The cause of wood blackening pollution and its prevention and solution
2024-04-16 12:08:28
1 Features and causes
The most difficult thing to deal with wood discoloration is blackening. The main cause of discoloration is iron adhesion, as well as internal factors such as mold and wood.
The discoloration of iron pollution is caused by the contact of phenolic components in wood with iron, which causes chemical contamination to produce black compounds. It mainly occurs in heartwood parts containing many phenolic components, mostly in small spots or filaments, and sapwood is rare, and iron filings are visible in the center of spotted pollution. Every 1 square meter of eucalyptus (Quercus), as long as 0.8mg of iron filings become ionic, it will cause blackening of the wood.
Black mold reproduction occurs mostly in nutrient-rich sapwood parts, and the discolored parts are convex cotton-like, and the boundaries between the discolored parts and the sound parts are not obvious.
The black heart phenomenon of cedar is caused by the internal factors of the wood, and it is banded black on the surface of the wood. Some of these blackenings have occurred during harvesting, while others occur after harvesting.
Blackening of wood after harvesting is caused by the weak alkaline action of inorganic ions in the wood, or the oxidation of phenolic components in wood in the air.
2 Removal and prevention of blackening
2.1 Removal of Iron Pollution Blackening and Prevention Iron pollution is caused by iron reacting with water to become iron ions and reacting with wood. The method of removing iron pollution is to coat the contaminated area with about 5% aqueous oxalic acid solution, and the black color of the wood can disappear immediately, but it will turn black after a long time. The stronger the light, the faster the wood discolors, and the more likely this color reversion occurs, for example, it will turn black after being placed in direct sunlight for 2 to 3 hours. In order to prevent secondary blackening, the wood can be treated with an aqueous solution of oxalic acid to remove the color, and then phosphate is applied immediately. In terms of price and safety, an aqueous solution of dihydrogen phosphate in a concentration of 5% is most suitable. Fig. 1 shows the photochromic result measured by the light-assisted test after the iron-contaminated eucalyptus was decolorized by oxalic acid, coated with sodium dihydrogen phosphate, and then coated with a polyurethane coating. For comparison, the data of unphosphorized and uncontaminated wood were also recorded. The discoloration of sodium dihydrogen phosphate and non-iron-contaminated eucalyptus was the same, while the oxalic acid-only wood was discolored. Serious color.
The specific methods to prevent iron pollution in the production and processing of wood products are as follows:
1) Avoid contact between iron and wood. In the anti-mildew treatment, the anti-mold agent aqueous solution is placed in an iron can, and then the material is placed therein for impregnation. Since iron is soluble in water and reacts with wood components, it is common to prevent the mold liquid and the surface of the material from becoming black. In order to prevent this from happening, the inner wall of the treatment tank can be coated to separate the iron and the treatment agent solution; when the hot press presses the plywood, if the water combination rate of the single board is too high, the surface of the board will become black, also because of the pressure plate. The iron ions are dissolved in the water of the veneer. To prevent blackening, a stainless steel plate or a hard aluminum plate can be placed between the hot plate and the wood.
(2) Avoid contact between water and iron as much as possible. When the iron is not in contact with the wood, such as when the veneer is cut, the cutting edge of the rotary cutting machine will hit the hard knot, and fine iron powder will continuously splash on the surface of the veneer. In addition, the veneer and the blade are not damaged. Close contact, etc. will cause the monopole to be contaminated with iron. Because the moisture content of the veneer is high, the wood attached to the iron powder portion and the stress concentration portion is likely to be spotted or filamentous. To prevent such pollution, the knife must be ground frequently to keep the blade in a sharp state, while the village is fully softened and then rotated.
(3) Add substances that quickly capture iron. When the boiled water is softened, the iron is dissolved in hot water, and the water dissolved in the iron ions is also contaminated by contact with the wood. In order to prevent such contamination, a ruthenium compound (such as ethylenediaminetetraacetic acid) which can rapidly react with iron ions and capture iron ions can be placed in hot water in advance.
(4) Use of iron substitutes. When the wooden fence made of nails is used outdoors, silky black pollution occurs in the nail part after rain. The prevention method can replace the nail with stainless steel and copper nails.
2.2 Removal and prevention of mildew contamination The black matter produced by the proliferation of the fungus is the fungus itself or. Its metabolites. The best way to remove it is to use alkaline bleach to decompose it. It can be coated or impregnated with about 1% aqueous sodium hypochlorite solution. However, this treatment will also decolorize the wood color and should be used with caution. Mold reproduction requires conditions such as nutrients, air, proper temperature and moisture, and eliminating these conditions can prevent mold-induced discoloration. For example, wood coating anti-fungal agents can not provide nutrients to mold, storage in low-temperature cold storage or drying immediately after material production.
2.3 Removal of black pollution from cedar and prevention The color change of cedar wood can be as deep as lmm below the surface of the wood and is not easy to remove. An effective measure to prevent blackening after harvesting is to apply an acidic substance, a telluride. From the perspective of not affecting the natural color of the wood as much as possible, the sawn wood can be coated with 5% phosphoric acid or an aqueous solution of oxalic acid. Blackened after harvesting is part of the plantation wood, which can be distinguished from the end of the log which wood has been blackened. If the end of the log has become black, the sawn board has turned black.
The most difficult thing to deal with wood discoloration is blackening. The main cause of discoloration is iron adhesion, as well as internal factors such as mold and wood.
The discoloration of iron pollution is caused by the contact of phenolic components in wood with iron, which causes chemical contamination to produce black compounds. It mainly occurs in heartwood parts containing many phenolic components, mostly in small spots or filaments, and sapwood is rare, and iron filings are visible in the center of spotted pollution. Every 1 square meter of eucalyptus (Quercus), as long as 0.8mg of iron filings become ionic, it will cause blackening of the wood.
Black mold reproduction occurs mostly in nutrient-rich sapwood parts, and the discolored parts are convex cotton-like, and the boundaries between the discolored parts and the sound parts are not obvious.
The black heart phenomenon of cedar is caused by the internal factors of the wood, and it is banded black on the surface of the wood. Some of these blackenings have occurred during harvesting, while others occur after harvesting.
Blackening of wood after harvesting is caused by the weak alkaline action of inorganic ions in the wood, or the oxidation of phenolic components in wood in the air.
2 Removal and prevention of blackening
2.1 Removal of Iron Pollution Blackening and Prevention Iron pollution is caused by iron reacting with water to become iron ions and reacting with wood. The method of removing iron pollution is to coat the contaminated area with about 5% aqueous oxalic acid solution, and the black color of the wood can disappear immediately, but it will turn black after a long time. The stronger the light, the faster the wood discolors, and the more likely this color reversion occurs, for example, it will turn black after being placed in direct sunlight for 2 to 3 hours. In order to prevent secondary blackening, the wood can be treated with an aqueous solution of oxalic acid to remove the color, and then phosphate is applied immediately. In terms of price and safety, an aqueous solution of dihydrogen phosphate in a concentration of 5% is most suitable. Fig. 1 shows the photochromic result measured by the light-assisted test after the iron-contaminated eucalyptus was decolorized by oxalic acid, coated with sodium dihydrogen phosphate, and then coated with a polyurethane coating. For comparison, the data of unphosphorized and uncontaminated wood were also recorded. The discoloration of sodium dihydrogen phosphate and non-iron-contaminated eucalyptus was the same, while the oxalic acid-only wood was discolored. Serious color.
The specific methods to prevent iron pollution in the production and processing of wood products are as follows:
1) Avoid contact between iron and wood. In the anti-mildew treatment, the anti-mold agent aqueous solution is placed in an iron can, and then the material is placed therein for impregnation. Since iron is soluble in water and reacts with wood components, it is common to prevent the mold liquid and the surface of the material from becoming black. In order to prevent this from happening, the inner wall of the treatment tank can be coated to separate the iron and the treatment agent solution; when the hot press presses the plywood, if the water combination rate of the single board is too high, the surface of the board will become black, also because of the pressure plate. The iron ions are dissolved in the water of the veneer. To prevent blackening, a stainless steel plate or a hard aluminum plate can be placed between the hot plate and the wood.
(2) Avoid contact between water and iron as much as possible. When the iron is not in contact with the wood, such as when the veneer is cut, the cutting edge of the rotary cutting machine will hit the hard knot, and fine iron powder will continuously splash on the surface of the veneer. In addition, the veneer and the blade are not damaged. Close contact, etc. will cause the monopole to be contaminated with iron. Because the moisture content of the veneer is high, the wood attached to the iron powder portion and the stress concentration portion is likely to be spotted or filamentous. To prevent such pollution, the knife must be ground frequently to keep the blade in a sharp state, while the village is fully softened and then rotated.
(3) Add substances that quickly capture iron. When the boiled water is softened, the iron is dissolved in hot water, and the water dissolved in the iron ions is also contaminated by contact with the wood. In order to prevent such contamination, a ruthenium compound (such as ethylenediaminetetraacetic acid) which can rapidly react with iron ions and capture iron ions can be placed in hot water in advance.
(4) Use of iron substitutes. When the wooden fence made of nails is used outdoors, silky black pollution occurs in the nail part after rain. The prevention method can replace the nail with stainless steel and copper nails.
2.2 Removal and prevention of mildew contamination The black matter produced by the proliferation of the fungus is the fungus itself or. Its metabolites. The best way to remove it is to use alkaline bleach to decompose it. It can be coated or impregnated with about 1% aqueous sodium hypochlorite solution. However, this treatment will also decolorize the wood color and should be used with caution. Mold reproduction requires conditions such as nutrients, air, proper temperature and moisture, and eliminating these conditions can prevent mold-induced discoloration. For example, wood coating anti-fungal agents can not provide nutrients to mold, storage in low-temperature cold storage or drying immediately after material production.
2.3 Removal of black pollution from cedar and prevention The color change of cedar wood can be as deep as lmm below the surface of the wood and is not easy to remove. An effective measure to prevent blackening after harvesting is to apply an acidic substance, a telluride. From the perspective of not affecting the natural color of the wood as much as possible, the sawn wood can be coated with 5% phosphoric acid or an aqueous solution of oxalic acid. Blackened after harvesting is part of the plantation wood, which can be distinguished from the end of the log which wood has been blackened. If the end of the log has become black, the sawn board has turned black.
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