Preparation And Properties Of Vacuum Coagulated Natural Rubber

Natural rubber?NR?is a polymer compound with excellent comprehensive properties.Which main component is cis-1,4-polyisoprene.It is a very important industrial raw material and it is used in production and life widely.The performance of NR is closely related to the processing of latex.Coagulation of natural rubber relax?NRL?plays an important role in the processing.This study use vacuum to coagulated natural latex,comparing natural coagulation and acid coagulation,to explore the effects of vacuum degree,latex concentration on physical and chemical properties of natural rubber,Mooney viscosity,molecular weight and its distribution,thermal stability,vulcanizated characteristics,crosslink density,mechanical properties.The processing performance of rubber obtained by different solidification methods was analyzed by rubber processing instrument.The relationship between vulcanized rubber structure and physical and mechanical properties was analyzed by NMR,crosslinking density meter and tensile testing machine.The dynamics of vulcanizate was analyzed by DMA Test.The experimental results show that the performance of NR has certain differences with the degree of vacuum.With the increase of the vacuum degree,the nitrogen content of NR first decreased and then increased.When the vacuum degree was-0.95 MPa,the natural rubber had the lowest nitrogen content,the plastic retention rate?PRI?gradually increases with the increase of vacuum degree,and the highest reaches 85%.With the increase of the vacuum degree,the molecular weight of the samples prepared by different vacuum degrees showed a bimodal distribution.From the viewpoint of vulcanizated rates VC1 and VC2.The crosslinking density of NR decreases with the increase vacuum degree,and the relative molecular mass between adjacent crosslinks increases.As the vacuum degree increases,the tensile strength of the vulcanizate increases slightly.Study shows that the nitrogen content of natural rubber increased and the ash content increased as the concentration of latex increased through exploring the effects of different concentrations on the properties of vacuum-coagulated NRL.Plastic initial value?P₀?did not change much,and the PRI decreased as the latex concentration increased,it indicates that NR has better aging resistance when the latex concentration is lower than 26%within the latex concentration range studied.When the latex concentration is 28%,the Mooney viscosity of NR is the largest.As the concentration increases,the crosslink density decreases first and then increases and the tensile strength of NR decreases.The vulcanization rate of the compound is faster with the concentration decreasing.When the concentration of the latex is 24%,the tensile strength is 20.37 MPa,and the 100%modulus and 300%modulus have little change,the elongation at break is at most 843%and the tear strength is at most 30.07kN/m.Through the discussion of vacuum degree and latex concentration,vacuum coagulation was carried out the best coagulation process was vacuum degree of-0.95MPa and latex concentration of 24%.At the same time,the effects of different coagulated methods on the properties of natural rubber were investigated by comparing acid coagulalion and natural coagulation.Studies have shown that the nitrogen content and ash content ofnatural coagulated rubber?NR-n?are higher than vacuum coagulated rubber?NR-v?,higher than acid coagulated rubber?NR-a?,PRI of NR-v is the largest for physical and chemical properties.The glass transition temperature?T_g?of the NR-vis lower than that of the NR-n,and is lower than that of the NR-a.Strain scanning,frequency scanning and temperature scaning of NR made by three different solidification methods are carried out:the elastic modulus?G'?of NR-v<NR-NR-a.The loss factor?tan??of NR-v>NR-n>NR-a,so the NR-v has the best processing performance,followed by the NR-n,and the NR-a is the worst,NR-v has a faster vulcanization rate.NR-a has the lowest crosslink density,and the NR-v has the highest crosslink density.From the viewpoint of physical and mechanical properties,the tensile strength and elongation at break of NR-v are higher than those of NR-n and NR-a.The dynamic mechanical property test shows that tan? of the NR-v and the NR-In is higher than that of the NR-a.The storage modulus of the sample prepared by different coagulation methods is basically consistent with the temperature change trend.When the temperature is low,the storage modulus?E'?of the vulcanized rubberobtained by natural coagulation is the highest,the NR-v is second,and the NR-a is the lowest.