Study On Thermal Oxidation Resistance Of Epoxidized Natural Rubber

Epoxidized natural rubber (ENR) is a newly rubber, which is gained by epoxidation of natural rubber (NR) employing performic or peracetic acid. ENR shows low gas permeability, excellent oil resistance, and good anti-wet skid resistance, coupled with highly damping properties, but ENR has poor aging resistance because of acid-catalysed ring-opening reaction of expoxide groups in the aging of ENR.In the paper, semi-efficient vulcanization (semi-EV) and epoxidized natural rubber having25mol%of epoxidation (ENR25) were used throughout the study. The effects of calcium stearate loading, types of antioxidants and lanthanum stearate (LaSt) loading on vulcanization characteristics, cure kinetics, crosslink densities, mechniacal properties and thermal stability of ENR25were investigated. The anti-aging mechanism of ENR25was studied by thermogravimetric analysis (TGA) and Fourier Transformation Infrared Spectrum (FTIR).The results of study on the effect of calcium stearate concentration on properties of ENR25show that the incorporation of calcium stearate could accelerate the vulcanization of ENR25; the ENR25culcanizates with lphr calcium stearate shows the best mechanical properties; the thermal-oxidative resistance of ENR25vulcanizates with increasing loading of calcium stearate.The results of study on the effect of types of antioxidants on properties of ENR25show that MB could accelerate the vulcanization of ENR25obviously and has the best mechanical properties; the ENR25vulcanizats with antioxidant4020gives the best thermal-oxidative resistance, better thermal stability and mechanical property.The results of study on the effect of LaSt loading on properties of ENR25show the incorporation of LaSt could accelerate the vulcanization of ENR25; with the increasing loading of LaSt, the crosslink density of ENR25vulcanizates decreases, but the tensile propertiy increases, and the ENR25vulcanizates with the addition of lphr LaSt has the highest tensile property due to some "instantaneous complex" produced in the tensile process of ENR25. The result of TGA shows that the ENR25vulcanizates with the incorporation of0.5phr LaSt has the best thermal-oxidative resistance and better thermal stability. The NdSt exerts significant oxidation-resistant effect in ENR25vulcanizates in three ways.(1) NdSt ions can capture free radicals during the process of autoxidation, thus make the chain reaction discontinue and inhabit the autoxidation process.(2) Secondly, the complex structure formed in the ENR25vulcanization because of complexation of Nd ions can make the oxidation difficulty to go on.(3)The coordination between oxygen atom and Nd ions can form chelate to improve the stability of expoxide groups. The comparation of the effect of LaSt and antioxidants on aging resistance of ENR25was studied. It is shown that the antioxidative property was superior to that of antioxidant RD,4010N A and MB, but it was not superior to that of antioxidant4020. Thermal stability of ENR25with LaSt was better than antioxidant RD,4010NA, MB and4020.