Preparation And Characterization Of Halogen-free Flame Retardant Polystyrene Foam

Expandable polystyrene foam has a.unique closed cell honeycomb structure,which gives it a high performance,low water absorption,dielectric properties and insulation performance all at an excellent level.However,the structure of polystyrene foam determines its high air circulability,low limiting oxygen index,high heat release rate and very serious smoke generation.Its chemical structure determines that the combustion phenomenon of polystyrene is hard to stop,so it inclines to cause fire in building,external wall insulation and other fields.The flame retardance of polystyrene foam can be improved by coating method.Among all kinds of flame retardants,red phosphorus is an ideal phosphorus-rich substance with excellent flame retardant efficiency.The expanded graphite is able to form a substantial char layer under the heat of fire.Intumescent flame retardants are a series of environmental friendly halogen free flame retardants,which are suitable for application in polystyrene foam.Apart from that,the new bio-based flame retardant is in the new stage of development in the field of flame retardants.Its natural and biodegradable characteristics are consistent with the idea of green environmental protection oin the field of material modification.Firstly,the high efficiency flame retardant red phosphorus and expanded graphite powders were used to bind the flame retardant on the surface of EPS beads after the pre-foaming stage.After that,the EPS foam was prepared by post-foaming molding.When the ratio of red phosphorus to expanded graphite was 1:1 wt,the limit oxygen index of EPS foam reached 26.9%with short self extinguishing time.Both the heat release rate and the maximum smoking rate of the foam decreased significantly.Phosphorus-containing aggregates appeared in the char residue after burning,and adhered to the surface of graphite layers.Besides,the thermal stability of the sample was obviously higher than that of the pure sample,and also higher than the theoretical values obtained by fitting the thermogravimetric curves of the components.The flame retardant mechanism of EPS composites was deduced.Red phosphorus and expanded graphite synergistically formed a more visible carbon layer,isolating oxygen and flammable volatiles,terminating combustion chain reaction and protecting matrix.Secondly,melamine-glyoxal(MG)oligomer was synthesized by modifying the thermosetting melamine resin used in traditional flame-retardant EPS,which reduced the free formaldehyde content and improved the solid content and utilization efficiency.On the basis of amino resin,phosphorus-nitrogen intumescent flame-retardant resin PMG was synthesized,which was mixed with expanded graphite flame-retardant EPS.In the formulation,the limit oxygen index of E-70PMG/16EG samples reached to 32.3%.In cone calorimetry tests,the peak heat release rate was only 172 kW/m2,and the maximum smoke release rate was shown as 0.2 m2/s,much lower than the corresponding value of pure EPS foam.The EPS sample coated with PMG resin formed a carbon layer with considerable quality during combustion.Finally,bio-based flame retardant,starch phosphorylated carbamate(SPC)was synthezed and used to improve the flame retardancy of PS foam by cladding.When the foam was coated with 45 phr of SPC,the oxygen index of the foam reached 28%.The maximum heat release rate in the air was reduced to 365 kW/m2 cone calorimeter test,and the oxygen index reached 35.2%after adding 90 phr of SPC.The addition of SPC made the EPS foam composite achieve better smoke suppression.The maximum rate of smoke generation from the sample decreased to 0.3 m2/s from 1.1 m2/s of the pure sample.