Study On The Preparation Of New Charring Agent And Its Properties

Charring agent is an important component of intumescent flame retardant(IFR)and one of the key substances that affect the flame retardant effect of IFR.In recent years,the successful application of triazine charring agent not only improves the flame retardant effect of intumescent flame retardant,but also improves the water resistance and mechanical properties of flame retardant materials.Nevertheless,the charring agents still exist some problems,for example,products generally contain about 1.0 % chlorine,which can not fully meet the user's halogen-free requirements for flame retardants,large amount of wastewater containing sodium chloride and waste gas containing acetone are produced in the production process.In this paper,in order to overcome the shortcomings of existing triazine charring agents,a novel type of triazine charring agent-polyol modified melamine formaldehyde resin was designed and synthesized by using melamine,formaldehyde and polyols as raw materials and according to the following step: first,melamine was hydroxymethylated with formaldehyde,then etherified with polyols,and finally condensed.Five kinds of melamine formaldehyde resins modified by polyols(pentaerythritol,ethylene glycol,propylene glycol,diethylene glycol and triethylene glycol)were synthesized,which were respectively called as charring agent-1,charring agent-2,charring agent-3,charring agent-4 and charring agent-5.The results showed that the optimum synthesis conditions of charring agent were as follows: n(melamine): n(formaldehyde): n(pentaerythritol)= 1:7.5:5,n(melamine): n(formaldehyde): n(diol)= 1:7.5:8,the pH of hydroxymethylation reaction being about 9,the temperature being 75 ?,the time being 1 h,the pH of etherification reaction being approximately 1.5,the etherification time being 2-2.5 h at 55 ?,and followed 2 h at 80 ?.Under the above conditions,the yields ofcharring agent-1 to charring agent-5 were respectively 99.52 %,99.65 %,80.28 %,48.15 % and 63.73 %,and the mass yields were respectively 30.24 %,32.26 %,26.47 %,16.32 % and 21.44 %.The results of thermogravimetric analysis(TGA)revealed that the thermal stability and charring property of charring agent-1 and charring agent-2 were good,but that of charring agent-2 was better.The temperatures of charring agent-1 and charring agent-2 for 2 % of thermal weight loss rate were respectively 214 ? and 227 ?,the temperatures for the maximum thermal weight loss rate were respectively 359 ? and 393.25 ?,Their residual rates at700 ? were respectively 19.98 % and 22.45 %.The flame retardancy of five charring agents was studied by limit oxygen index(LOI)determination,vertical combustion test(UL-94)and cone calorimetry test(CCT).IFR prepared by combining charring agent-1 and charring agent-2respectively with ammonium polyphosphate(APP)(referred as IFR-1 and IFR-2)has good flame retardant effect in polypropylene(PP),while IFR prepared compounding other three charring agents respectively with APP has poor flame retardant effect in PP.When w(charring agent-1): w(APP)= 1:3,the dosage of IFR-1 is 30 wt.% based on the total weight of materials,LOI of flame retardant PP is29.8 %,vertical combustion level is V-0.Compared with pure PP,the peak heat release rate(PHRR),total heat release(THR),the average mass loss rate(MMLR)and the average effective combustion heat(MEHC)decreases respectively by77.03 %,12 %,50 %,and 14.68 %.When w(charring agent-2): w(APP)= 1:3.5,the dosage of IFR-2 is 28.5 wt.%,LOI of flame retardant PP is 26.5 %,vertical combustion level is V-0.Compared with pure PP,when IFR-2 is 30 %,PHRR,THR,MMLR and MEHC decreased by 78.58 %,9.43 %,56.98 % and 16.3 % respectively.Compared with charring agent-1,the mass ratio of charring agent-2 to APP is smaller,but the flame retardant effect of IFR is better.TGA showed that the initial decomposition temperature of both flame retardant PP was lower than that of PP,and IFR-1/PP was the lowest,which indicated that the addition of IFR-1 and IFR-2 reduced the thermal stability of PP,and IFR-1 had a greater impact.The pyrolysis gas chromatography-mass spectrometry analysis(PyGC-MS)and the analysis of residues obtained in CCT showed that IFR used flame retardant mainly through condensed phase.The polymetaphosphate formed by thermal decomposition of APP promotes the dehydration of charring agent to formnon-combustible compounds containing C,N,O and P.Under the action of inert gas from IFR/PP decomposition,the above substances expand and foam in the melting state,forming a dense and continuous intumescent carbon layer which results in flame retardant effect by insulation of heat,oxygen and preventing the volatilization of pyrolytic products.