| Hydrogenated nitrile butadiene rubber(HNBR) is a high-performance rubber with combination of excellent mechanical property, oil resistance, thermal aging resistance, and chemical stability, which can be widely used in diverse applications including mechanics industries, automobile, oil field and chemical industries. Carbon nanotube(CNT) with large aspect ratio, nanometer diameter and other unique structural characteristics, is an important nano filler in rubber industry. In recent years, the study on preparation and properties of HNBR/CNT nanocomposites has become a hot area of research.In this paper, we prepared the HNBR/MWCNT nanocomposites with HNBR as matrix and multi walled carbon nanotubes(MWCNT) as the nano filler. Then, the effect of MWCNT contents, aging time and aging treatment of hot oil on stress-strain, stress softening and stress relaxation of HNBR/MWCNT nanocomposites were investigated. And the HNBR/MWCNT nanocomposites were characterized by FT-IR, TGA, SEM and EDS analysis.First, the Mooney-Rivlin equation and Ogden model were used to study the tensile and compression stress-strain behavior of the composites respectively. It was found that the tensile stress, tensile modulus, compression stress, compressive modulus and compressive strain energy density of the composites were increased along with the MWCNT content increases. The retention rate of tensile or compressive stress and modulus of the aged composites were found to increase with the increase of the amount of carbon nanotubes. Contrast with the aging in uncompressed aging condition, the composites got a lower retention rate of tensile or compressive stress and modulus after aging in compressed aging condition.Secondly, the stress softening of composites during cyclic compression was investigated. The results show that the composites had a higher stress softening with the MWCNT content increased in composites. The stress softening degree of pure vulcanized rubber was 17.34%, while the stress softening degree of composite with 8wt.% MWCNT was 22.82%.The stress softening of composite was decreased after hot oil aging. Additionally, the stress softening degree of compressed aging composite was lower than uncompressed aging one. The stress softening of a composite with 8wt.% MWCNT aged 12 days in hot oil under compression was 15.79%, while, it was 17.65% under uncompressed condition.Then, we built a stress relaxation model which contains three Maxwell elements and a parallel spring for exploration of the physical relaxation behavior of composite materials. The results show that the relaxation time of the composites was decreased with the increasing of the amount of MWCNT in the composites. In addition, the chemical stress relaxation behavior of the composite aged in hot oil under compression was also studied. It was found that the higher the content of carbon nanotubes in the composites, the lower the aging rate constant k of the composites. The K of the composite with 4wt.% MWCNT was 0.300. But, when the content of carbon nanotubes increased to 8wt.%, the K was dropped to 0.206.Finally, the aging characteristics of the composites were characterized by FT-IR, TGA, SEM and EDS analysis. FTIR analysis showed that the HNBR/MWCNT composites have a stable molecular structure. The position, size and shape of the main infrared absorption peak of the composites were basically the same after aged in hot oil with different aging time. TGA analysis showed that the composites have excellent heat resistance. When the composite with MWCNT content of 8wt.% was aged in hot oil for 16 days. The temperature of maximum decomposition rate(Tmax2) which corresponding to the decomposition of rubber molecular chain was decreased by 4.2℃, the decline was only 0.89% compared with the composite before aging. SEM analysis showed that the edge position of aged composite has the roughest surface. EDS analysis revealed that the C elements content in an aged composite was decreased gradually, while the content of O was gradually increased from the inside to the edge position. This indicates that the edge position of the aged composite has the highest degree of oxidation. Furthermore, the O elements content of compressed aging composite was higher than uncompressed aging one in the same position of composite. |
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