First, the development of wood fire retardant treatment technology
In China, 5,000 years ago, wood was applied to the outside of the wooden column to prevent fire. Later, the large wooden beams and columns were wrapped with varnish and then coated with incombustible materials such as clay and gypsum. In coastal areas, seawater treated with seawater has long been used to build lighthouses. In the 1960s, China successfully developed non-expanded fire retardant paints, such as peroxyethylene fire retardant paint. In the 1970s and 1980s, successful intumescent fire-retardant coatings, such as amino resin fire-retardant coatings, were used as veneer-type fire protection coatings for wood materials. After the 1980s, many universities and research institutes in China have carried out research work on wood flame retardant treatment. In 1990, the Ministry of Public Security listed "China's Flame Retardant Technology Status and Related Policy Research" in the fire science and technology development plan, and instructed Sichuan Fire Research Institute as the project leader, and participated in the establishment of six universities and colleges including Beijing Institute of Technology. the study. In April 1994, a research report was proposed. At present, a large number of wood flame retardant products have appeared on the market in China, and most of them use ammonium polyphosphate or fixed flame retardant with amino resin.
Second, the flame retardant principle of wood fire retardant
The flame retardant route of the flame retardant is: inhibiting thermal decomposition of wood at high temperature; suppressing heat transfer; and suppressing oxidation reaction of gas phase and solid phase. The above flame retardant pathways are not isolated, but complement each other, complement each other, and cause each other. A flame retardant tends to have more than one flame retardant effect and has its own side surface. Therefore, two or more composite components are generally selected in the wood flame retardant formulation, and the components complement each other to enhance the flame retardant effect and synergistic effect.
Wood fire-retardant treatment can be divided into surface coating treatment and immersion treatment according to the treatment process. The surface coating is applied to the surface of the final processed wood and its products, coated with a flame retardant or a flame retardant coating, or adhered to a non-combustible substance on the surface thereof, and the flame-retardant purpose of the heat insulation and oxygen barrier is achieved through the protection of the layer. The advantage of surface coating is that it can effectively control the spread of fire, less dosage, less impact on the physical and mechanical properties of wood, convenient operation and simple equipment. The disadvantage is that once the protective layer is broken, the flame retardant properties disappear.
Fireproof coatings for wood coating are classified into non-intumescent fireproof coatings and intumescent fireproof coatings according to the flame retardant function of fireproof coatings.
The non-intumescent fire-retardant coating protects the substrate by the flame retardancy or non-combustibility of the coating itself, or by an anaerobic insulating film that releases a non-combustible gas under the flame and forms a glaze on the surface. Non-intumescent fireproof coatings are divided into organic and inorganic types. Non-intumescent inorganic fireproof coatings have good heat resistance, non-combustibility, no smoke, easy availability of raw materials, low price and convenient construction. However, the coating has poor adhesion, is not resistant to moisture, and is prone to cracking. Non-intumescent organic fireproof coatings include alkyd fire retardant coatings, polyurethane fire retardant coatings, epoxy fireproof coatings, and polyvinyl chloride fireproof coatings.
Intumescent fireproof coatings are more varieties than non-intumescent fireproof coatings and have superior performance. They are the development direction of world fireproof coatings. After the intumescent fireproof coating is heated, firstly, the binder in the coating softens and melts, and then the foaming agent reaches the decomposition temperature to release the non-combustible gas, and expands to form a foam layer. At the same time, the dehydrated carbonization catalyst decomposes to form a strong acidic substance, which undergoes a condensation reaction with the foam layer material. When the viscosity of the melt increases, the height of the foam layer increases, and further crosslinking reaction occurs. When the volume of the foam layer reaches a maximum, the foam layer is solidified and charred to form a porous sponge-like carbonized layer structure, and the carbon-containing foam layer has a good oxygen barrier function.
The intumescent fireproof coating consists of a base material, a flame retardant system, an auxiliary agent and a dispersion medium, and has a solvent-type intumescent fireproof coating and a water-based intumescent fireproof coating.
Another method of wood flame retardant treatment is immersion treatment, and the flame retardant used is yttrium phosphate flame retardant, zirconium borate flame retardant, ammonium polyphosphate flame retardant and the like. The flame retardant treatment is divided into two types: atmospheric pressure method and vacuum-pressure method. The atmospheric pressure method is to soak the wood in a flame retardant agent having a low viscosity under normal pressure. The pressurization method is to place the wood in a high-pressure tank, first draw a vacuum, and then pressurize the flame-retardant agent into the interior of the wood. The flame retardant effect of the wood after immersion treatment depends on the drug absorption amount of the drug. The amount of drug absorption depends on four factors, one is the structural characteristics of the wood, the other is the performance of the flame retardant, and the third is the moisture content of the treated wood. Fourth, the flame retardant treatment method, the depth of the flame retardant agent immersed in the interior of the wood depends on the flame retardant treatment method.
Third, the application and problems of wood fire retardant technology
Flame retardant wood is mainly used in:
1. Flame-retardant building structural materials and components for industrial and civil buildings. Such as load-bearing columns, roof supports, fire door frames, etc.
2. Used as interior decoration material for buildings. The Code for Fire Protection of Interior Decoration Design of Buildings stipulates that the burning performance grade of natural wood is B2 grade, which cannot be used as the ceiling decoration material of various places, and the flame retardant treatment can solve the problem that the burning grade of the decoration material is not enough, that is, it can satisfy Reality needs without reducing overall security performance.
3. Used as interior decoration materials for vehicles and ships.
4. Used in the military sector, such as wooden crates for arms and ammunition.
5. For underground buildings, such as tunnel supports in mines.
Wood fire retardant technology has been widely used, but there are still some problems in use. First, there are many kinds of fireproof coatings currently on the market. The units that use the materials are not used according to the use of substrates. For example, steel fireproof coatings are used on wood. The fire protection requirements are not met, and it is time-consuming and time-consuming. The second is to unilaterally promote the function of fireproof coating, intentionally exaggerating the use of fire protection, and there is a misunderstanding in the use. For example, it is considered that the fire performance level of wood can reach Class A (non-combustible) and can be used in any place, but actually Even fire-retardant wood burning performance grades can only be used as B1 grade finishing materials and are not suitable for all locations. Third, during the construction process, it does not work according to the degree. For example, in the decoration project, other materials are often attached to the natural wood, and then the exposed wood is painted or sprayed with fireproof coating without coating the hidden parts. In addition, the construction unit cuts corners, does not follow the operating procedures, does not know the spraying technology, arbitrarily estimates the coating thickness, does not apply the coating according to the specified coating ratio, or the number of paintings is not enough, or does not overcoat according to the specified drying time. The public security fire-fighting institutions also lack the necessary quality inspection methods and uniform acceptance technical standards in supervision and inspection. They cannot quantitatively analyze and measure the flame-retardant degree, which affects the effect of fire-retardant treatment.
To solve the above problems, it is necessary to strengthen the quality inspection work and carry out sampling inspection on the wooden materials used in the building renovation project according to the grade requirements specified in the specification. Increase publicity and education, so that construction and construction units select flame retardants that meet fire protection requirements. Strengthen the standard management of wood flame retardant materials market and other aspects.
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