Study On Curing Behavior And Properties Of Hydrogenated Nitrile Rubber

Hydrogenated nitrile rubber(HNBR)has excellent physical and mechanical properties and is widely used in automotive industry,aviation industry and petroleum industry.However,there are few basic researches on the principle and kinetics of HNBR vulcanization,and the high-temperature mechanical properties and service life of HNBR need to be improved.This paper firstly studied vulcanization reaction kinetics of HNBR,and vulcanization kinetics equation was established to optimize the curing process conditions.Therefore,HNBR composites with excellent properties were prepared.To further improve the mechanical properties at high temperature,heat-resistant material of PPTA pulp was added into material formula,and the mechanical performance of HNBR composites at high temperature was improved.In order to prolong service life of HNBR composites,property of thermal-oxidation aging resistance was studied.This paper expounds the following three parts.In the first part,vulcanization kinetics of HNBR reinforced by hydroxyl zinc mono-methacrylate(HZMMA)was studied.Applying HZMMA and carbon black as reinforcing agents,dicumyl peroxide(DCP)as vulcanizing agent,hydrogenated nitrile rubber(HNBR)composites were prepared.The exothermic process of vulcanization was studied with the method of non isothermal differential scanning calorimetry(DSC)at different heating rates.Through the simulation of a n kinetic model,using Kissinger equation and Crane equation,and with the extrapolation method of characteristic temperatures-heating rates,the kinetic parameters,the temperature and time of the vulcanization reaction were calculated.Mechanical properties of the composite prepared under the optimized vulcanization conditions were investigated.The reaction order n of the vulcanization of the system is 0.95,the apparent activation energy is123.59 kJ/mol,and the optimized vulcanization temperature and time are 165.62 ?and 16.94 min.Under the optimized vulcanization conditions,the mechanical properties of HNBR composites reinforced with HZMMA were as follows: the tensile strength could reach 27.6 MPa,the modulus at 100% reached 17.8 MPa,the elongation at break was 160% and the permanent set was 2.5%.In the second part,mechanical properties of HNBR/PPTA pulp/HZMMA under high temperature were studied.PPTA pulp was isolated with carbon black for pretreating.Combining PPTA pulp,HZMMA,and carbon black together asreinforcing agents,hydrogenated nitrile rubber composites were prepared.SEM displayed PPTA pulp pretreated was wrapped of a layer of carbon black particles on the surface and uniformly dispersed in rubber matrix.With the addition of PPTA pulp in the system,the hardness of HNBR composites increased,the elongation decreased,and tensile permanent deformation became larger.With the ambient temperature rose up to 70 ?,the composite strength and elongation at break sharply decreased.5 phr and above of PPTA pulp would enhance the strength of the composite and under the high temperature,the strength decline trend significantly slowed down;TG and DSC showed that with the increase of the content of PPTA pulp,glass transition temperature Tg and thermal stability of the composite,decreased first and then increased.With the addition of PPTA pulp,elasticity of hydrogenated nitrile rubber composites reduced,and stiffness increased.The content should not be too much;Adding 5 phr and above of PPTA pulp could significantly enhance the strength of the composites under high temperature.In the third part,property of HNBR composites' thermal-oxidation aging resistance was studied.Hydrogenated nitrile rubbers with different saturation were used to prepare composites.After thermal-oxidation aging,the changes of mechanical properties,cross-linking density and hardness with aging time were tested.The effect of TAIC in the formula on performance of thermal-oxidation aging resistance was evaluated,and the change of glass transition temperature of composites after aging was characterized by using DSC.The results showed that the higher the saturation was,the longer time of thermal-oxidation aging resistance was,and the longer the performance maintained.With thermal-oxidation aging going,HNBR composites would be over cross-linked,showing the hardness increased,the glass transition temperature Tg increased,the strength reduced,and the elongation at break decreased.Brittle transition happened to composites.After 40 hours of thermal-oxidation aging at 170 ?,the tear strength of the HNBR composite without TAIC obviously decreased slowly,which was better than that of the composite with TAIC.TAIC as an unsaturated cross-linking agent,it enhanced strength of HNBR composites before aging.During aging,it aggravated the aging process,accelerated the over cross-linking,and reduced service life of HNBR composites.Saturation is an important index for HNBR composites' performance of thermal-oxidation aging resistance.Higher saturation is,stronger ability of thermal-oxidation aging resistance is.The addition of TAIC decreased HNBR composites saturation,and reduced the ability of thermal-oxidation aging resistance.