Electric Double Layer Structure Of Nature Rubber And Its Effect On The Stability Of Natural Rubber Latex

Electric Double Layer structure of nature rubber is an important content of the research on surface chemistry of natural rubber colloid system.The improvement of the double layer theory of natural rubber latex has important theoretical and practical role in regulating the stability and flocculation of natural rubber latex.This experimental study combined with the previous research results,through the study of the electric phenomenon of natural rubber latex reveals the characteristics of the double layer structure of natural rubber particles.The natural rubber latex was treated by enzyme decomposition(alkaline protease,lipid enzyme)and high speed centrifugation,combined with the chemical composition,morphological structure and electrokinetic phenomena were studied.To clarify the relationship between the stability of natural latex and the surface protein and lipid,and to test the stability of the natural rubber latex after removing protein or lipid.This article described the principles and methods of ions distribution in the electrical double layer of natural rubber latex particle.The research content mainly includes the study of electrokinetics over a broad range of NaCl electrolyte concentrations(1-100 mmol/L)and pH values(2-9),describe the electric field behavior under the condition,draw the different curves.Secondly,the distribution of surface lipids and proteins on the surface of rubber particles and the effect of the amount of charge were analyzed.Finally,investigated cation(Al3+,Fe3+,Fe2+,Cu2+,Mn2+,Co2+,Ca2+’ Na+)and anion(CH3(CH2)11OSO3-Cl-,NO3-,Br)on the natural latex shielding effect and further improve the natural latex particle surface electric double layer structure model.By means of SEM and TEM to analysis of the interfacial structure of NR particles,we could conclued that the natural rubber were formed by the hydrophobic core and packed by monolayer,which formed by the mixed of protein and lipid.Natural rubber electric double layer structure is provided by surface adsored protein and lipid to have negative charge,positive obtained from metal ions and other non rubber constituents.The surface charged properties of NR latex particles are not only related to the ionization of the surface lipids and proteins,but also with the changes of electrolytes and pH environment.The general situation of natural rubber latex showed negative properties with negative charge,zeta potential is-44.9mV,u is-3.5μm cmV-1s-1.As the concentration of electrolyte NaCl increased from 1.2 to 100mmol/L,point of zero electrophoresis(PZM)from 4.18 to 2.56.This phenomenon is consistent with recently soft particle electrophoresis dynamics theory results,which indicating the presence of anions and cations around the NR particles.PZM is strongly dependent on the concentration of electrolytes,indicating that the electrostatic properties of the NR surface are controlled by the surface lipid protein,in which the effect of the protein on stability is greater than that of the lipid.Natural rubber membrane structure is by a monolayer of mixed lipids-proteins composition,but not bilayer structure.The metal ion content of natural rubber latex was detected by inductively coupled plasma mass spectrometry(ICP-MS).Most of the metal ions are dissolved in the serum phase in a free form,which can be removed by centrifugation.Such as centrifugal nature rubber latex iron ions from 59.07 down to 2.565 μg/g,copper ion by 38.09 fall to 5.17μg/g,magnesium ions decreased from 2258.88 to 160.9 ug/g.The electrokinetic phenomena of natural rubber latex were detected by laser Doppler electrophoresis.With the increasing electrolyte concentration,the negative electrophoretic mobility of natural fresh latex decreased accordingly.Under the same condition of concentration,the order of anionic affect on natural rubber latex’s electrophoretic mobility and conductivity was NaCl>NaBr>NaNO3>SDS(sodium dodecyl sulfate sodium).The descending order of compressing the electric double layer efficiency of metal cation was Al3+>Fe3+>>Fe2+>Cu2+>>Mrn2+>Co2+>Ca2+>Na+.There was a special situation that high metal cations such as copper ions,iron ions and aluminum ions could invert the latex’s charged nature.pH and electrolyte and the Morphology analysis showed that these electrolytes change latex’s pH environment,leading to latex agglomeration,even emulsion breaking.