Study On Thermo-oxidative Reclamation Of Waste Tire Rubber And Its Application

China has rapidly developed into the largest rubber manufacturing and consuming country,resulting in a large amount of waste rubber.If these waste rubbers are improperly treated,they will have a bad impact on the environment.Recycling the waste rubbers into new materials not only helps protect the environment,but also alleviates the shortage of resources in our country.The traditional recycling method of waste rubber is to break only the cross-linked bonds in the rubber network under an inert atmosphere,but keep the main chain intact.The reclaimed rubber is still a filler with dozens of microns due to the low degree of reclamation.However,the industrial production by the traditional recycling methods is often accompanied by serious“secondary pollution”and high energy consumption process（～800 k W?h/t）,which seriously restricts the development of these recycling method.Therefore,it is of great significance to develop green and efficient recycling methods for waste rubber to achieve carbon peak and neutrality goals.In this paper,the typical tire rubber natural rubber（NR）and styrene butadiene rubber（SBR）were selected as the research objects.Based on the main chain and cross-linked sulfur bond prone to thermo-oxidative reaction,a high-efficiency thermo-oxidative reclaiming method of waste tire rubber was developed.The main chain and cross-linked sulfur bond were broken by adjusting the thermo-oxidative reaction conditions to prepare deep reclaimed rubber（sol content>40%）.Then,the internal（structure of rubber network,reaction sites,etc.）and external factors of thermal oxygen reaction of tire rubber were studied.The effects of temperature,oil,atmosphere and initiator on the reclaiming were explored.Finally,the reclaimed rubber was used to prepare rubber products and road asphalt,and its application performance was evaluated.Firstly,natural rubber（NR）and styrene butadiene rubber（SBR）were token as the research objects,which were the main component of tire rubber.The weight loss rate and the sol content of NR vulcanizate increased in air atmosphere compared with nitrogen atmosphere.The turning point of thermo-oxidative reclamation was obtained when the reaction time was about 7.5 min at 240℃.After thermo-oxidative reclamation,the sol content of NR vulcanizates significantly increased,its molecular weight decreased and its distribution became narrow,accompanied by the release of sulfur dioxide（SO₂）and carbon containing oxide gases.It indicated that the oxidative breakdown of the crosslinks and main chain successively occurred,leading to the rapid destruction of the crosslinked network.Different from NR vulcanizates,SBR vulcanizates has obvious carbonization phenomenon at 240℃.At 150℃and 210℃,the sol content of SBR vulcanizates gradually increased at the initial stage of thermo-oxidative reclamation,and then decreased after reaching the maximum value,indicating that the network of SBR vulcanizates degraded and then re-crosslinking reaction occurred.Secondly,the oxidative reaction of tire rubber powder at different temperatures was studied.Under aerobic condition,the weight loss and sol content of tire rubber powder increased with the increase of temperature,and the molecular weight of the sol decreased gradually.The sol content reached 55.9%after 10 min of de-crosslinking under aerobic condition.Carbonyl and sulfoxide functional groups were found in the products accompanied by the formation of H₂O and CO₂.The sol content increased as the generation of gas,indicating that the main chain and crosslinking bonds of rubber were effectively broken.According to the modified Friedman method,the activation energy of the complex oxygen reaction of rubber powder was calculated and the results showed that the reation followed autocatalytic oxidation mechanism.Thirdly,the oxidative reaction of SBR vulcanizates in the presence of soybean oil and hydrogen peroxide（H₂O₂）was studied because SBR vulcanizates are difficult to be degraded and recycle.With the increase of soybean oil,the content of SBR vulcanized sol increased to 47.8%at 150℃,and the molecular weight of the sol decreased.The gel products contained hydroxyl and carbonyl functional groups,and crosslinking density of the gel obviously decreases.On this basis of the above results,the oxygen reaction of SBR vulcanizates induced by H₂O₂ under low temperature was studied.With the increase of H₂O₂,the content of sol in the crosslinking product of SBR vulcanizate increased and reached up to 100%at 100℃and molecular weight of the sol decreased,and the carbonyl groups in the gel increased with time.In addition,the kinetic analysis showed that the addition of H₂O₂ reduced the initial reaction activation energy of the oxidative reaction of SBR vulcanizates.The addition of H₂O₂ and soybean oil can improve the degree of breakdown of SBR vulcanizate and reduce the re-crosslinking reaction.Finally,the application of the reclaimed rubber in rubber products and road asphalt materials was studied.Reclaimed rubber was prepared by oxidative reclamation.A small amount of the reclaimed rubber was applied to the tire tread rubber and a high proportion of the rubber was added to prepare different adhesive layers of conveyor belt.The results showed that the vulcanized rubber containing the reclaimed rubber has shorter curing time,better static mechanical properties,thermal stability and solvent extraction resistance compared with conventional reclaimed rubber.In addition,the reclaimed rubber,as a high-performance modifier and asphalt component,was used to prepare high viscoelastic modified asphalt and modified asphalt with high addition.It was found that the high temperature and low temperature properties of high viscoelastic modified asphalt were better compared with SBS modified asphalt.The water stability,rutting resistance and low temperature performance of the asphalt mixture with the reclaimed rubber were better than those of SBS modified asphalt mixture.The modified asphalt and its mixture prepared with high content of the reclaimed rubber had good water stability and high and low temperature performance.This paper abandoned the traditional recycling methods（only breaking the crosslinking bond）and developed a thermo-oxidative reclamation（both breaking the crosslinking bond and breaking the main chain）.The reclaimed rubber was prepared the with high sol content,which provided a theoretical basis and reference for the industrialization of rubber recycling to reduce energy consumption and cost.The reclaimed rubber was applied for rubber products and modified asphalt in different proportions,and its high value-added applications were initially promoted.In view of the increasing number of used car tires（mainly SBR）,the degradation degree and temperature of vulcanized SBR rubber were improved and the temperature was reduced,which provided reference for the recycling of car tires.