| As a type of important polymer material,rubber has been widely used in national defense,military industry and daily life due to its unique high elasticity and other outstanding comprehensive performance.However,most of rubber materials,containing a large number of isolated carbon-carbon double bonds?-C=C-?and active allyl hydrogen structures in the molecular chain,are extremely prone to aging under the conditions of heat,oxygen?O2?,light,ozone?O3?,and stress,etc.Specifically,the thermo-oxidative aging,as the most common aging form,could significantly deteriorate the physical or chemical properties of rubber materials,which will cause the premature failure of rubber products and even lead to safety accidents.Adding antioxidants is the most convenient and effective way to delay rubber aging,but most antioxidants are liable to migrate from the rubber matrix because of its low molecular weight,especially at high temperatures or in liquid.The migration of antioxidants not only reduce the protective efficiency but also contaminate the surrounding environment.Therefore,understanding deeply the mechanisms of rubber aging,the protective mechanisms of antioxidant,and taking certain measures to suppress the migration of antioxidants are of important practical significance for improving the aging resistance of rubber.In this subject,styrene-butadiene rubber?SBR?and natural rubber?NR?,two types of extensively used rubbers,were selected as the base materials.Combining experiments and molecular simulation,we mainly focus on the research of the rubber aging and anti-aging mechanisms,the modification of antioxidants,and the migration of antioxidants,and thus summarizing the effect of antixodants on the aging properties of diene rubbers and exploring a new path of theory and experience combination for the rubber aging reseach.The specific study contents can be summarized as the following four parts:?1?A new kind of antioxidant functionalized silica?SiO2-g-MC?filler was prepared by grafting antioxidant N-?4-aniline phenyl?maleic imide?MC?onto the surface of silica?SiO2?via 3-mercaptopropyl trimethoxysilane?KH590?.The effects of SiO2-g-MC on reinforcement and anti-aging properties of solution-polymerized styrene butadiene rubber?SSBR?were studied by experimental and computational methods.It was found that the reinforcement of SiO2-g-MC was much more effective than that of SiO2 in SSBR matrix because of its better dispersion and stronger interfacial interaction between SSBR and SiO2-g-MC.In comparison with SiO2 or KH590 modified silica?SiO2-KH590?,SiO2-g-MC filled SSBR blend showed more ideal vulcanization characteristics.The results of quantum mechanics?QM?simulation indicated that the dissociation energy of N-H bond in MC(333.1 kJ·mol-1)was lower than that of C-H bond in SSBR(the lowest values:338.4 kJ·mol-1),thus MC could preferentially dissociate hydrogen to capture peroxy radical?ROO·?,thereby retarding the thermo-oxidative process of SSBR composites.Furthermore,SiO2-g-MC could not only suppress the migration of MC but also decrease the adverse effect of MC on the vulcanization reaction of SSBR.Consequently,SiO2-g-MC/S SBR composite presented more outstanding mechanical properties than SiO2-KH590/MC/SSBR composite during the thermo-oxidative aging process,suggesting that SiO2-g-MC could be used as a functional filler for the preparation of high performance SSBR composites.?2?A novel bonded primary-secondary antioxidant?MBC?was synthesized by the thiol-ene click reaction between primary antioxidant MC and secondary antioxidant 2-mercaptobenzimidazole?MB?.Then,the antioxidation behavior of MBC in SBR matrix was systematically studied combining experiments and molecular simulation.It was discovered that MBC reduced the deceleration effect of MC on the vulcanization reaction of SBR,thereby improving the processing efficiency and mechanical properties of SBR composite.As against crystal MB or MC,MBC with a relatively high molecular weight,amorphous structure,and comparatively low solubility parameter manifested lower migration and better dispersion in SBR matrix.Furthermore,MBC containing aromatic amino and thioether groups could not only treminate peroxy radical?ROO·?but also decompose hydroperoxide?ROOH?,thus greatly improving the thermo-oxidative stability of SBR.As a result,in contrast to MB/SBR or MB/MC/SBR composite,MBC/SBR composite exhibited the best mechanical properties retention and relatively high temperature at oxidation exothermic peak during the thermo-oxidative aging process.?3?Through the thiol-ene click reaction of accelerator 2-mercaptobenzothiazole?MBT?with antioxidant MC,a novel accelerator functionalzed antioxidant?BTC?was synthesized successfully.Then,the effects of BTC on the vulcanization and antioxidation of SBR composite were comprehensively investigated by experiments and molecular simulation.The results showed that BTC could not only decrease the adverse influence of MC on the cross-linking density of SBR composite but also accelerate the vulcanization reaction as an accelerator.Compared with crystal MBT or MC,BTC having a high molecular weight,amorphous structure,and relatively low solubility parameter presented lower migration and better dispersion in SBR matrix.Moreover,the aromatic amino and thioether structures in BTC played an important role in enhancing the thermo-oxidative aging resisitance of SBR composite.Consequently,compared with MBT/SBR or MBT/MC/SBR composite,BTC/SBR composite showed the remarkable comprehensive properties,namely,high vulcanization reaction rate,excellent mechanical properties,and good thermo-oxidative stabilization,indicating that BTC could be used as a prospected multifunctional rubber additive for the fabrication of high-performance SBR composites.?4?The thermo-oxidative aging stability of antioxidant N-isopropyl-N'-phenyl-p-phenylenediamine?4010NA?/SiO2/NR composite was assessed by the changes of mechanical properties and chemical structure.Then,the physical and chemical influence of 4010NA and SiO2 on the thermo-oxidaive aging of NR was analysized by experimental and computational methods.The results indicated that?a?the addition of SiO2 could not only decrease O2 permeability of NR composite but also restrain the migration of 4010NA,thus improving the thermo-oxidative stabilization of NR and the long term protective efficiency of 4010NA;?b?4010NA could quickly capture peroxy radicals due to its lower dissociation energy and transition state energy barrier,thereby greatly retarding the thermo-oxidative process of NR composites;?c?the vulcanization accelerated effect of 4010NA made 4010NA/SiO2/NR composite have an appropriately high cross-linking density,which is favor of the improvement of mechanical properties.It followed that 4010NA/SiO2/NR composite manifested more remarkable mechanical properties than 4010NA/NR or 4010NA/CB/NR composite during the course of thermo-oxidative aging. |
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