| There are many problems of the dispersion of silica in rubbermatirx，such as poor compatibility，unstable，hard scattered et al. Therubber surface modification has various drawbacks too. To enhance NRwith silica, an in situ method was proposed to graft polymer onto fillersurface. Via FT-IR, TGA, Elemental Analyzer, and Rubber ProcessingAnalyzer studied the system of process and mechanism of the in situreaction. A possible reaction model was proposed. The chemical structure,relaxation of structure and performance, morphology of NR filled withsilica were studied in this paper.The Si69/NR mixture’s DSC experiments showed that severalexothermic peaks between140to175℃arose obviously, while therheometer at150℃torque figure showed that the mixture appeared atypical reaction of curing process and the torque first increased andincreasingly in flat finally, because Si69’s carbon-sulfur bond rupture,product free radicals involved the crosslinking reaction with doublebond of the rubber chain. FTIR spectra appeared some organic peak ofthe carbon-hydrogen bonds of Si69/silica mixture from coupling agent，it concluded that silanol from silica and ethoxy from silane reactedduring in situ reaction. ARES showed the Payne Effect of NR modifiedin situ with silica was weaker than that of NR filled with silica,indicating the network of filler particle was weak in NR matrix whichwas of great benefit to rubber processing, especially dimension stabilityof product. On the other hand, By TGA and ATR analysis, it revealedthat Si69added as a bifunctional organosilane coupling agent wascharacterised by two functions: one for the adhesion to the hydrophilicsilica surface, the silane moiety; the other for adhesion to orenhancement of the compatibility with the hydrophobic NR matrix.According to the above experiments facts, a more reasonable responsemodel of the in situ modification reactions was proposed.The compatibility of rubber and fillers was studied by bound rubber,Kraus plot, SEM and AFM. The bound rubber content of in situ modified NR increased obviously. It could be concluded that the size of modifiedsilica diminished because the aggregates of silica were broken bymechanical and chemical force. The dispersion of modified was stableresulted from the repulsion force between the filler and polymer. AFMphoto of NR vulcanizte showed the particle size of silica was about39nmin matrix. The results show that the in situ modification can not onlyimprove silica dispersion in rubber matrix, but also increase thefiller-rubber interaction of silica filled NR vulcanizates.The crosslinking density of the compound and vulcanizates werecharacterized by NMR, and the results were compared with those gotfrom equilibrium swelling method. Crosslinking density of NR increasedlinearly, spin-spin relaxation time and spin-lattice relaxation timedecreased with increase of Si69amount. The results also showed that thein situ reaction took placed in brabender high temperature mixer. Themechanical properties of NR vulcanizate in situ modified with silica/Si69increased. The strength increased by56%and stress at300%elongationincreased by104%when with4phr modifier. Tear strength and hardnessall increased. The dynamic mechanical properties of NR vulcanizateswere measured with rubber process analyzer and DMTA. NR in situmodified with silica has lower loss factor in the range from50to80℃and higher glass transition temperature, indicating in situ modificationdecrease the roll resistance of NR vulcanizate, the product will be used inshock absorber or tyre filed.According to the above researches we arrived at conclusions that allthose properties of Si69in situ modified silica reinforce NR compositematerial improved obviously. Via the modification, the chemical structureof material is changed, the interaction between silica and rubber isenhanced, the dispersion of fillers, the static and dynamic properties ofvulcanizates are improved well. |
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