Preparation And Properties Of Ceramifying Fireproof Polysiloxane Sealant

Ceramifying polysiloxane composites are one of novel fireproof elastomer materials,which show the similar processing and mechanical properties to common silicone rubber at room temperature.When being exposed at high temperature or fire environment,the composites will be transformed into self-supporting ceramics to prevent the flame from burning the inner of the materials so as to achieve the purpose of flame resistance and fireproofing.Ceramifying polysiloxane composites are widely used in aerospace,architectural decoration,electric wire and cable industries and so on.As one kind of room temperature vulcanization（RTV）silicone rubbers,RTV polysiloxane sealants have the advantages of simple construction and stable performance.In this paper,the effects of wollastonite and intumescent flame retardants（MPP/Di PE）on the properties of RTV polysiloxane sealants and their ceramic residues obtained after ablation were investigated,and the polysiloxane sealants and their ceramic residues were characterized by TGA,SEM,EDS,FT-IR,TG-FTIR and infrared thermography analysis.The flame retardant,fireproofing and ceramifying mechanism of the polysiloxane sealants was explored.Firstly,wollastonite was modified by silane coupling agent KH570,and the effects of the ratio of modified wollastonite and nano calcium carbonate（Ca CO₃）on the properties of polysiloxane sealants and the ceramic residues were investigated.The results showed that as the weight proportion of the modified wollastonite increased from 0 to 100%,the processability of the polysiloxane sealants was improved,the tensile strength increased from 1.7 to 2.5 MPa,and the shape stability of the ceramic residues was improved,and the three-point bending strength initially increased and then decreased with a maximum value of 12.5 MPa.Compared with nano Ca CO₃,modified wollastonite is more effective to improve the processability,the tensile strength and the porcelain property of the polysiloxane sealants.Secondly,the effect of the modified wollastonite loading on the properties of the polysiloxane sealants and the ceramic residues were investigated.When the content of modified wollastonite increased from 0 to 160 phr,the tensile strength of the polysiloxane sealants increased from 0.8 MPa to 1.3 MPa,the shape retention of the ceramic residues were improved,and the three-point bending strength initially increased and then decreased with a maximum value of 7.9 MPa.As the content of the modified wollastonite is 80 phr,the polysiloxane sealants show the superior comprehensive properties.Finally,the effect of the intumescent flame retardant（MPP/DIPE）loading on the properties of the polysiloxane sealants and the ceramic residues were investigated.When the content of the intumescent flame retardants increased from 0 to 120 phr,the oxygen index increased from 32.1%to 36%,and the vertical burning test achieved a UL 94 V-0 rating at 60phr loading,the shape of the ceramic residues gradually became regular.And the ablation area of the samples reduced and the heating rate decreased from 248.9 to 65.1℃·min^-1 when the backside temperature increased from the room temperature up to 180℃,and the maximum temperature of the backside of the samples decreased from above 350℃to 256℃,and the percentage of the ablation area of the samples decreased from 9.29%to 3.89%with a back-surface temperature higher than 180℃.The ablation area,backside temperature and heating rate of the samples are reduced with the increased corporation of the intumescent flame retardants.Consequently,the polysiloxane sealants show the superior comprehensive properties when the content of the flame retardants is 60 phr.