Deproteinization And Properties Of Natural Rubber

Natural Rubber (NR) is a natural macromolecule that has excellent propertiesand wide range of applications. But a certain amount of proteins, present in the NR, iseasy to make high hygroscopicity and deterioration of heat, electrical conductivity andother properties of NR, especially the emergence of NR products proteins allergyproblems. These problems limit the application of NR in certain areas. On the otherhand, proteins can promote the vulcanization and enhance the anti-thermal oxidationof NR. The low proteins content will result in poor properties of NR that they can’tsatisfy the requirements. In order to balance the two aspects and expand theapplication fields of NR, it’s necessary to prepare the NR with low-protein and high-performance.In this paper, the removal of proteins in NR was carried out by incubation ofnatural rubber latex (NRL) with trypsin and urea in the present of surfactantsrespectively. Low-protein NR was prepared by centrifugation and washing. Thenitrogen content and molecular structure of the raw rubber, mechanical properties,crosslinking network and anti-thermal oxidation of vulcanized rubber were examinedto investigate the effect of the deproteinized process on proteins content andproperties of NR. The mechanical properties, crosslinking network, anti-thermaloxidation and compression set properties of low-protein NR were examined to studythe effect of the proteins content and fillers on the properties of NR.The results showed that the treatment process of urea and trypsin with NRLcould significantly reduce the proteins content in the NR. Compared to urea, trypsincould remove the proteins more effectively. Nitrogen content of the NR, treated withtrypsin, was reduced to0.063%from0.435%under the optimum condition. Betterdeproteinization could be achieved by twice processing with sodium dodecyl sulfate(SDS) during the deproteinizing process. The deproteinizing process only removedthe proteins in the NR without affecting the molecular structure of NR.The treatment process of urea and trypsin with NRL reduced the mechanicalproperties and anti-thermal oxidation of NR. The properties of urea-treated sampleswere superior to the trypsin-treated samples under the condition of the same proteincontent of NR. The tensile strength of urea-treated samples and trypsin-treatedsamples decreased11.9%and17.1%than raw NR respectively, and the tensilestrength retention rates of urea-treated samples and trypsin-treated samples reduced to 74.0%and73.2%respectively after90℃×24h aging.With the decrease of the proteins content of NR, the mechanical properties,crosslinking network and anti-thermal oxidation were gradually decreasing andcompression set was gradually increasing. When the proteins content of NR wasreduced to0.394%, the tensile strength of NR was decreased by30.4%.The improvement of mechanical properties by carbon black (CB) and silica werebetter than any one of the two fillers. The tensile strength of CB-Silica/NRnanocomposites was10.5%higher than CB/NR nanocomposites and12.8%higherthan Silica/NR nanocomposites.