1. The combustion mechanism of PU rigid foam
PU rigid foam is a cross-linked thermosetting material, and the combustion mechanism is dominated by condensed phase combustion. The combustion process: ignition→coagulation reaction occurs in the condensed phase→carbonation layer forms on the surface of the condensed phase→the thermal decomposition product of the condensed phase enters the gas phase combustion zone→the gas phase reaction zone completes the combustion reaction and releases a large amount of heat.
The characteristic mechanism of PU hard foam combustion is to form a carbonized layer on the surface of the condensed phase. This carbonized layer can effectively hinder the transfer of heat and high temperature reaction products into the solid phase in the gas phase reaction zone, and shield the heat transfer. Reduce the rate of flame propagation. Therefore, the flame retardant measures for PU rigid foams are mainly to reduce the decomposition rate of the condensed phase, improve the compactness and thickness of the carbonized layer, and use PIR (polyisocyanurate structure) foam and chemical or physical expansion flame retardant. The agent and the PU rigid foam having the flame retardant molecular structure can all improve the flame retarding effect of the surface carbonized layer.
2. Combustion mechanism of polystyrene (EPS/XPS) foam
Polystyrene foam is a kind of thermoplastic material. Its combustion mechanism is mainly composed of gas phase combustion as the main control zone. Under the condition of no flame retardant, the carbonization layer is not formed on the surface. The combustion process: ignition→solid phase thermal decomposition reaction→solid phase decomposition product directly enters the gas phase zone→the gas phase zone completes the combustion reaction and releases a large amount of heat. Since the burning surface of the polystyrene combustion process has no carbonized layer structure, the heat release rate of polystyrene is generally larger than that of PU hard foam. Another characteristic of polystyrene combustion is that droplets are generated during the combustion process, and the droplets tend to enlarge the combustion surface, resulting in secondary combustion, which is also an important reason for the fast rate of polystyrene flame transmission. The TVCC fire situation confirmed the fatal shortcomings of polystyrene in the fast transfer of flame rate.
Carbon and its compounds A wide variety of carbons can also be alloyed with iron, the most common being carbon steel; graphite and clay can be used to make pencil cores for writing and painting, and graphite can also be used as a lubricant and pigment as a glass. Molding materials for electrodes and electroplating, electroforming, electric motor brushes, and neutron deceleration materials in nuclear reactors; coke can be used in barbecue, drawing materials and ironmaking industries; gem-quality diamonds can be used as jewelry, industrial Diamond is used for drilling, cutting and polishing, as well as tools for machining stones and metals.
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