The Preparation And Properties On Intumescent Flame-retardant PP Based On Ammonium Polyphosphate

Polypropylene(PP) has been widely used in many fields due to its low cost, rich raw material resources, easy processing, excellent mechanical properties, and so forth. However, its limiting oxygen index(LOI) is only 17 ~ 18% and without char residue during burning. Its combustion heat is also among the highest of polymers. These disadvantages have restricted its widespread application. Therefore, it is important and necessary to improve the flame retardancy of PP. In this paper, three kinds of flame retardant polypropylene composites were designed and prepared with melt blending technique. Their comprehensive performances were characterized and the correlative mechanism of flame retardation systems was discussed. The main works and conclusions are listed as follows:1) Ammonium polyphosphate(APP), epoxy resin-coating APP(EP-APP) and silane-coating APP(Si-APP) were compounded with pentaerythritol(PER) respectively as intumescent flame retardant(IFR) to modify PP. The research shows that Si-APP has the best synergistic effect with PER among all APP mentioned above. The reason probablely attributes to its polysiloxane shell. When the mass ratio of Si-APP and PER is 3:1 and the general additive amount is 20%, vertical burning performance of FR-PP can reach UL94 V-1 and the LOI value is 30.2%. Furthermore, PP/Si-APP system achieves better flame retardancy by addition of SiO2 or ZnB as synergistic agents than only adding Si-APP/PER.Especially, SiO2 shows better beneficial flame-retarded effect than ZnB.2) A commercial phosphorus-nitrogen flame retardant(SR201A) and organo-modified montmorillonite(OMMT) were compounded as flame retardant to prepare flame-retarded PP with melt blending technique. The effects of the additive amount of flame retardant system and the component proportion were investigated. The research showed that there is a good synergistic effect between SR201 A and OMMT. FR-PP has good fire retardant effects, and its vertical burning performance can reach UL94 V-0 and the LOI is 36.8% when added 20% SR201 A and 5% OMMT. OMMT can not only enhance the carbon residue formation,but also migrate to the surface of char layer during combustion. The resulting intumscent char layer can barrier effectively the exchange of gas and heat, thus make PP achieve good flame retardancy.3) A commercial phosphorus-nitrogen flame retardant(SR201A) were compounded with a commercial bromine-antimonium-containing flame retardant masterbatch(M) to prepare low-bromine-containing and high-flame-retarded PP. The research showed that there is a certain synergistic effect between SR201 A and M. When added 16% SR201 A and 4% M, the vertical burning performance of FR-PP can reach UL94 V-2 and the LOI is 31.4%. Meanwhile, the mechanical performance of FT-PP is also improved. Its notched impact strength and bending strength are improved as much as 22.4% and 14.9% respectively. Furthermore, both ZnB and ZnO have good synergistic effect with SR201A/M system.They are able to deposites on the surface of char layer during combustion, thus form more compact and solid intumescent char layer.