| As a good elastic material,natural rubber has many excellent features such as high elasticity,high strength,good insulation and the like,and is widely used in the fields of tires,hoses,rubber gloves,conveyors and the like,and it plays an increasing-ly important role in our life.However,due to the influence factors such as the collec-tion place of natural latex and the processing mode,the study of natural rubber main-ly focuses on the varieties of rubber trees,the system of rubber tapping,the solidifica-tion and the production process.There are few reports on the research of natural rubbers in different seasons and different areas.Based on the previous researches,this paper has made a preliminary exploration on the processability,dynamic mechanical properties and aging properties of natural rubbers.The microstructure and properties of natural rubbers in different seasons and in different areas have been systematically studied.The main work done in this paper and the research results obtained are as follows:(1)The molecular weight and processability of natural rubber were characterized by Mooney viscometer,GPC gel permeation chromatograph,Ubbelohde viscometer,Wallace rapid plastometer,VMA flow analyzer,RPA2000,and the test conditions of RPA the study.The results showed that the molecular weight measured by gel permeation chromatography,the viscosity average molecular weight measured by Ubbelohde viscometer,the plasticity measured by rapid plasticity index P0,the flow index measured by VMA,the elastic modulus G 'measured by RPA,Loss factor tan ?,stress relaxation coefficient can be used to characterize the molecular weight of natura-l rubber,with good correlation between each other.The elastic modulus G ',loss factor tan ?,stress relaxation coefficient by RPA and plasticity P0 determined by rapid plasticity index can be well reflected the processability of natural rubber,and the test is fast and convenient.And RPA strain sweep at 120 ?,0.1HZ,the difference of two natural rubber SCRWF and SCR20 elastic modulus G 'and loss factor tan? is the largest;The difference between the elastic modulus G 'and the loss factor tan? of the two natural rubbers SCRWF and SCR20 is the largest at 120 ?,while the strain has little effect on the loss factor tan? and the elastic modulus G' of frequency sweep.(2)The effects of molecular weight,carbon black dosage,carbon black type,accelerator dosage,stearic acid dosage and aging time on the dynamic mechanical properties of natural rubber were studied.The results show that the low molecular weight crude rubber is slightly better than the high molecular weight rubber in wet skid resistance.However,to reduce the tire rolling resistance and energy consumption,the molecular weight of raw rubber should be appropriate;With the increase of the amount of carbon black,the peak value of tan? of the vulcanizates decreases,while the tan ? of the vulcanizates increases with the amount of carbon black in the high elastic state;The tan? peak of the vulcanizates increases with the increase of the particle size of carbon black,while the tan ? of the high-modulus vulcanizates decreases with the increase of the size of the carbon black;As the zinc oxide content increases,the peak value of tan ? decreases,while the tan? value of the vulcanizate in the high-elastic state increases as the zinc oxide content increases;The glass transition temperature Tg of the vulcanizates after aging in the glass transition region is slightly larger,and the loss factor tan? of the highly elastic vulcanizates decreases first and then increases as the aging time increases.(3)The characterization of aging properties of natural rubber was studied.The results show that the ratio of the elastic modulus G 'of the natural rubber before and after aging has a good correlation with the anti-oxidation index PRI,and the ratio of the elastic modulus G' before and after aging under low strain is similar to the value of the anti-oxidation index PRI equal.In the process of aging,the natural rubber undergoes redox reaction to form hydroxyl,peroxide,ether,ester and other structures,and the gel content and cross-linking density XLD are reduced.The rubber molecular weight MC at the cross-linking point increases and the longitudinal relaxation time T2 decreases.And the aging properties of the natural rubber gel content reduction and crosslinking density reduction is greater than the anti-aging ability of good natural rubber.(4)The microstructure and physical mechanical properties of natural rubbers in different seasons were studied.The results showed that in summer,the natural latex had the narrowest particle size distribution,the smallest average particle size,the highest total solids content and dry rubber content,and the highest average molecular weight.In winter,the natural latex has the widest particle size distribution,the largest average particle size,the lowest total and dry gum content,the smallest average molecular weight,and the natural elemental latex has the highest nitrogen element content,the highest PRI,the best thermal stability,followed by autumn,winter;DMA test showed that natural rubber had the lowest roll resistance in summer,followed by autumn and winter with the highest rolling resistance.On the other hand,winter natural rubber had the best wet slip resistance,followed by autumn and winter natural rubber with the worst wet slip resistance.(5)The microstructure and physical mechanical properties of natural rubber from different areas were studied.A low resistance to rolling,high resistance to slipping vu-lcanizates was obtained by blending Myanmar gum with northern Thailand rubber and the two natural rubbers were optimized in the tread rubber.Malaysian standard rubber 3# has the best processability,followed by Myanmar standard rubber 4#,southern Tha-iland standard rubber 2#,northern Thailandr standard rubber 1#,and domestic full latex 5#.;In terms of mechanical properties,Malaysian Standard rubber 3# and North Thailand Standard rubber 1# have the highest tensile and tensile strengths and the best wear resistance;The domestic full latex 5# has the lowest tensile stress and tensile strength and the worst wear resistance,but it has the best elasticity and tear resistance;The DMA test showed that Malaysian standard rubber 3# and Myanmar standard rubber 4# had the best wet skid resistance,and domestic full latex5# had the worst wet skid resistance;The rolling resistance of Malaysia standard rubber 3#,Myanmar standard rubber 4#,and South Thailand standard rubber 2# are approximately equal,and the rolling resistance of domestic full latex 5# is minimal.Myanmar standard rubber 4# is mixed with standard rubber 1# in northern Thailand.When the combined ratio is 4-6,the dynamic mechanical properties are optimal.(6)The influence of different mastication times on the plasticity and mechanical properties of natural rubber was studied.When the number of mastication is 10 times,20 times,30 times,the Thailand rubber and domestic rubber Mooney viscosity,P0 value of plasticity decline the fastest,slow down after 30 times;The result of RPA strain scanning showed that the value of G 'of natural rubber decreased with the increase of plasticizing frequency and the tan? of loss modulus increased with the increase of plasticizing frequency;With the increase of mastication frequency,the mixture release temperature decreased,the Payne effect gradually weakened,and the Payne effect of domestic rubber became more significant;In terms of mechanical properties,the tensile stress of natural rubber in Thailand is generally slightly larger than that of domestic rubber.Thailand natural rubber over the roller 20 times the tensile strength reached a maximum of 23.53 Mpa,while the domestic plastic over the roller 30 to reach the maximum value of 22.76 Mpa. |
PDF Full Text Request