The Devulcanization Technology Of Waste Tire Rubber In Supercritical Fluid

The waste tire rubber is difficult to degrade in natural environment and pollute the environment. There are huge demands for rubber resources in our country, and it needs to recycle of waste tire rubber to alleviate pressure on domestic demand. Supercritical fluid has been widely concerned in the degradation of waste tire rubber due to the features of high solubility, high diffusivity and permeability. But there is less research on the application of supercritical fluid to recyle the actual waste tire rubber and the establishment of a set of feasible technology scheme. In thisthesis, waste tire rubber was devulcanized using supercritical fluid as medium. The optimal technological condition of devulcanization of waste tire rubber and the property change of the reclaimed rubber were studied under the condition of different medium and different devulcanized agent, and a set of feasible analysis theory and method was provided. The main research contents are as follows:(1)Waste tire rubber was devulcanized with supercritical carbon dioxide as a medium and diphenyl disulfide (DD) as devulcanized regent. The optimal conditions of devulcanization were obtained by experiment:reaction temperature240℃, reaction pressure15MPa, reaction time2h and the amount of DD25%. Under this condition, the sol content is54.14%, and the number average molecular weight is15164g/mol, and the polydispersity is1.855. Analysis showed that the thermal stability increased and Tg increased60-70℃after devulcanization. The main chain and crosslinking network was interrupted and the agglomeration in the rubber due to the crosslinking of the waste tire rubber disappeared. The conclusions from mechanism analysis were that the main factors influencing the main chain rupture was the reaction temperature, and the main role of the devulcanized agent was to interrupt crosslinking.(2)The devulcanization efficiency of the waste tire rubber with supercritical carbon dioxide as a medium and2,2’-dibenzamidodiphenyldisulphide(DBD) as devulcanized regent was studied, and compared with the results using DD as devulcanized agent. Results show that the devulcanization efficiency using DBD had a gap with using DD as devulcanized agent in supercritical carbon dioxide. The optimal conditions of devulcanizationare as follows: reaction temperature240℃, reaction pressure18MPa, reaction time3h and the amount of DBD10%. Analysis shows that Tg of reclaimed rubber increased about20℃, which was less than the change of product’s Tg using DD as devulcanized agent. After reaction, the amide group attached to the rubber molecules. DBD was good at interrupting multi-sulfide bonds.(3) The devulcanization efficiency of waste tire rubber is better using supercritical ethanol as the medium. The optimal conditions of devulcanization are as follows:reaction temperature270℃, reaction pressure9MPa, and reaction time1h. Under this condition, the sol content was59.56%, and the number average molecular weight was38235g/mol, and the polydispersity was1.99. Adding devulcanized agent DD could promote the degradation of tire rubber, and the effort was more obvious in the low reaction temperature. Analysis shows that the main reactant was natural rubber in the degradation process of tire rubber. After devulcanization, the thermal stability increased and Tg increased about30℃, and multi-sulfide bonds and disulfide bonds changed into mono-sulfide bonds. The fracture of main chain was less, and the molecular weight of sol fraction was higher. At the same time, the advantages and disadvangtages of supercritical carbon dioxide and supercritical ethanol in rubber devulcanization were compared.