Synthesis And Flame Retardant Property Of The Melamine Formaldehyde Resin Modified With Polyhydroxy Compounds

Intumescent flame retardant(IFR)is a kind of green flame retardants with great development potential,and charring agent is an important component of IFR.At present,commonly used charring agent is macromolecular triazine charring agents synthesized from cyanuric chloride,which has serious environmental and safety problem.Therefore,our research group has designed a new macromolecular triazine charring agent-melamine formaldehyde resin modified with polyhydroxy compound(polyol)(hereinafter referred to as the modified resin),but its synthesis with water as solvent has some problems such as low weight yield and difficult to cyclic utilization of the unreacted polyols.Consequently,a variety of the modified resins were synthesized by a solid reaction process,and their properties were evaluated in detail.Six kinds of the modified resins were synthesized by a solid reaction process through the etherification and polycondensation of hexahydroxymethyl melamine(HMM)respectively with THEIC,glycerol(GLY),pentaerythritol(PER),trimethylolpropane(TMP),ethylene glycol(EG)and propylene glycol(PG),and their structures were characterized by FT-IR and solid ¹³C-NMR.In view of the yield and performance of the product,the optimum synthesis conditions are as follows:The resin modified with THEIC:n(N-CH₂OH):n(alcohol hydroxyl)=1:1.38,reaction is carried out at 130?and lasting for 4 h;The resin modified with PER:n(N-CH₂OH):n(alcohol hydroxyl)=1:1.38,reaction is carried out at 130?and lasting for 1 h;The resin modified with GLY:n(N-CH₂OH):n(alcohol hydroxyl)=1:1.13,reaction is carried out at 140?and lasting for 1 h;The resin modified with TMP:n(N-CH₂OH):n(alcohol hydroxyl)=1:1.25,reaction is carried out at 150?and lasting for 1 h;The resin modified with EG:n(N-CH₂OH):n(alcohol hydroxyl)=1:1.00,reaction is carried out at 60?and lasting for 1 h;The resin modified with PG:n(N-CH₂OH):n(alcohol hydroxyl)=1:1.00,reaction is carried out at 80?and lasting for 1 h.The amount of catalyst is 1%based on the total weight of HMM and polyol.Under the above conditions,the weight yields of the resins modified with THEIC,GLY,PER,TMP,EG and PG are 88.89,75.60,83.78,75.94,71.83 and71.07%respectively,and the water solubility was 0.311,0.231,0.183,0.184,0.143and 0.207 g/100 m L water respectively.The type of polyol has a great influence on the yield and water solubility of the product.The thermal stability and charring property of the above modified resin(residual at 750?)were evaluated by thermogravimetric analysis.The results show that the polyol modification improves significantly the initial thermal stability and charring property of HMM,but the type of polyol affects obviously the above properties.For example,the temperature of the loss of 2 wt%for the resins modified with THEIC,GLY,PER,TMP,EG and PG increases from 100?of HMM to 241,172,199,175,198 and 191?respectively,while the residual at 750?increases from 9.48%to 10.66,18.94,15.75,8.41,18.73 and 17.81%respectively.TG-MS analysis shows that the content of the self etherification product of HMM in the modified resin affects the initial thermal stability of the product.The synergistic flame retardancy of the modified resin and ammonium polyphosphate(APP)was evaluated by vertical combustion test and limiting oxygen index measurement.The results show that polyol modification significantly improves the synergistic effect of HMM,and the type of polyol has a markedly impact on the synergism,the resin modified with THEIC performs the best,the resin modified with PER perform the second,the resins modified with GLY,EG and PG perform poorer,and the resin modified with TMP performs the worst.For example,when the flame retardant reached level UL-94 V-0,the minimum loading of APP/HMM is 34%,while that of APP/the resin modified with THEIC-4,APP/the resin modified with GLY-2,APP/the resin modified with PER-4,APP/the resin modified with EG-2,APP/the resin modified with PG-1 and APP/the resin modified with TMP are 24%,30%,28%,30%,30%and 34%respectively.The type of polyol also has a obvious influence on the color of the flame-retardant PP,the color of the flame-retardant PP is brownish yellow due to the resin modified with GLY,while the resin modified with PER is light yellow,and the others are between the both.The equivalence ratio of N-CH₂OH and alcohol hydroxyl has a little influence on the synergism of the modified resin and the color of the flame retardant PP.The results of the water resistance test show that the type of polyol has a significant influence on the water resistance of the flame retardant PP,and the water resistance of PP/APP/the resin modified with THEIC and PP/APP/the resin modified with PER is much better than that of PP/APP/the other modified resins as well as PP/APP/THEIC and PP/APP/PER.The determination results of melt index and mechanical property show that the types of modified resin has a little effect on the mechanical property of the flame retardant PP,but obvious influence on the melt fluidity of the flame retardant PP.