Reactive flame retardant, also known as structural flame retardant, is a kind of flame retardant that participates in the reaction and binds to the main chain or branch of the polymer during the polymerization or polycondensation process, and overcomes the addition. The flame retardant is easy to migrate, does not lastly maintain the flame retardant effect and destroys the physical properties of the foam. Its stability is good, it is not easy to disappear, the addition amount is small, the toxicity is small, and the influence on polymer performance is also small. The flame retardant element or group can be introduced by an isocyanate or a polyol, and due to technical and cost reasons, a method of introducing a flame retardant element into the isocyanate is currently less used. Such flame retardant polyols mainly include halogen-free phosphorus-containing polyol Exolit OP550, phosphorus-containing reactive flame retardant An-tiblaze PR82, halogenated polyether polyol Ixol M125, and organic phosphorus halogen compound reactive flame retardant FRT-4 , tetrabromophthalate diol, tris(dipropylene glycol) phosphite, diethyl N,N-bis(2-hydroxyethyl)aminomethylphosphonate, and the like. Huang et al. prepared a montmorillonite nanocomposite (c-MMT) by ion exchange. The nitrogen-phosphorus structure containing quaternary ammonium salt was successfully inserted into the interlayer of nano-montmorillonite and added to the polyurethane foam. Among them, the results of the cone calorimeter measurement showed that the peak rate of heat release (PHRR) of the PU system with c-MMT (20% by mass) was reduced by 25% compared with the standard PU. Scanning electron microscopy shows that c-MMT contributes to the formation of carbonaceous material and makes it more evenly distributed during PU combustion, which hinders the transfer of heat and air to the internal substrate, thus effectively playing a flame retardant role. The BASF patent describes a foaming system consisting of a halogenated polyol, a brominated polyol, a flame retardant, and a catalyst, a surfactant, a foaming agent, etc., and the flame spread index of the prepared PUF product, smoke The density exceeds the US flame retardant standards ASTME-84 and FM 4880.
Rotaru et al. synthesized a new polyether polyol with high nitrogen content and good thermal stability by Mannich reaction using diethanolamine, paraformaldehyde, cyanuric acid, propylene oxide and other raw materials, and prepared this Mannich polyol. PUF foam. The results show that PUF foamed by this Mannich polyol has better mechanical strength due to the presence of isocyanuric ring in PU foam system, and has better thermal stability than traditional aliphatic PU foam system. And higher flame retardant efficiency.
Paciorek Sadowska J et al. synthesized a reactive boron-containing flame retardant polyol using N,N'-bis(methylene epoxy-2-hydroxyethyl) urea and a boronic acid derivative, compared with standard PUF. For PUF prepared from such a boron-containing flame retardant polyol, when the mass fraction of boron-containing polyol is increased from 1% to 4%, the compressive strength of PUF is increased from 241.9 kPa to 398.7 kPa. Through the flame test, PUF added with boron-containing polyol can reach the self-extinguishing level with a retention of up to 91.2%, while the standard PUF retention is only 67.3%. The results show that the boron-containing flame retardant polyol is not only a polyol raw material reacted with isocyanate, but also boron and chlorine in the PUF structure can play a flame retarding role. Yanchuk et al. prepared a series of vinyl diphosphate salts and applied them to PUF to improve the flame retardancy of PUF. Experiments show that with the increase of vinyl diphosphate salt content, the flammability of PUF is significantly reduced, and it is extinguished from fire. Biomass resources are abundant and renewable in nature. With the introduction of various environmental laws and regulations and people's awareness of energy conservation, biomass PUF has attracted people's attention. Melissa Heinen et al. used phosphoric acid soybean oil extracted from plants to react with phosphoric acid to prepare phosphorylated polyols, and then reacted with different ratios of phosphorylated polyols with glycerol and ethylene glycol polyesters, using pentane as a blowing agent. A phosphorylated PUF is obtained. SEM, SDT-FTIR and flammability test results show that the phosphorylated PUF produced has the same flame retardancy as commercial products, and the LOI of phosphorylated PUF can even be higher.