双层包裹聚磷酸铵微胶囊合成及其在环氧树脂中阻燃研究

采用原位聚合法制备了蜜胺树脂(MF)和环氧树脂(EP)双层包裹聚磷酸铵(APP),得到一种新型核壳结构的微胶囊阻燃剂(EMFAPP).用傅里叶红外光谱(FTIR)和扫描电镜(SEM)对微胶囊的核壳结构进行了表征;用极限氧指数(LOI)、垂直燃烧等级测试(UL 94)对EMFAPP在EP中的阻燃性能进行了研究.EMFAPP在EP基体中阻燃性能优异,当其添加量大于7%时EP/EMFAPP均通过UL 94 V-0级,LOI值达27.0%以上.与未包裹APP相比,EMFAPP耐水性明显提高;经水处理(75℃,6天)后,EMFAPP/EP仍可保持良好的阻燃性能.采用热重分析对EMFAPP及其阻燃复合物的热降解行为进行了研究,EMFAPP能够促进成炭,EP/EMFAPP(8 wt%)在700℃残炭率达16.2%,但其低温稳定性有所下降.此外,利用热失重-红外联用对EMFAPP/EP的热降解行为进行了研究,探讨相关阻燃机理.

PREPARATION OF DOUBLE SHELL MICROENCAPSULATED AMMONIUM POLYPHOSPHATE AND ITS FLAME RETARDANCY IN EPOXY COMPOSITE

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.