Preparation Of Phosphorous-Containing Silicone Resin And Application In Silicone Rubber As Flame Retardant

Both silicone resin and silicone rubber belong to organic polysiloxane,and their main chain is composed of Si-O-Si structure.Thereforethey possess good compatibilitydue to structural similarity The difference between the two structures lies in the side groups.The side groups of silicone resin not only have organic groups,but also have many different kinds of compounds.The different properties of silicone resin are provided by different side groups.For example,when carbon-containing functional groups are introduced,silicone resin can also react with compounds which will react with carbon functional groups.However,the side group of silicone rubber are just methyl,vinyl,phenyl and other organic groups.Firstly,this paper designed and synthesized eight kinds of silicone resin,they are Si R-Me,Si RVi-Me,Si RP-Me,Si RPVi-Me,Si R-Ph,Si RVi-Ph,Si RP-Ph,Si RPVi-Ph,respectively.There are four kind of phosphorus-free silicone resins and four kinds of phosphorus-containing silicone resins by introducing phosphorus groups in above the four kinds of phosphorus-free silicon resin.The structures of the eight kinds of silicone resin were characterized by nuclear magnetic resonance(NMR)and fourier infrared spectroscopy(FT-IR).And then,the eight kinds of silicone resins were added in dimethyl vinyl silicone rubber as flame retardant additives Finally,a series of modified silicone rubber with different amounts of silicone resin were prepared.The mechanical properties of modified silicone rubber were investigated.When adding the 30 phosphoru-free silicon resin,silicon rubber tensile strength is reduced from 8.85 MPa to 8.01 MPa,the elongation at break increased by 842% to 940% and tear strength by 13.67 N/mm up to 23.56 N/mm left and right sides,after adding silicone phosphorous,the tensile strength of the silicone rubber was reduced by 10%,while the elongation at break increased 12% and tear strength increased by 70%,that does not contain phosphorus silicon resin for silicone rubber has certain reinforcing effect;In addition,the LOI value of silicone rubber can be increased from 20.8% to 23%.When phosphorous-contanting silicone resin was added,the mechanical properties of silicone rubber decreased to a certain extent.The tensile strength decreased from 8.85 MPa to 6.99 MPa,the elongation at break decreased from 842% to 700%,and the tear strength decreased from 13.67 N/mm to 12.89 N /mmThe flame retardant performance of the modified silicone rubber was measured bythermogravimetric analyzer(TGA),vertical burning test(UL94)and limiting oxygen index(LOI)test.The results showed that the phosphorus-containing silicone resins endow the silicon rubber with excellent flame retardant property.When added 30 phosphorus-containing silicon resin,the LOI value of modified silicone rubber increased from 20.7% to more than 27.0%,and the UL94 level also achieved V-0 level;The addition of phosphorus-free silicone rubber can also achieve a certain degree of flame retardant effect.The combustion behavior and flame retardant mechanism of modified silicone rubber were analyzed by cone calorimetry test of modified silicone rubber,as well as UL94 test,scanning electron microscope(SEM)and energy dispersive spectroscopy(EDS)ofresidue after combustion.\It can be seen from the cone calorimetry test that the HRR and THR of silicone rubber with phosphorus-containing silicone resin decreased to a certain extent,while the total amount of smoke generation of modified silicone rubber increased owing to the introduction of phenyl groups,which generated CO and CO2 during combustion.are Based on the analysis of the residue after combustion,it can be seen that the phosphate groups plays an important role in flame retardant mainly in the solid phase,through the phosphate ester groups at high temperature to generate phosphoric acid andmetaphosphoric acid to promote the formation of carbon layer to improve the flame retardant property.