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4 Wood modification method
The modification of sawn timber or wood parts by physical and chemical methods can also achieve the purpose of controlling deformation. Since the modification treatment requires an increase in production cost, it is used when the product has special requirements.
4.1 Physical and Chemical Treatment
Physical methods include cover treatment, intracellular filling, and cell wall inflation. Using paraffin oil, beeswax, linseed oil, tung oil and cinnamon resin for water or water treatment, the wood can have better water infiltration and anti-penetration effect; treated with thermosetting PF resin, in addition to inflating the wood In addition, the high temperature methylol phenol at the high temperature forms a hydrogen bond or a chemical bond with the methylol group of the wood, which not only stabilizes the size, but also improves the strength, corrosion resistance and wear resistance of the sawn timber. In addition, water-soluble polyethylene glycol (PEG) is deposited and inflated on the wood cell wall to replace the moisture in the wood, which can also reduce the shrinkage deformation of the sawn timber.
Chemical methods include reduction of hydrophilic groups (heat treatment), displacement of hydrophilic groups (lipidation, etherification reaction), grafting of polymers (epoxy resin, wood-plastic composite treatment), cross-linking treatment of door radiation, formaldehyde treatment) Wait. Heating 160～180 C heat treatment of sawn timber, causing lignin to flow, chemical change of hemicellulose, and bonding of hydroxyl groups in cellulose molecular chain to form hydrogen bond, increasing the stability of sawn timber, but its strength is affected by Certainly affected. The sawn timber is treated with an agent such as acetic anhydride, thioacetic acid, and acid chloride, and the hydrophilic hydroxyl group in the wood is replaced with a hydrophobic acetic acid group, thereby forming an inflation effect to stabilize the size of the sawn timber.
In addition, both the isochlorination treatment and the formaldehyde crosslinking reaction can improve the dimensional stability of the sawn timber.
4.2 Compound Recombination
The use of impregnation, infusion and compounding methods allows the sawn timber to be compounded with other materials, which not only improves dimensional stability but also increases its strength. An impregnated wood formed by impregnating a sawn timber with a synthetic resin; impregnating a dried sawn timber with a low melting point metal or alloy and a metal salt (such as lead, tin, chromium and its alloys and ferrous sulfate), and cooling to form a metal wood; Ethylene monomer infused with sawn wood into a plasticized wood. Further, glulam and plywood which are mechanically suppressed by a cross lamination method (or a recombination method) are used.
5 Other control methods
The change caused by the expansion and contraction of the sawn timber is very small, and is generally not considered. Only in the case of special requirements, the modification method can be considered. Frozen logs can be considered for sawing after heat treatment in the log tank.
The sawn timber is deformed by external force during the stacking process, which can be solved by selecting a reasonable stacking method and adding a spacer. For structural members such as bridges, the maximum load to be subjected to the allowable stress of the wood shall be limited to the elastic limit, and the rheological properties of the creep caused by the long-term load of the member shall be taken into account. A reduction factor of .67. The thin plate is steamed or high-frequency heated, pressurized and shaped, and has a good dimensional stability effect.
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