Synergistic Effect Of Polyoxometalates On Intumescent Flame Retardant Polypropylene

Intumescent flame retardant(IFR)is a kind of environment friendly flame retardants,and wildly used in many fields.However,the flame retardant efficiency of IFR is not satisfied.Generally,in order to pass the UL-94 V-0 testing,in polypropylene(PP)composites,no less than 25 wt% APP/PER is needed.Too much addition of flame retardants would decrease the mechanical properties of PP and rise its price.So it is pressing to improve the flame retardant efficiency of IFR.Compared with other methods,adding synergist is more simple and efficient.In this paper,we synthesized 5 kinds of polyoxometalates(POMs)as synergists,and studied their synergist effect to ammonium polyphosphate/ Pentaerythrotol(APP/PER = 3/1)in PP composites.The mechanism of flame retardant is speculated,and the main research contents are as follows:1)[BMim]6Co W12O40(Co W1)and [BMim]5Co W12O40(Co W2)are prepared,and the synergistic effect of Co Ws on flame retardancy of PP/IFR composites is studied.With the addition of 16 wt% IFR and 1 wt% Co Ws,the PP composites achieve the UL94 V-0 rating and get LOI value 28.0,27.5,respectively.Additionaly,the PP composites with 14 wt% IFR and 1wt% Co W1 can reach the UL-94 V-1 rating,but the flame retardant property of PP composites with Co W2 added is unsatisfied.This indicates that the addition of Co Ws improves the flame retardant properties of PP/IFR composites,and the synergist effection of Co W1 is better than Co W2.Furthermore,a suitable content of Co Ws can accelerates the reactions between APP and PER at early degradation,promotes the char formation and enhances the quantity of char at high temperature.The color of PP composite with Co Ws added is lighter,compare to other POMS,that provides more potential applications.2)[BMim]6Co W12O40(Co W1),[BMim]3PMo12O40(PMo),[BMim]4Ge W12O40(Ge W)and [BMim]5BW12O40(BW)are prepared and applied as synergists in PP/IFR composites,and the flame retardancy of PP/IFR composites is studied.The results indicate that the POMs all have good synergistic effect on PP/IFR composites,and the synergistic performance of PMo is the best.With the addition of 16 wt% IFR and 1 wt% Co W1,PMo or Ge W,the PP composities reach UL-94 V-0 rating.Even if the total content of flame retardant decrease to 15 wt%,the PP composities with PMo added reach UL-94 V-0 rating.3)The mechanism of synergistc effect of different POMs are discussed further.It is found that POMs have a significant influence on the thermal degradation behavior of IFR.They can accelerate the reactions between APP and PER at early degradation,promote the char formation and enhance the quantity of char at high temperature.As the TGA result shows,the synergistic effect in PP composites of POMs are ordinal for PMo> Co W1 > Ge W >BW.In addintion,POMs haven’t alter the structure of char layers,but change the formation time of char layers.The excellent synergist can accelerate the PP/IFR to release gas at suitable time,then a high quality of the carbon layer is getted.