RU2339504C2 - Method of deep impregnation of wood - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: preliminary vacuumising is performed at the pressure of 0.05-0.08 MPa, as well as heating of impregnating solution and wood in the same vacuum device, submerging wood into impregnating solution, or in separate vacuum devices, then transferring impregnating solution into vacuum device with wood with preservation of vacuum, wood that is submerged into impregnating solution is maintained in vacuum, after that pressure is increased in vacuum device up to the atmospheric or excessive pressure is pulled, impregnating solution is removed, after wood maintenance it is dried, components of impregnating solution are fixed in wood with the help of fixing compound that forms thermally stable and water-insoluble substances during interaction with impregnating solution. At that processing with fixing compound is done by method of "hot and cold baths", and drying of wood is carried out until residual humidity is 20-25%.

EFFECT: improvement of physical and chemical consumer characteristics.

3 cl, 3 ex

Description

The invention relates to the development of protective reinforcing compositions and technology for deep impregnation of wood, mainly hardwood, to improve its physico-chemical and consumer characteristics.

The advantages of wood as a building and structural material are well known. At the same time, the wood is hygroscopic, easily susceptible to the destructive effects of the atmosphere, has low bio-resistance and high fire hazard.

Their well-known methods of deep wood impregnation are the most effective and important autoclave-diffusion methods (I. G. Romanenkov, F. A. Levites. Fire protection of building structures. M., Stroyizdat, 1991, p.129-131). When implementing a typical variant of autoclave-diffusion impregnation, it is possible to reach the depth of impregnation of aqueous solutions with a healthy sapwood of wood up to 5 mm. The deeper penetration of the impregnating composition into the wood is impeded by the gases dissolved in it and, primarily, carbon dioxide, whose solubility in one volume of water at 20 ° C is 0.88 volumes. Other dissolved gases may also be present in concentrated impregnation solutions. Getting from the working tank into a vacuum autoclave with wood, the impregnating solution immediately “boils” from the gases that are rapidly released from it. At the phase boundary, between the impregnating liquid and the surface of the evacuated wood material, a "gas cushion" is formed that impedes or sharply reduces the ability of liquid to penetrate into the pores of the wood. Part of the solution, which entered the cells and cavities of the timber, continues to emit residual amounts of gas in it, since the wood was previously evacuated. Air-gas plugs, which are formed in the cells and cavities of wood, inhibit the impregnation process even more. The operations have to be repeated many times, which not only increases the time and energy consumption for wood impregnation, but also leads to a decrease in productivity, and if thermally or hydrolytically unstable compounds are used in the impregnation compositions, the compositions can change from one vacuum impregnation cycle to another.

The patent RU 2011511 implements the principle of creating a gradient pressure between the impregnating liquid and wood. The impregnation process is carried out in a hermetically sealed impregnation chamber filled with material and an impregnating liquid and connected to a container in which a deep vacuum is created. At the time of a quick (pulsed) connection of the vacuum chamber and the impregnation tank using a special device in the impregnation chamber there is an abrupt decrease in pressure. As follows from the table given in the said patent, as a result of the implementation of the proposed technology, the absorption of the protective and / or coloring solution (in% by weight of wood) ranges from 4.36% to 63.8%, on average 30-31%), which is completely insufficient to give the wood the necessary level of fire protection, biological resistance, mechanical strength and other characteristics. As is known (I. G. Romanenkov, F. A. Levites. Fire protection of building structures. Moscow, Stroyizdat, 1991, p.130-131), for transferring wood to the 1st group of fire-retardant efficiency (GOST 13363, NPB- 251) it is necessary to introduce at least 90-120 kg of flame retardant per 1 m ^{3 of} material into it, which at the maximum possible concentrations of the most common flame retardants of about 20-22% should be 500-600 kg of impregnating solution per 1 m ^{3 of} wood, i.e. about 100-110%.

As shown in examples of the practical application of the proposed method in a semi-industrial version, the absorption levels of the impregnating solution reach 120-150% by weight of the treated wood, which is much higher than the average standards that provide maximum fire protection.

In the patent FR 2658445, selected as a prototype, describing a method and technology for processing wood or other porous materials in order to stabilize their geometric parameters, reduce porosity and hygroscopicity, the principle of creating a pressure difference between the processed material and the impregnating liquid is also well known and used in practice, for example, antiseptics and wood preservation. The chemical nature of the impregnating compositions and their behavior under the conditions of a vacuum created in the apparatus (monomers of diallyl phthalate, styrene, initiator of the polymerization reaction) do not require vacuum treatment in order to degass them, since initially they do not contain dissolved gases that interfere with the impregnation. At the same time, the mandatory stage of heating the wood and the impregnating liquid before the impregnation, necessary in the proposed method, is contraindicated in the technology of impregnating wood with monomers of diallyl phthalate, styrene, their polymerization initiators, used organic solvents, since an increase in temperature accelerates the polymerization process.

An object of the invention is to improve the quality and durability of wood impregnation, increasing the depth and uniformity of fixation of the components of the impregnating solutions.

The technical result is achieved in a method of deep impregnation of wood, including preliminary evacuation and heating of the impregnating solutions, preliminary evacuation and heating of the wood, impregnation of the wood, treatment with fixing compositions. In this case, preliminary evacuation and heating of the impregnating solutions and wood are carried out in a single vacuum apparatus, immersing the wood in an impregnating solution, or in separate vacuum apparatuses, then transferring the impregnating solution to a vacuum apparatus with wood while maintaining the vacuum. Preliminary evacuation is carried out at a pressure of 0.05-0.08 MPa. The wood, immersed in the impregnating solution, is kept in vacuum, after which the pressure in the vacuum apparatus is increased to atmospheric pressure or excessive pressure is created. Upon completion of the impregnation, the impregnation solution is removed, the wood is dried, the wood is treated with fixing compositions using the “hot-cold baths” method. As fixing agents, compositions are used that, when interacting with impregnating solutions, form thermally stable and water-insoluble substances. Drying of wood is carried out to a residual moisture content of 20-25% after aging of the wood.

The method is as follows.

Pre-evacuation step

The impregnating solution is evacuated in a separate vacuum apparatus until a constant, time-constant pressure of about 0.05-0.08 MPa is established, the solution is heated and, while maintaining a vacuum, transferred to a vacuum apparatus with wood, similarly previously evacuated and heated. Preliminary evacuation of the impregnating solution and wood can be carried out in one vacuum apparatus, while the wood is immersed in a heated impregnating solution, after which a vacuum is created.

As a result, degassing of impregnating solutions and wood takes place, which excludes the possibility of formation of “gas plugs” in the wood in the subsequent process of its vacuum impregnation and provides complete (through) impregnation in one cycle.

Stage of impregnation

After pouring the evacuated wood with the estimated amount of degassed impregnating solution, its supply is stopped, the impregnating apparatus is disconnected from the vacuum apparatus with wood. Maintain a vacuum for 3-4 hours. Then the vacuum is vented to atmospheric pressure or an excess (up to 2 atmospheres) pressure is created above the impregnating liquid and the wood is impregnated until the level of the solution drops, i.e. before the termination of its absorption by wood. Until the end of the impregnation process, the timber should always be under a layer of impregnating liquid. At the end of the impregnation, the impregnation solution is removed.

The stage of aging and drying

During the impregnation, the impregnating solution does not have time to penetrate and evenly distribute in all the anatomical structures of the treated material. Therefore, the impregnated wood is kept for one day at room temperature, after which it is chamber-dried.

As you know, raw birch wood (planks, beams) practically does not lend itself to “forced” drying, undergoing cracking, warping, longitudinal transverse deformations. Even with the most mild drying conditions in drying chambers, the reject rate is 50-60%.

Treated by the proposed methods, the woods of birch, alder, poplar and other hardwoods are easily and without any defects subjected to drying in dryers of any type, even in the most severe temperature conditions. At the earliest stages of drying, due to the evaporation of part of the water from the treated wood in cells, cavities, conducting bundles and other structural and anatomical elements, the concentration of the impregnating solution reaches its saturation limit and the microcrystallization of substances introduced into the wood begins. There is reinforcement, a kind of "cementing" of the cell walls, cellulose fibers of the wood with microcrystals of the components of the impregnating composition. The material hardens, loses its ability to crack, warp, longitudinal and transverse deformations. In fact, already at the intermediate stages of drying, wood becomes a qualitatively new material. It becomes possible to carry out further drying (according to the humidity required by the technological regime of 25-30%) in hard conditions, reducing time and saving energy resources by 3-4 times.

After convective drying to a level of 25-30% moisture, the wood is subjected to the last technological operation — fixing the components introduced into it.

Stage of fixation

The wood is loaded into the impregnation baths, poured with a hot solution of a fixing composition and impregnated in the “hot-cold baths” mode. The amount of absorbed solution determines the completion of the fixation process.

The essence of fixing is reduced to immersion of hot (t ~ 70 ° С) timber removed from a convection drying chamber, which is immediately transferred to a cold bath with a fixing solution.

Typical composition of the fixing solution "F-1".

1. Bischofite 8.5-9.7% (wt.) 2. Aluminum sulfate 13.5-16.0 3. Oxalic acid 1.04-1.6 4. Water rest

Due to the sharp cooling of hot wood when it is immersed in a cold bath with a solution of "F-1" in the wood cavities, a rarefaction occurs, i.e. a vacuum is created. Its depth is not as significant as in vacuum impregnation, but sufficient to absorb 60-80 kg of fixing solution per 1 m ^{3 of} wood. Entering a chemical interaction with previously introduced substances (ammophos, urea phosphate), the components of the fixing solution turn into practically insoluble, chemically stable and high-melting salts: aluminum phosphates, magnesium ammonium phosphate, magnesium oxalates. All of these substances are also effective flame retardants, antiseptics and “cementing” materials. Having formed in wood, these insoluble compounds create an insurmountable barrier both on the path of the initially introduced components to the outside, and on the path of atmospheric moisture, precipitation, and other destructive atmospheric components inside the tree, i.e. perform the role of a protective screen, while cementing, hardening wood, protecting it from fire and biodeterioration. The wood is further dried.

When choosing chemicals for impregnating and fixing solutions suitable for vacuum impregnation of wood, the following conditions and requirements must be met: chemical compatibility of the components and stability of the solutions during storage and operation; environmental cleanliness and safety of both constituent components and finished formulations; high functional properties of the compositions; availability and relatively low cost of components; high solubility of the main components of the compositions and their hydrolytic stability; a sufficiently high thermal stability of solutions, the absence of volatile and gaseous products when working with solutions and during the operation of treated wood; preservation of color, texture, aesthetic properties of processed timber; non-hygroscopicity; lack of extraneous odors; Compatibility with adhesives and paints.

Given the above requirements, for example, the following composition of impregnating and fixing compositions can be proposed:

- impregnating composition: 1 - ammophos, 2 - urea phosphate, 3 - antiseptics, 4 - defoamers (surfactants), 5 - water;

- fixing composition: 1 - bischofite, 2 - aluminum sulfate, 3 - oxalic acid, 4 - water. Depending on the purpose of the modified wood (the characteristics of the wood are associated with the purpose: flammability, hardness, the possibility of woodworking, compatibility with adhesives and paints, hygroscopicity, UV resistance, moisture resistance, biodegradation, etc.), other recipes can be selected both impregnating and fixing compositions (see. Examples). By changing the chemical composition of the impregnating and fixing solutions, their concentration, treatment modes and time, and other process parameters, it is possible to obtain wood with predetermined properties.

As a result of treatment with fixing solutions, the possibility of washing out the functional components of the impregnating solutions from the wood is excluded, reinforcement and hardening of the cell walls and other elements of the anatomical structure of the wood are achieved, its strength parameters sharply increase, the hygroscopicity decreases, the biostability increases, etc. More than a quarter of the total mass of wood obtained is accounted for by the mineral component. Essentially, in this way, “mineralized wood” is created on the basis of wood - a new structural and building material.

The most complete and uniform impregnation in the proposed technology is achieved when processing hardwood (birch, linden, oak, aspen, poplar, alder). Resin zones, which occupy a significant part of the mass of coniferous wood, impede the penetration of impregnating solutions into the wood.

The proposed method of deep (through) wood impregnation provides non-flammability, fire-retardant efficiency of wood at the level of group I (according to GOST 16363 (NPB-251)), biological resistance to the damaging effects of parasitic fungi and insects, weather resistance, non-hygroscopicity, high strength characteristics. The soft and low-value wood processed by our method and technology (alder, poplar, etc.) turns into a durable high-quality building and construction material suitable for the manufacture of non-combustible doors, frames, stairs, arch ceilings, parquet tiles, etc.

Example 1. The estimated amount of timber with a relative humidity of 18-25% is placed in an autoclave, the apparatus is sealed and vacuum to a residual pressure of 0.08-0.05 MPa. At the same time, evacuation and heating of the impregnating solution to its complete degassing are carried out in an apparatus in communication with the impregnating autoclave with evacuated wood. The process is considered complete when the achieved vacuum remains unchanged for 20-30 minutes.

After that, the hot impregnating solution is transferred, while maintaining the vacuum in the system, into the autoclave with wood in such an amount that the impregnating material is constantly under the layer of impregnating liquid. Maintaining the temperature of the solution in the range of 60-70 ° C and the vacuum for 3-5 hours, warm the lumber, after which the vacuum in the impregnating autoclave is released, the pressure is increased to 1.6-2.0 atm and the impregnation process is carried out until the impregnation of the wood ceases solution, which takes from 3 to 6 hours.

At the end of this stage of impregnation, the pressure in the autoclave is brought to atmospheric pressure, the excess of the impregnating solution is pumped into a reserve tank, the wood is removed and maintained to equalize the concentration of the impregnating solution in the entire mass of wood at room temperature for 24 hours. Then carry out chamber drying of the impregnated wood.

As a result of chamber drying of wood, impregnated to 23% moisture, then processing it with a fixing solution by the method of "hot cold" baths and final drying to 8% humidity, "mineralized" birch wood with a density of 0.78 g / cm ³ (780 kg / m ³ ).

In the above example, the following parameters are fixed: 1. Relative humidity of wood 24.0%; 2 Temperature of the impregnation solution before pouring: initial 16 ° C the ultimate 70 ° C 3. The time of evacuation (degassing) 2 h 20 min 4. Initial vacuum (over cold solution) 0.06 MPa 5. Vacuum over a heated solution 0.012 MPa 6. Vacuum over evacuated wood 0.073 MPa 7. Evacuation time of wood 1 h 30 min 8. The time of heating the wood under a hot impregnated solution 5 h 9. The time of impregnation of wood after the discharge of vacuum and pressure increase up to 2 atm 10 h

Preserving the appearance, texture, more pronounced pattern of annual rings, modified birch wood is practically non-combustible, has high hardness, but lends itself to any type of woodworking, is well polished and polished, compatible with adhesives and paints, is not hygroscopic, and is resistant to ultraviolet radiation, atmospheric moisture, biodegradation.

Example 2. In a vacuum apparatus load 1 m ³ (645 kg) of birch timber with a size of 60 × 80 × 3400 mm and an initial wood moisture content of 27%. The timber stack is fixed with clamping devices, the apparatus is sealed and poured ~ 2 m ^{3 of} impregnation solution prepared according to the recipe No. 1- "P".

Recipe "P-1". 1. Ammophos 15.0-18% (wt.) 2. Urea phosphate 5.3-8.5 3. Defoamers 0.3-0.5 4. Water rest

An impregnating solution is prepared by sequentially dissolving the above components of the substances in water and adding the missing amount of water to it to achieve an impregnating solution concentration in the range of 23-26% (wt.), The density of the solutions is ~ 1.14-1.17 g / cm ³ .

After pouring the impregnating solution into the wood autoclave, the heating device is turned on and the temperature of the solution is adjusted to 75-80 ° C. The wood is heated in a hot impregnating solution for 3-5 hours, as a result of which the structural and anatomical elements of the tree are softened, the vacuum pump is turned on and the process of synchronous degassing of the wood and the impregnating solution begins. Gradually increasing the vacuum, adjust the boiling intensity of the impregnating solution and, cooling it, bring the pressure in the impregnation chamber to the level of 0.05-0.08 MPa. The evacuation process lasts 3-4 hours. The completion of degassing is judged by the cessation of the fall of the vacuum in the system after the vacuum valves are shut off and the vacuum pump is turned off. From this moment, the process of wood impregnation is started, for which the vacuum is released, the pressure in the apparatus is increased to 1.2-1.3 MPa and the wood is impregnated until the level of the impregnation solution is stopped (control is carried out using a water meter). The process is completed in 4-5 hours. After the wood impregnation process is completed until the level of the impregnation solution is reduced, the excess is pumped into a reserve tank, the remainder of the impregnation solution released from the treated wood is drained, the apparatus is unloaded, the timber is transferred to a convection drying chamber. As a result of the above operations, the difference in the initial and final volumes of the impregnating solution is used to find the amount of solution absorbed by the wood.

The result of the above example: The initial mass of wood: 645 kg The mass of wood after impregnation 1370 kg The mass of absorbed solution 725 kg The concentration of the solution with% of the mass. 23% The mass of dry components of flame retardants and antiseptics introduced into the wood 166.7 kg / m ³ .

When performing all the above operations with the same timber, impregnating solution, temperature conditions and all other conditions, with the exception of the stage of preliminary heating of wood with a hot impregnating solution, it is possible to introduce 43-47 kg / m ^{3 of} “dry” flame retardant antiseptic components into the timber (standard 90-120 kg / m ³ ), which is completely insufficient to give wood incombustibility, fire and bioprotection, strength characteristics.

Example 3. Prepare an impregnating solution of the following composition:

Recipe "P-2". 1. Ammonium phosphate (monosubstituted) 130 kg 2. Oxyethylidene diphosphonic acid 30 kg 3. Trisodium phosphate 40 kg 4. Urea (urea) 40 kg 5. Ammonium tetrafluoroborate 2 kg 6. Defoamers (“Penta-91”) 0.1 kg 7. Water 758 l.

Subsequent operations are similar to those described in example No. 2, with the only difference being that the process of evacuating and heating the impregnating solution and evacuating the wood is carried out in various apparatuses. In the first apparatus, heating and vacuum degassing of the impregnating solution is carried out, increasing the vacuum to a residual pressure in the autoclave in the range of 0.05-0.08 MPa.

In the second autoclave, 220 kg (~ 0.3 m ³ ) of birch boards with a relative humidity of 31% and assortment sizes of 40 × 280 × 3300 mm are loaded, fixed in the set position and vacuum to a residual pressure of 0.048 MPa, after which both autoclaves are not depressurized , pump hot degassed impregnating solution from the first autoclave into the second, with wood. The temperature of the impregnating solution is maintained at a level of 60-65 ° C for 3 hours and after heating the wood, while maintaining a given vacuum, can withstand another 1 hour. Then the vacuum is released, overpressure is created in the autoclave (~ 1.3 MPa) and the wood is impregnated to a predetermined absorption level of the impregnating solution, performing all the technological operations described in example No. 2.

The following parameters are fixed: 1. The initial volume and weight of wood 0.3 m ³ (220 kg) 2. Original wood moisture 31% 3. The geometric parameters of the material 40 × 280 × 3300 mm 4. The initial volume of the solution introduced into the autoclave 600 l 5. The mass and density of the solution m = 688 kg, p = 1,147 6. The temperature of the degassed solution 68 ° C 7. The time of degassing (evacuation) 1 h 20 min 8. Vacuum in the apparatus with wood after 0.12 MPa impregnation solution pouring 9. Vacuum before impregnation 0.073 MPa 10. The heating time of wood Σ 4 hours 11. Timing process 5.5 hours 12. Overpressure at the time of impregnation 0.3 MPa 13. The amount of solution absorbed into the wood 167.4 kg 14. The amount of substances introduced into wood 40.5 kg (135 kg / m) 15. Density of wood dried after impregnation 0.74 (740 kg / m).

All subsequent operations on drying the impregnated wood, processing with fixing solution, final drying are similar to those previously described in example No. 2.

The composition of the "F-2." 1. Calcium chloride 10.5-13.0% (wt.) 2. Magnesium chloride 3,5-5,4 3. Ammonium chloride 3.0-6.2 4. Water the rest (up to Σ100%)

Received wood with a density of 762 kg / m ³ and characteristics for such parameters as fire resistance, combustibility, bactericidal activity, hardness (according to Shore), weather resistance, hygroscopicity similar to wood treated in example 2. The wood retained its appearance and natural shade of freshly sawn wood, due to the presence in it of a large amount of microcrystalline calcium phosphate.

Claims (3)

1. The method of deep impregnation of wood, characterized in that they carry out preliminary evacuation at a pressure of 0.05-0.08 MPa and heat the impregnation solution and the wood in one vacuum apparatus, immersing the wood in an impregnating solution, or in separate vacuum apparatuses, then transferring the impregnation the solution in a vacuum apparatus with wood while maintaining a vacuum, withstand the wood immersed in the impregnating solution in vacuum, and then increase the pressure in the vacuum apparatus to atmospheric or create excessive pressure set, the impregnating solution is removed, followed by drying timber holding timber carried fixation components in the impregnation solution timber fixing structure formed by the interaction with the impregnating solution are thermally stable and water-insoluble substances. 2. The method according to claim 1, characterized in that the treatment with a fixing composition is produced by the method of "hot baths". 3. The method according to claim 1, characterized in that the wood is dried to a residual moisture content of 20-25%.