Guanidine sulfamate and guanidine phosphate are used as expansion additives

The expansion property is produced by the joint action of burning polymer surface coking and foaming, and is currently widely developed for flame retardant, which is characterized by low impact on the environment. Of all flame retardants, intumescent flame retardants have received great attention because they have the lowest total fire hazard when they are fire resistant. The earliest expansion coating material was applied in 1938, and the expansion flame retardant mechanism refers to the formation of a foam insulation layer between the fire and the substrate. In particular, its expansibility depends mainly on the ratio of carbon, nitrogen and phosphorus atoms in the compound. Although the expansive coating can provide good fire protection for the substrate, it also has some disadvantages, such as water solubility, brushing problems, and higher costs.

The flame retardant of plastic materials is generally achieved by adding flame retardant additives to plastics during processing. Since processing requires additives to be able to withstand temperatures of up to 200 ° C, or even higher, expansive flame retardant systems without sufficient thermal stability cannot be added to plastics. The phosphater-pentaerythritol system has been studied as an expansive flame retardant material. For example, systematic studies of a mixture of polyphosphate amine and pentaerythritol have shown that expansion occurs during combustion. Therefore, new expansion materials with appropriate thermal stability have been synthesized to obtain better flame retardant properties.

The most important inorganic nitrogen-phosphorus compound used as an intumescent flame retardant is polyphosphonamine, which is used in intumescent coatings and rigid polyurethane foams. The most important organic nitrogen compounds used as flame retardants are melamines and their derivatives, which are used in expansive varnishes or lacquers. Melamine is used in soft polyurethane foam and melamine cyanurate is used in unreinforced PA. In some countries, guanidine sulfamate is used as a flame retardant for PVC wall paint. Guanidine phosphate is used as a flame retardant in fabric fibers, and melamine phosphate mixtures are used as flame retardants in polyolefin or glass fiber reinforced PA.

All of the compounds mentioned above, polyphosphate amines, melamines, guanidine and their salts, apparently have acceptable environmental effects. The mechanism of PA-6 containing APP, pentaborate amine (NH4B5O8, APB), melamine and their salts was studied by combustion and thermal decomposition. The results show that APP reacts with PA-6 to produce alkyl polyphosphate, which is the precursor of expanded carbon. On the surface of the burning polymer, APB forms an inorganic glassy layer that prevents the oxidation of the carbon and prevents the diffusion of the flammable gas. Melamine and its salts break the H-C-C (O) bond in PA-6, increasing the crosslinking and coking of the polymer. Adding 10% to 30% (by mass) of APP to PA-6 has no effect in low molecular weight polymers (low molar mass) because the limiting oxygen index (LOI) remains at 23 to 24, equivalent to unflame retardant PA-6. However, at 40% and 50% additions, the APP was very effective, with LOI increasing to 41 and 50, respectively.