Synergistic Effects And Mechanism Of Modified Silica Sol Flame Retardant Systems On Silk Fabric

The sol-gel method has unparalleled advantages in textile functional finishing due to its simple technology,mild process,good film formation and easy physical or chemical modification in the sol stage.Due to the limited use of halogen flame retardants,some other single flame retardants have the problems of high price and poor effect.Through the compounding of flame retardants,the synergistic effect of flame retardant elements can be used to make up for the deficiency of single flame retardant,and the relationship between the amount of flame retardant,performance and cost can be balanced.In recent years,the flame retardant compound system has been widely studied,but the research on the synergistic flame retardant mechanism of the sol gel flame retardant system has rarely been reported.Therefore,based on the previous research of the research group,the flame retardant synergistic effect and mechanism of the compound system are discussed by using the silica sol flame-retardant silk system as a template.Using silica tetraethyl orthosilicate as the hydrolytic precursor,sol-gel method was used to prepare silicon/nitrogen,silicon/boron,silicon/phosphorus two component sol system and silicon/boron/nitrogen,silicon/boron/phosphorus,silicon/phosphorus/nitrogen three element sol system by physical doping or chemical hybridization,which urea,cyanoguanidine and melamine cyanurate(MCA),boric acid,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO),hydroxyethylidene diphosphonic acid(HEDP)is added to the silica sol either alone or in combination of two or two.Then the silk was treated with these flame retardants.Through the oxygen index meter(LOI),micro calorimeter,vertical combustion,smoke density box and thermogravimetric analyzer tests,it can be seen that all flame retardant systems have improved the flame retardancy of silk in varying degrees.Among them,silicon/phosphorus/nitrogen system has the best flame retardancy,the LOI has increased from 24.0%to 49.6%,the initial pyrolysis temperature has increased,the charring rate has increased,and the heat release rate has slowed down.The total heat release decreased,the maximum smoke density decreased,and the smoke suppression performance improved significantly.Calculating the synergistic index of different flame retardant systems according to Lewin formula.Firstly,in silicon/nitrogen flame retardant system,silicon/nitrogen(urea)and silicon/nitrogen(MCA)have synergistic effects on LOI and vertical combustion performance;all silicon/nitrogen flame retardants have additive effects on heat release performance;silicon/nitrogen(urea)and silicon/nitrogen(cyanoguanidine)have synergistic effects on carbon stability;all silicon-nitrogen sol-treated fabrics has been improved in smoke suppression performance.In conclusion,silicon/nitrogen(MCA)sol has the best flame retardancy and synergistic effect.Secondly,in silicon/boron,silicon/boron/nitrogen,silicon/boron/phosphorus flame retardant systems,silicon/boron and silicon/boron/nitrogen(cyanoguanidine)have synergistic effects on LOI and vertical burning properties;silicon/boron/phosphorus(HEDP)has a synergistic effect on heat release performance;silicon/boron/nitrogen(cyanoguanidine)has a synergistic effect on char formation stability;silicon/boron sol have the best smoke suppression performance.The smoke suppressing properties of the silicon/boron/nitrogen or silicon/boron/phosphorus ternary sol system are improved.On the whole,the silicon/boron/phosphorus(HEDP)sol has the best flame retardancy,and the silicon/boron/nitrogen(cyanoguanidine)synergistic effect is the best.Finally,in the silicon/phosphorus,silicon/phosphorus/nitrogen flame retardant systems,silicon/phosphorus(HEDP)/nitrogen(urea,cyanoguanidine)and silicon/phosphorus(DOPO)/nitrogen(urea,cyanoguanidine)sols have synergistic effects;except for silicon/phosphorus(DOPO),silicon/phosphorus(HEDP)/nitrogen(MCA),silicon/phosphorus(DOPO)/nitrogen(MCA),which only add up in heat release properties,other jflame retardant systems all have synergistic effects;silicon/phosphorus(DOPO),silicon/phosphorus(HEDP)/nitrogen(urea,cyanoguanidine,MCA)have synergistic effects on carbon stability;via silicon/phosphorus(HEDP)/Nitrogen(cyanoguanidine)finished silk fabrics have the best smoke suppression performance,and other silicon/phosphorus or silicon/phosphorus/nitrogen sol systems have improved smoke suppression performance.On the whole,the silicon/phosphorus(HEDP)/nitrogen(urea)sol has the best flame retardancy and synergistic effect.Combined with data from the flammability test,fourier transform infrared(FT-IR)spectrum,scanning electron microscopy,and pyrolysis gas chromatography-mass spectrometry were used to characterize the morphology,structure,and pyrolysis products of treated silk fabric and residues after combustion.The results show that the flame retardancy of Si/N sol is mainly caused by endothermic reaction and melt covering reaction.Si/B sol acts as a flame retardant through endothermic reaction,release of gases,and melting coverage.Si/P sol achieves flame retardancy by forming an acid to promote formation of a carbon layer,free radical formation and melting coverage.Si/B/N,Si/B/P,Si/P/N ternary sol systems combines the above advantages and exhibits superior flame retardant effect after compounding.In terms of water wash resistance,the flame retardant separate finishing system<binary compound system<ternary compound system.Although the preparation of silicon,nitrogen,boron,phosphorus flame retardant into a sol matrix can improve the combination with silk fiber,but nitrogen,boron and phosphorus flame retardants do not remain stable in the silica sol matrix and are easily removed during subsequent water washing.In addition,tests on the physical and mechanical properties of the fabric showed that the strength and whiteness of the sol-treated silk had a slight decrease,which had a certain influence on the silk hand.