| Natural rubber is one of the most excellent rubber products with comprehensive properties.It is mainly used in tire industry,especially in rubber hose,belt,conveyor belt,radial tire and rubber shoes.With the development of automobile industry and various rubber-related processing and manufacturing industries,the demand for natural rubber is increasing.Although most of the countries producing natural rubber in the world are located near the equator,the differences in the micro-structure and properties of natural rubber will be affected by regional differences,climate differences and planting latitudes.At present,most studies focus on the comparison of structure and properties between natural rubber and synthetic isoprene rubber,or on the influence of different tapping seasons on the structure and properties of natural rubber in the same region.However,few studies have been reported on natural rubber produced in different regions.Four kinds of 20#standard natural rubber are selected from Malaysia,India,Thailand and China,hereinafter referred as SMR,SIR,STR and SCR respectively.The structure and properties were studied.The results showed that the order of zero shear viscosity of natural rubber from different regions was SIR>SMR>STR>SCR,so it could be inferred that the order of molecular weight was SIR>SMR>STR>SCR.The thermogravimetric curves of natural rubber in different regions were smooth,with only one step.The temperature of decomposition was about 200℃,and the temperature of intense decomposition was about 350℃.The molecular chains of four natural gums from different regions have different CH3/CH2 groups,and the order of 3,4 isomer content was:STR>SIR>SMR>SCR.The melting curves of the natural rubber after isothermal crystallization at-25℃show obvious double peaks.The crystallization has two crystalline forms of alpha and beta.The order of crystallinity was:SMR>SIR>SCR>STR,and the order of crystallization speed was:SIR>SMR>SCR>STR.The order of self-reinforcing ability of four natural rubber was:SCR>SMR>SIR>STR.The glass transition temperatures of SMR and SCR are higher than those of SIR and STR.When the same amount of carbon black（50 phr）was filled in the natural rubber from different regions,the dispersion of carbon black in the blend was as follows:the dispersion of carbon black was the best in SMR,followed by STR and SIR,and the worst in SCR.The order of interaction strength between carbon black and natural rubber is STR>SIR>SMR>SCR,and the comprehensive mechanical properties of SMR vulcanizate were the best,and STR vulcanizate has high elongation at break.When the same amount of CNT（5 phr）was filled in natural rubber from different regions,the dispersion of CNT was different from that of carbon black.The dispersion of CNT was the best in SMR,followed by STR and SIR,and the worst in SCR.The comprehensive mechanical properties of SMR vulcanizates were the best,followed by SIR,SCR and STR,but the elongation at break of SCR and STR vulcanizates was higher.Four kinds of dispersants were added to SMR natural rubber with excellent properties,and it was found that carbon black had the best dispersibility in SMR rubber without dispersant.It showed that dispersant was a kind of processing aid,reducing Mooney value,but it was not helpful to the uniform dispersion of fillers.The physical and mechanical properties of SMR vulcanizate did not improve after adding dispersant,but decreased. |
