Flame Retardant in Wood-based Panel Production

Flame Retardant in Wood-based Panel Production

Chemical agents used to prevent wood-based panels from igniting or to delay their combustion are called flame retardants or retardants.

As building materials, the flame retardancy of wood-based panels is an important performance index, and all kinds of wood-based panels without flame retardant treatment are flammable materials. The flammability of wood-based panels limits their use. Therefore, improving the flame retardancy of wood-based panels is a problem that should be solved in the production of wood-based panels.

To improve the flame retardancy of wood-based panels, flame retardants are mainly used to treat wood-based panels. Flame retardants can be single or several complex compounds, inorganic salts or organic compounds. Processing methods, fire retardants can be applied in the production of wood-based panels, raw materials (veneers, particles, etc.) or plain boards soaked or painted. The wood-based panels treated by these methods have fire protection function, to a certain extent, reduce smoke generation, reduce open fire combustion and flame spread. However, general fire retardants can not stop the above three situations at the same time.

Fire retardant should have the following conditions: good flame retardancy; stable chemical performance; non-corrosive, harmless to people and animals; in coordination with production process, it has little impact on the strength and water resistance of sheet products; it does not affect gluing, paint and other secondary processing; it is rich in resources and cheap.

There are many kinds of fire retardants. Fire retardants for wood-based panels are mainly classified as follows:

(1) Phosphorus-nitrogen flame retardants

Including all kinds of phosphates, polyphosphates and ammonium salts, this kind of fire retardant mainly contains two elements, phosphorus and nitrogen, which both play a flame retardant role. Because of their synergistic effect, it is the best kind of flame retardant. Among phosphates, ammonium hydrogen phosphate (NH4) 2HPO4 has the best flame retardant effect. Ammonium polyphosphate (APP) is a series of phosphorus-nitrogen polymers. The higher the degree of polymerization, the better the flame retardant effect. It has resistance to loss and no frost on the surface of the plate.

Phosphorus-nitrogen flame retardant decomposes in flame, releases a large amount of non-flammable ammonia and water vapor, which plays a role in delaying combustion. It also has condensation effect and forms polyphosphoric acid. Polyphosphoric acid is a powerful dehydration catalyst, which can dehydrate and carbonize wood materials, form carbonization layer on the surface of combustion substrates, and reduce the heat transfer rate.

(2) Boron flame retardant

Boric flame retardants include boric acid, borax, sodium polyborate, ammonium borate and other borides. Boron flame retardant is an intumescent flame retardant, which produces water vapor when heated and expands itself to form a covering layer, which acts as heat insulation and air insulation, thus achieving the purpose of flame retardant.

Take boric acid as an example:

B2O3 softens into a glass-like film and covers the surface of the substrate, which has the function of heat insulation and oxygen exhaustion.

Boric acid can reduce flameless combustion and smoke combustion, but it can promote flame propagation, while borax can inhibit surface flame propagation. Therefore, these two substances are often used together. The common weight ratio is borax: boric acid = 1:1, which is characterized by high solubility in water and can adjust the pH value of the solution to make it neutral, thus reducing the corrosion of metals. The advantages of flame retardants such as boric acid and borax are both anti-corrosion and insecticidal functions, with little toxicity and little impact on the strength of the base material, but easy to precipitate is its serious. Insufficient, affect the gluing and surface quality.

(3) Amino Resin Flame Retardant

Amino resin flame retardant is prepared by the reaction of dicyandiamide, melamine and other organic amines with formaldehyde, urea and phosphoric acid under certain conditions. There are many kinds of wood-based panels, which are prepared according to the composition, proportion and reaction conditions, and used for impregnation or brushing treatment of wood-based panels. Its flame retardant mechanism is to foam at 150 – 180 (?) C to prevent fire and release nitrogen at high temperature to dilute the oxygen content in ambient air.

Commonly used are urea-dicyandiamide-formaldehyde monophosphate resin and melamine-dicyandialdehyde monophosphate resin.

Fire retardant coating is applied on the surface of wood-based panels. It has the functions of decoration, anticorrosion, aging resistance, prolonging service life, and also makes wood-based panels have flame retardant function.

Fire retardant coatings are usually classified into inorganic type and organic type according to the composition of the base material. According to fire protection performance, it can be divided into two types: expansion type and non-expansion type. Non-expansive fire retardant coatings are basically based on sodium silicate, mixed with inorganic salts such as asbestos, mica and boride. This kind of coating basically relies on its own high flame retardancy or non-flammability to achieve flame retardant purposes. Intumescent fire retardant coatings are based on natural or synthetic macromolecule polymers, adding foaming agent and carbon source to form a fire retardant system. A honeycomb or sponge like carbon foam layer is formed in fire, and the effect of heat insulation and oxygen isolation is achieved.

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