A method of improving the fire resistance of wood by physical or chemical methods. The purpose is to slow down the burning of wood, so as to prevent the occurrence of fire, or to gain time and quickly eliminate the fire that has already occurred. Wood is a flammable material with high hydrocarbon content. So far, there is no way to keep wood from burning when it is near the fire source. The requirement of wood flame retardant is to reduce the burning speed of wood. Reduce or block the flame propagation speed and accelerate the carbonization process of the combustion surface. This is very important for industrial sectors such as construction, shipbuilding and vehicle manufacturing.
general situation
In the 4th century BC, the ancient Romans knew that wood was soaked in vinegar, and then alum solution was used to enhance its fire resistance. In ancient Greece, Egypt and China, it was also impregnated with seawater, alum and brine to improve the flame retardancy of wood. But until 15 ~ 16 century, the methods of flame retardant treatment were relatively simple. It was not until 17 ~ 18 century that patented flame retardants and treatment methods began to appear. However, as an industrial technology, wood flame retardant was first developed in some industrialized countries in Europe and America at the end of 19 and the beginning of the 20th century, and formed a flame retardant treatment industry. In the 1940s, the need of war accelerated the development of this industry. In 1950s and 1960s, inorganic salts were still the main flame retardants, but more and new composite flame retardants were adopted, which enhanced the flame retardant effect. After 1960s, organic flame retardants, especially resin flame retardants, were developed, which made it possible to overcome the shortcomings of easy loss and moisture absorption of inorganic salts.
Mechanism of wood combustion and flame retardant When wood is exposed to high temperature of 100℃, the moisture in wood begins to evaporate. When the temperature reaches 180℃, combustible gases such as carbon monoxide, methane, methanol and tar with high ignition point begin to decompose and produce; When the temperature is above 250℃, wood pyrolyzes rapidly, releasing a large number of combustible gases, which can be ignited and burned under the action of oxygen in the air; At 400 ~ 500℃, the wood components are completely decomposed and the combustion is more intense. The highest temperature produced by combustion can reach 900 ~ 1 100℃.
When wood is burned, the surface layer gradually carbonizes, forming a carbonized layer with lower thermal conductivity than wood (about 1/3 ~ 1/2 of the thermal conductivity of wood). When the carbonized layer reaches enough thickness and remains intact, it becomes a heat insulation layer, which can effectively limit the speed of heat transfer to the inside and make the wood have good flame resistance. Taking advantage of this characteristic of wood and taking appropriate physical or chemical measures to isolate it from combustion sources or oxygen can completely make wood nonflammable, difficult to burn or block the spread of flame, thus achieving the effect of flame retardant.
Wood flame retardant methods include chemical methods and physical methods.
The chemical method is mainly to treat wood with chemical agents, that is, flame retardants. The mechanism of flame retardant is to form a protective layer on the surface of wood to isolate or dilute oxygen supply; Or decompose at high temperature, releasing a large amount of non-combustible gas or water vapor, and diluting the combustible gas released during wood pyrolysis; Or delay the temperature rise of wood, making it difficult to reach the temperature required for pyrolysis; Or improve the forming ability of charcoal and reduce the heat transfer speed; Or cut off the burning chain and let the fire go out quickly. A good flame retardant is safe, effective, durable and economical.
According to the methods of flame retardant treatment, flame retardants can be divided into two categories: ① flame retardant impregnant. Wood was injected by whole cell method. It can also be divided into two categories: inorganic salts and organic substances. Inorganic salt flame retardants (including single agent and compound agent) mainly include diammonium phosphate [(NH) HPO], ammonium dihydrogen phosphate (NHHPO), ammonium chloride (NHCl), ammonium sulfate [(NH)SO], phosphoric acid (HPO), zinc chloride (ZnCl) and borax (NaBaO 10HO). Organic flame retardants (including polymers and resins) mainly include MDP flame retardants made of formaldehyde, melamine, dicyandiamide and phosphoric acid, and UDFP amino resin flame retardants made of urea, dicyandiamide, formaldehyde and phosphoric acid. In addition, a self-extinguishing flame retardant such as organic halogenated hydrocarbon is also under development. ② Flame retardant coating. Spraying on the wood surface. It is also divided into inorganic and organic: inorganic flame retardant coatings mainly include silicates and non-silicates. Organic fire retardant coatings are mainly divided into expansion type and non-expansion type. The former, such as tetrachlorophthalic anhydride alkyd resin fire retardant coating and acrylic latex fire retardant coating. The latter such as perchloroethylene and chlorophthalic anhydride alkyd resin.
Physical method is a method to take measures from the wood structure. Mainly improve the structural design, or increase the cross-sectional size of the component to improve its flame retardancy; Or strengthen heat insulation measures to prevent wood from being directly exposed to high temperature or flame, such as wrapping and sealing components with incombustible materials, installing a firewall, or adding a fire baffle in the wood frame structure, blocking the circulation of hot air with a cross structure, preventing the flame from passing through, and preventing or delaying the temperature rise of wood.
In industrialized countries, chemical methods play a major role in wood fire prevention or flame retardant treatment; In the past, structural measures were mainly used in China, and later chemical methods also developed to some extent. With the increase of high-rise buildings and underground buildings, the development of aviation and marine transportation, the maintenance and protection of ancient buildings and cultural relics, and the application and improvement of wood fire-retardant treatment will become an urgent need.
One of the main uses of wood flame retardant LF- 1 produced by Liaocheng Lianfeng Chemical Co., Ltd. is to produce B-and C-grade flame retardant wood that meets GB8624-2006 "Classification of Combustion Performance of Building Materials and Products".
This product does not contain any other toxic and harmful substances.
LF- 1 flame retardant not only has excellent flame retardant performance, but also can improve the mechanical properties of products, reduce the formaldehyde emission of products, and avoid environmental pollution caused by free formaldehyde.
Compared with the prior art, the invention is characterized in that
1. has no effect on the adhesive strength of the product.
2. The moisture absorption performance is low, and the equilibrium moisture content of the product in high temperature and high humidity environment is consistent with that of ordinary board.
3. It has no influence on the secondary processing performance of veneer and paint.
Flame retardant mechanism
According to the synergistic effect of phosphorus-nitrogen-silicon-boron-sodium, LF- 1 flame retardant was developed.
In case of fire, this compound will produce a series of chemical reactions:
(1) Reflect the heat radiation of the heat source back to the plate, and reduce the temperature of the plate.
② The flame retardant decomposes and absorbs a lot of heat, thus reducing the surface temperature.
(3) The steam and other inert gases generated by thermal decomposition reduce the oxygen concentration around the product and interrupt the combustion chain reaction.
(4) The glassy coating produced by foaming and melting greatly reduces the transfer of oxygen and heat to the interior of fiberboard.
⑤ Quickly combine with the high-energy substance H+ released by wood thermal release to avoid its combustion reaction with oxygen.
Safe to the environment
Environmental protection and toxicology of building materials have attracted increasing attention.
Halogen-containing flame retardants are extremely harmful to the environment and are only used in composite materials and polymers.
LF- 1 flame retardant is developed according to the synergistic effect of phosphorus, nitrogen, silicon, boron and sodium, and does not contain any harmful components to the environment.
Technology of producing flame retardant wood by using flame retardant LF- 1
The flame retardant LF- 1 is white granular fine powder;
PH value (10g/100 ml H2O): 5.5 ~ 7.0.
Water solubility: 30g/100ml H2O(25℃).
Unit density: 600 ~ 700 kg/m3
Water content: less than 3%
Production technology of flame retardant wood-atmospheric pressure impregnation method;
1. Put 750kg of water into a container, add 250kg of flame retardant LF- 1, and stir to dissolve the flame retardant into a transparent solution;
2, putting the wood into a flame-retardant impregnation treatment tank for fixation;
3. Adding a flame retardant into the flame retardant impregnation treatment tank, wherein the liquid level of the flame retardant is more than 65438+/-00 cm higher than the upper surface of the wood;
4. Introducing a heating medium into the heating pipe to keep the temperature of the flame retardant solution at 55-60 DEG C;
5. According to the kind and thickness of wood, the soaking time is 1 ~ 120 hours;
6. Flame retardant absorption: dry flame retardant/dry wood = 1 1 ~ 13%. 3 ~ 5 pieces of wood with the same specifications are taken in advance, labeled and weighed (G0), and the samples are dispersed and put into an impregnation tank; After soaking for a period of time, take out the sample and weigh it (g1); Flame retardant absorption =25*(G 1-G0)/G0. If the flame retardant is not absorbed enough, extend the impregnation time;
7. Take out the wood;
8. Dry to proper water content.
Production technology of flame retardant wood-vacuum high pressure impregnation method;
1. Put 750kg of water in the container, and then add 250kg of flame retardant LF- 1. Stirring to dissolve the flame retardant into a transparent solution;
2. Put the wood into a high-pressure impregnation tank and cover it;
3. vacuumize to 600-650 mm Hg and keep it for 30-60 minutes;
4. Open the valve connected with the flame retardant storage tank, introduce the flame retardant into the high-pressure impregnation tank through vacuum, release the vacuum when the flame retardant is full of the impregnation tank, and close the vacuum valve;
5. Slowly increase the pressure to 0.8 ~ 1.2 MPa and keep it at 1 ~ 4 hours. The heat preservation time depends on the type and thickness of wood;
6. Flame retardant absorption: dry flame retardant/dry wood = 1 1 ~ 13%. Take 3 ~ 5 pieces of wood with the same specifications in advance, label and weigh them (G0). The samples were dispersed in the dipping tank, dipped for a period of time, then taken out and weighed (G 1), and the flame retardant absorption was 25 * (G 1-G0)/G0. If the flame retardant is not absorbed enough, extend the impregnation time.
7. Relieve pressure, discharge chemicals, and close the booster valve and the valve connecting the flame retardant storage tank;
8. Vacuum to 600 ~ 650 mm Hg, and keep it for 10 ~ 15 minutes;
9. Remove the vacuum and take out the wood;
Drying to proper water content.
test result
Research progress on flame retardant properties of wood and wood-plastic composites
project
rule
result
fire resistance
Figuera
≤250 W/s
98
Logical file system
& lt sample edge
miss
THR600
≤ 15MJ
8.7
Smola
≤ 180m2/s2
Fifty-six
TSP600
≤200 square meters
27
Burning droplets/particles
Less than 10 second
not have
The flame retardant mechanism of wood mainly includes covering theory, thermal theory, nonflammable gas dilution theory, free radical trapping theory, carbon content increase and volatile matter reduction theory; The flame retardant treatment of wood-based panels is mainly two methods: adding flame retardant and plate treatment. High pressure treatment is the most important industrialization method at present. Phosphorus, nitrogen and boron flame retardants represented by LF- 1 and LF-2 are still the mainstream of wood flame retardants. The research on flame retardancy of wood-plastic composites is still in its infancy, and wood fiber and matrix are generally used for flame retardancy. Developing high-efficiency intumescent wood flame retardant and applying nanotechnology to the manufacture of wood flame retardant, and developing multifunctional composite flame retardant with high flame retardant efficiency, low smoke, low toxicity and environmental protection will be the development direction of flame retardant research in the future.