1 Wood discoloration and cause Wood discoloration refers to the color change of wood caused by the environment (light, oxygen, water content, temperature) and microorganisms. The causes of discoloration can be divided into two categories: one is chemical discoloration; the other is fungal discoloration.
1.1 Wood chemical discoloration Wood contains a large amount of tannins, pigments, polysaccharides, phenols and alkaloids and other organic matter. Under the action of light and oxygen, the phenolic compounds containing benzene ring structure in the chemical composition of wood occur. Oxidation, discoloration; tannins in chemical composition are in contact with metals for a long time, and are prone to complexation and discoloration. The common chemical discoloration depth is shallow and the discoloration is relatively uniform, which does not affect the quality and utilization of wood.
1.2 Wood fungus discoloration The main chemical composition of wood is cellulose, hemicellulose and lignin. Under suitable conditions, it can promote the reproduction and growth of common fungi. Common fungi discoloration is mildew and blue. change. Wood surface is often black, green, white and other spots, that is, mildew, which is mostly caused by poor ventilation, high ambient temperature and high humidity. The molds causing mildew are mainly Aspergillus niger and Trichoderma viride. The wood surface caused by wood mildew has a small range of discoloration. Harmful needles are black or light green; black spots on hardwood. The main hazard of wood quality comes from the discoloration of sapwood, often referring to wood blue change, color change in addition to blue, as well as black, pink, green and so on. The fungus that causes blue is the genus of the genus Diptera, the genus of the genus. The blue change of wood is not only found on the surface and end of the wood, but also often penetrates into the interior of the wood, causing deep discoloration, which directly affects the appearance and finishing of the wood and reduces the use value of the wood.
2 The phenomenon of color change and its causes of imported Pinus sylvestris.
2.1 The discoloration phenomenon of oak and pine The initial surface of Pinus sylvestris var. mongolica is blue-green. After shaving 2-3 mm, it is obviously reduced or even removed. It indicates that it is in the initial stage of blue transformation and is limited to the surface range. Some surface area is small, the area after shaving increases, the color is obviously reduced after 10-20mm shaving, but it can not be eliminated; in the later stage of discoloration, the wood is black blue, nearly light black, 50mm thick plate can be transparent. The blue change of Pinus sylvestris var. mongolica in the Alashankou area of â€‹â€‹Xinjiang often occurs from May to October, and it is lighter in winter and spring. The logs of the occurrence site are common at the end and the bark peeling site, and the plate is commonly found at the end and the stacking of the pallets.
2.2 Analysis of the reasons (1) Temperature: The color-changing fungus has a temperature suitable for breeding in May-October (Xinjiang), and the temperature most suitable for growth is 22-25Y. (2) Humidity: The transportation of wood is often carried out by wet materials. The moisture content is 20%, and the fungus is suitable for growth. (3) Nutrients: Wood contains a lot of sugars and starches, and there are enough nutrients needed for fungal growth. This is especially true for Pinus sylvestris. (4) Air: Most fungi require oxygen for growth, and wood exposed to the air provides enough oxygen for fungal growth. (5) Processing cycle: After the harvesting, the wood stagnant time is too long and the sawing process is not dried in time. (6) Protective measures: No effective protective measures have been taken for logs and sawn timber. 3 Prevention and control of the importation of Pinus sylvestris var. sylvestris According to the cause of discoloration and the actual conditions in production, we have achieved the following measures.
3.1 Apply two lime water (CaC0:) to the end and bare parts before importing the logs.
3.2 Before the import of the square material (18) (18cm), it is required to spray a sodium pentachlorophenolate (NaPcP) dilution or other anti-blue modifier.
3.3 After the logs and squares are sawed at the port, they are dried in time. Before the sawn timber is dried, the ends are painted with furfural resin (uF) (or diluted paint). Drying at high temperature in the dry can completely kill the fungus.
3.4 If the sawn timber cannot be dried in time and at high temperature, it can be dried by the atmosphere first. The stacking base is higher than 50cm, facing north and south, and there are many northwest winds in the area. Air dry to 20% below the moisture content and transport.
3.5 Dry finished products are packed in 2-4m: one package, outsourced with waterproof plastic cloth, and lowered by forklift. It is easy to load and unload and facilitate transportation. Conclusion Russia is China's most important importer of softwood. The import of Pinus sylvestris var. mongolica accounts for a large proportion. The wood blue change is the main use defect of the wood. It is of commercial value to prevent and control it in time. Liu Xianzhong (College of Forestry, Xinjiang Agricultural University, Urumqi 830052, China)
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