| The molecular structure and component of natural rubber changes with the different production process., so its mechanical properties as well as their resistance to ozone aging do. The differences of natural rubber (NR) in nitrogen content, Po, PRI, processing performance, crosslink density, dynamic mechanical properties and properties of resistance to ozone aging were explored under7production processes with different solidification methods and different drying method. TGA and FTIR were used to study the changes of thermal stability and functional groups after NR ozone aging. On this basis, the effects of different non-rubber components(protein, acetone soluble matter,water-soluble material)on NR ozone resistance were studied. It lays a theoretical and experimental foundation through a series of discussion for the production of high-performance ozone resistance NR.When studying the production process, it was found that natural rubber has a low nitrogen content and the tensile strength and tear strength was up to25.62MPa and30.70MPa respectively after microorganisms solidification. They were superior to other processes. As the same time, its thermal aging property was worse than acid solidified and its variation rate of mechanical properties was only7.9%after aging for8h under a ozone concentration of50pphm. Its ozone cracking time was up to945min which was much higher than other production processes.. It had an excellent thermal stability. The thermal degradation temperature of the process was higher than others, the cross-linking density and DMA tests results showed that NR’s Mq was minimum in this process and its crosslinking points were more than others. The glass transition temperature(Tg) increased by about6℃. Its resistance to wet ski and rolling resistance did not have a significant change. With the extension of ozone aging time, the unsaturated double bond on NR molecular chain reduced gradually, and the corresponding carbonyl groups increased, indicating that the reaction of ozone with NR mainly occurred on the main chain.It was found that, the nitrogen content of NR decreased with the increase of the amount of the enzyme subtilisin. While its mechanical properties rised first and then falled. When the enzyme dosage was0.15%, it showed a best performance available to20.3MPa during reducing the content of protein. Protein has an important impact on the anti-aging properties of natural rubber, and lower content of protein could improve its anti-aging ability. However, its specificity would be broken no matter how much content of protein it reduced. Comparing LPNR before and after ozone aging and thermal aging, it was found that protein played a significant role in the anti-aging process and the anti-aging ability increased with the content of protein partly reduced. Besides, the RPA analysis results also showed that the elastic modulus could be improved and the loss factor could be reduced with the content of protein partly reduced. The crosslink density and DMA tests results showed that, when the enzyme dosage was0.15%, the crosslink density is the maximum. At this time, Tg of NR was littlely changed, the tanδ of NR became lower in0℃and50-80℃compared with the blank, which is effectively explained that lower protein help to improve their resistance to wet abrasion resistance and reduce losses. The FTIR analysis could be better able to explain the protein act in the reaction during ozone aging.NR-CW experiment well proved that water-soluble material had a great influence on the mechanical properties of NR. However, it only reduced the properties of NR with thermal aging and almost had no effect on the ozone aging. The crosslinking density and elastic modulus were effectively reduced when reducing water-soluble materials. So did Tg. The FTIR analysis can more effectively prove that water-soluble material had little effect on the ozone resistance NR.NR-CA experiments further demonstrated that acetone insoluble played a important role in promoting cross-linking reaction.With acetone solubles decreased, the mechanical properties of NR-CA decreasd. The variation of mechanical properties could be reduced to as large as70.25%after thermal aging. Although the NR-CA obviously declined in mechanical properties after ozone aging, the variation rate of mechanical properties were almost identical. There is no significant change compared with the blank. The reduction of acetone insolubles can reduce the elastic modulus of NR and its crosslink density was also decreased greatly. At the same time, Tg of NR rised, the range of NR-CA’s Tg was narrow. Its tan8also increased at0℃and at50-80℃compared with the blank. Amines participated in the anti-aging ozone reaction and generated-NO2containing compound by FTIR. |
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