| Silicone rubber is a kind of very important silicone products,the unique chemical structure gives its excellent heat resistance.With the rapid development of science and technology,people seek higher performance silicone rubber composite materials,especially aerospace,transportation,nuclear nuclear power and defense and other fields of silicone rubber heat resistance made a higher demand.In this thesis,three kinds of silica,the fumed silica(FSi),precipitated silica(PSi)and modified precipitated silica(MPSi),were used to enhance the high temperature vulcanized silicone rubber(SR),respectively.The SR composites obtained were denoted as FSI-X,PSI-X,MPSI-X(X represented silica loading and equaled to 20,50,80,respectively).The effect of surface chemical properties,morphology and different loading on the mechanical and thermal properties of silicone rubber composites were investigated comprehensively.The results showed that FSi had a largest specific surface area and high hydroxyl content,and these two values for PSi and MPSi was lowest and medium,respectively.Under the same silica amount,the enhancement effect of silica for SR had the following order:FSi>PSi>MPSi.All SR composites exhibited the best overall mechanical propertiest as they had been filled with 50 phr of various silica.The retention rate of tensile strength was in order of FSI-X>PSI-X>FSI-X.Then,in order to improve the heat resistance of FSI-50,the graphene oxide(GO)was prepared and modified using KH-570 in our Lab,and the resulting GO and functionalized graphene oxide(FGO)was used as filler and the corresponding GO/SR and FGO/SR composites with 50 phr of the fumed silica(FSi)were obtained.The effect of the incoporation of GO or FGO with different amount on the mechanical and thermal properties of FGO/SR composites was investigated systematically.The TGA results showed that the thermal stability of GO/SR and FGO/SR composites is evidently better than that of SR composites such as FSI-X,PSI-X,MPSI-X(X=20,50,80,respectively).Among these composites with different GO or FGO concentrations,the initial decomposition temperature of 0.25%GO-SR composite with 0.25%of GO is 36?higher than that of SR composite,while 0.25%FGO/SR composite with 0.25%of FGO has the best thermal stability,it's initial decomposition temperature was increased by 48?compared with SR composites.The apparent activation energy of the composites increased from 169.7 kJ/mol of SR composite to 240 and 272.2 kJ/mol,respectively,as a result of incoporation of GO or FGO.In conclusion,it was showed that GO and FGO play a inhibited role in the thermal degradation process of silicone rubber.Although the mechanical properties of GO/SR and FGO/SR composites reduced to some extent,the retention rate of mechanical properties was improved obviously after hot air aging.Moreover,FGO is better than GO in improving the stability of SR composites in hot air.Among all composites with GO or FGO,the FGO/SR composite containing 0.50 phr of FGO had the highest retention rates of tensile strength and tear strength,reaching to 96.11 and 104%,respectively.Finally,the functionalized multi-walled carbon nanotubes(FMWCNTs)were first prepared by modifying carboxylated multi-walled carbon nanotubes(MWCNTs)with bi-hydroxyl terminated polysiloxanes.MWCNTs,FMWCNTs and FMWCNTs-FGO mixture were used as filler,respectively,and correspond ingly,MWCNT/SR,FMWCNT/SR and FGO/FMWCNT/SR composites filled with 50 phr of FSi were prepared.The effect of the incorporation of MWCNTs,FMWCNTs and FGO/FMWCNTs on the mechanical and thermal properties of the resultant SR composites was explored completely.The inhibiting effect of these fillers for the thermal degradation of SR composite was also surveyed.The experimental results indicated that the mechanical properties of SR composites reduced with the increase of MWCNTs or FMWCNTs,but the thermal stability of MWCNT/SR and FMWCNT/SR composites was improved clearly when undergoing a hot aging for 24 h at 250?.For MWCNT/SR composite with 0.50 phr of MWCNT,the tensile strength and retention rate was 7.14 MPa and 84.20%,and for FMWCNT/SR composite with 0.50 phr of FMWCNT,these two values were 7.58 MPa and 88.97%,which were evidently higher than those(5.52 MPa and 64.56%)of the blank SR composite with 0.50 phr of FSi,respectively.Furthermore,the thermal stability of FGO/FMWCNT/SR composites was better than that of blank SR composite after hot aging,although their mechanical properties decreased with the increase of FGO loading,and regrettably lower than those of relevant FMWCNT/SR composites.From TGA,the heat resistance performance of composites was researched.Compared with the blank SR composite,the initial decomposition temperature,T10%,T50%and Tmax of 0.50%MWCNT/SR were increased by 41,45,36 and 33?,respectively,and the increases of those values for 0.50%FMWCNT-SR were not always dramatic.However,the initial decomposition temperature,T10%,T50%and Tmax of A(0.25%FGO/0.5%FMWCNT/SR composite)were increased by 37,42,52 and 56?,respectively.On the other hand,the thermal stability of MWCNT/SR,FMWCNT/SR and FGO/FMWCNT/SR composites was all significantly was superior to that of blank SR composite. |
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