Studies On Halogen-free Flame Retardant EVA Composites

The flammability of ethylene-vinyl acetate copolymer(EVA)severely restricts its application in related fields.In this paper,bisphenol A-bis(diphenyl phosphate)(BDP),pentaerythritol(PER)and calcium aluminum hydrotalcite(Ca Al-LDHs);phenolic resin(PF),melamine formaldehyde resin coated ammonium polyphosphate(MFAPP)and magnesium hydroxide(MH);char forming masterbatch(TM)and ammonium polyphosphate(APP)compounding halogen-free flame retardant systems were used for EVA,the main results are as follows:BDP,PER and Ca Al-LDHs were employed to construct a new type of intumescent flame retardant system(IFR)as acid source,carbon source,gas source with carbonfixation,respectively,which was used for flame retardancy of EVA.The related properties of the composites were characterized by means of vertical combustion instrument(UL-94),oxygen index analyzer(LOI),thermogravimetric analyzer(TGA),cone calorimeter(CCT),scanning electron microscope(SEM)and universal testing machine.The results indicate that adding a proper amount of Ca Al-LDHs has carbonfixing effect.When BDP/PER/Ca Al-LDHs mass ratio is 1/2/22 and the total addition amount is 50 wt.%,LOI,UL-94,tensile strength and elongation at break reaches 27%,V-0 level,10.76 MPa,96.58%,respectively.Moreover,the peak heat release rate(pkHRR)and total heat release(THR)of the composites are lower,the ignition time(TTI)and combustion time are longer,and a compact and complete carbon layer is formed.Another intumescent flame retardant system was prepared with phenolic resin(PF)as carbon source,ammonium polyphosphate which coated with melamine formaldehyde resin(MFAPP)as acid source,magnesium hydroxide(MH)which could enhance carbon fixation ability as gas source,which was used for EVA.UL-94,LOI,TGA,CCT and SEM measurements show that the flame retardant effect of PF/MFAPP/MH system is better than that of PF/APP/MH system.When the mass ratio of PF/MFAPP/MH is2/1/2 and the total addition amount is 50 wt.%,the LOI of composite is 26.5%,UL-94 reaches V-0 level,the tensile strength is 7.71 MPa,and the elongation at break is298.88%.The final carbon residue is 32.28%,which is increased by 2.71% higher than the theoretical calculation value.Moreover,both pk-HRR and THR are reduced,and the carbon layer formed has a compact and complete structure.The reactive extrusion product of triglycidyl isocyanurate(TGIC)and melamine(MEL)was used as the char-forming masterbatch,which was compounded with APP to form a new IFR system for flame retardant EVA.The ring-opening reaction during melt blending,as well as the flame retardant and water absorption properties of EVA composites were studied by means of Fourier Transform Infrared(FT-IR),LOI,UL-94,TGA,SEM,tensile strength and water absorption tests.The results show that when TGIC/MEL mass ratio is 1/3,the ring-opening reaction of amino group with epoxy group is sufficient.When the total addition of TM/APP(1/3)is 40 wt.%,the LOI value of EVA composite material is 28.5%,and UL-94 reaches the V-0 level.EVA/TM/APP composites have lower water absorption and higher mechanical properties due to the decrease of the number of hydrophilic hydroxyl groups in the system.After adding APP as an acid source and gas source,the carbon layer after burning of the EVA composites becomes continuous and compact,and the carbon formation amount increases by14.54%.Moreover,the flame retardant system of TM/APP can improve the flame retardancy and thermal stability of EVA.