Extraction And Analysis Of Water-soluble Substance In Natural Rubber Latex And Its Effects On Properties Of Narural Rubber

The aim of this paper is mainly to study the composition of small-molecular-weight water-soluble substance (s-WSS) and its effects on the properties of natural rubber films. Small-molecular-weight water-soluble substance was obtained from fresh natural rubber latex by a series of procedures such as separating the fresh natural rubber latex by the hollow fiber with a cut-off molecular weight10000. The extracted s-WSS was proved that it was very pure after the small-molecular-weight water-soluble substance was detected by gas chromatography. The content of water-soluble substance in natural rubber latex was2.4%. The content of small-molecular-weight water-soluble substance and water-soluble proteins was2.18%and0.22%According to the analysis of IR, it can be known that the main elements of small-molecular-weight water-soluble substance are C, H and O. While the main functional groups of s-WSS are hydroxyl and the main components of s-WSS are alcohols. According to the analysis of s-WSS from IR and HPLC-MS, it is conjectured that small-molecular-weight water-soluble substance (not including sugar) is composed of C3H4N4O6, C7H14O6, C11H13N3O5, C11H20O7and C6H22N8Small-molecular-weight water-soluble substance in natural rubber latex contains several kinds of metal ions and they were analyzed by ICP-MS. The concentrations of several kinds of metal ions in natural rubber latex are ferric irons (217μg/L), manganese irons (454μg/L), copper irons (592μg/L), magnesium irons (244μg/L) and calcium irons (6366(j.g/L). Anions in natural rubber latex was analyzed by ion chromatography. The content of Cl-+, NO3-, PO43-and SO42-in the natural rubber latex is2.5ppm,5.9ppm,59.1ppm and90.9ppm.The tensile properties and tear properties were measured using the Electromechanical Universal Testing Machine. The tensile strength of the prepared composites can be increased at first and then decreased by adding s-WSS into natural rubber. And the highest value in tensile strength reached at1wt%loading of s-WSS. The tear strength of the prepared composites can be improved by adding s-WSS into natural rubber. It showed moderate increase when s-WSS content is increased to2wt.%. However, the tear strength of the sample containing3wt%s-WSS s is improved by about30%compared with the sample without adding s-WSS. The elongation at break of the prepared composites decreased by adding s-WSS into natural rubber. The tensile strength of natural rubber films after thermal oxidative aging decreases with the content of s-WSS in natural rubber films increasing. The tear strength of the prepared composites after thermal oxidative aging increased markedly and then decreased by adding s-WSS into natural rubber. The elongation at break of the prepared composites after thermal oxidative aging decreased by adding s-WSS into natural rubber.The effects of small-molecular-weight water-soluble substance on dynamic performance of natural rubber films was analyzed by dynamic mechanical analyzer (DMA) and rubber process analyzer (RPA). Based on the experimental results of DMA, it could be known that the storage modulus of natural rubber films decreased at first and then increased with the content of s-WSS increasing in glassy state. In glassy transition, the storage modulus of all the films decreased markedly and the peak temperature of loss modulus increased after adding s-WSS to natural rubber films. In rubbery state, the storage modulus of all the films continued to decrease at first and then reached to a stable value with the temperature increasing. The peak values of tanδ decreased after adding s-WSS to natural rubber films. According to the experimental results of RPA, the storage modulus of all the films increased with the frequency increasing and the loss factors changed little. The storage modulus of all the films decreased with the strain increasing. The storage modulus changed little in temperature range60to90℃and the curves of tan5were flat. The storage modulus increased at first and then decreased in temperature range90to120℃and there was a peak in every curve of tanδ.The thermal oxidation degradation of the natural rubber films was analyzed by Thermogravimetric Analysis. It can be known that s-WSS can lead lower initial degradation temperature and the bigger degradation temperature range of the two stages. Therefore, the s-WSS in natural rubber latex promote the thermal oxidation degradation of natural rubber films.