Design,Preparation,and Mechanism Study Of Ceramic Fire-retardant Silicone Rubber Composite Materials

Silicone rubber(SR)has excellent properties of air permeability,electrical insulation and resistance to high and low temperatures,and is widely used in medical materials,seals,wires and cables,and other fields.At the same time,the introduction of porcelain-forming fillers and ceramic agents can prepare vitrified SR,giving the material higher fire resistance to meet the urgent need for safety protection in special fields such as new energy,high-speed rail and nuclear power plants..However,there are many shortcomings in the application of SR,including the fact that the organic structure in SR is highly flammable,and the Si-O-Si groups will form a loose silicon oxide layer during combustion,making it unable to extinguish flames.Adding commonly used ceramic fillers and aids is not sufficient to make SR composites have good flame retardancy and low-temperature ceramic ability,which is not conducive to the safety protection of fire retardant materials in the fire scene.This paper is based on the design concept of efficient flame retardancy and ceramic and uses a surface modification,synergistic enhancement,and other technical means to prepare SR composites with higher flame retardancy and ceramic ability.We also systematically study their thermal stability,flame retardancy,ceramic characteristics,and action mechanisms,which are of great significance for the wide application of flame retardant SR in the safety field.The specific research is divided into the following aspects:1.Based on calcined kaolin and glass powder as porcelain-forming filler and flux,respectively,combined with phosphate flame retardant,the ceramifiable flame retardant SR composites were prepared.The effects of different kaolin contents,softening points,and compositions of commercial glass powders on the thermal stability and ceramic properties of the SR composite were investigated.A formula with phosphate glass powder as the flux was selected,melamine polyphosphate(MPP)was used to replace some kaolin to prepare flame retardant and ceramifiable SR and corresponding composite materials with trimethoxyvinylsiloxane modified powders were also prepared.Cone calorimetry and a universal testing machine were employed to study the effect of MPP content and powder modification on the flame retardancy and mechanical properties of the SR composite before and after ceramic.The flame retardant mechanism and ceramic process of the materials were analyzed by X-ray diffraction(XRD),Fourier transforms infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),and scanning electron microscopy(SEM).Results showed that the addition of MPP can effectively reduce the thermal hazard of the composite and enhance the strength of the ceramic-like body obtained after calcination.When the proportion of MPP was 15 wt%,the bending strength of the sample after 1000℃calcination exceeded 15 MPa.Moreover,powder modification could restore the mechanical strength deteriorated by MPP.2.To further improve the mechanical properties and flame retardant ceramic properties of SR composite materials,as well as the poor water resistance of phosphate glass powder,anhydrous zinc borate,cerium oxide,lanthanum oxide were mixed with phosphate glass powder for calcination.Methylphenyl cyclosiloxane was then used as a hydrophobic coating and compatibilizer and grafted onto the surface of the glass powder through ball milling to obtain corresponding modified hydrophobic glass powder GF-LaM,GF-CeM,and GF-ZnBM.Study the effect of the composition of modified glass powder on the flame retardancy and ceramicization of silicone rubber composites.The results show that compared with untreated phosphate glass powder,silane modified GF LaM,GF CeM,and GF ZnBM glass powder have relatively high hydrophobicity;The incorporation of GF-LaM,GF-CeM and GF-ZnBM significantly delayed the time to peak heat release(PHRR)(tPHRR)compared to phosphate glass powders,with SR composites using GF-ZnBM having the largest tPHRR and the smallest fire spread index(FGI),indicating the excellent fire safety performance of SR/Zn-GF;The composites(SR/La-GF,SR/Ce-GF and SR/ZnB-GF)prepared using GF-LaM,GFCeM and GF-ZnBM exhibited smaller volume change rates after calcination at 1000℃,indicating that GF-LaM,GF-CeM and GF-ZnBM have a positive effect on promoting the formation of dense ceramicized layers in SR composites.In addition,by calculating the activation energy of silicone rubber composite materials using thermogravimetric data at different heating rates,it was found that SR/Zn-GF had the lowest activation energy,while SR/Ce-GF had the highest overall activation energy.However,through backplate burning tests,it was found that SR/Zn-GF had the best fireproofing capability.3.In order to effectively balance the filling amount with the flame retardant,ceramicization and mechanical properties of SR,ionic liquid-assisted potassium chloroplatinate reduction deposition to calcined kaolinite was used to achieve effective dispersion of highly efficient Pt catalyst in SR and effectively inhibit the agglomeration of Pt clusters during high-temperature vulcanization,which was applied to the matrix to prepare ceramicized flame retardant high-performance SR composites.The effect of platinum containing kaolin content on the fire safety performance of SR composite materials was studied through UL-94,limiting oxygen index,and cone calorimetry tests.Silicon rubber composite materials were calcined at different temperatures,and the ceramic forming effects of different products were compared through three-point bending tests.The microstructure and crystal form changes of the calcined samples were studied through SEM and XRD to speculate and reveal the ceramization process and mechanism The results showed that the LOI of silicone rubber composites with platinum containing kaolin was higher than that of silicone rubber composites SR/G45 prepared with kaolin,and compared to SR/G45 without grade in UL-94 testing,SR/GPt2 could reach V-0 grade;The bending strength of the samples calcined at 800℃ for SR/G-Pt1,SR/G-Pt2,and SR/G-Pt3 is higher than that of SR/G45,which is close to 5MPa.At 1000℃,the strength of the four samples is basically the same.By calculating the activation energy of the silicone rubber composite material,it was found that the overall activation energy of SR/G45 was higher than that of SR/G-Pt2 with the addition of platinum containing kaolin.At the same time,through backplate burning tests,it was found that SR/G-Pt3 showed better protective ability.