The Study On The Structure And Properties Of NR/SiO₂ Composites By Wet Compounding Mothod

Silica (SiO2) is an excellent reinforcing filler only second to the carbon black in rubber industry. It is widely used in rubber compounds for tire with high wet skid resistance and low rolling resistance. However, the compatibility between silica and non-polar rubbers, such as natural rubber (NR), is rather poor due to the large amount of strong intermolecular hydrogen bonds exsisted among the silanols on the silica surface, leading to its severe agglomeration and weak interaction between silica and NR. As a result, since there is a lack of homogeneous distribution of silica in the rubber matrix, a dramatic reduction in the mechanical properties of the vulcanizates would be observed. This paper aimed to maximize the filler dispersion in the rubber and the enhancement of rubber-filler interaction for better mechanical properties.The natural rubber/silica (W(NR/SiO2)) composites was prepared by wet compounding technology with liquid natural rubber (LNR), epoxidized natural rubber(ENR-25, ENR-50), silane coupling agent (Si-69, KH-570) as compatibilizer. The Payne effect, glass transition temperature (Tg), silica dispersion morphology in NR matrix, crosslinking densities (XLD), dynamic mechanical properties and mechanical properties of composites were characterized by rubber processing analyzer (RPA),differential scanning calorimetry (DSC), scanning electron microscopy (SEM),nuclear magnetic resonance instrument (NMR), dynamic mechanical analyzer (DMA)and Zwick testing machine. The compatibilizing mechanism for W(NR/SiO2)composites of five kinds of compatibilizers and bonding mechanism between silica and NR were also investigated.The results showed that comprehensive performance of W(NR/SiO2)vulcanizates was optimum when the natural rubber latex concentration was 30 wt%and silica concentration was 20 wt%. Compared with dry mixing method, the mechanical properties of W(NR/SiO2) vulcanizates had significant improvement, the tensile strength and tear strength increased by 32.38% and 13.78% respectively when silica was 60 phr. With liquid natural rubber (LNR) as compatibilizer, the Payne effect is obviously decreased; the silica dispersion significantly improved; when silica is 60 phr, Tg is observed from -56.61? shift to -59.57? and bound rubber content is observed from 40.24% increase to 44.02%; the NNM results show XLD have great enhancements, transverse decay time decrease 4.20 ms, 5.84 ms and 7.86 ms when addition of SiO2 is 30 phr, 50 phr and 70 phr respectively. All of which can be ascribed to the stronger filler-rubber interfacial interaction that silica limites the extensibility of rubber chains. It is reveal that LNR has better compatibility, which is attributed to LNR reaction with both NR and SiO2 to form compatibilizing interface.With epoxidized natural rubber (ENR) as compatibilizer, the compatibilizing effect of ENR-25 is more significant, the Payne effect decreased, XLD and bound rubber content increased, transverse decay time decrease in the presence of ENR. It is revealed that ENR has good compatibility, which contributing to interactions epoxide groups of ENR and Si-OH of silica could form hydrogen bonding and/or chemical bonding leading stronger rubber-filler interaction. With silane coupling agent as compatibilizer, the compatibilizing effect of Si-69 is more significant, the Payne effect decreased, XLD and bound rubber content increased, transverse decay time decrease in the presence of Si-69. In addition, the vulcanizates with five kinds of compatibilizers behaved combination of higher wet skid resistance, lower rolling resistance and higher abrasion resistance performance. The optimal and worse order of five kinds of compatibilizers to improve the wet skid resistance of composite materials as follows: ENR-50 >ENR-25 >Si-69 >KH-570 >LNR; and for lower rolling resistance as follows: Si-69 >ENR-25 >LNR>ENR-50 >KH-570; and for abrasive resistance as follows: Si-69 >ENR-25 >KH-570 >ENR-50 >LNR.Wet compounding method realize the good filler dispersion in the rubber and the use of LNR, ENR and silane coupling agent obtain good compatibility between NR and silica, leading to stronger rubber-filler interaction. The wet compounding process is simple and the vulcanizates has excellent comprehensive performance, especially with a wet resistance and low rolling resistance and can be used as a car tire tread compound, it has great significance to the development of rubber industry.