Preparation Of Thermally Reversible Rubber Modulated By Nitroxide

The traditional rubber was vulcanizing with covalent bond,leading to an irreversible network structure.The rubber material was difficult to recycle and reuse,which caused black pollution to the environment and seriously threat to people’s health.If the rubber material could be processed to restore its original performance after being abandoned,then it could give full play to the use value of the material.Endowing rubber with thermo reversible structure is an effective method to realize the repeated processing of rubber.In this study,the rubber was directly cross-linked by the preparation of a thermo reversible crosslinker with nitroxides instead of the traditional crosslinker,so that the rubber could be thermoreversible and reprocessed.In this study,DTEMPO was synthesized and applied to the preparation of DSBR.The structure and crosslinking mechanism of DSBR were characterized by Infrared spectroscopy(FTIR),nuclear magnetic resonance hydrogen spectrum(~1H NMR),differential scanning calorimetry(DSC)and electron spin resonance(ESR).It was proved that the reaction of nitroxides was react with carbon-carbon double bond on rubber molecular chain in the process of crosslinking.In the process of thermal reversibility,alkoxyamines were broken down at high temperature to produce carbon radicals and nitroxides,and rebonded at low temperature.It was found that DTEMPO has the function of crosslinking styrene butadiene rubber by comparing with the rubber reacted by monofunctional crosslinker.The modulus analysis showed that the modulus of DSBR decreased at high temperature and increased at low temperature.The results of swelling experiments in xylene showed that DSBR would be de-crosslinked at high temperature.The tensile test showed that with the increase of DTEMPO content,the mechanical strength of DSBR increased first and then decreased.When DTEMPO content was 10phr,the tensile strength reached 7.46MPa,and the elongation at break reached 1057%.Compared with the irreversible sulfur crosslinked SBR,DSBR had higher mechanical strength and excellent reprocessing performance.Another reversible crosslinker STEMPO was prepared and applied to the preparation of TBR.It was proved by FTIR and ESR that the cleavage of alkoxyamines at high temperature resulted in the formation of carbon radicals and nitroxides,and the formation of alkoxyamine structure at low temperature during the repeated processing of TBR.The tensile test showed that the tensile strength of TBR was 4.29MPa and the elongation at break was 518%when the amount of STEMPO was 15phr.TBR also exhibited good reprocessing performance.The results show that the addition of silica can strengthened TBR.When the content of silica was30 phr,the tensile strength of TBR reached 9.08 MPa and the elongation at break reached 322%.Moreover,TBR filled with silica also had good reprocessing ability.