Research On Preparation Technology And Performance Of Special Rubber Sealing Materials

Rubber is one of the most commonly used elastic sealing materials,and its performance stability in complex environments directly determines the service reliability of rubber sealing components.Seal failures,especially those caused by high-temperature,friction and material structure damage,will not only cause the destruction of the seal structure,but also cause huge economic losses,environmental pollution and personal injury accidents.Therefore,how to study the performance change mechanism of rubber sealing materials in complex environments and improve the optimization level of their own structure has become a scientific problem that needs to be solved urgently in the current service process of rubber sealing materials.Based on the performance evaluation and application of rubber sealing materials for aircraft cabin doors,this thesis will focus on the high temperature aging characteristics and aging resistance mechanism of rubber sealing materials and the preparation and characterization of aerospace fabric-rubber sealing materials,and conducts a series of studies on the high temperature resistance formula,after high temperature aging the mechanical properties,the friction properties of rubber sealing materials and the friction and bonding properties of the fabric-silicone rubber sealing materials.The main contents are as follows:First,using the nitrile rubber sealing material as the matrix,the influence mechanism of average and local crosslinking density on mechanical properties of nitrile rubber seal material before and after thermo-oxidative aging is studied.It is analyzed that the tensile strength of nitrile rubber increases first and then decreases with the increase of crosslinking density.Based on the diffusion-limited oxidation(DLO)effect,the gradient distribution of the local crosslinking density of the matrix is measured,and the distribution imbalance of crosslinking points in the thermo-oxidative environment is revealed as an important reason for hindering the stress dispersion during the stress process and causing the decrease of mechanical properties.The competition relationship between molecular chain crosslinking and fracture under high temperature compression environment is studied,and the growth mechanism of compression residual deformation under aging environment is explained.The interval strain model is established,and the tensile properties of rubber are tested based on the displacement accumulation method,which confirms the reliability of digital image correlation(DIC)for the large deformation measurement of rubber in complex environments.Second,on the basis of crosslinking density test and analysis method,the mechanism of mechanical properties change of silicone rubber(phenyl)composites under thermo-oxidative environment is further explored.Based on the good high-temperature protection of CeO2 and graphene,CeO2/graphene silicone rubber(phenyl)composites with excellent high-temperature resistance are designed and prepared.It is revealed that the scavenging of free radicals by CeO2 and the ?-? conjugation effect formed by graphene and phenyl groups are important factors to improve the high temperature resistance of silicone rubber(phenyl)composites.Combined with the thermal analysis kinetics,the average activation energy E of the thermal degradation of the silicone rubber(phenyl)composites is calculated,which further verified the heat-resistant mechanism of CeO2 and graphene during the thermo-oxidative aging process.Mechanical tests show that based on the good thermal protection effect of CeO2(2 phr)and graphene(0.8 phr)on the matrix,the tensile strength and elongation at break of silicone rubber(phenyl)composites aged at 300?/48 h remains at 4.67 MPa and 180%,respectively.Third,based on the good thermal protection effect of CeO2 and graphene,the changes of friction coefficient(COF)and wear morphology of CeO2/graphene silicone rubber(phenyl)composite before and after thermo-oxidative aging are explored.Through the measurement of the surface crosslinking density and the observation of the surface morphology,the influence of the surface matrix hardness,roughness and defects on the friction coefficient and wear rate of the silicone rubber(phenyl)composites are studied.The good thermal protection effect of CeO2 and graphene on the matrix and the self-lubricating effect of graphene can help to reduce the wear rate of the materials.However,the addition of excess grapheme(1.5 phr)will reduce the resistance of the surface matrix to cyclic shear,causing the wear rate of matrix after aging to increase from 4.24×10-3 mm-3/N·m at 0.8 phr graphene 4.44×10-3 mm-3/N·m.Fourth,through the comparison of the friction coefficient and wear morphology,it is confirmed that the surface polyester fabric can significantly improve the wear resistance of the silicone rubber matrix.Silicone rubber composites with double layer fabrics are designed and prepared.Based on the service environment,the differences in wear morphology and the change of friction coefficient in the dry/wet/high-temperature/oil-immersed environment are studied.The effects of sliding rates,external loads and fabric yarn directions on the friction properties of the fabric-silicone rubber composites are observed.It is pointed out that the pulling and breaking effect of high load(25 N)on the fabric fibers in a wet environment is an important reason for the damage to the original structure and surface of the fabric.Finally,through the modification of the silicone rubber matrix and the improvement of the adhesive compounding process,the bonding properties of the fabric and the silicone rubber is improved.Based on tests such as stretching,tearing,and peeling,it is confirmed that 0.2 phr titanate is used as the optimal content to enhance the bonding properties between silicone rubber and fabric.The contact angle test,FTIR characterization and peel test showes that the addition of titanate is helpful to improve the adhesivity of silicone rubber.As the titanate content increases from 0 phr to 0.2 phr,the contact angle of the silicone rubber surface are decreased from 123.33°to 108.39°.The surface wettability of the modified silicone rubber is significantly enhanced,which is an important reason for the improvement of the bonding properties between silicone rubber and polyester fabric.In addition,based on the difference in the tensile modulus of the fabric yarns,the effects of the peeling state of the outer fabric and the interaction between the inner fabric and rubber on the peel strength and peel elongation of the fabric-silicone rubber composite are obtained.The research results will provide valuable reference for the exploration of high-temperature aging mechanism of rubber sealing materials and the evaluation of their comprehensive performances.Meanwhile,the researches on the friction behavior of fabric-silicone rubber sealing material under multiple working conditions and the improvement of the bonding and compounding process of fabric and silicone rubber will provide reliable experimental support for the application of aerospace fabric-rubber sealing material.