环氧天然橡胶接枝高分散白炭黑增强天然橡胶复合材料的制备及表征

PREPARATION AND CHARACTERIZATION OF THE NATURAL RUBBER COMPOSITES REINFORCED BY EPOXY NATURAL RUBBER GRAFTED SILICA WITH GOOD DISPERSIBILITY

基于白炭黑表面硅羟基与环氧基团的可反应性,利用Haake流变仪的高温高剪切作用,在170℃下,实现了环氧天然橡胶(ENR)对白炭黑的固态原位接枝,制备出一种高分散疏水型白炭黑.探讨了白炭黑和ENR的反应配比对增强性能的影响,确定合适的反应比例为3∶1.FTIR、TGA和TEM的分析结果证实了ENR被接枝到白炭黑表面上.对比研究了接枝前、后白炭黑对增强天然橡胶(NR)复合材料性能的影响,测试结果表明接枝白炭黑在天然橡胶中具有良好的分散性并能明显改善对天然橡胶的增强效果;接枝于白炭黑表面上的环氧天然橡胶分子玻璃化转变向高温偏移,使该复合材料在常温下具备优异力学性能的同时也体现出了高动态滞后的特点.

A kind of hydrophobic silica with good dispersibility was prepared first. The silica and epoxy natural rubber（ENR） were blended in Haake internal mixer at high temperature in a powerful shear force filed,and so the grafted silica was made through in-situ grafting reaction between the hydroxyl groups of silica and the epoxy groups of ENR. The grafting processes were performed as follows：first,the silica should be dried about 24 h at 100℃ in an oven to remove the free water molecules that absorbed on the surface of silica. Secondly, the grafting reaction temperature was chosen at 170℃ that confirmed by the test result of a Monsanto MDR-2000 moving die rheometer, and the weight proportions between silica and ENR were chosen to be 1 ： 1,2 ： 1 and 3 ： 1 separately in this study. Thirdly, ENR was mixed in HAAKE internal mixer about 1 min, then silica was added to react with the ENR for another 15 min before discharged, and the outputs named ENR-grafted silica were obtained as we wanted. In order to obtain an appropriate grafting condition, the effect of different weight proportions between silica and ENR on the stress-strain curves of natural rubber composites reinforced by the grafted silica was discussed. Through analyses of the reinforcement effect, the appropriate proportion between silica and ENR was chosen to be 3：1. FFIR, TGA and TEM analysis results indicated that ENR was successfully grafted onto the silica surface. FTIR result of the grafted silica showed the new absorptions. The peaks at 2966,2929 and 2862 cm^-1 are assigned to C—H stretching vibrations. The absorption band at 1660 cm^-1 is characteristic of C—C stretching. The stretching vibration of epoxy groups that should be at 870 cm^-1 was missing, suggesting the epoxy groups were almost used up to react with silanol groups. A new shoulder peak appears at 3640 cm^-1 , which is ascribed to —OH stretching of C--OH which is the result of the reaction of silanol groups and ENR. TGA curves revealed ENR grafted silica showed a new step between 348 ～ 449℃ due to the decomposition of ENR, and the grafting rate reached 21.3%. TEM images indicated the size of silica agglomerates became small obviously after modification because of the grafting layer preventing the silica particles from conglomerating. Then, compared with the silica without grafting, the properties of NR composites filled with grafted silica were investigated. The ＂Payne effect＂ results indicated that the grafted ENR molecules reduced the silica-silica interaction by enhancing the rubber-silica interaction, and so the grafted silica had better dispersibility in natural rubber （NR） composites. Mechanical properties test of NR composites proved that the grafted silica could more effectively improvethe reinforcement effect due to the strong interface combination between silica and ENR. DMA results showed that the temperature of glassy transition of ENR bound to the silica surface shifted to higher temperatures. Consequently, the composite contained the grafted silica had high strength and high hysteresis at the same time on the normal temperature. So the composites have potential application in the shocking absorber products, the tire of racing cars, and so on.