Wood is a natural organic material with obvious biological properties and is easily attacked by bacteria, insects, marine borers and other organisms. Before use, according to different application environments, the use of appropriate preservatives and proper treatment can effectively delay the decay of wood. As people's living standards improve, the demand for wood is also increasing. The forest resources that can be harvested in China are very limited, and it is unrealistic to hope that the use of large amounts of foreign exchange to import timber. Based on the domestic market, making full use of existing resources and taking the road of sustainable development is the only way for the development of China's timber industry. Anti-corrosion treatment of wood and prolonging the service life of wood products are one of the important ways to save wood and protect forest resources. China currently uses very little wood after preservative treatment, and most of them use traditional wood preservatives that are harmful to humans and the environment. Therefore, it is necessary to understand the progress of wood preservatives and to develop and develop new wood preservatives.
Overview of research and use of traditional preservatives
So far, the most common method to prevent wood decay is to use chemical agents to prevent corrosion. Water-soluble preservatives are currently the most used, accounting for about 3/4 of the total preservative use. The water-soluble preservatives mainly include: copper chromium arsenic (CCA), copper chromium boron (CCB), fluorochrome arsenic (FCAP), ammonia-soluble copper arsenate (ACA), and acid copper chromate (ACC). These agents have been widely used, with CCA being the most used, accounting for about 60% of the water-soluble preservatives used. At present, the work related to CCA is mainly the research on the solidification and microscopic distribution of CCA in wood.
Due to the narrow range of single preservatives against wood rot fungi and insects, two or more preservatives are generally mixed in a certain proportion, which not only overcomes the shortcomings of the use of a single preservative, but also produces some new ones. characteristic. At present, composite preservatives have been widely used in countries all over the world and have achieved good results.
Research progress on new wood preservatives
Due to the many shortcomings of traditional preservatives, people are forced to study and find new preservatives that are harmless to humans and animals, environmentally friendly, and only toxic to microorganisms. There are many preservatives that meet the above requirements. At present, more researches include water-soluble alkyl ammonium compounds (AAC), ammonia-soluble alkylamine copper (ACQ), boride, and copper dimethyl dithiocarbamate ( CDDC) and oil-soluble chlorothalonil (CTL), organic iodide (IPBC), and the like.
2.1 new water-soluble preservatives
2.1.1 Ammonia-soluble alkylamine copper (ACQ, Ammoniacal Copper Quats)
ACQ is a wood protection agent developed by CSI of the United States. It has been approved by the US Environmental Protection Department and has been standardized. It has been included in the AWPA standard and is mainly produced in Canada, the United States and other countries. It has been put into commercial application as a new generation of wood protection agent. .
According to the AWPA standard, there are three types of ACQ, namely ACQ-A, ACQ-B and ACQ-D. Among them, ACQ-A and ACQ-B were listed in the AWPA standard P5 in 1992, and ACQ-D was included in the AWPA standard P5 in 1995. The difference between Type A and Type B is only the ratio of copper to quaternary ammonium salt. There is no volatilization of ammonia in the D type, the operating conditions are improved, the cost is reduced, and the treated material does not change color.
The commercial ACQ stock solution is dark blue, and when the antiseptic treatment is performed, an irritating gas is volatilized. ACQ has good permeability and is very effective for large-scale wood treatment. For the hard-to-soaked Chinese fir, the sapwood (105mm × 105mm × 1000mm) infiltration rate can reach 100%, the injection amount is above 300kg/m3 (wet quality); the log (100mm diameter, length 1000mm) injection volume reaches 500kg / M3 (wet mass) or more. Laboratory experiments show that when the amount of wood treated with ACQ is 0.7kg/m3 (in terms of copper), the mass loss rate is less than 10%, and the ratio of hygroscopicity to untreated is 0.88, which corrodes the nails. The ratio of sex to untreated is 1.42. When the holding amount reached 7.0 kg/m3 (in terms of copper), in the field experiment, 5a was only slightly decayed, and the underground portion of the control group 3a without any treatment was completely decayed. In addition, ACQ can also be used for the treatment of railway sleepers, and the effect is very good. Because ACQ has volatile gases during processing, operators need protective equipment.
ACQ has the following advantages: 1 has good anti-mildew, anti-corrosion and anti-insect properties; 2 has good permeability to wood, can be used to process large-sized, difficult-to-treat wood and wood products; 3 resistance to loss, long-lasting ; 4 low toxicity does not contain arsenic, chromium, phenol and other substances harmful to humans and animals. ACQ has become a new generation of wood protection agent that replaces CCA, which is widely used in countries all over the world. It has been put into use in the United States, Japan and Southeast Asia. At present, only the “China Railway ACQ Wood Preservative†evaluation of the Ministry of Railways Yingtan Wood Preservative Plant was approved.
2.1.2 Alkyl Ammonium (AAC)
Alkyl ammonium compounds (AAC) are a general term for tertiary ammonium salts and tertiary ammonium salts. They have a wide range of bioavailability, little impact on the environment, good natural degradability, and the appearance and processing properties of treated wood. Similar to untreated materials, it has potential applications. The drug was again included in the AWPA standard P8 in 1998. AAC is water-soluble as a wood preservative and is similar in price to copper-chromium-arsenic preservatives, but its anti-leakage effect is lower than that of copper-chromium-arsenic preservatives.
Among the alkylammonium compounds, quaternary ammonium salts have been used as wood preservatives. The quaternary ammonium salt is a cationic surfactant that has been introduced into the wood protection industry since its discovery of a long-chain alkyl quaternary ammonium salt with strong bactericidal properties more than half a century ago. The screening of quaternary ammonium salts as wood preservatives revolves around the following aspects:
1 Extensive bactericidal, that is, the product has strong killing and inhibiting ability against various wood rot fungi;
2 The product is less toxic, biodegradable, and has no adverse effects on the environment;
3 The product has good solubility in water, light and heat resistance, and storage stability is good;
4 The surface tension should be small, and the infiltration and permeability should be strong;
5 Compatibility with other preservatives and pesticides.
Currently, quaternary ammonium salt preservatives have been developed for many generations. In some developed countries, it is widely used as a wood preservative and wood anti-tarnishing agent, and some varieties can also be used as insect repellents. After studying the relationship between the structure and bactericidal power of quaternary ammonium compounds in detail, it is considered that dimethyldidecyl ammonium chloride (DDAC) is the most promising wood preservative and anti-tarnishing agent. DDAC has a natural affinity for wood and is fixed on wood by cation exchange. It can be used as a wood preservative in contact with the ground, but its fixation speed is slow, usually takes two weeks. It has been registered for use in some countries in Europe and America.
The research on DDAC abroad mainly focuses on the application of preservatives, anti-tarnish agents and anti-mold agents in combination with other agents. Basic research on anti-corrosion and sterilization mechanisms has not yet been systematically reported. The application research of DDAC in wood anti-corrosion has not been carried out in China.
2.1.3 Boride
In recent years, wood preservatives related to boron compounds have increased. As a wood preservative, boron salt is highly toxic to wood-damaging organisms, but it is low-toxic to humans and animals and economical. It has become a more important preservative. AWPA-related preservatives include pyrrole boron (CBA-A, 1995 P5 standard) and inorganic boron (1995 revised standard P5).
The surface of the wood treated with boride is clean, has no irritating odor, is safe to humans and animals and the environment, its pH value is close to neutral, and the wood does not change color after treatment, which has low influence on mechanical strength, and is convenient for coloring, painting and gluing.
Due to the outstanding advantages of boride, it has been widely used at home and abroad. However, when it is used alone, it is easy to lose and the size is unstable after processing. People generally add some additives to the boride preservative to help the boron to be fixed on the wood. Most of these additives are high molecular monomers and polymers, such as ethylene monomer, polyethylene glycol and urea-formaldehyde pre-shrinkage, high. The boiling point resin, etc., can improve the fixing performance of boron, inhibit the loss of boron, and also improve the other properties of wood. There are also some natural substances (proteins) and plant extracts (such as flavonoid tannins) to fix the boric acid on the wood, which improves the durability of boron in the wood. There are also simple physical methods, such as resin, paraffin, alkyd paint and other waterproofing agents applied to the surface of the wood to prevent or reduce the loss of boride.
2.1.4 Copper Dimethyldithiocarbamate (CDDC)
Studies on copper dimethyldithiocarbamate (CDDC) have focused on countries such as the United States and Canada, and were included in the AWPA standard P5 in 1994. Copper dimethyldithiocarbamate (CDDC) is prepared by first treating with copperamine or copper sulfate followed by double treatment with sodium dimethyldithiocarbamate (SDDC), by ligand exchange and wood group Partial interaction, a water-insoluble chelate formed in wood, in which the molar ratio of copper to SDDC is 1:2.
The effect of CDDC treated wood block against white rot and soft rot is better than that of CCA. The resistance to leaching is stronger than that of CCA and ACA, and the fixation time is short (fixed 1h after treatment). The CDDC treated wood will not decrease after drying at high temperature. Its strength index, no corrosion was found when it was in contact with medium carbon steel. The treatment process of CDDC is relatively simple, and the equipment of the CCA treatment plant can be used. When the anti-corrosion plant adopts this agent, the equipment input cost can be reduced.
Foreign studies on the chemical interaction of CDDC and wood and the microscopic distribution of CDDC in wood, the application of analytical tools include: environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) ), Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray analysis (EDXA). There is no relevant research and application in China.
2.2 New oil-soluble preservatives
2.2.1 chlorothalonil (CTL)
Chlorothalonil (2,4,5,6-tetrachloro-1,3 benzene) (CTL) is a widely used agricultural broad-spectrum fungicide. In the late 1970s, research on the use of chlorothalonil for wood preservation was initiated in search of alternatives to oil-soluble wood preservatives such as creosote and pentachlorophenol (PCP). In 1993, AWPA listed chlorothalonil as the oil-soluble preservative standard P8. The effect of chlorothalonil in the control of certain wood fungi is better than other dosage forms. It does not cause genetic mutations in mammals, can be combined with soil particles and is hardly soluble in water, does not pollute the water environment, and does not accumulate in the soil. It has a good effect on controlling basidiomycetes, termites and marine bored animals. In the UK, chlorothalonil is considered the drug of choice for pole protection. In recent years, chlorothalonil preparations have been widely used to prevent wood mold, discoloration bacteria, wood rot fungi, soil termites and related treatment processes. At present, China has been able to produce chlorothalonil, but due to cost and other reasons, there are not many applications as wood preservatives.
2.2.2 Organic Iodide
As early as the 1980s, 3-iodo-2-propynyl butyl methacrylate (IPBC) was used as a preservative to treat solid wood and composite materials. In 1998, it was revised to include the AWPA standard P8. Currently, IPBC oil-soluble formulations are mainly used for impregnating joinery. In the coastal city of Hawaii, USA, IPBC and chlorpyrifos have been used in combination to include joinery fittings, laminates, and glulam beams. The results showed that under the severe exposure conditions, the wood had good anti-corrosion and insect infestation after IPBC/chlorpyrifos treatment. Recent IPBC research has focused on compounding with other agents as a wood preservative in contact with the soil. Not yet produced in China.
Trends in the development of wood preservatives
With the development of economy and people's environmental awareness, wood protection technology faces new opportunities and challenges. Developing wood preservatives with low toxicity, high efficiency, non-polluting environment, selectivity and economy is the key to be solved urgently in this industry. problem. At present, the development of wood preservatives has the following characteristics:
â—† The use of copper as a fungicide is an important trend. Copper has a good inhibitory effect on fungi, good antiseptic effect, moderate price, soft environment and harm to humans and animals, so it is widely used in wood preservatives.
â—†Combination of biocide methods The development of new wood preservatives can have a wide range of applications, such as a wide range of applications. However, a good performance of the biocide composite configuration requires a large number of screening experiments.
â—† Preservatives that use a fixed mechanism of covalent bonding with wood components are the development direction. In this way, the preservative can form a stronger chemical bond with the components of the wood, reduce the loss thereof, and improve the long-term effect of the preservative.
â—† The anti-corrosion department generally selects excellent wood preservatives from the long-term insecticides and preservatives in related industries to reduce research costs and development costs. Various fungicides have been developed for use as wood preservatives such as DDAC (quaternary ammonium salts), TCMTB (benzophene), triazoles, chlorothalonil, and the like.
â—† Bio-preservation of phytochemicals extracted and developed with natural anti-corrosion properties is an important feature of 21st century wood preservatives, but the determination of active ingredients and the cost of large-scale extraction are the main problems of whether such preservatives can be industrialized.
Overview of research and use of traditional preservatives
So far, the most common method to prevent wood decay is to use chemical agents to prevent corrosion. Water-soluble preservatives are currently the most used, accounting for about 3/4 of the total preservative use. The water-soluble preservatives mainly include: copper chromium arsenic (CCA), copper chromium boron (CCB), fluorochrome arsenic (FCAP), ammonia-soluble copper arsenate (ACA), and acid copper chromate (ACC). These agents have been widely used, with CCA being the most used, accounting for about 60% of the water-soluble preservatives used. At present, the work related to CCA is mainly the research on the solidification and microscopic distribution of CCA in wood.
Due to the narrow range of single preservatives against wood rot fungi and insects, two or more preservatives are generally mixed in a certain proportion, which not only overcomes the shortcomings of the use of a single preservative, but also produces some new ones. characteristic. At present, composite preservatives have been widely used in countries all over the world and have achieved good results.
Research progress on new wood preservatives
Due to the many shortcomings of traditional preservatives, people are forced to study and find new preservatives that are harmless to humans and animals, environmentally friendly, and only toxic to microorganisms. There are many preservatives that meet the above requirements. At present, more researches include water-soluble alkyl ammonium compounds (AAC), ammonia-soluble alkylamine copper (ACQ), boride, and copper dimethyl dithiocarbamate ( CDDC) and oil-soluble chlorothalonil (CTL), organic iodide (IPBC), and the like.
2.1 new water-soluble preservatives
2.1.1 Ammonia-soluble alkylamine copper (ACQ, Ammoniacal Copper Quats)
ACQ is a wood protection agent developed by CSI of the United States. It has been approved by the US Environmental Protection Department and has been standardized. It has been included in the AWPA standard and is mainly produced in Canada, the United States and other countries. It has been put into commercial application as a new generation of wood protection agent. .
According to the AWPA standard, there are three types of ACQ, namely ACQ-A, ACQ-B and ACQ-D. Among them, ACQ-A and ACQ-B were listed in the AWPA standard P5 in 1992, and ACQ-D was included in the AWPA standard P5 in 1995. The difference between Type A and Type B is only the ratio of copper to quaternary ammonium salt. There is no volatilization of ammonia in the D type, the operating conditions are improved, the cost is reduced, and the treated material does not change color.
The commercial ACQ stock solution is dark blue, and when the antiseptic treatment is performed, an irritating gas is volatilized. ACQ has good permeability and is very effective for large-scale wood treatment. For the hard-to-soaked Chinese fir, the sapwood (105mm × 105mm × 1000mm) infiltration rate can reach 100%, the injection amount is above 300kg/m3 (wet quality); the log (100mm diameter, length 1000mm) injection volume reaches 500kg / M3 (wet mass) or more. Laboratory experiments show that when the amount of wood treated with ACQ is 0.7kg/m3 (in terms of copper), the mass loss rate is less than 10%, and the ratio of hygroscopicity to untreated is 0.88, which corrodes the nails. The ratio of sex to untreated is 1.42. When the holding amount reached 7.0 kg/m3 (in terms of copper), in the field experiment, 5a was only slightly decayed, and the underground portion of the control group 3a without any treatment was completely decayed. In addition, ACQ can also be used for the treatment of railway sleepers, and the effect is very good. Because ACQ has volatile gases during processing, operators need protective equipment.
ACQ has the following advantages: 1 has good anti-mildew, anti-corrosion and anti-insect properties; 2 has good permeability to wood, can be used to process large-sized, difficult-to-treat wood and wood products; 3 resistance to loss, long-lasting ; 4 low toxicity does not contain arsenic, chromium, phenol and other substances harmful to humans and animals. ACQ has become a new generation of wood protection agent that replaces CCA, which is widely used in countries all over the world. It has been put into use in the United States, Japan and Southeast Asia. At present, only the “China Railway ACQ Wood Preservative†evaluation of the Ministry of Railways Yingtan Wood Preservative Plant was approved.
2.1.2 Alkyl Ammonium (AAC)
Alkyl ammonium compounds (AAC) are a general term for tertiary ammonium salts and tertiary ammonium salts. They have a wide range of bioavailability, little impact on the environment, good natural degradability, and the appearance and processing properties of treated wood. Similar to untreated materials, it has potential applications. The drug was again included in the AWPA standard P8 in 1998. AAC is water-soluble as a wood preservative and is similar in price to copper-chromium-arsenic preservatives, but its anti-leakage effect is lower than that of copper-chromium-arsenic preservatives.
Among the alkylammonium compounds, quaternary ammonium salts have been used as wood preservatives. The quaternary ammonium salt is a cationic surfactant that has been introduced into the wood protection industry since its discovery of a long-chain alkyl quaternary ammonium salt with strong bactericidal properties more than half a century ago. The screening of quaternary ammonium salts as wood preservatives revolves around the following aspects:
1 Extensive bactericidal, that is, the product has strong killing and inhibiting ability against various wood rot fungi;
2 The product is less toxic, biodegradable, and has no adverse effects on the environment;
3 The product has good solubility in water, light and heat resistance, and storage stability is good;
4 The surface tension should be small, and the infiltration and permeability should be strong;
5 Compatibility with other preservatives and pesticides.
Currently, quaternary ammonium salt preservatives have been developed for many generations. In some developed countries, it is widely used as a wood preservative and wood anti-tarnishing agent, and some varieties can also be used as insect repellents. After studying the relationship between the structure and bactericidal power of quaternary ammonium compounds in detail, it is considered that dimethyldidecyl ammonium chloride (DDAC) is the most promising wood preservative and anti-tarnishing agent. DDAC has a natural affinity for wood and is fixed on wood by cation exchange. It can be used as a wood preservative in contact with the ground, but its fixation speed is slow, usually takes two weeks. It has been registered for use in some countries in Europe and America.
The research on DDAC abroad mainly focuses on the application of preservatives, anti-tarnish agents and anti-mold agents in combination with other agents. Basic research on anti-corrosion and sterilization mechanisms has not yet been systematically reported. The application research of DDAC in wood anti-corrosion has not been carried out in China.
2.1.3 Boride
In recent years, wood preservatives related to boron compounds have increased. As a wood preservative, boron salt is highly toxic to wood-damaging organisms, but it is low-toxic to humans and animals and economical. It has become a more important preservative. AWPA-related preservatives include pyrrole boron (CBA-A, 1995 P5 standard) and inorganic boron (1995 revised standard P5).
The surface of the wood treated with boride is clean, has no irritating odor, is safe to humans and animals and the environment, its pH value is close to neutral, and the wood does not change color after treatment, which has low influence on mechanical strength, and is convenient for coloring, painting and gluing.
Due to the outstanding advantages of boride, it has been widely used at home and abroad. However, when it is used alone, it is easy to lose and the size is unstable after processing. People generally add some additives to the boride preservative to help the boron to be fixed on the wood. Most of these additives are high molecular monomers and polymers, such as ethylene monomer, polyethylene glycol and urea-formaldehyde pre-shrinkage, high. The boiling point resin, etc., can improve the fixing performance of boron, inhibit the loss of boron, and also improve the other properties of wood. There are also some natural substances (proteins) and plant extracts (such as flavonoid tannins) to fix the boric acid on the wood, which improves the durability of boron in the wood. There are also simple physical methods, such as resin, paraffin, alkyd paint and other waterproofing agents applied to the surface of the wood to prevent or reduce the loss of boride.
2.1.4 Copper Dimethyldithiocarbamate (CDDC)
Studies on copper dimethyldithiocarbamate (CDDC) have focused on countries such as the United States and Canada, and were included in the AWPA standard P5 in 1994. Copper dimethyldithiocarbamate (CDDC) is prepared by first treating with copperamine or copper sulfate followed by double treatment with sodium dimethyldithiocarbamate (SDDC), by ligand exchange and wood group Partial interaction, a water-insoluble chelate formed in wood, in which the molar ratio of copper to SDDC is 1:2.
The effect of CDDC treated wood block against white rot and soft rot is better than that of CCA. The resistance to leaching is stronger than that of CCA and ACA, and the fixation time is short (fixed 1h after treatment). The CDDC treated wood will not decrease after drying at high temperature. Its strength index, no corrosion was found when it was in contact with medium carbon steel. The treatment process of CDDC is relatively simple, and the equipment of the CCA treatment plant can be used. When the anti-corrosion plant adopts this agent, the equipment input cost can be reduced.
Foreign studies on the chemical interaction of CDDC and wood and the microscopic distribution of CDDC in wood, the application of analytical tools include: environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) ), Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray analysis (EDXA). There is no relevant research and application in China.
2.2 New oil-soluble preservatives
2.2.1 chlorothalonil (CTL)
Chlorothalonil (2,4,5,6-tetrachloro-1,3 benzene) (CTL) is a widely used agricultural broad-spectrum fungicide. In the late 1970s, research on the use of chlorothalonil for wood preservation was initiated in search of alternatives to oil-soluble wood preservatives such as creosote and pentachlorophenol (PCP). In 1993, AWPA listed chlorothalonil as the oil-soluble preservative standard P8. The effect of chlorothalonil in the control of certain wood fungi is better than other dosage forms. It does not cause genetic mutations in mammals, can be combined with soil particles and is hardly soluble in water, does not pollute the water environment, and does not accumulate in the soil. It has a good effect on controlling basidiomycetes, termites and marine bored animals. In the UK, chlorothalonil is considered the drug of choice for pole protection. In recent years, chlorothalonil preparations have been widely used to prevent wood mold, discoloration bacteria, wood rot fungi, soil termites and related treatment processes. At present, China has been able to produce chlorothalonil, but due to cost and other reasons, there are not many applications as wood preservatives.
2.2.2 Organic Iodide
As early as the 1980s, 3-iodo-2-propynyl butyl methacrylate (IPBC) was used as a preservative to treat solid wood and composite materials. In 1998, it was revised to include the AWPA standard P8. Currently, IPBC oil-soluble formulations are mainly used for impregnating joinery. In the coastal city of Hawaii, USA, IPBC and chlorpyrifos have been used in combination to include joinery fittings, laminates, and glulam beams. The results showed that under the severe exposure conditions, the wood had good anti-corrosion and insect infestation after IPBC/chlorpyrifos treatment. Recent IPBC research has focused on compounding with other agents as a wood preservative in contact with the soil. Not yet produced in China.
Trends in the development of wood preservatives
With the development of economy and people's environmental awareness, wood protection technology faces new opportunities and challenges. Developing wood preservatives with low toxicity, high efficiency, non-polluting environment, selectivity and economy is the key to be solved urgently in this industry. problem. At present, the development of wood preservatives has the following characteristics:
â—† The use of copper as a fungicide is an important trend. Copper has a good inhibitory effect on fungi, good antiseptic effect, moderate price, soft environment and harm to humans and animals, so it is widely used in wood preservatives.
â—†Combination of biocide methods The development of new wood preservatives can have a wide range of applications, such as a wide range of applications. However, a good performance of the biocide composite configuration requires a large number of screening experiments.
â—† Preservatives that use a fixed mechanism of covalent bonding with wood components are the development direction. In this way, the preservative can form a stronger chemical bond with the components of the wood, reduce the loss thereof, and improve the long-term effect of the preservative.
â—† The anti-corrosion department generally selects excellent wood preservatives from the long-term insecticides and preservatives in related industries to reduce research costs and development costs. Various fungicides have been developed for use as wood preservatives such as DDAC (quaternary ammonium salts), TCMTB (benzophene), triazoles, chlorothalonil, and the like.
â—† Bio-preservation of phytochemicals extracted and developed with natural anti-corrosion properties is an important feature of 21st century wood preservatives, but the determination of active ingredients and the cost of large-scale extraction are the main problems of whether such preservatives can be industrialized.
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