Development And Properties Of Easy Processing Natural Rubber/Silica Wet Compound

Natural rubber/silica（NR/SiO₂）composites have been widely used in the field of“green tire”because of their high wet skid resistance,wear resistance and low rolling resistance.There are some defects in the preparation of NR/SiO₂composites by traditional dry mixing,such as complex process,flying dust,environmental pollution and high labor intensity.In addition,the silica in NR/SiO₂composites prepared by dry mixing mainly exists in the form of aggregates,which is difficult to achieve nano dispersion,so its application is limited to a certain extent.The preparation of NR/SiO₂composites by wet refining method can solve these problems.Wet refining method can not only simplify the mixing process,reduce the mixing energy consumption and avoid dust flying.The most important thing is that the wet refining method can make the dispersion of silica in the natural rubber matrix reach the nano level.However,silica in NR/SiO₂wet compound is easy to agglomerate again after dispersion because it contains hydroxyl and epoxy alkyl.At the same time,the isomerization group contained in the molecular chain of natural rubber makes it easy to have branching and crosslinking reaction during the drying and storage of wet compound,which makes NR/SiO₂wet compound still have the disadvantage of high viscosity,resulting in great difficulty in later processing and higher processing energy consumption.In this paper,aiming at the problem that polar groups are easy to agglomerate on the surface of silica,a non-toxic and easy to prepare plasticizer is added in the wet refining method of natural rubber latex and silica slurry to solve this problem.To solve the problem that the molecular chain of natural rubber contains aldehyde groups and is easy to produce branched crosslinking,the natural rubber latex is modified with constant viscosity reagent,and the NR/SiO₂composite is prepared by wet refining method the modified natural rubber latex with silica slurry.Both methods can reduce processing energy consumption and prepare NR/SiO₂wet compound with low Mooney viscosity and good processability.Naphthenic oil（NAP）,a traditional plasticizer,is a petroleum derivative,which is rich in sources and non-toxic.In this paper,nap was emulsified to prepare a uniform emulsion.Theemulsion was mixed with natural rubber latex and silica slurry to prepare composites to reduce processing energy consumption.The effects of naphthenic oil as a plasticizer on Mooney viscosity,physical and mechanical properties,dynamic mechanical properties and silica dispersion of natural rubber/silica composites were studied.According to the experimental data,compared with NR/SiO₂composites,the Mooney viscosity of NAP/NR/SiO₂composites is significantly reduced,the Payne effect is significantly weakened,and the processability is significantly improved.When 10 phr plasticizer NAP was used,the mechanical strength of the composite was less different from that of NR/SiO₂composite,and the elongation at break was significantly increased and the heat and oxygen aging properties and flexural properties of the composite were improved.Functional bio-based plasticizers cardanol and epoxidized soybean oil（ESO）are derivatives of agricultural and sideline products.They have functional groups,phenolic hydroxyl group and epoxy group respectively,which have unique chemical properties.In this study,the plasticizer emulsion was prepared after emulsification,and the composites（Cardanol/NR/SiO₂and ESO/NR/SiO₂）were prepared by wet refining method with natural rubber latex and silica slurry to reduce processing energy consumption.The optimal dosage of functional bio-based plasticizer and its effects on the processing properties,vulcanization properties,physical and mechanical properties,dynamic mechanical properties and silica dispersion of NR/SiO₂composites were explored.The experimental results show that using cardanol and ESO as plasticizers of NR/SiO₂composites can effectively reduce the Mooney viscosity and Payne effect of the composites,reduce the agglomeration of silica and improve the processing properties.Compared with NR/SiO₂composites,the vulcanization speed of cardanol/NR/SiO₂composites is accelerated and the tensile strength is reduced,while the vulcanization speed of ESO/NR/SiO₂composites is slowed down and the tensile strength is improved.Both plasticizers can greatly improve the elongation at break of NR/SiO₂composites and enhance their heat and oxygen aging resistance,flexion resistance and wet slip resistance.The amino group and amide group in the molecular chain of constant viscosity reagent hydroxylamine hydrochloride（HH）and alkyl hydrazine compound（OP）can react with the aldehyde group on the main chain of natural rubber,inhibit the aldol condensation reaction of aldehyde group and reduce the chain branching and crosslinking of natural rubber.In this study,modified NR/SiO₂composites（HH-NR/SiO₂and OP-NR/SiO₂）were prepared by HH,OP viscosity reagent modified natural rubber latex and silica slurry,in order to explore the types and dosage of modifiers and their effects on Mooney viscosity,vulcanization characteristics,physical and mechanical properties,dynamic mechanical properties and dispersion properties of NR/SiO₂composites.The test data show that the modified NR/SiO₂composite has low Mooney viscosity and crosslinking density,weak Payne effect and excellent processability.The vulcanization rate of the modified composite decreased.The mechanical properties of OP-NR/SiO₂composites with 0.1phr and 0.2phr OP and HH-NR/SiO₂composites with 0.1phr HH have been improved,and they have excellent heat and oxygen aging resistance and flexion resistance.At the same time,the dispersion of silica has also been improved.