Study On The Halogen-free Flame-retardant Waterborne Polyurethane

The waterborne polyurethane (WPU) has the advantages of slight smell, non-pollution, energy saving and so on, taking the water as the dispersion medium. Its development and application obtains more and more attention with the constant improvement of environmental laws and regulations. The WPU material is easy to fire, likely to cause major personnel casualties in the use. Therefore, it is necessary to carry out flame-retardant treatment to the WPU, and fire retardant water-based polyurethane is an important direction in functional.With increasing emphasis on environmental protection today, halogen flame retardants is gradually being replaced, because it does not meet environmental requirements and can release toxic gas leading to death in the fire. In the situation of searching for environmental protection and safe flame retardants, phosphorus and silicone flame retardant have aroused widespread attention, as the important species of halogen-free flame retardant, overcoming effectively the shortcomings of halogen flame retardants. In order to preparate theflame retardant WPU, this paper in three ways chooses the reactive flame retardant [(bis (2-hydroxyethyl) amino) methyl] ethyl phosphate (FRC-6) which has the element of phosphorus (P) in molecule, the nano-silica sol (SRJ) containing the silicon element (Si), which is a find of inorganic flame retardants, these two types of flame retardant compounded together to achieve the purpose of coordination.A series of waterborne polyurethane emulsion were synthesized, which were modified with organic phosphorus (P) of flame retardant. Polyether 210 (N-210), isophorone diisocyanate (IPDI), [(bis (2-hydroxyethyl) amino) methyl] diethyl (FRC-6), diethylene glycol (EX), dimethylol propionic acid (DMPA), and 3-(2-aminoethyl) aminopropyl methyl dimethoxy silane (KH-602) were used as the basic monomer. The influence of the amount of FRC-6 on polyurethane (PU) water resistance, thermal properties, flame-retardant properties was tested by IR, water absorption, thermal analysis (TGA), limiting oxygen index (LOI), micro-combustion calorimetry (MCC), and so on. The results showed that, with the addition of FRC-6, both initial thermal decomposition temperature and heat release rate of polyurethane were reduced, and the water resistance was also decreased, while the carbon yield was improved. The oxygen index was 28% and vertical burn test indicated that the flame retardancy of polyurethane had reached UL-94V-2, when the P content within FRC-6 was 2.31% in the prepolymer. Polyurethane material was from the flammable into a flame, and flame-retardant performance was greatly improved. Organophosphorus compounds play the flame-retardant role mainly through condensed-phase flame-retardant mechanism. Polymer first has to a certain temperature to burn, and in the heated process, the C-P bond in the polymer ruptures becaue of its lower bond energe, then the groups including P react with oxygen to produce phosphoric acid, and next generate particle phosphoric acid and finally obtain poly(vinylidene phosphoric acid). Poly(vinylidene phosphoric acid) as condensed-phase plays the flame-retardant role in two aspects:on the one hand, it covers the surface of polymer in the form of glass membrane, isolating oxygen and stopping burning, on the other hand, it has strong dehydration function and can take the oxygen in the polymer urethane because of it is a kand of stong acid, as a result, promoting polymer to dehydrate to form carbonized layers, reducing or preventing the producing of combustible gas and playing the retardant role.A series of WPU emulsion modified with silica were obtained by the manner of mechanical dispersion, while the nano silica (SiO2 aqueous solution) was measured into the water-based polyurethane emulsion. The modified polyurethane was tested by infrared, water absorption, hardness, mechanical properties, thermal analysis and oxygen index, and the structure was characterized. Also the resistance, thermal properties and flame retardant properties of waterborne polyurethane were studied by changing the addition of silica sol. The results showed that the addition of silica sol which was inorganic flame retardants improved the water resistance, hardness, mechanical properties of the material, while the heat resistance of the material had also been greatly improved. Oxygen index test found that the oxygen index was 26%, when the mass fraction of the Si element was 3.41% in the polyurethane prepolymer.P/Si retardants modified polyurethane was prepared by adding the measured nano-silica sol into the polyurethane emulsion flame-retardant modified with organic phosphorus. The flame-retardant and thermal stability of polyurethane were tested, and the major functional groups in the collaborative system were characterized by Fourier transform infrared spectroscopy. The study found that the oxygen index of PU was from 17% to 33.5% and vertical burn test indicated that the flame retardancy of polyurethane had reached UL-94V-0, when P, Si element was a certain ratio in the mixed system. This showed that the two elements of P, Si has a good synergistic flame retardant effect in the PU.