Inorganic flame retardants are good thermal stability, non-volatile, decomposition does not produce corrosive gases, low prices, polyurethane materials used in the more common flame retardant additives, including metal hydroxides, nitrogen, phosphorus, silicon And boron and other flame retardants. In developed countries, the use of inorganic flame retardants can account for more than 60% of the consumption of flame retardants, which in China less than 10%. The disadvantages of inorganic flame retardants are also more prominent, such as the addition of large, poor compatibility with the matrix material, often improve the flame retardant performance, while reducing the other properties of the material. The current direction of development is mainly focused on ultra-fine, microencapsulated and complex collaborative technology.
1.1 metal hydroxide flame retardant
Flame retardant PU metal hydroxide used in the main flame retardant magnesium hydroxide (MH) and aluminum hydroxide (ATH), in particular, the use of their complex, with good synergy. ATH and MH through the decomposition of endothermic and generate water vapor to play a flame retardant performance, while promoting the matrix into the carbon at the same time with the matrix after the formation of dense charcoal charcoal combustion, thereby slowing the heat to prevent oxygen from entering, And the formation of droplets, with low smoke, non-toxic, cheap and so on. Zhang Lintian and other nano-MH and methyl phosphonic acid dimethyl ester (DMMP) used in combination, blended into the PU prepolymer, prepared flame retardant PU elastomer, the results show that the two have a synergistic flame retardant, DMMP can optimize the distribution of nano-MH in the matrix material, the prepared flame retardant PU oxygen index (LOI) up to 43%, tensile strength increased by 75%. TAO Yaqiu and so on discussed the MH, ATH and urea three kinds of flame retardant compound or the use of PU foam on the combustion performance of the study found that ATH and MH flame retardant in the use of its flame retardant effect is lower than urea, but The effect of flame retardant between them is better than the effect when used alone. For the MH and ATH easy to absorb moisture and uneven distribution of particle size, the main use of complex synergistic technology, surface modification and particle size nano to be improved.
1.2 inorganic phosphorus flame retardant
Mainly include ammonium polyphosphate, red phosphorus and various phosphates, phosphorus flame retardant flame retardant mechanism is mainly coagulation phase flame retardant and gas phase flame retardant, such flame retardants are usually used as the main flame retardant. Nitrogen-based flame retardants mainly include melamine (MC), melamine cyanurate and other triazine compounds, generally by decomposition of endothermic or non-combustible gas to play a role in flame retardant. This type of flame retardant is usually colorless, low toxicity, low smoke, low cost, anti-ultraviolet radiation, but poor flame retardant efficiency. In the actual industrial production, phosphorus and nitrogen-based flame retardants are often used in combination, adding nitrogen and phosphorus flame retardant PU in the combustion, will form a lot of P-N bond, making the Lewis acid increased, is conducive to dehydration Carbonylation reaction, and nitrogen-containing groups in the phosphide R-O-P bond after nucleophilic attack, resulting in a large number of phosphorus-containing non-volatile amine salt, with the role of blocking the fire, the use of the two Greatly enhance the flame retardant effect, but in practical applications, often also need to add zinc borate, zinc molybdate and other flame retardant synergist. (CMA) was prepared by using MC and hydroxyphenoxyphosphine acrylic acid as raw materials, and the flame retardant was used for the corrosion of flexible polyurethane foam. The results show that the synthesized CMA has good compatibility with the matrix during the foaming process. When the addition amount of CMA is equal to or more than 10%, the sample can be tested by Cal117A flame retardant property. SinghH and so on to urea, melamine, phosphoric acid and formaldehyde and other raw materials to prepare a new phosphorus - nitrogen flame retardant, and the flame retardant in the polyurethane foam in the flame retardant effect. The results show that the flame retardancy of the polyurethane rigid foam is obviously improved after adding the flame retardant compared with the pure substrate, and after combustion, a large amount of residual carbon layer is generated. The carbon layer is separated from the flame by the substrate, and the LOI increases from 17.8% To 23.8%, the smoke density test shows that both in the flame burning or smoldering conditions, the flame retardant can inhibit the production of smoke and reduce the production of smoke. Ma Ruiying et al. Used in-situ polymerization method to synthesize microcapsules containing red phosphorus-nitrogen flame retardants with superfine red phosphorus as core material and melamine formaldehyde as shell material. The microstructure of microcapsule red phosphorus and its effect on PU The results show that the thermal stability of the coated red phosphorus is improved from 247 ℃ to 430 ℃, and the thermal stability of the microcapsule flame retardant in PU foam is 8%, PU foam bubble from 21.0% to 29.5%.