The Preparation And Characterization Of Thermal Conductive Composites Based On CM/EPDM Elastomeric Alloys

With the rapid development of Electronic technology,thermal conductive composites based on rubber show wide application as thermal conductive and thermal interface materials.However,with the addition of thermal conductive fillers,the mechanical properties of composite materials decrease dramatically.The preparation of heat conductive composites with high thermal conductivity and low loads of filler is still a challenge that needs to be solved urgently.In this thesis,Chlorinated polyethylene rubber(CM)and Ethylene Propylene Diene Rubber(EPDM)blends have been choosing as the matrix of thermal conductive composites because of its phase separation.CM/EPDM/BN thermal conductive composites were prepared by adding BN in CM/EPDM blends with the weight ratio of 50/50.The thermal conductivity of the composites was improved by the orientation of BN by using open mill.The selective localization of BN was induced,and the conduction path was obtained with a lower percolation threshold.The main contents are as follows:The chain structures and sequence structures of chlorinated polyethylene rubber(CM)with different chlorine contents from different manufacturers were investigated through FTIR and solid-state NMR.Tensile strength and elongation at break of CM with different brands were tested.The influence of microstructure on the macroscopic properties was analyzed.Results show that with highest chlorine atom content,CH420 showed the most homogeneous chlorine atom distribution and the elongation at break reached 742%while the tensile strength being 10.1 MPa.The dynamic mechanical properties and thermal stability of CM with different chlorine content were investigated.Results show the glass transition temperature of CH420 increased to 4℃,and its weight loss rate was also the fastest.CM1035X showed higher tensile strength,lower Mooney viscosity and better thermal stability.CM/EPDM blends with different ratio were prepared,Peroxide curing agent was been used as Co vulcanizing agent.The vulcanization characterization and mechanical properties of CM/EPDM blends were tested.The CM phase in CM/EPDM blends was vulcanized by Thiazide curing system,and xylene was used as the solvent of EPDM.Phase structures of CM/EPDM blends with different ratio were observed under scanning electron microscope.The results showed that when the ratio of CM/EPDM was 50/50,the CM/EPDM blends form the co-continuous phase.CM/EPDM/BN thermal conductive composites with different size and dosage of BN filled were prepared,the orientation of BN was obtained by open mill,and the selective localization of BN in EPDM phase was induced by better affinity between BN and EPDM.The distribution and structures of BN in blends were observed by scanning electron microscope and the thermal conductivity,mechanical properties,compression heat build-up and stability of composites were characterized.The influence on properties of composites made by the size and dosage of BN and orientation and selective localization of BN were analyzed.The results showed that the mechanical properties of CM/EPDM/BN composites decreased with the increase of BN particle size,which results in the decrease of tensile strength and elongation at break.Using 10μmBN as the filler,with the increase of BN content,the mechanical properties of CM/EPDM/BN composites increased first,after the content of BN beyond 30wt%,the mechanical properties began to decrease.When the content of BN is 30wt%,the tensile strength reached 8.7MPa and the elongation at break reached 405%.The thermal conductivity composites filled with 100μmBN showed the best thermal conductive property compared with other sizes of BN filled composites.With increasing BN content,thermal conductivities of CM/EPDM/BN composite increased.The thermal conductivity of composite reached to 1.8Wm-1K-1 with the BN content of 40wt%.Using CM/EPDM as the matrix,the selective localization of BN can effectively reduce the thermal percolation threshold.The thermal percolation threshold of CM/EPDM was reduced from 30wt%to 20wt%compared with using pure EPDM as matrix and filling with the same BN.The CM/EPDM blends can effectively decrease the compression heat build-up compared with pure CM.After adding BN,the compression heat build-up increased first.With increasing of thermal conductivity,compression heat build-up of composites decreased.