Fundamental and Applied Research of SR/SSBR Blends for High-performance Tread
Supervisor:wu you ping
Tire industry is the biggest department of rubber industry.Tread is not only the most important part of tire,but also the performance decision part of automobiles as the only part that contacts with road.Capable mechanical properties are the basic requirements of tread.The optimized performance among the conflicts between abrasion resistance,wet-skid resistance and rolling resistance is the key of high-performance tread.Silicone rubber(SR)is an organic-inorganic hybrid rubber which is synthesized without the demand of the reducing petrol resources.The unique Si-O-Si backbones endow SR the ultra-low glass transition temperature,outstanding heat resistance and aging resistance.In present research,SR was applied in tread compounds,aiming to enhance the abrasion resistance and reduce the rolling resistance.However,the low viscosity,low mechanical strength and poor compatibility in thermodynamics and curing characteristics with solution polymerized styrene-butadiene rubber(SSBR)were the limitations of SR applied in tread compounds.These science and technology issues and the design and adjustment of SR/SSBR tread compounds and processes are the main topic of this research.The research includes four parts as following:(1)Silica/SR masterbatches were prepared before mixed with SSBR,which aiming to match the low viscosity of SR to the high viscosity of SSBR to facilitate the blending process;Fumed and precipitated silica and peroxide curing system were chosen as the basic formula by two experiments.Based on these knowledge,the influence of SR/SSBR blending ratios to the static and dynamic properties of the composites were studied.The results showed the introduce of SR drastically improved the abrasion resistance and kept the wet-skid resistance steady,but the mechanical strength was decreased and hysteresis was increased.The compatibility in thermodynamics and curing characteristics between SR and SSBR,and the filler-rubber interactions were targeted as the three main issues to solve.(2)To solve the issue of incompatibility of SR/SSBR blends,trimethylolpropane tris(3-mercaptopropionate)(TMPMP)was chosen as a coupling agent between chains of SR and SSBR.Thiol-ene click reactions were used as in-situ interface compatibilization reactions.The difference of vinyl content between SR and SSBR was ingeniously used:the excessive TMPMP first reacted to the trace vinyl groups of SR,forming TMPMP modified SR(T-SR),and then the redundant mercapto groups on T-SR reacted with SSBR during mixing under high shearing rate,completed the two-step in-situ interface coupling.The two-step process significantly reduced the domain size of SR and improved the shortcomings of weak strength and high hysteresis of SR/SSBR tread.This industry-friendly technique would extend SR applications.(3)Filler dispersion is the key to enhance mechanical strength and to reduce rolling resistance of tread rubber.The facilitate of silica dispersion by TMPMP was found and investigated.The mechanism was studied by means of modeling chemicals.The mercapto groups of TMPMP were further modified by vinyltriethoxysilane(VTES)through thiol-ene click reactions,which constructed a series of coupling agents with decreased mercapto groups and increased siloxy groups to adjust the filler-modifier and modifier-rubber interactions.The results showed the multiple hydrogen bonds enhanced filler-modifier interactions so that facilitated the silica dispersion and favored composites properties in low strain region;the chemical bonds between filler and modifier favored properties in high strain region;the multiple mercapto groups coupled multiple chains that prevented silica from re-agglomerating.This work optimized the chemical structure of coupling agents with multiple functional groups and gave an insight of filler-rubber interactions control.(4)For co-vulcanization issue of SR/SSBR blends,the impact of commonly used silane coupling agent bis[3-(triethoxysilyl)propyl]tetrasulfide(TESPT)to the curing of SR and SSBR were first investigated independently.The results showed the TESPT reduced the curing efficiency of peroxide on SSBR and almost prevent the curing of SR with low vinyl content,which is the causes of the co-vulcanization issue.Thus TESPT was replaced by VTES and the influence of different co-curing agents were investigated.However,without TESPT,the performance of SR/SSBR decreased,disregard the improved co-vulcanization,showed the central position of silica dispersion.So that the high vinyl content SR was synthesized to rebalanced the impact of TESPT.Through the investigation of vinyl content on the performances of blends,vinyl content of 5%was the primary option.Furthermore,the high vinyl content of SR facilitated the in-situ compatibilization by TMPMP in one-step process,gained compatibility without loss on co-vulcanization.Finally,the combination of coupling agent TESPT,commercial SR with 5%of vinyl content and anti-scorch agent was chosen to achieve the optimized cost,processability and performance.The resultant SR/SSBR tread composites feature outstanding abrasion resistance,acceptable decrease of strength and no loss on wet-skid resistance and rolling resistance.