Synthesis And Applications Of Epoxidized Silicone Rubber & Composites

Silicone rubber is a unique material with both organic and inorganic characteristics,which endow it with remarkable properties such as heat resistance,chemical stability,electrical insulation,wear resistance,weather resistance,and ozone resistance.However,its poor thermal durability at high temperatures,low residual weight ratio,and low polarity limit its use in extremely high-temperature applications and blending with polar materials.To address these issues,this thesis explores the molecular structure design of epoxidized silicone rubber and its composite materials.The research content mostly included in this article is as follows:(1)Epoxidized vinyl silicone rubber [V(34-84)E6 EMVQ] with a vinyl content of 34%-84% and an epoxy content of 6% was created by adding various amounts of vinyl groups through anionic ring opening polymerization to the silicone rubber’s side groups and introducing epoxy groups to some of the vinyl groups directly through epoxidation.Thermal gravimetric analysis(TGA)results revealed that an increase with in vinyl content on the side groups of epoxidized silicone rubber in air environment may greatly increase the residual rate of EMVQ at high temperature,with a maximum of 72.3%;Subsequently,through characterization methods such as thermogravimetric infrared spectroscopy(TGA/FT-IR),nuclear magnetic resonance silicon spectroscopy(29Si-NMR),and scanning electron microscopy(SEM),combined with density functional theory(DFT)research,it was found that EMVQ with high vinyl content can effectively inhibit the backbiting degradation of the main chain through side group oxidation and free radical cross-linking reactions under hot air atmosphere,thereby forming a dense network structure,This provides a theoretical basis and design idea for solving the common problem of main chain backbiting and cyclization degradation in the thermal degradation process of traditional silicone rubber.In addition,the introduction of epoxy groups increases the EMVQ adhesive strength by nearly26 times compared to PDMS.(2)Based on the design of the molecular structure of EMVQ to give consideration to the characteristics of high-temperature oxidation stability and adhesion,in order to apply it to the field of thermal protection of the internal insulation layer of solid rocket motors,we prepared ablative resistant vinyl epoxide silicone rubber based composites and investigated the effects of different fillers such as fumed silica,aramid fiber,aramid fiber/carbon fiber blends,the vinyl content of the matrix,and vulcanizing agents on the ablative properties of the composites,silicone rubber based composites with excellent ablation performance were selected.The results demonstrate that fumed silica is ineffective as an anti-ablation additive and only acts as a mechanical support in composite systems;AF has a minimal impact on enhancing the ablation performance of composite materials when used as a single fiber filling;When the number of AF/CF blends is 6 parts each,fiber blending can significantly improve the ablation performance of the composite by consolidating the carbon layer and improving the thermal stability of the EMVQ matrix.Increasing the vinyl content of the EMVQ matrix is helpful for creating a dense carbonized layer structure of the composite during the ablation process.However,it should be avoided to add too much vulcanizing agent to cause a large consumption of vinyl groups during the vulcanization process.(3)Through the use of molecular structure design,epoxidized silicone rubber(ESR)with various epoxy group contents was created in an effort to address the issue of the severe incompatibility between conventional silicone rubber and polyamide 6(PA6).PA6/PDMS/ESR composites were prepared by introducing ESR as an interfacial compatibilizer into the PA6/PDMS system.The effects of the amount of ESR-5 and different epoxy content ESR on the interfacial properties and notch impact properties of the composites were investigated.The results show that when the content of ESR-5 is 10 wt%,the particle size of the dispersed phase of PA6/PDMS/ESR-5 composite is refined to 710 nm,and the interface thickness is increased to 184 nm,showing excellent interfacial properties.Excellent microstructure and interfacial properties contribute to the formation of effective toughening mechanisms and improve the notched impact strength of the composites.The notched impact strength of the composite material system with an ESR-5 content of 10 wt% at-60 ℃ is 13.1 k J/m~2,compared to PA6 and PA6/PDMS systems,the lowtemperature brittleness of PA6 is significantly improved by 469.6% and 52.3%,respectively,offering a novel concept and theoretical foundation for epoxidized silicone rubber toughened nylon matrix composites.In addition,high-strength and high-toughness PA6/PDMS/ESR-5/CF composites were created using CF as a fiber reinforcement system to address the issue of rigidity reduction brought on by ESR toughening PA6.