Synthsis Of The Monodisperse Nanosilicna And Study On The Properties Of Reinforced Rubber Composites

Silica as the filler that can replace carbon black at present,which is used to reinforce rubber with the incomparable advantages.For example,silica when used to reinforce tire tread rubber can reduce the rolling resistance of the tire,and ensure the wet skid resistance without poor wear resistance.Considering the nanoparticles size,structure and surface activity into the influence factors of silica reinforced rubber.In this paper,we controled the initial particle size and morphology of silica,compared the difference in reinforcing rubber performance between the monodisperse and precipitated silica which were in differernt aggregation state and explored the reinforcement mechanism,influencing factors and the feasibility of monodisperse silica.The main results are as follows.The aqueous solution of lysine can catalyze the hydrolysis and condensation of tetraethyl orthosilicate?TEOS?to prepare monodisperse nanosilica particles;By changing the types of co-solvents,the ratio of TEOS,lysine,water and silica seeds,using"seed regrowth technology",monodisperse nanosilica particles with particle size ranging from 10to 110 nm could be obtained;As particle size was<60 nm,"bottleneck pores"exhibited;While particle size increased to 100 nm and above,the pore structure was“cylindrical pores”,indicating a dense block mass similar to sphere.When the lysine was replaced by lysine hydrochloride,introducing triethylamine to neutralize the hydrochloric acid molecule in the lysine hydrochloride structure;By using lysine hydrochloride and triethylamine instead of lysine with"seed regrowth technology"to catalyze the hydrolysis and condensation of TEOS,the monodisperse nanosilica with particle size range of 55-135nm could also be obtained;The pore structures on silica surface transformed from“cylindrical pores”with uniform and regular shape at small particle size to“slit pore”with a uniform size and a regular shape at large particle size.Natural rubber/silica composites were prepared via latex compounding technology with different amounts of the monodisperse?AS?and precipitated silica?PS?.As the amount of silica increased,the scorch time of composites shortened,the processing safety reduced,and the vulcanization rate slowed down.Among them,the NR/AS composites exhibited higher processing safety than that of NR/PS,while the former had lower crosslink density.Therefore,the modulus at 300%elongation of the former was lower than that of the latter at the same amount of silica.The tensile strength combined with bound rubber content and wear resistance of the modified AS?MAS?filled NR vulcanizates were always higher than that of modified PS?MPS?filled NR composites.Meanwhile,the network structures of former was weaker.TEM results showed that in rubber matrix,the dispersion of AS changed from“bead-like”structure before modification to independent morphology after modification.The dynamic mechanical properties of the vulcanizates showed that the wet skid resistance of NR/MAS vulcanizate was equivalent to that of NR/MPS vulcanizate,meanwhile the former had lower rolling resistance than the latter at 30 phr silica.While the amount of silica increased to 70 phr,the former was not as wet skid resistant as the latter,and the rolling resistance of the former was still lower than the rolling resistance of the latter,which is beneficial to reduce the fuel,while still need to be strengthen the wet slippery safety performance.Natural rubber/silica composites were prepared via latex compounding technology of monodisperse silica?AS?with different sizes?specific surface areas?.The four kinds of AS were with average particle size of 26,36,45,56 nm,which had no change in the surface pore structure after modification by TESPT,and were still"bottleneck pores";The BET surface area decreased as the particle size increased,and the tendency of decrease became slower.For NR/MAS vulcanizates,as the AS size increased,the tensile strength and elongation at break of the vulcanizates increased first and then decreased,the peaks reached at 45 nm.The modulus at 300%elongation decreased first and then increased,the minimum reached at 45 nm.The Akron wear loss reached the maximum,indicating the worst wear resistance at the same time.Besides,the filler network structure in rubber matrix gradually decreased.In terms of dynamic mechanics,the modified 56 nm AS filled with NR vulcanizate had the highest T_g and the highest loss,meanwhile to be the highest wet skid resistance and the lowest rolling resistance balance.Different amounts of water-soluble silane coupling agent Si747 were used to pre-modify the monodisperse?AS?and precipitated silica?PS?,then filled ESBR to prepare composites.The comprehensive results showed that 15%Si747 modified AS?MAS?and20%Si747 modified PS?MPS?had the lowest relative intensity at 3400 cm^-1 in the FTIR spectrum and the largest mass loss of TGA.The mass loss of latter was greater than that of the former.The introduction of Si747 promoted the vulcanization process of ESBR/SiO₂compounds.At the same amount of Si747,the scorch resistance of ESBR/MAS compounds was slightly lower than that of ESBR/MPS;Nevertheless,the former had lower vulcani-zation rate and better processing performance.The"Payne effect"of ESBR/MAS rubber compounds was lower than that of ESBR/MPS,indicating that the filler network structure of ESBR/MAS compounds was weaker,and the filler dispersibility were better.Comparing the ESBR/MAS vulcanizate of 15%Si747 and ESBR/MPS vulcanizate of 20%Si747,the former improved the wet skid resistance by 4.27%and decreased the rolling resistance by13.92%;The tensile strength and elongation at break increased by 14.8%and 62.4%,respectively,while the hardness and 300%modulus decreased by 13.1%and 53.2%,respectively.Both had their own advantages.The comprehensive properties of modified monodisperse silica?AS?and precipitated silica?PS?at different pH?3,7,9,12?filled ESBR composites were compared.The MAS with 15%Si747 and MPS with 20%Si747 at pH=9 had the lowest relative intensity at 3400cm^-1 in the FTIR spectrum,and the largest mass loss of thermal weight of TGA.As pH increased,the scorch resistance of the ESBR/SiO₂ compounds weakened;the vulcanization time shortened and the vulcanization rate significantly increased.At pH=9,ESBR/MAS compounds had the highest processability and crosslink density.At the same time,ESBR/MPS compounds were with higher processability and crosslink density.Both of the compounds had the lowest"Payne effect",indicating that the filler network structures were the weakest and the filler dispersion were the best at pH=9.At the same time,the"Payne effect"of the former performed lower than the latter,indicating better dispersion of MAS.MAS and MPS filled ESBR vulcanizate were with the highest wet skid resistance and the lowest rolling resistance balance at pH=9.In summary,after the above analysis and comparison,we believe that the monodisperse silica can replace some of precipitated silica for rubber reinforcement,and some properties?such as the tensile strength,the elongation at break,the filler dispersion,the decreased rolling resistance?of rubber/silica vulcanizates can be improved to some extent as result,which is of certain significance.