| Natural rubber latex is not only a kind of renewable strategic resource,but also the important industrial raw material for national economy.The natural latex obtaining from rubber trees,is vulnerable to enzymes,metal ion and bacteria,leading to the deterioration,and hence affecting the quality of the rubber products.In order to slow down the deterioration process,the inclusion of preservatives into latex is an effective method.Nowadays,ammonia is a conventional preservative for fresh natural rubber latex,and the combination of TMTD/ZnO and ammonia are the traditional preservatives for concentrated rubber latex.Notably,the preservation effect of ammonia for latex can hardly meet the factory needs.This is because that ammonia has the disadvantages,such as effumability,strong stimulation,and the environmental pollution.Therefore,the research and development of a new type of natural rubber latex without ammonia or low ammonia storage system has become a hot research topic.To date,some preservatives,such as fomaldehyde,sodium sulfite,hydrogen peroxide,and chitosan,have been reported for the application in natural rubber latex,unfortunately,there is not a kind of preservatives applied in the production.In this experiment,zinc sulfate and self-made preservatives A have been chosen for the preservation of fresh natural rubber latex,and self-made combined preservatives A3,compound preservatives B3 of concentrated natural rubber latex,respectively.The aim is to solve the problem of the preservation time of ammonia and to explore the new preservation system of natural rubber latex.Research contents including efFect of preservatives types and amount on latex VFA value,pH value,potential and particle size distribution,viscosity,mechanicalstability and thermal stability of colloidal properties.Effect of preservatives types on the six indicators,rubber thermal degradation temperature and glass transition temperature.Effects of preservatives types on tensile strength,tear strength and other mechanical properties of vulcanized rubber.The effect of inorganic salts preservatives on fresh natural latex shows that with 0.1%zinc sulfate on fresh latex,the VFA value of fresh latex is gradually increased,but the rate of increase is less than that of ammonium carbonate,zinc acetate and ammonia hydroxide.When the fresh latex is preserved with zinc sulfate,16 hours later,VFA value of latex is only 0.093.According to the analysis of the bacterial colonies in the plastic film,when latex is preserved with zinc sulfate and ammonia,the bacterial colonies of the former are less than the latter,which means as latex preservative,zinc sulfate is better than ammonia.Malvin particle size analyzer is used to analyze the stability of the latex.The latex potential value is-34.1mV,which means the latex is in stable condition.Vulcanized latex made by Zinc sulfate preserved latex shows excellent processing performance.ATR-FTIR spectrum analysis shows that the characteristic peaks of the zinc sulfate and ammonia hydroxide preserved latex are similar,and that means using zinc sulfate as preservative will not destroy the molecular chain structure of the latex.The effect of self-made preservatives A on the preservation of fresh latex shows that the higher concentration of A,the lower VFA of latex.When the fresh latex is preserved with A,60 hours later,VFA value of latex is 0.047,lower than that of fresh latex preserved by 0.3%ammonia,which VFA value is 1.136.Malvin particle size analyzer is used to analyze the particle size of latex.The average particle size value of A is lower than that of ammonia,which value is 20nm.That means the stability of latex preserved by A is good.Compared with vulcanized latex made by ammonia preserved latex,A preserved latex has 0.01%less impurity,0.03%less ash content,and higher Po and PRI value.That means A can improve latex aging resistance performance.DSC analysis shows that the Tg of latex preserved by A and ammonia are-63℃ and-62℃,which means the frozen chain segment initial movement temperature of these two kinds of latex is similar.According to the effect of compound preservatives on the preservation of concentrated latex,VFA values of latex preserved by the compound preservative A3 and B3 are 0.035 and 0.033 after 90 days.Both of them are lower than that of ammonia.Their viscosity is 36mpa.s and 41mpa.s.Both their mechanical stability time is more than 650s.SEM analysis shows that latex particles are complete and no emulsification is found,which means A3 and B3 keep good stability of latex.Compared with ammonia,they respectively have 28%and 42%higher of tensile strength,12%and 4%higher of tear strength.The research has showed that zinc sulfate is good for fresh natural latex preservation and can effectively keep its stability.Also zinc sulfate is more effective on bacteriostatic action than ammonia.Self-made preservatives A helps improve latex aging resistance performance.Concentrated latex preserved by compound preservatives A3 and B3 meet the industrial production requirements,and the mechanical properties of the vulcanized latex are excellent.The research provides theoretical basis for the application of new preservatives in the production,which is of great significance in latex preservation and worthy of further industrial development. |
