Chemical methods for impregnating wood
OVERVIEW
The intriguing history of wood impregnation. More than five thousand goods are ready, including boards, adhesives, oils, dyes, sugars, polymers, cellulose, alcohols, synthetic fibers, feeds, medications, disinfectants, and explosives—many of which have been derived from wood for millennia. Recently, the board product and composite material industries have witnessed the introduction of new wood products, particularly with improved quality and features. Both the price and demand for wood products are clearly rising.
Due to three drawbacks that restrict its application, wood material offers numerous benefits over other materials. These include:
a) Because of its organic chemical makeup, wood can be damaged by termites, tunneling beetles, wood-destroying fungi, and sea borers.
b) Wood is capable of absorbing water molecules that have free hydroxyl groups, and the amount of water absorbed is contingent upon the air’s relative humidity. As a result, the three dimensions of wood vary according to the substrate’s moisture level.
c) The substance wood is combustible. This priceless product needs to be shielded from termites, borers, beetles, fungi, and fire to prolong its useful life and find new applications. It also needs to be dimensionally stabilized by applying a water-repellent agent and chemically cross-linked by combining and enhancing specific chemical processes.
Wood preservation is getting more and more crucial:
to save forest resources;
b) to safeguard wood that has more sapwood;
c) to permit the use of timber species that are not durable;
d) to encourage the utilization of substitute materials;
e) to lessen the requirement for exorbitant demand;
f) to offer social and economic advantages.
wood impregnation. Wood preservatives
OVERALL WOOD PRESERVATIVE CHARACTERISTICS
a) They have to be poisonous to pests, fungi, and marine life.
b) They must not exhibit any unfavorable characteristics when handled or used.
c) They must be durable and possess appropriate qualities for the uses for which they are suggested.
d) They ought not to be caustic.
e) Their cost shouldn’t be high.
Tar-based oils:
Creosote: Originally, an oil derived from wood was referred to as creosote. The earliest industrial wood preservative is coal-tar creosote, which has been widely used for more than 150 years. A brownish-black, greasy liquid known as creosote is created when hard coal carbonizes. Creosote is the portion of coal tar that boils between 200 and 400 degrees Celsius. Its chemical makeup is extremely complex. Hundreds of chemicals, mostly hydrocarbons, together with trace amounts of tar acids and tar bases, are found in creosote. Instead of focusing on the chemical makeup, specifications are based on certain physical attributes. Because creosote is insoluble in water and thus resistant to leaching, it is a very good preservative that also has a high electrical resistance and doesn’t corrode metal.
It also keeps wood from fading and cracking. Railroad ties should survive at least 30 years, creosoted posts over 60 years, and marine posts over 40 years. Usually, creosote is administered using the empty cell method; occasionally, it is applied using the hot and cold open tank method. Creosoted wood is not typically used in food or seed containers because it releases volatile components that are poisonous to plants and gives off aromas that tarnish food.
Paint on wood can still be done with creosote. Because creosote can catch fire, it is not utilized as a mining prop. Occasionally, other compounds are added to creosote to improve its qualities and efficacy. Lentinus lepideus cannot break down creosote pillars in the ground when 2% pentachlorophenol is added. To prevent the marine borer Limnoria tripunctata, copper preservatives are used. Arsenic trioxide is applied in small amounts to strengthen the preservation qualities against termite attack. In the full-cell process, the loading of creosote is 400 kg/m3, but in the empty-cell process, it is 140 kg/m3 (1-4).
Carbolineum, also known as anthracene oil, is tar oil that has a higher percentage of high-boiling fractions. While minimal penetration is obtained, it is typically applied by pressure impregnation, although it can also be done by brush, spray, or immersion.
To achieve more effective preservation, carbolineum is chlorinated to generate carbolineum avenarius.
Lignite Oil: Lignite is the source of this tar oil.
Peat Tar: Similar to wood tar in its qualities, peat tar is manufactured and utilized in Ukraine.
Wood Tar: Wood tar oil, also known as creosote, is one of the tar fractions that are derived from the destructive distillation of wood. Stockholm tar, or softwood tar, was formerly extensively produced and widely used in timber construction by brush application. Although its preservative action and durability are lower, wood tar creosote was once used as a preservative for impregnating timber, providing excellent penetration because its viscosity is rather lower than coal tar creosote.
Shale tar: It is produced by distillation of bituminous shale tar. Until recently, tar was used for impregnating railway sleepers in Estonia and Lithuania.
Petroleum products: These products are used as a diluent for mixing with creosote. P4 oil is an oil designed to be mixed with creosote. Creosote/petroleum mixtures of 20-50 and 70-30 are usually used.
Oil-Based Preservatives:
Oil-based or organic solvent-based preservatives consist of active chemicals, insecticides and/or fungicides dissolved in an organic solvent such as petroleum distillate. Of the millions of organic chemicals, only less than ten can be used as active ingredients in formulations. The use of these chemicals provides long-term protection because of their natural insolubility in water. Once the organic solvent evaporates, the active chemicals remain in the wood.
Pentachlorophenol: Pentachlorophenol, known as penta or PCP, is the most important and widely used fungicide of the organic solvent-based preservatives. The commercial product produced by direct chlorination of phenol contains about 85% PCP. It is extremely toxic to fungi, insoluble in water and resistant to leaching, non-volatile and non-corrosive to metals. A 5% solution of PCP in heavy oils is used for treatments.
Lindane and Dieldrin: Lindane was discovered in 1912 and used as an insecticide since 1940, one of the most important insecticides, does not accumulate in the environment. Dieldrin developed and used as an insecticide in 1948 is persistent in the environment. They are insoluble in water, chemically stable, and highly toxic to insects. Lindane is used for spraying or dipping hardwood logs against Lyctus beetles in woodworking by immersion or double vacuum processes and for in situ remedial treatments against insect attacks in buildings. Dieldrin is used in woodworking for termite protection and is also mainly used as an aqueous dispersion for pre-treatment of the ground against termites. It is used as a 0.8% solution in petroleum solvent.
Copper 8-quinolinolate: Copper 8-quinolinolate known as Copper-8 is a relatively new preservative. It is produced by the condensation of copper 8-quinolinolate and nickel 2-ethylhexanoate. Copper-8 is a yellow-brown solid that is dissolved in organic solvents using nickel 2-ethylhexanoate to give a green solution. It is toxic to wood pests except termites, but relatively harmless to animals and plants. This preservative is used in wood material used for food containers, refrigerators, seed boxes, and greenhouses. The treatment solution should contain 0.045% Cu.
Copper naphthenate: A preservative first used in the 1920s as “Cuprinol” gives a dark green waxy solution in organic solvents and waxy solution in organic solvents, and the waxy surface of the wood prevents repainting. It is toxic to wood pests except termites and does not corrode iron and steel. Copper naphthenate is mainly used as a paint preservative in boat maintenance. Treatment solutions contain 1-2% Cu.
Bis(tri-n-butyl) oxide: is known as tributyl tin oxide, TnBTO, or TBTO, an excellent fungicide, more effective than PCP, insoluble in water, and soluble in many organic solvents. TBTO has less toxicity to humans than PCP. This preservative is mainly used as a fungicide in woodworking and as a general preservative in boat maintenance. TBTO is used as 0.5-1.0% solutions.
Water-based preservatives:
They are used for the impregnation of mine stands, residential buildings, food tanks, and cooling towers. Preferred for structural elements that are not intended to be painted and have no odor. The concentration of solutions is about 5%.
Ammoniacal copper arsenate (ACA): This is known by the trade name Chemonite and contains copper hydroxide (57.7%), arsenic trioxide (40.7%) and ammonia (1.5-2.0%).
Acid copper chromate (ACC): This product known as Celcure consists of copper sulfate (50%), sodium dichromate (47.5%), and chromium trioxide (1.68%).
In the case of CCA type A preservatives, the trade name Greensalt was applied to the product used for treating poles and the name Erdalith to the product used for treating wood. CCA-Type
A is marketed as Boliden Salt K-33, while CCA-Type C is marketed as Tanalith C and Celcure A.
Zinc chloride (79.5%) and sodium dichromate (18%) make up chromated zinc chloride (CZC), a preservative.
The Wolman-type preservatives known as fluor-chromate-arsenate-phenol (FCAP) are a combination of sodium fluoride, chromate, sodium arsenate, and 2,4-dinitrophenol. Sodium pentachlorophenol has recently taken the place of 2,4-dinitrophenol in treating wood to prevent yellowing. Preservatives of the Wolman type, or FCAP, are available in a variety of forms and trade names. Triolith, Minolith, Fluoxyth, Flunax, Tanalith U, Triolith U, Osmolit U, Osmolith UA, Wolmanith U, Wolmanith UA, Trioxan U, Trioxan UA, and Basilit U, Basilit UA were these. The FCAP type A and type B composition is listed below (%).
Other water-soluble preservatives: zinc chloride, zinc meta-arsenite (ZMA), copper chromated zinc chloride (CuCZC), chromated zinc arsenate (CZA) and copper chromated zinc arsenate (CuCZA).
Weathering agents: Wood quickly loses its aesthetic appeal when left unprotected against weathering. Frequent soaking and drying results in splitting and cracking, and UV radiation breaks down the wood’s surface to produce materials that rain can wash away. Additionally, the growth of mold and fungi in cracks and fissures stains the wood.
Paints and varnishes: These methods are the best for preserving the look of wood since they cover the wood fully and prevent any damage from occurring. A thin layer of clear varnish keeps the wood from getting wet and shields the surface from UV ray damage. Regretfully, even though these coatings offer strong resistance to precipitation, they are powerless to stop humidity variations brought on by seasonal variations in relative humidity. As a result, variations in relative humidity may cause painted wood to shrink or swell, which will break and fracture the surface covering. After water seeps into the wood, mold and other stain-causing fungi start to grow on the surface. Just 6% of the 200+ varnishes evaluated in an English study offered consistent protection for more than a year. Typically, maintenance entails expensive cleaning and re-varnishing.
Stabilizers and water repellents: A water-repellent treatment seals a building material’s pores to keep water from penetrating. Water-repellent waxes, such as paraffin waxes, are widely recognized and utilized in wood preservation formulas. Although cheap and effective, aromatic and aliphatic hydrocarbon resins only solidify when their solvent is lost; they re-dissolve when solvents are coated on them. You can also use natural drying oils, such as linseed oil. Alkyd resins are relatively costly yet can prevent these problems. To avoid these issues, a combination of waxes, hydrocarbon resins, and alkyds is typically utilized. The most well-known water repellents are organosilicon compounds, however, they have several drawbacks with heavy organic oils and waxes.
High-performance silicones that adhere well to wood are appropriate for wood applications because they offer strong resistance to deterioration when wet. Unsaturated chains can be found in organoaluminum compounds, and hydrophobic ones can offer superior adhesive bonding between wood and alkyd systems. Polyoxyaluminum systems make up commercial Manalox products. When formaldehyde is applied to wood while an acid catalyst is present, the hydroxyl groups on neighboring chains cross-link, diminishing the wood’s size and elasticity. Acetylation, or treating the wood with acetic anhydride in the presence of a potent acid catalyst, dramatically lowers the wood’s hygroscopicity and boosts its ability to withstand fungal growth. All of these chemical treatments work as long as the wood is fully soaked.
The process of impregnating wood that retains a lot of chemicals is known as swelling. This is how some resin systems, including Impreg, have been applied in systems. Wax made of polyethylene glycol, such as MoDo, PEG, and Carbowax, is also used to treat swelling. These devices are specifically employed to stabilize floor blocks and archaeological items. The Madison recipe is the most well-known hydrophobic preparation. Paraffin, pigments, and a binder made of boiling linseed oil with zinc stearate and pentachlorophenol make up the composition, which offers water resistance, color retention, and resistance to mold and mildew stains. The Madison recipe suggests employing a binder to increase weather resistance. The water-based treatment in the Royal procedure, designed for treating external joinery, is succeeded by a deep treatment using a drying oil.
Anti-filaments:
Treatments for impregnation: In 1905, the o Minolith, was a fire retardant. The mixture included a significant amount of rock salt triolith, which served as a fire retardant and preservative for usage in mines. Developed in 1930, zinc chloride, boric acid, and phosphates were the ingredients of Celcure F. 60% ammonium sulfate, 10% diammonium phosphate, 10% borax, and 20% boric acid make up the monolith. Ammonium sulfate, boric acid, sodium sulfate, boric acid, and sodium dichromate are other components of pyresote. Typical fire retardants contain hygroscopic and leachable chemicals. Ammonium phosphates, ammonium sulfate, zinc chloride, boric acid, and borates are the most favored constituents. A preservative found in the American product Non-Com Exterior polymerizes in the wood to create a non-corrosive material with strong leaching resistance. Flame retardant purity is achieved using the full-cell procedure. Catalysts like antimony oxide can be utilized with halogenated substances like bromophenols, chlorinated paraffins, and chloronaphthalenes.
Coatings on the surface: Coatings on the surface stop flames from spreading. Hospitals, hotels, restaurants, kitchens, museums, and gyms all employ these coatings.
Intumescent coatings: These coatings soften and release non-flammable gasses when they come into contact with fire. Foam is produced when the coating captures the gasses. After that, the flame retardant hardens, separating the surface from the flames.
Non-intumescent coatings: A few of them have components that obstruct combustion processes chemically. Others that are silicate- or borate-based melt in the fire to create a glassy layer of protection.
Chemicals that prevent stains: The sapstains that cause green wood and worn coating systems are caused by superficial molds and sapstain fungi, which are not effectively controlled by conventional wood preservative formulations. Despite its extreme toxicity, sodium pentachlorophenate has been shown to be a useful chemical. A number of borax and sodium pentachlorophenate combination formulations have been used extensively; the most often used is one part borax and one part sodium pentachlorophenate. To save on transportation, Pentabor eliminates 50% of the water from crystallization. It has been discovered that trihalomethylthio substances are also useful. It has been discovered that Folpet (Fungitrol 11) is highly active. Dichlorofluorocarbons Dichlorofluanid (Preventol A4) and Fluorfolpet (Preventol A3) are efficient substances. One stain-preventing substance that has been employed is the Madison formula, which has a pigmented and water-resistant composition.
Preservatives that stop alder, hornbeam, and beech from browning:
Commercial chemicals have been used to stop brown stains from appearing right away after felling, including Immutol B, Wolmanol-Buchenschutz, Xylamon ASR, and Besileum. For cross-sections, a mixture of 85% tar and 15% asphalt is also used to avoid splitting and cracking.
WOOD PRESERVATIVE OILING
Wood preservatives based on water don’t wash out when used. Because of its considerable insolubility in water, copper naphthenate likewise exhibits resistance to washout. The products with a high percentage of exposed surface area and high retention tend to leach the fastest during the first few months of use. Exposure to strong water flow, low pH, and organic acids that are soluble in water all promote leaching.
wood impregnation. STORAGE MANAGEMENT
WOOD PREPARED FOR PRESERVATION THERAPY
Debarking: While some mills use mechanical peeling, others use high-pressure water jets.
Treatment: Before beginning the preservation process, any machine or manual labor on the wood must be completed. Before being processed, the treated wood must first be cut to the proper size and have its surface properly treated.
Drying: The wood is dried using either a kiln or air drying.
Steaming: The permeability of wood is significantly increased by steaming it in steam tanks filled with plants.
To guarantee that the preservative solution permeates the wood of difficult-to-impregnate species in two directions along the grain, incision is the procedure of cutting tiny slits or cuts in the wood.
Compression: The wood is compressed by passing it through heavy rollers, which causes a little structural change that facilitates the preservative solution’s easy and uniform penetration.
Bathing and spraying: By allowing bacteria to dissolve and enlarge the cavities, bathing and spraying enhance the absorption of the preservative.
wood impregnation. PRESERVATION METHODS
Treatments for unseasoned wood preservation:
Diffusion mechanisms
Osmosis method: A widely applied technique
The best osmosis technique. Freshly cut and wet wood, usually poles, have their debarked surface treated with a highly concentrated and water-soluble substance. For one to three months, the poles are coated with an impermeable material to guarantee that the diffusion process proceeds as planned. Water, NaF, dinitrophenol, starch, and glue are the ingredients in the preparation used for pine, spruce, and fir.
Procedures for displacing sap
Boucheri method: For recently cut, unsbarked poles, the well-known sap displacement method is applied. Pipes link the capsules on the butt end of the poles to a tank that holds 1.5% copper sulfate. Within a few days, the sap from the poles is removed by the preservative that flows into the capsules from the upper tank. The Slurry Seal Process and the Gewecke Pressure and Suction Method are further options to this technique.
Wood impregnation. Processes without pressure:
The easiest ways to apply preservatives are with a brush and sprayer. It is only possible to penetrate the surface by 1–5 mm.
Deluge: This is a lumber treatment. Wood slowly travels through a brief tunnel before being doused with organic solvent-based preservatives.
Dipping: Dipping is immersing the wood for anywhere from five to ten seconds to a week or more in a tank that contains the preservative. Applying is more effective than brushing, spraying, and flooding at higher diffusion rates. Treating joinery requires brief immersion times.
The thermal process is another name for the open tank hot and cold treatment procedure. For at least six hours, hot preservative is fed into a tank until the poles are fully submerged in the preservative solution. Upon pumping the preservative from the treatment tank to the storage tank, cool preservative solution is promptly poured into the tank. More impregnation of the wood results from the cold solution partially vacuuming the wood cells.
The best techniques for preserving wood are high-pressure treatments. In a steel pressure vessel, the wood undergoes a chemical treatment under high pressure.
The goal of the full-cell method, also known as the Bethell process, is to preserve as much preservative as possible in the wood. In the full-cell process, chemicals based on water and petroleum are always utilized. Only when treating specific unique structural elements—like marine pilings—with a high rate of preservation retention is creosote utilized in this treatment. The Bethell procedure consists of five steps:
a) Perform a 15–60 minute initial vacuum (635 mm Hg).
c) Pouring the preservative solution into the vessel.
d) Apply pressure for 1-6 hours (10–14 kp/cm2).
c) After the pressure is released, drain the preservative.
Procedures for empty cells (Rüping): Generally speaking, techniques have been devised to use less creosote in treatments with the same penetration. in therapies with an equivalent penetration. There isn’t a first vacuum in this process, and the compressed air trapped inside the wood causes a significant amount of creosote to be ejected, leaving behind finely treated cell walls.
There are five steps in the process:
The starting air pressure was 4 kP/cm2.
b) Pouring preservative into the container.
b) A pressure period lasting one to three hours (10–14 kp/cm2).
c) After the pressure is released, drain the preservative.
f) Final vacuum (10 minutes, 600 mm Hg).
Lowry procedure: In contrast to the Rüping procedure, this technique involves pumping the cap preservative into the vessel at room pressure. Compared to the Rüping process, less solution is squeezed out of the wood and there is no initial vacuum or pressure.
Oscillating Pressure Method (OPM): Several cycles of pressure and vacuum are used to achieve better penetration because the Bethell method is difficult to apply on highly resistant timbers. There is a vacuum of 720 mm Hg and a high pressure of 8 kp/cm2. Chemicals that dissolve in water are used to treat green or seasoned wood; they are often CCA formulations. The technique is particularly applied to poles composed of hardy species like fir and spruce.
Method of Alternating Pressure (APM): This modified approach cycles the pressure between 8 kp/cm2 and atmospheric pressure. The method can also be applied to untreated, hard-to-impregnate wood, preventing the wood from drying out.
Ultra High Pressure (HP) Method: To improve preservative penetration and retention in eucalypt species that are challenging to impregnate by other methods, a full-cell process is introduced employing a pressure of about 70 kp/cm2.
Impurity of Wood. Treatments Under Low Pressure:
Double Vacuum Process: In the UK, this technique has achieved amazing industrial success.
hundreds of installations. The method is ideal for the needs of the woodworking industry because the wood can be painted, coated, or bonded within days of treatment. The treatment is divided into five phases.
a) For pine, the initial vacuum should be 250 mm Hg (3 minutes), and for spruce, 625 mm Hg (10 minutes).
b) Pouring a preservative solution—typically an organic solvent type—into a vessel having a rectangular or circular cross-section.
c) Approximately 2 kP/cm2 of pressure for 3 minutes for pine and 1 hour for spruce.
c) After the pressure is released, draining the preservative.
e) A final vacuum of 20 minutes at 500 mm Hg.
In situ restoration techniques Bandaging technique: To prevent deterioration and increase service life, pre-made bandages containing Pol-Nu Type and Wolmanit-TS are applied to ground line transmission poles.
Cobra approach: This approach was created as a way to fix transmission poles on overhead lines as well. Wolman-type salt is often injected into the pole using a needle.
The Drilled Hole Method is applied to timber buildings that are particularly susceptible to degradation, including piles in water and bridges. A solid preservative is poured into 15–25 mm diameter holes and sealed to allow the wood to be chemically impregnated through diffusion.
Impregnation of Timber. WOOD’S POST-TREATMENT PROPERTIES AFFECTING APPLICATION
Strength: Preservatives based on water usually lessen the mechanical qualities of wood. The load-bearing capacity is not reduced by the treatment below limits that are deemed acceptable. Although there may be a minor loss of strength, the incision offers more protection. Serious weakening of the wood may be seen if the steam treatment period is not shortened. The wood cells may break under high pressure, particularly in low-density wood. Significant strength loss is seen when wood is treated to an acceptable chemical loading using standard industrial preservative procedures.
Flammability: The flammability of wood treated with water salts is not increased. Nonetheless, there is a higher risk of fire when wood has recently been treated with creosote or heavy oil mixtures. Mine supports are therefore treated with water salts. Creosote-treated wood no longer poses a fire risk after a few months.
Electrical conductivity is unaffected by creosote or preservatives derived from organic solvents. Electrical conductivity is marginally altered by substances found in water, although these differences are negligible and may be disregarded in most situations.
Wood impregnation. Security
Structures and household and commercial uses: Due to its disagreeable and annoying smell, creosote-impregnated wood is rarely utilized in home construction. Wood intended for residential use is preserved using either double vacuuming with organic solvent-based preservatives or pressure treatment with chemicals based on water. Warehouses, commercial buildings, and agricultural structures employ wood that has been impregnated with water-based preservatives and creosote as transmission poles.
Containers for seeds, mushrooms, and greenhouses: Treated CCA wood can be used; wood coated with creosote or PCP is not advised.
Garden toys and playground equipment for kids: You can use water-based preservatives that are fixed in wood completely safely. Re-drying the wood to 22% moisture, softening it, and then drying it again eliminates deposits that are visible on the surface. It is also advised to apply two coats of water-resistant finish as a precaution. Wood that has rotted is inappropriate.
Animal pens: The majority of preservatives are safe to use in these settings. The above-mentioned procedures should be followed to remove deposits from wood treated with water-soluble salts and to air dry creosoted wood. Avoid using PCP in preservatives.
Food containers: Avoid using decayed wood for food storage. For containers, copper 8-quinolinolate is advised. Wood-fixed preservatives, like CCA, can be utilized completely safely as long as surface deposits are eliminated in the manner previously mentioned.
The stability of wood dimensions and its chemical modification
The dimensional instability of wood as a result of variations in relative humidity is one of its drawbacks. Wood is treated to improve specific qualities and to prevent various changes in various dimensions.
hydrophobic concoctions
a) Resins phenolic
c) Polymer-ethylene
d) Wood-polymer composites, where monomers polymerize in wood
e) acetic anhydride combined with a catalyst to acetylate the substance.
