Plywood has many advantages such as light weight, good strength, small heat transfer coefficient, easy processing and good decoration. It is widely used in interior decoration and furniture making, but it has the characteristics of easy combustion. In the event of a fire, this material will spread quickly and easily cause a large fire loss. To this end, people pay great attention to the research on flame retardancy of plywood and fire safety characteristics.
First, the burning characteristics of plywood
Ordinary plywood is a flammable material. When the temperature around it is suitable, carbonization, ignition and combustion will occur, and spontaneous combustion will not occur. Plywood is heated under low temperature conditions for a long time, and flameless combustion also occurs, which is rare.
The form of plywood burning is a form of thermal decomposition combustion. When the plywood starts to contact the fire source, it first evaporates water by heat, generates heat, and precipitates some incombustible gases. Then the outer layer begins to decompose the flammable gas, with hydrogen and methane as the most, while releasing heat, and begins to oxidize intensely, and there is flame burning. When the wood that makes up the plywood is completely decomposed, the flaming combustion stops and turns into the flameless combustion stage. Plywood burns violently, and when it is dehydrated at high temperature, it will produce a lot of carbon monoxide, which is the main danger of fire. In addition, when other gases generated in the combustion combine with water vapor, they form a strong irritant, which directly endangers people's lives.
Second, the flame retardant treatment of plywood
Flame-retardant treatment means that after the flame-retardant treatment, the plywood is slowly charred in case of fire, which can effectively suppress the flame spread, suppress the rate of occurrence of harmful gases, reduce it to a minimum, or leave the fire at rest, without continued smoldering.
To solve the flame retardant problem of plywood, we must first pay attention to the following problems. First, to maintain the original decorative, the treated plywood should be suitable for various renovations. Second, the main physical and mechanical properties meet the requirements for use. Third, it is easy to process. In addition, the metal should be corrosive or non-corrosive. Any method of processing must meet these requirements.
(1) Flame retardant treatment method
At present, the flame retardant treatment process of foreign plywood is roughly divided into three types, namely, dipping method, lamination method and coating method.
1. Impregnation method
The flame retardant impregnating solution is impregnated into the formed plywood by pressurization (or decompression), and dried and solidified.
2, lamination method
The flame retardant is added to the binder, configured into a flame retardant rubber sheet, and then glued, formed, and hot pressed to obtain a flame retardant plywood. This method requires the panel to be thin and has a thickness of less than 1 mm. For example, a urine aldehyde resin, a oxycyanamide resin, a resorcin resin, or the like is used, and red phosphorus and a halide (such as barium chloride, tetrabromopropane, etc.) are added to the resin itself or a mixed resin thereof. The binder presses the veneer into a flame retardant plywood.
3, coating method (surface treatment method)
The configured flame retardant or various fireproof coatings are applied to the surface of the plywood by brushing or spraying, and then dried naturally or manually. It can be applied as many times as needed.
In combination with the above methods, the impregnation method is complicated, and the sheet produced by the lamination method has poor flame retardancy, and the coating method is not very satisfactory. In order to make the plywood both flame retardant and maintain the original texture of the wood, overcoming some of the disadvantages of the above treatment methods, a dip lamination method has been studied in China. It manufactures flame retardant plywood by first dipping the panel and then applying the flame retardant glue.
First, effective flame retardant components such as boride, phosphide, and halide are selected, and an appropriate amount of penetrant is added to prepare an impregnation liquid under certain conditions. Through the impregnation process, the flame retardant penetrates into the cell cavity, cell wall and cell gap of the wood to obtain a flame-retardant veneer. Then prepare the flame retardant glue, select the polymer phosphorus compound which is insoluble (or poorly soluble) in water and does not react with the binder under certain conditions as the main flame retardant of the flame retardant glue, and add an appropriate amount of auxiliary flame retardant And a reinforcing agent, uniformly mixed in a binder to form a flame retardant glue. Glue, bundling, hot press forming.
The flame-retardant plywood is produced by the method, the equipment process is simple, the flame retardant performance of the plate is excellent, the decoration is good, and the application range is wide.
(2) Flame retardant treatment agent
The flame retardants currently used in plywood and other wood products are as follows:
1. Boride: It is a kind of inorganic flame retardant with more varieties. There are mainly zinc borate, barium metaborate, boric acid, borax, ammonium fluoroborate and the like. These compounds form a solid solution at high temperatures, coating the surface of the material, insulating the air, and promoting carbonization.
2. Phosphate: Phosphorus-containing compounds are classified into inorganic and organic. The inorganic flame retardant mainly includes ammonium polyphosphate, ammonium dihydrogen phosphate, strontium phosphate, ammonium hexafluorophosphate and the like. Organic flame retardants mainly include trihydropropyl phosphate, tetramethylolphosphonium chloride, triphosphate, etc., and there are many varieties of phosphorus compounds, and the application range is wide. They have the effect of promoting charring and preventing flame spread at high temperatures.
3. Halogen compounds: Halogen-containing flame retardants are mostly organic halides such as tetrabromobisphenol A, tetrabromopropane, various halogenated phosphates, and the like. Inorganic flame retardants are zinc chloride, barium chloride, ammonium bromide and the like. They react with high temperature to form hydrogen halide, react with active free radicals generated during combustion to form poorly reactive groups, prevent chain reactions and reduce combustion rates.
In addition, bismuth titanium compounds and the like are flame retardants excellent in flame retardant effect.
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