Size stabilization method

There are many classification methods for the method of stabilizing wood size. US A. J. Starnm put these

The method is divided into five categories: 1 mechanically inhibited by cross-lamination; 2 internal or

External finishing; 3 reduce wood hygroscopicity; 4 chemical cross-linking of wood cell wall components;

Learning drugs to premature the cell wall.

L, C. Palka 's classification method for wood size stabilization is shown in the table.

8

*Shown. This classification method is not whether or not chemical treatment is used, but whether it is fine or not.

The chemical reaction of the cell wall components is carried out to separate the wood size stabilization treatment into physical methods and chemistry.

Two major categories of law. This is also a broad definition of classification, sometimes both physical and chemical.

Difficult to divide

.

Physical law

1

. Waterproof treatment

Waterproof treatment is to improve the resistance of wood to water wetting and soaking, which only has resistance to wetting.

The performance is called water repellency. Regarding the strict distinction between wood waterproofing and water repellency, no research report has been reported so far.

Reported, but mainly water repellent treatment.

Water repellent is a relative interface phenomenon between solid surface and water droplets, just like wetting

in contrast. The nature or extent of water repellency is affected by the chemical nature of the solid surface, the amount of adsorbed molecules, and the surface.

Influence of factors such as roughness and porosity.

The test results of various water repellent treatments on wood show that only one year after being placed outdoors for one year, only waxy

The water repellent of the ingredients is the most durable. Contains linseed oil (preferably mixed with paraffin), varnish and silicone

The effect of the water repellent on outdoor exposure is getting worse. In addition, an effective water repellent can absorb the atmosphere.

The pollutants cause the brightness to drop.

The water-repellent rate of the treated materials such as silicone oil and paraffin wax can reach 75 % to 90 %, and the expansion resistance ratio is 70 % to 85 %. Practice has shown that the mixed water repellent is better than a single one, and the concentration of paraffin contained is greater.

The higher the water rate, the less the water-repellent treatment material is exposed to outdoor water content changes, and the dimensional stability is good.

Various methods for stabilizing wood size

square

law

With

Body method

Physical law

  1. Try to make small changes in size when sawing;

  2. . Wetting treatment according to the conditions of use

  3. Fiber direction cross-lamination integrated balance:
    4. a . Vertically intersecting plywood, oriented strand board, b. non-oriented combination of particle board, fiberboard;

  4. Covering treatment:
    5. a outer surface coating, veneer, b , inner surface covering impregnated water-repellent treatment, wood-plastic composite;

  5. Fill the cell cavity:
    6. a . Non-polymeric drug-polyethylene glycol treatment, b . Polymeric pharmaceuticals for the manufacture of wood-plastic composites;

  6. Cell wall expansion:
    7. a non-polymeric drug polyethylene glycol, various salts and sugar treatment, b polymerized drug phenolic resin treatment

Chemical method

  1. Reducing the heat treatment of the hydrophilic group;

  2. Substituting a hydrophilic group for etherification (chloroethylation, etc.), esterification (acetylation, etc.);

  3. Grafting of polymers:
    4. a addition reaction epoxy treatment, b . Free radical reaction to produce wood-plastic composites with vinyl monomers;

  4. Cross-linking reaction
    5. Y -ray irradiation, formaldehyde treatment

The water repellency of the wood is improved after the wood is treated with the phenyl alcohol extract of the bark of Pinus radiata, Pinus koraiensis and Pinus koraiensis.

The reason is that fatty acids and hydroxy fatty acids produce a directional alignment on the surface of the wood. Concentration

5 % of two

After treatment with chromium oxide solution, the wood is resistant to erosion, has good weather resistance, and has low hygroscopicity and good water repellency. this

In addition, there are other metal oxides, such as zinc oxide, zinc hydroxide and other water-repellent effects attributed to metals.

Oxide reacts with the basic structural unit of lignin, guaiacol, to form a water-insoluble complex.

When treated with zinc oxide and zinc hydroxide, it forms a zinc complex with lignin. But when it is processed on a large scale

Due to the presence of strong acid or strong base, it has a deteriorating effect on wood.

2

. Moisture treatment

Use finishing or veneer to delay the diffusion of moist air in wood and reduce wood to water vapor

The rate of sorption, thereby reducing the rate of expansion and surface cracking. The effect of surface finishing depends on the coating

The nature of the environment and the environment in which they are located. All known finishes on the outer surface of wood or

There is more or less penetration of moisture, and its osmosis increases with time. Relatively wet

Degree of periodic variation or weathering test time extended to

The water-repellent effect of these coatings is actually more than 1 year.

Has basically disappeared. Commonly used exterior surface coating materials are grease paint, natural resin paint, phenolic resin

Paint, alkyd paint, nitrocellulose paint, amino resin paint, polyester paint, acrylic paint, polyurethane paint, etc.

In addition, the water-repellent material can be dissolved in a volatile solvent to produce a low viscosity and good fluidity.

The solution is injected into the interior of the wood, and the water repellent material remains on the inner surface of the wood when the solvent evaporates.

The treatment method is called inner surface coating treatment or internal finishing method. This method is often applied to machining components

Temporary moisture protection and temporary protection. Natural resin, wax, and dried rosin, lacquer, etc.

The oil or the like is dissolved in an alkane solvent and then injected into the wood to have a short-term moistureproof effect. As in

The addition of preservatives (such as pentachlorophenol) to the solvent also gives the wood a certain preservative effect.

This coating (coating) treatment can only reduce the rate of water vapor and water conduction in the wood.

Delaying or delaying expansion or contraction caused by changes in moisture, but not changing the final balance of wood

The water rate, its effectiveness against moisture and water repellency is low and short-term.

The low molecular weight phenolic resin is injected into the wood and heated to produce condensation and polymerization.

Late insoluble resin. The wood is dimensionally stable and can be modified to other properties.

When treated with phenolic resin or urea-formaldehyde resin, it will resist swelling as the resin content in wood increases.

(shrinkage) rate increases when the resin content reaches

When 30 % to 40 %, the rate of swelling (shrinkage) increases slowly.

Goldstein

Et al. believe that dimensional stability is closely related to the content of methylol phenol. Resin polymerization

The lower the degree of combination, the higher the content of methylol phenol, and the higher the rate of swelling (shrinkage) of the treated wood. In low relative

The molecular weight resin contains more methylol phenol, which can be shaped with the hydroxyl groups in the wood by high temperature curing.

Hydrogen bonding or chemical bonding. In addition, when treated with a low molecular weight resin, it is better than water.

The swelling effect produced by the material is still large and has obvious compatibilizing effect, which is beneficial to increase the swelling resistance.

(shrinkage) rate, it can be seen that the treatment of phenolic resin with low relative molecular mass stabilizes the wood size

The principle is to make the wood compatibilize and form hydrogen bonds.

High relative molecular mass resin is deposited in the cell cavity, similar to the internal finish, only the inhibitor

The effect of the speed of the inch change, and can not fundamentally improve the stability of the wood size.

The degree of curing of the resin during treatment also has a significant effect on the rate of expansion (shrinkage), and the hardening state is only up to

It has sufficient hardness when it reaches a certain state.

The treatment also has an effect on the mechanical properties of the wood. If the anti-pressure is stronger than the untreated material

Increase the dish size, increase the flexural strength and flexural modulus of elasticity

30 %, hardness and wear resistance are also

Increase, wood toughness is about lower than untreated wood

112 , tensile strength is also reduced. High relative molecular mass

Resin has better toughness, tensile strength and static bending strength than wood treated with low molecular weight resin.

Further, since the hygroscopicity of the phenol resin-treated material is reduced, electrical insulation is thereby changed. And not

Compared to the treated material, the relative humidity is

At 30 %, the intrinsic resistance is increased by about 10 times, and the relative humidity is

90

When the % is increased by 100 to 100 times, the treatment material with an expansion resistance of 60 % to 70 % does not produce

Decaying, it also has an effect on preventing ants and insects.

Phenolic resin is also suitable for the treatment of veneers, and it is possible to manufacture laminated villages or laminates with treated veneers.

wood. Resin treatment in the manufacture of particleboard and fiberboard improves both strength and dimensional stability.

4

. Polyethylene glycol treatment

Impregnation or finishing of polyethylene glycol can make the expansion and contraction of wood smaller, which can reduce wood cracking, warping, torsion, deformation and so on. It is a commonly used wood compatibilizer.

The wooden warship ( wasa ) preserved in the suburbs of Stockholm, Sweden , uses borax and boric acid.

(proportion

3 : 7 ) Polyethylene glycol with a relative molecular mass of 4,000 , prepared as a solution sprayed on the hull

On, to prevent cracking and decay and preserve it to this day. Japan preserves unearthed wood, woodwork, and woodcarving art

The original form is usually treated with polyethylene glycol.

(2) Properties of polyethylene glycol

It is a chain polymer obtained by the addition reaction of ethylene oxide with water or ethylene glycol.

Low molecular weight polyethylene glycol

It is compatible with water in any proportion and can almost completely replace the moisture in the swollen wood. Research, use phase

Molecular mass

1000 polyethylene glycol is the most. The average relative molecular mass is 1000 to 1500 ,

Suitable as a compatibilizer. Relative molecular mass exceeds

3500 , because of the large molecular size, it is not easy to enter

The cell wall of human wood.

( 2 ) Polyethylene glycol treatment of wood

Polyethylene glycol is suitable for the treatment of warm materials and raw materials, generally under normal pressure impregnation, the process is for example

under:

Test for birch wood with 30 mm (radial) X 30 mrn (chordwise) X 5 mm (longitudinal)

Piece, the relative molecular mass is

a 25 % to 30 % aqueous solution of 1000 or 1500 polyethylene glycol ,

The temperature is normal temperature to

80 ° C (according to requirements), immerse the test piece in the solution, the time is 15 ~ 200

Min

Or longer. Then, remove the wood test piece from the solution, and wipe the surface of the test piece with paper or the like.

The solution was dried in an oven and compared to the untreated material. Determination of treated and untreated specimens in dry and wet

The dimensional change in the state, the expansion resistance (shrinkage) rate and the compatibilization rate are calculated, and the dimensional stability is evaluated.

( 3 ) Properties of polyethylene glycol treated materials

1 dimensional stability. With 30% polyethylene glycol aqueous solution, heating at a temperature of (55 Soil 5) ℃

Impregnation

After 20 h , the dimensional stability of four wood specimens such as masson pine was as shown in Table 8 . 2 is shown. By the table

The data shows that the diameter and chord direction of the treated material are significantly reduced, and the shrinkage resistance rate (

ASE ) significantly improved,

Highest reach

68 . 74 . %.

Polyethylene glycol is immersed in the cell wall of the human swelling state, and polyethylene glycol in the cell wall at low relative humidity

The alcohol remains in a swollen state, and the polyethylene glycol becomes an aqueous solution at a high relative humidity, maintaining swelling, unit mass

The amount of PEG produced by the polyethylene glycol is even greater than that of water. Therefore, the size of the treated material is stable.

The formulation is mainly the compatibilizing effect of polyethylene glycol.

The moisture absorption of low molecular weight polyethylene glycol treated materials under the same relative humidity conditions

Larger, if the relative molecular mass is too high, the water solubility performance is deteriorated, and the dimensional stability is also lowered. therefore,

The commonly used relative molecular mass range is

1000 ~ 1500 , the concentration of its aqueous solution is 25 %

30

%. The higher the moisture content of the wood, the higher the content of polyethylene glycol, so the swelling resistance

The higher the rate, the better the raw material is better than the dry material.

The polyethylene glycol treatment is generally carried out in the liquid phase, and it can also be carried out in the gas phase using ethylene oxide. That is

Trimethylamine is used as a catalyst to polymerize ethylene oxide in wood to form ethylene glycol and polyethylene in the cell wall.

M

Alcohol, when the mass increase rate is 22 % to 25 %, the anti-expansion (shrinkage) rate is about 65 %. This treatment

There is a problem in that unreacted trimethylamine deteriorates the material.

2 other properties. Mechanical properties: compressive strength, flexural strength and wear resistance of treated materials

The amount of ethylene glycol retention decreases and the toughness increases.

It can be seen from the stress relaxation in the process of moisture absorption that the untreated material has a maximum stress, while the treated village is

Monotonous reduction.

Due to the compatibilization effect of polyethylene glycol on wood, there is no strengthening of the cell wall, and the microfibril movement ratio

The untreated material is easy, and the slip phenomenon may occur under both compressive and tensile stresses. Lateral load

When the cell wall is easily deformed, the ratio of oil to pine is also high.

Dryness: Polyethylene glycol treated material is hygroscopic and difficult to desorb. The higher the polymer content, the higher the swelling pressure.

Low, the harder it is to dry. The treated material has little cracking when it is dried quickly or at high temperature, and the volume shrinkage rate during drying is also

Small, can improve the pass rate of veneer drying. If the raw material is dried in a polyethylene glycol solution due to thermal diffusion

The coefficient is larger than in air and the water content decreases faster.

Gluing: through various concentrations of polyethylene glycol (relative molecular mass 1000 ) aqueous solution

The research results of the gluing performance of the yellow birch veneer showed that casein glue, cold pressed urea-formaldehyde glue, hot pressed phenolic

Glue, polyethylene glycol content has no effect on the bonding strength and wood breaking rate at room temperature, for other adhesives, poly

The more the ethylene glycol content, the worse the gluing quality. Because the cohesive force of the wood itself changes after the polyethylene glycol treatment

Small, the material surface can absorb more water, thus affecting the interface bonding force. Low relative molecular mass of polyethylene

The diol is compatible with water-soluble adhesives and is added to water-soluble phenolic resins.

30 % polyethylene

Alcohol (relative molecular mass is

200 ), the surface wettability of the material can be improved, and the glue layer can also be prevented.

It is self-drying before hot pressing, which is good for cementation.

Wood treated with polyethylene glycol (for molecular masses 400 and 1500 ), for oily coatings or

The adhesion of alkyd coatings is worse than that of untreated materials.

Corrosion resistance: West treated with various concentrations of polyvinyl alcohol M (molecular weight 1000) solution

Add spruce wood, then use

The enzites trabeasl 7 strain was subjected to a 3 month culture test. Polyethylene II

The alcohol content is reached

When it is more than 18 %, the wood does not cause decay. This is due to the moisture of polyethylene glycol

It has a strong absorption effect, and the water required for the survival of fungi in the cell wall is reduced.

In addition, polyethylene glycol prevents the cracking of the plywood panel and improves the dimensional stability of the wood-based panel.

It has a unique role in preventing light discoloration and improving the light resistance of bleaching villages.

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