Delayed catalysts are also known as polyurethane delayed catalysts. They have a longer operating time than conventional catalysts and do not interfere with later curing.
The delayed catalyst itself is also a type of positive catalyst, and when added to a catalyst-free system, it only speeds up the reaction rate of the system, not inhibits it.
Thermosensitive catalysts are also a type of delayed catalyst.
The effect of flame-retardant additives can be attributed to several mechanisms: one is the formation of chemical bonds between the flame-retardant additive and the reinforced material, for example, carbon black generates crosslinks in the elastomer through free radical reactions; the other is the flame-retardant additive It works mainly through the occupied volume. For example, the fillers used in thick-coated steel structure fire-resistant coatings and tunnel fire-resistant coatings enhance the strength and adhesion of the fire-resistant coating, reduce its cost and dry and wet density, etc.; In some areas around the additive particles, the structure and properties of the resin polymer are different from those of the bulk polymer matrix.
The surface area causes the overall material to become hard, with lower deformability and higher strength. The resin polymer segment passes through the main polymer matrix. The valence bond or secondary bond is connected to the surface of the filler, which in turn produces the positioning of some adjacent chain segments. Due to the restriction of molecular movement in the interface between flame retardant additives and resin polymer, the glass transition temperature of the resin is increased, which can improve the physical and chemical properties of fire retardant coatings such as strength, water resistance, weather resistance, and flexibility. When the molecules are subjected to mechanical stress with energy absorption, they can slide off the surface of the flame retardant additive. Therefore, the impact energy can be more uniformly dispersed and the impact strength is improved.
In the use of flame retardant additives, the uniform dispersion of flame retardant additives is particularly important, because as many resin polymer chains as possible are connected to the surface of free flame retardant additives to achieve good results.
In addition, it is required that the selected flame retardant additives should improve the flexibility and hardness of the fire retardant coating to some extent, such as spherical flame retardant additives such as calcium carbonate or glass microspheres. Experiments have proved that only fiber flame retardant additives can significantly improve the strength of fire retardant coatings. The use of spherical flame retardant additives cannot increase the load deflection temperature (often called heat distortion temperature) to the same level as fiber flame retardant additives. Flaky flame retardant additives such as talc or mica can significantly increase the heat deflection temperature. Fiber is particularly suitable as a reinforcing agent. When the fiber flame-retardant additive material is stretched, the local tensile stress is transferred to the plastic/fiber interface through shear force and dispersed on the surface of the fiber.
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