epoxy/Al₂O₃（13.8vol%）are1.160W/（m K）,0.909W/（m K） and0.425W/（m K），respectively,132.0%，102.4%and72.8%higher than that of each of the resin matrix.（e） Thermal stability of the composite after adding Al₂O₃filler,5%weight loss temperatureof UPE/Al₂O₃, LLDPE/Al₂O₃and Epoxy/Al₂O₃are467℃,461℃and366℃, respectively,11.5℃13℃and34℃，higher than the pure matrix. Three composites all have good dielectricproperties and electrical properties.4UPE/NG, UPE/CF and UPE/GS compositesGraphene oxide（GO） is prepared by modified Hummers method. GO is mixed with UPE inwater-ethanol solution, then GO is reduced by hydrazine hydrate. At last, UPE/GS is prepared bythe hot press method. UPE/NG and UPE/CF composites are prepared by powder mixing in ethanoland compression-molded methods. Influences of the three kinds of carbon materials on electricconductivity and thermal conductivity performances of UPE composites. The main conclusions are as follows:（a） FT-IR and XRD is used to characterize the structure of graphene. AFM and TEM are usedto characterize the graphene morphology. TGA is used to study the thermal stability of graphene.The results above show that the graphene is prepared.（b） If the composite is more dense and the crystal structure of the filler is more regular, thethermal conductive path will be easy to formed. Thermal conductivity of the composite order isUPE/NG>UPE/CF>UPE/GS, which is related to the structure of the composites. UPE/NGcomposite has regular structure and the density gradually increases with the increasing filler.UPE/CF composite is regular on the overall structure of the material, but still has a certainagglomeration, and the density has little change. The density of UPE/GS material decreases withthe increasing GS, GS join introduces a lot of gaps. Thermal conductivities of UPE/NG（60phrNG）、UPE/CF（60phr CF）and UPE/GS（10phr GS）composites are3.257W/（m K）、0.778W/（m*K） and0.52W/（m K）, respectively,556.7%,56.9%and4.8%higher than that of UPE matrix.（c） When the filler content is10phr, electric conductivity order of the three composites isUPE/CF>UPE/GS>UPE/NG. The electric conductivity order is not same as thermal conductivityorder, showing that the electric conductivity mechanism is not same as the thermal conductivitymechanism. Electric conductivity mechanism is mainly affected by the electronic conductivity, notaffected by the interface so large. Thermal conductivity mechanism is percolation theory andthermal is mainly transmitted by phonon combined with some electronic thermal conductivity.Thermal conductivity is also influenced by the interface and the interface effect is very big. Soelectric conductivity mechanism cannot simply be transformed to thermal conductivity mechanism.The two mechanism are not the same thing.