| Addition-curable liquid silicone rubber is a kind of non-toxic,heat-resistant,flexible thermosetting transparent silicone rubber with Si-O bond as the main chain polydimethylsiloxane.During the vulcanization of addition-curable liquid silicone,there are no by-products.In addition,ALSR has low molding shrinkage,high conversion and deep vulcanization,and the vulcanized silicone rubber has excellent heat resistance,insulation,aging resistance,radiation resistance,and ozone resistance.It has been widely used in electronics and electrical appliances,petrochemical industry,machinery manufacturing,construction,aerospace,communications,medical,health fields and so on.However,due to the non-polar organic groups and lacking of reactive functional groups on the vulcanized surface of ALSR,the adhesive properties between ALSR and various substrates are poor.In order to improve the adhesion with substrates,three kinds of tackifiers containing active groups were synthesized,and the effects of different tackifiers on the bonding properties of addition liquid silicone rubber were studied.Firstly,the effects of two kinds of single group tackifiers on the comprehensive properties of silicone rubber were investigated.A series of ALSR formulations with different components and ratios were prepared,and the mechanical properties and bonding properties of the cured products were measured.The results showed that the bonding and mechanical properties of ALSR were the best when the epoxy and acryloxy tackifiers were 0.6 phr and 0.8 phr,respectively.The peel strength between ALSR and aluminum and the tensile strength of ALSR vulcanizate were 1.92 kN/m,4.02 MPa and1.66 kN/m,3.8 MPa,respectively.While the peel strength and tensile strength of ALSR without addition of tackifiers were 0.1 kN/m and 3.04 MPa,respectively.At the same time,the tackifier has an obvious effect on the vulcanization of ALSR.It can obviously promote the vulcanization of ALSR when the dosages of tackifiers are less than 0.6 phr and 0.8 phr.But when the dosage exceeds a certain range,it would inhibit the vulcanization of ALSR.Secondly,the composite silicone tackifier containing epoxy group and acryloxy group was synthesized by hydrosilylation of polymethylhydrosiloxane(PHMS)with silane coupling agent.The structure of the composite tackifier was characterized by Fourier transform infrared spectroscopy(FT-IR)and nuclear magnetic resonance hydrogen spectroscopy(~1H-NMR).The effects of molar ratio of reactants,reaction temperature and reaction time on the structure and adhesion promoting performance of the tackifier were investigated.The results showed that the optimum synthesis conditions of the compound tackifier were as follows:the ratio of reactants was 1:1.5,the reaction time was 4 h,the reaction temperature was 80?,the concentration of platinum catalyst is 0.15 ppm.Under these conditions,the adhesion properties between ALSR and aluminum can be improved obviously,and the peel strength of ALSR containing composite tackifier is 4.12 kN/m.By adding tackifiers into ALSR,the effects of the amount of tackifiers on the adhesion properties,viscosity,vulcanization properties and mechanical properties of ALSR were studied.The results showed that when the dosage of compound tackifier is0.8 phr,the bonding property between ALSR and aluminum can be significantly enhanced.Furthermore,composite tackifier could remarkably influence the vulcanization of ALSR.When the dosage of compound tackifier is less than 0.8 phr,it can promote the vulcanization of ALSR,but when the dosage exceeds 0.8 phr,it can inhibit the vulcanization of ALSR.The adhesive properties of ALSR were improved significantly with the increase of curing temperature or curing time after adding compound silicone tackifier.This may be due to the reason that the active groups need to act at higher temperature for a period of time to form a strong interaction with the metal surface,and significantly increase the bonding effect. |
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