China is rich in bamboo resources, and bamboo is known as the second forest resource, which is an important substitute for wood. However, since bamboo contains more nutrients than ordinary wood, it is easy to produce decay, mildew and insects under warm and humid conditions, shortening the service life. Studying the decay characteristics and anti-corrosion technology of bamboo materials is of great significance for rational and efficient use of bamboo resources and alleviation of the contradiction between supply and demand of wood.
Bamboo resource status
There are more than 75 species and 1,250 species of bamboo in the world, and the bamboo forest area is about 2
2 million hm2. China has abundant bamboo resources, with 39 genera and more than 500 species of bamboo, mainly distributed in 167 counties in 12 provinces (districts) of Fujian, Jiangxi, Hunan, Zhejiang, Sichuan, Guangdong, Anhui, Guangxi, Hubei, Yunnan and Jiangsu. City), China's bamboo forest area accounts for about 1/4 of the world's bamboo forest area, accounting for 2.84% of the national forest area. Therefore, the development and utilization of bamboo resources has realistic and long-term significance for alleviating the contradiction between China's timber supply and demand and further promoting the formation of forestry industrialization.
Anticorrosion of bamboo
Bamboo grows fast, has high yield, early material and wide application. Compared with wood, bamboo has certain differences in structure and properties. It is characterized by high strength, good toughness and high hardness of bamboo. Its main mechanical properties are comparable to hard broad-leaved trees, and it has a wide range as an engineering structural material. Develop application prospects. However, bamboo contains more nutrients, including protein content of 1.5% to 6.0%, soluble sugars of about 2%, starches of 2.02% to 5.18%, fats and waxes. From 2.18% to 3.55%, bamboo and bamboo products are prone to decay, mildew and insects when stored and used under warm and humid conditions. Therefore, the anti-corrosion treatment of bamboo is more important.
Most of the anti-corrosion treatment of bamboo is based on the anti-corrosion treatment method of wood. However, due to the great difference in the anatomical structure of bamboo and wood, it is not possible to mechanically apply the anti-corrosion treatment method of wood.
Anatomical properties and handleability of bamboo
The anatomical characteristics of bamboo have their own characteristics. The internode cells are all longitudinally arranged. Unlike the thin-walled cells and ray cells that are radially distributed like wood, the treatment agent and water cannot penetrate in the ray direction. After the bamboo stems mature, the ducts and screens almost no longer have lateral permeability due to the deposition of colloidal materials and the accumulation of the invaders. The surface of the bamboo is covered with a hard thin layer rich in silicon and wax, so it is difficult for the preservative to penetrate from the radial direction. Due to the difference in the above structure, bamboo is more difficult to handle than wood. Viewed from a vertical perspective, the structure of the bamboo consists of thin-walled cells and vascular bundles (catheters and thick-walled fibers). The end-to-end catheters allow the vertical flow of fresh bamboo to flow very quickly. However, the vascular bundle is unevenly distributed in the bamboo stalk, and the vascular bundle is small and large in the peripheral part of the bamboo stalk, and the vascular bundle is large and small in the central part. The further away from the catheter, the lower the level of penetration, which in turn causes uneven distribution of the preservative in the bamboo. The catheter only accounts for 10% of the volume of the bamboo stalk, so the ability of the preservative to penetrate other tissues around the catheter is weak. The parenchyma that is not penetrated by the preservative is easily a breakthrough for early fungal attack.
Bamboo preservative treatment method
With the increasing prevalence of bamboo anti-corrosion treatment, many countries have studied the anti-corrosion treatment technology of bamboo. According to Japanese reports, resole phenolic resin synthesized with phenol and formaldehyde is a low molecular weight and low viscosity water-soluble preparation with good permeability to bamboo. After the resin is infused with bamboo, heat treatment or acid treatment can produce a water-insoluble ternary structural polymer compound, which is odorless, non-toxic, non-bleeding and volatilized, and has long-lasting anticorrosive properties. Bamboo treated with this preservative, whether used indoors or outdoors or buried in the soil, is not attacked by fungi, and no preservatives are reversed from the bamboo, and its anticorrosive performance is superior to that of commonly used preservatives. However, the cost of treatment with phenolic resin is higher. Nanjing Forestry University dips bamboo products with 0.2% phoxim solution for 3min, bamboo mites through 2~3
d death, the efficacy can be maintained for more than 1 year. The medicament is low in toxicity and long in efficacy, and is an ideal anti-caries agent for the production of bamboo products. Adding 1% of the additive (borax: boric acid: 1; 1) to 5% of the new benzalkonium solution was used to prevent mildew of the bamboo product and also achieved good results. In addition, Nanjing Forestry University has studied the liquid phase acetylation test of Phyllostachys pubescens. The test results show that the liquid phase acetylation treatment of bamboo tablets for a certain time, the acetyl weight gain rate (WPG) of 12.97%, the sample weight loss rate is zero, the anti-corrosion effect is excellent. However, this method is more complicated and costly.
Preservative for bamboo
Preservatives for bamboo are generally divided into four types: fumigant, tar, oil, and water. Fumigants such as ammonia and sulfur mainly act on the surface of bamboo, which is difficult to act on internal fungi and easily pollute the air. The most widely used tar type preservative is creosote, which contains carcinogenic polycyclic aromatic hydrocarbons. It has been eliminated; oil-soluble preservatives such as pentachlorophenol not only have high processing costs, but also are harmful to human health; because water-soluble antiseptics have low toxicity, good effect and no odor, they are currently used more. And mostly composite preservatives.
Commonly used bamboo preservatives
The International Bamboo and Rattan Organization (INBAR) recommended ten formulas for composite preservatives for bamboo in 1994 (mainly from Indian standards). The American Wood Preservation Association (AWPA) developed 17 water-soluble and oil-soluble wood preservatives in 1998. Standard formula. However, some of these agents are highly polluting in the environment. In recent years, they have been banned or restricted in some countries. For example, sodium pentachlorophenol has been banned in most countries. CCA has banned arsenic, and the United States and the European Union have issued regulations. It was banned from use in civilian applications in 2004.
New preservative
Water-soluble low-toxic preservatives are the future direction of preservative development. Currently, low-toxic and high-efficiency preservatives have been developed including: water-soluble alkyl ammonium compounds (AAC), ammonia-soluble quaternary ammonium copper (ACQ), borides, and double Copper dimethyldithiocarbamate (CDDC) and oil-soluble copper/zinc naphthenate, chlorothalonil (CTL), organic iodide (IPBC), pyrethroid, and the like.
Development trend of bamboo anti-corrosion technology
Bamboo anti-corrosion technology should be further studied with reference to the existing achievements in the field of wood anti-corrosion. The focus should be on: (1) developing high-efficiency and low-toxic preservatives suitable for bamboo characteristics; (2) finding more suitable methods for anti-corrosion treatment of bamboo; (3) In-depth study of the anchoring mechanism of bamboo preservatives. In addition, the use of bamboo modification method for anti-corrosion treatment is also a development direction, for example, the use of low molecular weight polycondensate such as phenolic or melamine formaldehyde resin to infiltrate into the bamboo and then polycondensation, or liquid phase acetylation treatment, the advantage is that the corrosion resistance is good, However, the processing cost is high and it is not suitable for widespread use.
At present, the development of wood (bamboo) preservatives has the following characteristics: (1) the use of copper fungicides is an important trend; (2) the use of compound fungicides to develop new types of broad-spectrum, low-volume use and other advantages Composite preservatives; (3) The use of co-bonding means to fix preservatives with wood (bamboo) components is the development direction; (4) The anti-corrosion department generally selects long-acting insecticides and preservatives from related industries. And the development of excellent wood preservatives can reduce research costs and development costs; (5) Biological preservatives extracted and developed from phytochemicals with natural antiseptic properties are important features of 21st century wood (bamboo) preservatives However, the determination of the active ingredients and the cost of large-scale extraction are the main problems of whether such preservatives can be industrially produced. Domestic and foreign research on bamboo anti-corrosion has been carried out in many aspects, but the use of new low-toxic preservatives to treat bamboo has not been implemented in China. The selection of high-efficiency, low-toxic, environmentally-friendly preservatives for bamboo anti-corrosion remains to be studied.
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