The Flame Retardance And Mechanism Of Bismaleimide/Aluminum Phosphate Composites

High performance polymers with outstanding integrated properties have beenincreasingly required by the rapid development of cutting-edge fields such as electronicinformation, new energy, aerospace, insulation and so on. Flame retardance becomes oneessential property besides good processing characteristics, high thermal and mechanicalproperties. However, almost all polymers are lack of flame retardance. Lots of researcheshave proved that the addition of flame retardants into a polymer is an easy and effectiveway to prepare flame retarding polymers. Recently, inorganic flame retardants haveattracted wide attentions because of their low toxicity and non-corrosiveness, which canmeet the developing trend of green and high efficient flame retardants. However, highloading is the commom problem of inorganic flame retardants, so looking for a new kindof inorganic flame retardant with high efficiency is the subject of this study.First, bismaleimide resin (BD)/commercially available aluminium phosphate (cAP)composites were prepared. The flame retardant tests (limiting oxygen index test andmicroscale combustion calorimeter) show that BD/cAP composites have significantlyimproved the flame retardancy than BDresin. The flame mechanism of cAP and the effectof cAP on the thermal stability and charring process of BD resin were studiedsystematically.Second, from the perspective of designning molecular morphology, three differentmorphologies of AP were synthesized through controlling the reaction temperature byhomogeneous precipitation method. The synthesized APs are spherical (sAP), hexagonal(hAP) and wafer (wAP), and all of them are NH4+-AP. After thermally treated at150oC,the treated hAP (t-hAP) has similar particle size (1-2μm) as cAP, but they have quitedifferent chemical and morphological structures. Thus, BD/t-hAP and BD/cAP composites with different contents of fillers were prepared, and their flame retardancy and mechanismwere intensively investigated. BD/t-hAP composites could not be ignited under theirradiation flow at35kW/m2, however, BD/cAP composites could, preliminarily meaningthat t-hAP has much better flame retarding effect than cAP. In order to make a quantitativecomparison, the sparking manner was used to carry out cone calorimeter tests for bothBD/t-hAP and BD/cAP composites. Cone calorimeter results show that t-hAP is anefficient flame retardant with outstanding smoke suppression. With the addition of only5wt%t-hAP into BD resin, the peak and total heat releases (pHRR and THR) is42.3and47.8%of that of BD resin, respectively; moreover, the total smoke production (TSP) isonly32.7%. The pHRR, THR and TSP of BD/5cAP composite are71.3%,76.5%and66.5%of that of BD resin, respectively. These attractive data demonstrate that t-hAP notonly has much better flame retarding effect than cAP, but also exhibits advantage overclassic flame retardants such as Mg(OH)2and Al(OH)3. The good flame retarding effect oft-hAP is mainly attributed to three effects resulting from the unique structure of t-hAP.First, the strong hydrogen bonding between t-hAP and DBA endows t-hAP with gooddispersion in BD resin and thus high crosslinking density of BD/t-hAP composite. Second,hexagonal sheet structure of t-hAP has good flame barrier ability, and the formation of charlayer reinforced with t-hAP can act as an effective barrier to resist the transmittance of heat.Third, t-hAP can release H2O and NH3to dilute flammable gas during combustion.