Effect of wood preservative treatment on wood perf

2022-07-22
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After wood is invaded by fungi, its cells change color, its structure gradually becomes loose and brittle, and its strength and durability are reduced. At the same time, it is easy to corrode in worm eaten and humid air. Therefore, wood used in some humid environments needs to undergo anti-corrosion treatment. Although wood preservative treatment can protect wood and reduce the waste of wood resources, it also has some defects. If the preservative treatment of wood is not good or appropriate, or the use of preservative wood is incorrect, some traditional preservatives and their preservative treated wood will cause some slight harm

wood preservation refers to the technology of preventing wood from being eroded by insects, bacteria and other organisms. As one of the wood processing techniques, it is widely used in the protective treatment of rod, square and plate to prolong the service life of wood and reduce the consumption of wood. The main method of wood preservative treatment in the world is to use an insoluble water-based preservative to put pressure on wood in a closed vacuum tank and inject the preservative into wood fiber at the same time. After pressure treatment, the wood is more stable, and the anti-corrosion wooden pavilion can effectively prevent mold, termites and insects from invading the wood. Thus, the treated wood has excellent corrosion resistance for long-term use in outdoor harsh environment. Now let me explain the relevant knowledge of wood preservative treatment

why use wood preservatives

wood is a natural organic material with obvious biological characteristics, which is easy to be invaded by bacteria, insects, marine borers and other organisms. Before use, according to different application environments, selecting appropriate preservatives and proper treatment can effectively delay wood decay. With the improvement of people's living standards, the demand for wood is also increasing. China's forest resources that can be harvested are very limited, and it is unrealistic to hope to use a large amount of foreign exchange to import timber. Based on the domestic situation, making full use of existing resources and taking the road of sustainable development is the only way for the development of China's wood industry. Preservative treatment of wood and prolonging the service life of wood products are one of the important ways to save wood and protect forest resources. Nowadays, few wood is used after preservative treatment in China, and most of them are traditional wood preservatives that do great harm to human beings and the environment. Therefore, it is necessary to understand the progress of wood preservatives and develop new wood preservatives

characteristics of wood preservatives

(1) high toxic effect: the effectiveness of wood preservatives is mainly determined by their toxicity to pests. The greater the biological toxicity to wood, the stronger the preservative effect. Generally, other agents should be added to the wood. First, it can prevent corrosion and enhance the stiffness, strength and durability of the wood

(2) good durability and stability: wood preservatives should have relatively stable chemical properties. After being injected into wood, they are not easy to volatilize, not easy to lose, and maintain their toxicity for a long time

(3) strong penetration: wood preservatives must easily penetrate into the interior of wood and have a certain depth of investment

(4) high safety: wood preservative has high toxicity to various bacteria and insects that endanger wood, but at the same time, it is low or non-toxic to humans and animals, and will not cause pollution or damage to the environment. With people's concern for the environment and sustainable development, high-efficiency and environmental friendly composite wood preservatives have received due attention, such as isu30 and isu40 of Shanghai Omer

(5) low corrosivity: preservatives should be less corrosive to various metals, and neutral ones are ideal

(6) little damage to wood: after preservative treatment, the mechanical strength, good texture and pleasant color of wood should not affect its serviceability

(7) low price and wide supply: in order to promote the development of wood preservative industry, wood preservatives must have sufficient supply, and the price of raw materials is low and competitive

classification of wood preservatives

(I) water borne (water-soluble) preservatives: wood preservatives that are soluble in water and take water as the carrier. Such as CCA, ACQ, CA-B, CB-A, ACZA, ACC, CC, etc

(II) organic solvent (oil borne, oil soluble) preservative: a wood preservative containing pesticides, fungicides or a combination of the two and dissolved in organic solvents. Such as pentachlorophenol, chlorothalonil, copper naphthenate, and copper 8-hydroxyquinolinic acid

(III) oil preservatives: anticorrosive oil, coal tar, anthracene oil

methods of wood preservative treatment

wood preservative treatment is to inject wood preservatives into the interior of wood with the help of treatment equipment and appropriate treatment technology (or method), so that the preservatives are evenly distributed and fixed in the wood, forming a water-insoluble protective layer with a certain degree of toxicity or resistance to bacteria and insects, playing the role of bacteria and insects prevention. Theoretically, the interior of wood is penetrated by preservatives, and its content reaches the inhibitory concentration of bacteria and insects, which is ideal. A large number of experiments show that the main indicators to measure the quality of wood preservative treatment are the drug loading and penetration of preservatives

with the help of the huge pressure difference inside and outside the wood, the preservative is usually impregnated into the deep interior of the wood and evenly distributed, which can ensure the quality of the preservative treatment, and its products are widely used. Non pressurized treatment is suitable for temporary storage of wood and treatment of special rigid materials (such as veneer and wood chip) due to the low drug loading and shallow penetration of preservatives. In addition, when pressurized, the anti-corrosion liquid is in a closed system and is not exposed to the atmosphere, which has little impact on workers and the surrounding environment. Therefore, at present, the anti-corrosion treatment used in industry requires pressure treatment

soaking method

under normal temperature and pressure, soak the wood in a tank or pool containing preservative solution, and the wood is always below the liquid level. The soaking time depends on the tree species, wood specifications, moisture content and agent type, and the specific content is subject to the specified agent retention and penetration. In order to improve the treatment effect, ultrasonic and heating devices can be set in the soaking solution, and surfactants can be added to improve the permeability of wood. Depending on the immersion time, the immersion method can be divided into instant immersion (from seconds to minutes), short-term immersion (from minutes to hours) and long-term immersion (from hours to one month). It is suitable for veneer and remedial anti-corrosion treatment, as well as temporary wood storage treatment. http://www.168pd.com/

diffusion method

according to the principle of molecular diffusion, with the help of water in wood as the carrier of agent diffusion, the agent diffuses from high concentration to low concentration and spreads to the deep layer of wood. Therefore, the wood treated by diffusion method must meet the following conditions: ① the moisture content of small wood is high enough, usually more than 35% - 40%, and the green wood is the best; ② Water borne agent (diffusion type), with high solubility and slow curing; ③ The ambient temperature and humidity are high. According to the operation process, the diffusion method can be divided into paste diffusion method, immersion or spray diffusion method, bandage diffusion method, drilling diffusion method (or drip diffusion method) and two agent diffusion method. The diffusion method has less equipment investment and simple production process. Easy to apply and promote in the vast rural areas. Similar to this method is the tree sap replacement method

hot and cold tank

uses the principle of thermal expansion and cold contraction to make the gas in the wood expand and contract, resulting in pressure difference, so as to overcome the penetration resistance of the liquid, that is, the wood is heated in the hot liquid. Make the air in the small wood expand, part of the water also evaporates, the internal pressure of the wood is higher than the atmospheric pressure, and the air and water vapor overflow to the outside. At this time, quickly put the wood in a cooler liquid, the wood suddenly cools, the air in the wood produces negative pressure due to shrinkage, and the cold liquid seeps into the wood. According to the treatment method and the configuration of the cold tank, it can be divided into double tank alternating method, single tank hot and cold liquid alternating method and single tank cooling method. Due to the low treatment efficiency (compared with the pressure method), the energy consumption per unit product is large. It is generally used for small batch wood preservative treatment

editor's summary: so far, the most commonly used method to prevent wood decay is to use chemical agents for corrosion prevention. At present, water-soluble preservatives are used most, accounting for about 3/4 of the total use of preservatives. In order to prolong the service life of wood, we can use an appropriate amount of wood preservatives, which is also saving wood and protecting forest resources

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