Construction of epoxy resin coated ammonium polyphosphate-polypropylene flame retardant system
In order to construct an intumescent polypropylene(PP)flame retardant system,epoxy resin coated ammonium polyphosphate microcapsules(EP-APP)were prepared by in-situ polymerization to improve the material compatibility of APP and PP.Meanwhile pentaerythritol(PER)was selected as a carbon-forming agent forming an intumescent flame retardant(IFR)with EP-APP to prepare PP/EP-APP/PER flame retardant composites.The water solubility of microcapsules was used as an index for the microcapsule coating process optimization,the effects of the mass ratio of EP-APP and PER and the addition of IFR on the flame retardant properties and mechanical properties of the composites were investigated,and the reaction mechanism of EP-APP and PER in IFR was analyzed.The results show that when the amount of EP is 10 wt%of the APP amount and the dosage of the curing agent triethylenetetramine(TETA)is 15 wt%of the EP amount,the curing reaction temperature of 40℃(1 h)+70℃(1 h),the EP-APP microcapsules with excellent water resistance can be prepared.When the IFR addition amount is 25 wt%and the mass ratio of EP-APP to PER was 3∶1,the limiting oxygen index(LOI)of the prepared PP/APP/PER flame retardant composites reaches 35.0%,and the vertical combustibility reaches UL 94 V-0 grade,and the material maintaines good tensile properties.Thermogravimetric analy-sis shows that the decomposition reaction of IFR can be divided into three stages.First,EP-APP reacts with PER after thermal decomposition,forming a substance containing phosphate bonds.Then,the ester compounds produce stable cyclic esters and release H2O and NH3.Finally,the above products form bicyclic and polycyclic phosphates and carbonize at high temperature to form a dense carbon layer,which is oxygen and heat insulation to play a role of flame retardant.
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