Study On Synthesis And Flame Retardant Performance Of Theic Modified Melamine Formaldehyde Resin

Intumescent flame retardant(IFR)is a kind of environmental friendly flame retardant,which has great development potential,and charring agent is an important part of IFR.At present,the commonly used carbon forming agent is macromolecular triazine carbon forming agent,but it contains about 1%chlorine,so a large amount of refractory Na Cl wastewater is generated in the preparation process.As a kind of small molecule triazine compound with multi hydroxyl group,THEIC has excellent carbon forming ability,but it is very soluble in water,so the water resistance of the composite is very poor.However,the synthesis of macromolecular triazine char from THEIC can not only overcome the above problems of existing macromolecular triazine char,but also overcome the shortcomings of THEIC.In this paper,two synthetic methods were used to prepare melamine formaldehyde resin modified by THEIC,namely,melamine(MEL),THEIC and paraformaldehyde were used as raw materials to prepare a kind of melamine formaldehyde resin modified by THEIC(short name charring agent-1)through hydroxymethylation,polycondensation and etherification reaction.Using hexahydroxymethyl melamine(HMM)and THEIC as raw materials,a kind of melamine formaldehyde resin modified by THEIC(short name charring agent-2)through direct polycondensation etherification under solid state conditions.The structure of the product was characterized by IR and ¹³C NMR.The thermal stability of charring agent was determined by thermogravimetry(TGA).The thermal stability of sutebao charring agent Su(short name charring agent-Su)was the best,while THEIC was the worst.The thermal stability of charring agent-2 was slightly better than that of charring agent-1.Intumescent flame retardant(IFR)was prepared by compounding charring agent and ammonium polyphosphate(APP).The flame retardancy of IFR for polypropylene(PP)was evaluated by testing the flame retardancy of IFR.The results show that when the flame retardant PP reaches grade V-0,the minimum addition of charring agent-1/APP,charring agent-2/APP,THEIC/APP and charring agent-Su/APP are 32%,32%,40%and30%,which means that the charring agent-Su has the best flame retardant performance,while there is no significant difference between charring agent-1 and charring agent-2,which are slightly worse than charring agent-Su,while THEIC has the worst;However,the synthesis process of charring agent-1 and charring agent-2 is simple,only a small amount of waste gas is produced in the synthesis process,and the product does not contain chlorine,while a large amount of waste water is produced in the synthesis process of charring agent-Su,and the product contains about 1%chlorine.The results of water resistance test of flame retardant PP showed that the water resistance of charring agent-Su/APP/PP was the best,and that of THEIC/APP/PP was the worst.The results of CCT showed that the peak mass loss rate(PMLR),average mass loss rate(MMLR)and combustion parameter value of the charring agent/APP/PP decreased significantly compared with PP,and the fire performance index(FPI)increased significantly,which indicated that the addition of IFR could significantly inhibit combustion,reduce fire intensity,slow down the pyrolysis rate and combustion rate.The effect of charring agent-1/APP/PP was the best,and that of THEIC/APP/PP was the worst.The values of PMLR,MMLR and combustion parameter value of the APP/PP,charring agent-2/PP and charring agent-Su/PP are similar to those of PP,and FPI is also similar to PP and much smaller than that of IFR/PP,which indicates that the effect of APP or charring agent alone on inhibiting combustion,thermal decomposition and combustion rate is extremely poor.The flame retardant mechanism of IFR was studied by thermogravimetric analysis and composition and structure analysis of CCT residue.The results showed that CCT residue was composed of incombustible or refractory amorphous carbon,graphitized carbon,other carbon and nitrogen compounds and polymetaphosphoric acid,and about 90%of the residue was water soluble.Under the action of inert gases such as water vapor,N₂,NH₃,CO₂ and CO decomposed by charring agent and APP,the interwoven residue foams and expands to form a continuous and dense expansion layer.The expansion layer has flame retardant effect through heat insulation,oxygen isolation,preventing further decomposition of the substrate and volatilization of decomposition products.The charring agent affects the compactness of CCT residue structure,thus affects the flame retardancy of PP.The structure of CCT residues of charring agent-1/APP/PP,charring agent-2/APP/PP and charring agent-Su/APP/PP is more compact,so the flame retardancy is better.