Microencapsulated ammonium polyphosphate (EMFAPP) with double shell (melamine-formaldehyde resin and epoxy resin) is prepared by in situ polymerization

which is a typical intumescent flame retardant containning an acid source ammonium polyphosphate (APP)

a blowing agent melamine formaldehyde (MF) and a carbonization agent epoxy resin (EP).Its structure is characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM).The flame retardancy of EMFAPP in EP is studied by limiting oxygen index (LOI) and UL 94 tests.EP/EMFAPP samples can pass V-0 in UL 94 test when the content of EMFAPP is more than 7%

and their LOI value is higher than 27.0%.After water treatment (75℃

6 days)

EP/EMFAPP maintains good flame retardancy while the flame retardancy of APP in EP decreases greatly.So after microencapsulation

the water resistance of EP/EMFAPP was improved remarkably.The thermal stability of EMFAPP and EP/EMFAPP is evaluated by thermogravimetric analysis (TGA).Residue char of EP/EMFAPP (8 wt%) is as high as 16.2% at 700℃.EMFAPP can promote EP to form residue char which will play a great role in the combustion process of polymer composites.Further more

the thermal degradation behaviors of EP/EMFAPP are investigated by thermogravimetry-Fourier transform infrared spectroscopy.Based on the above results

the flame retardant mechanism is discussed.In the process of combustion

EMFAPP releases polyphosphoric acid (PPA) and NH3 firstly.With the increase of temperature

PPA reacts rapidly with OH group of EP resin to release H2O which can reduce the flammability of EP in gaseous phase.Then

along with the degradation of main chain of EP

PPA may react with the oxidised products formed during the thermal degradation and stimulate the formation of a char.After heating beyond a critical temperature

the char begins to swell and then to expand to form an intumescent charred layer.The presence of the charred layer can retard the transfer of heat and prevent underlying materials from further thermal destruction.