| Natural rubber(NR),which is the biosynthetic natural polymer with excellent comprehensive performance,is an irreplaceable strategic material.NR with complex ingredients contains rubber hydrocarbon and non-rubber components(proteins,lipids,water-soluble substances,acetone soluble substances and mineral salts).The kinds and content of NR ingredients depend on cultivation factors,such as cultivated species,seasons,age of rubber trees,tapping modes,planting soil,fertilizers,etc.These changes of rubber ingredients can result in NR with different properties.Therefore,it is very significant for us to study the effect of cultivation factors on the properties of NR.The main results of this paper are as following.(1)RRIM600,7-33-97,PR107,8-79 hevea clone,and polyploid hevea clone with the same tree age are chosen as the research objects.The results show that the contents of total solid and dry rubber are highest for the polyploid hevea clone.7-33-97 hevea clone has higher ash content and N content and PR107 specie has higher impurity content,acetone soluble substances content and volatile fatty acids content.RRIM600 hevea clone has higher P0,mooney viscosity,gel content and molecular weight,compared with other species.In addition,RRIM600 hevea clone with the greatest maximum torque and minimum torque owns the shortest vulcanization time and scorch time.These show that RRIM600 hevea clone has shorter vulcanization time and faster vulcanization rate.RRIM600 hevea clone owns the highest tensile strength and tear strength.The thermal degradation reaction of all research object is one-step reaction.PR107 hevea clone has the best thermal stability and its thermal degradation reaction is completely.PR107 hevea clone has the highest crosslinking density.(2)The properties of RRIM600 specie young rubber trees and RRIM600 specie old rubber trees are investigated.The results show that total solid content and dry rubber content of old rubber trees are higher than that of young rubber trees.During tapping period,NR latex concentration decreases nonlinearly with increase of tapping time and the size distribution of latex is unimodal.The properties of RRIM600 specie rubber materials catch up with that of No.5 standard rubber.RRIM600 specie young rubber trees have better plasticity.The tensile strength and tear strength of rubber materials from RRIM600 specie old rubber trees obtained at August are best and that of RRIM600 specie young rubber trees obtained at July are best.The thermal stability of NR materials from RRIM600 specie old rubber trees is better than that from RRIM600 specie young rubber trees.(3)The properties of RRIM600 specie rubber trees with ethrel stimulation and RRIM600 specie rubber trees without ethrel stimulation are investigated.The results exhibit that NR latex concentration,surface tension and particle size decrease with the increase of tapping period.NR latex with ethrel stimulation shows larger average particle size,compared with NR latex without ethrel stimulation.NR from early stage of tapping has higher molecular weight and gel content than NR from late stage of tapping.NR from medium term of tapping owns stable vulcanization time and the difference between maximum torque and minimum torque.NR from medium term of tapping shows higher mechanical properties.NR latex from late stage of tapping shows lower thermal stability.(4)The natural rubber of PR107 strain rubber tree was obtained by tapping with 2%ethephon and micro cutting with different concentrations of ethylene gas.The colloidal properties,raw rubber properties,rubber structure,processability and mechanical properties of the obtained NRL were analyzed.Stimulating rubber tapping can increase the concentration of latex and thus increase the output of rubber.Among them,the dry rubber content of 20% ethylene Spunlaced latex is high,and the content of non rubber components,calcium ions,magnesium ions and volatile fatty acids is the lowest among 20% ethylene Spunlaced latex.In addition,the colloidal stability of latex is good.In general,the low concentration gas tapping method is worth popularizing.Gas cutting can improve the oxidation resistance of rubber samples,mainly because the PRI values of 20%etgnr and30%etgnr are larger;Low concentration stimulation treatment can effectively improve the aging properties of vulcanized natural rubber.Stimulation treatment can improve the hardness of the compound,reduce the fluidity of the rubber material and reduce the crosslinking density of the vulcanizate.The molecular weight of NR treated with different stimuli decreased,the molecular weight distribution coefficient increased,and the crosslinking density decreased;The branching degree of NR obtained by conventional tapping is higher than that obtained by gas pricking micro cutting;The elastic modulus and activation energy of NR treated by stimulation decreased,the flow index of rubber increased,and the fluidity of NR improved. |
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