WO1982001848A1 - Procede de conservation du bois - Google Patents

Procede de conservation du bois Download PDF

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Publication number
WO1982001848A1
WO1982001848A1 PCT/AU1981/000172 AU8100172W WO8201848A1 WO 1982001848 A1 WO1982001848 A1 WO 1982001848A1 AU 8100172 W AU8100172 W AU 8100172W WO 8201848 A1 WO8201848 A1 WO 8201848A1
Authority
WO
WIPO (PCT)
Prior art keywords
wood
copper
arsenic
chrome
bath
Prior art date
Application number
PCT/AU1981/000172
Other languages
English (en)
Inventor
John G Schroder
Original Assignee
John G Schroder
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by John G Schroder filed Critical John G Schroder
Priority to BR8108888A priority Critical patent/BR8108888A/pt
Priority to AU78097/81A priority patent/AU7809781A/en
Publication of WO1982001848A1 publication Critical patent/WO1982001848A1/fr
Priority to FI822602A priority patent/FI822602A0/fi

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
    • B27K3/02—Processes; Apparatus
    • B27K3/08—Impregnating by pressure, e.g. vacuum impregnation
    • B27K3/083—Impregnating by pressure, e.g. vacuum impregnation along the fibers, i.e. longitudinal impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
    • B27K3/16—Inorganic impregnating agents
    • B27K3/32—Mixtures of different inorganic impregnating agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K2240/00—Purpose of the treatment
    • B27K2240/20—Removing fungi, molds or insects

Definitions

  • This invention relates to a process for conditioning and preserving wood with a preservative solution.
  • the process applies to both oil-borne and water-borne preservatives.
  • the growth of wood occurs by the photo-synthesis system in which organic substances migrate down the phloem tissue to the ⁇ apwood where reactions take place in the Cambian layer to produce cellulose from the sugars and lignin from the aromatics to the wood cell.
  • the sugars proceed from poly-saccharides to he i-cellulose and to ⁇ iicrofybrils of cellulose.
  • Esters of benzoic acid and phenolic ethers such as catechol have been isolated from the sap streams of certain hardwoods.
  • the aro atics • condense to form long chain molecules to form the lignin which cements the microfybrils together.
  • Also present in the sap stream are such substances as ammonium tartrate, potassium di-hydrogen phosphate, magnesium sulphate, zinc sulphate, manganese sulphate, calcium sulphate and trace elements such as iron, sodium that are known' to be basic nutrients in the growth of organic matter.
  • These chemicals and the precursors to the manufacture of the wood substance are generally known as a substrate to the wood system.
  • Benzoic acid and catechol are both present in the sap stream and are known to have some toxic properties relating to fungi.” A mixture of the two appears to exert a synergistic effect which depresses the rate of growth of fungi to very low levels. The same materials are found in coal tar and possess toxic properties. These phenolics and benzoic acids have the property of being both water soluble and oil soluble, as such they- can set up equilibria between the oil phase and the aqueous phase in any wood system. They tend to wet the wood and to hold the oil in any oil-borne preservative within the wood system reducing the tendency of oil-borne preservatives containing such chemicals to bleed from the wood by syneresis.
  • a seasoning step is usually required before satisfactory penetration can be achieved.
  • the decay cycle commences and the destruction of the wood is enevitable and no amount of preservative applied afterwards will correct the situation.
  • reducing sugars are gradually extracted from the wood eventually causing formation of a sludge or precipitate in the solution.
  • chromates such as basic chromium chromate
  • basic copper chromate are in stable equilibria.
  • the toxic thresholds of these chromates than can exist and precipitate out of chromated copper arsenate solutions have been shown to be from 5 to 10 times higher than when basic copper arsenate is fixed out of a chrome-free solution. They form a sludge that is suspended in the solution deposits on the wood and can be toxic as well as a skin irritant.
  • OMPI timber posts so treated For round surfaces the arsenic can be 1.22 milligrams per 100 centimetres squared and the copper 1.46 milligrams per 100 centimetres squared. No tests are available for chromium but it is known to be a skin irritant. The disproportioning of preservative elements with penetration depth as happen in this situation leads to the solution becoming unbalanced as it moves into the wood system, becoming arsenic rich and copper lean. Much of the arsenic is lost by leaching.
  • wood is treated with a hot solution of copper chrome and arsenic whereby the precipitation of difficulty soluble salts by reducing - 5 -
  • U.S. Patent 3,957,494 of Oberley describes a chromated copper arsenate wood treating solutions in which the ratio of hexavalent chromium to trivalent chromium is between 4:1 to about 1:1 6 to improve the penetration of wood to ensure better retention of preservative in the wood and to improve stability of -treating solutions.
  • the solution contain an acid selected to maintain the desired pH while further improving solution stability and preventing corrosion.
  • Typical formulations of widely used CCA compositions of the prior art are listed in U.S. Patent 3,957,494 which when adapted to standardised American formulations have the following compositions in percent by weight.
  • the conditioning step as specified with acid preferably sulphuric acid with a pH of less than 2.8, effectively removes by hydrolysis reducing sugars which are rapidly extracted into the solution, releases resins and oils in refractory species such as Douglas Fir and enables the wood to be treated green without seasoning.
  • acid preferably sulphuric acid with a pH of less than 2.8
  • treating solution be of the copper chrome arsenate hot diffusion type in which the
  • CrO ⁇ content is of the order of 20% a bath of the solution containing copper ions, arsenic acid ions and chromic acid ions with the mole ratio of the copper to arsenic being such as to establish the acid copper arsenate equilibrium at a pH less than 2.8 and a temperature greater than 40°C in the wood system.
  • the solution has a sufficient concentration of chromic acid ions to form tertiary chromium arsenate in the wood to be treated and to provide a mole ratio of chromium to arsenic which will subsequently ensure that all or substantially all arsenic is precipitated and fixed as tertiary chromium arsenate in the wood to be treated.
  • the concentration of the chromic acid ions is such that pH of the aquaeous phase in the wood is kept below 4 and the precipitation and fixation reactions are substantially completed to prevent formation of chromates within and/or on the surface of the wood. It has been shown by experiment that the toxic threshold measured on the basis of retention of copper at a 0.2% /W % copper is from 5 to 10 times less when copper and arsenic are fixed from the acid copper arsenic solution as is the case when fixed from chromated copper arsenate solutions. This in effect means that the toxicity of the treatment when the copper chrome arsenate hot diffusion system is used is at least five times that when chromated copper arsenate solutions are used. This will result in a greatly increased life of the wood so treated or a lower level of application for a required service.
  • the treating solutions when using the CCAHD process after conditioning can be kept stable continuously by adjusting the pH down to below 2.8.
  • the control of the equilibrium within the wood system (provided the pH in the wood system is below 2.8 ⁇ is automatic as the equilibrium set up will be that of acid copper arsenate. This is relatively independent of the formulation in the solution outside the wood system. It has been found, however, that should CCA Type C salts with 47.5% of Cr0 3 be used, the chromic ion absorbs onto the wood system and is reduced causing a rise in the pH and the penetration is somewhat limited to the outer sapwood.
  • the conditioning step by removing the extraneous organic resins and oils from the substrate greatly improves the penetration of the oil-based preservative and permits it to move freely throughout the wood.
  • the conditioning process thoroughly wets the wood cell walls and the capillary passages particularly the mid lamella.
  • the oil carrier infuses into the wood system and the tar acids and bases, which are both oil and water soluble, will partition between the aqueous phase in the wood system and the oil phase thus fixing the preservative more securely to the wood system with little tendency for the oil carrier to bleed from the pole by syneresis.
  • the tar acid and tar base content of the oil-borne preservative have to be in excess of 20% for best results.
  • Oil-borne preservatives of the creosote high temperature type and containing tar acid contents of less than 10% are known to exude from the pole and also may be lost by evaporation. High phenol content may reduce evaporative losses.
  • the rate of decay can be related to a combination of boiling range and tar acid content. It has been shown that in the case of Australian Vertical Retort creosotes with a tar acid content of 15% and above, a reasonably good correlation is achieved between threshold retention of the preservative and the "Residual Phenolic Value", the latter being the product of the initial phenolic content of the creosote and the percentage of creosote remaining after weathering. Because tar acids contribute so much to toxicity particularly of low temperature creosotes, it follows that a minimum tar acid content of at least 15% should be specified for reasonable protection to be attained.
  • the conditioning step has been shown to improve the physical condition of sapwood particularly of young trees that are fast grown under plantation conditions.
  • Large tensile stresses are known to build up in the sapwood of young hardwood, particularly Eucalypt species that give rise to spring and bow in the freshly sawn timber. This greatly detracts from their application as sawn lumber.
  • the consequent radial strain gives rise to compressive stresses that causes the collapse of the wood cells in the inner region and because of the high intensity of the compression stresses and the low strength of the heartwood across the grain in comparison to along the grain invariably some radial splitting occurs at the ends.
  • the conditioning step appears to make the sapwood more elastic and enable to expand to absorb the increased load placed upon it, thus containing end-checking.
  • Conditioned wood that is stood on end to drain dries out quite rapidly.
  • the conditioning step releases bordered pits that would otherwise be cemented to the cell wall blocking the valves.
  • the removal of extractives lessens the tendency of the torus to fix to the valve and much better ventilation takes place through the wood during the drying phase. It has been found that within days of conditioning wood stood on end dries out into what can be described as kiln dried condition and removes the necessity for that process.
  • Phenols extracted from coal have been used as a natural base for manufacture of oil-based detergents.
  • Sulphuric acid sulphonates hydroxy benzene radicals known to be present in the sapstrea .
  • Alkyl olephics also present in the sap system condense to form alkyl-aryl molecules that are soluble and which cleanse the fibres of residual oils and resins that hinder the application of the preservation of the sapwood.
  • alkyl-aryl molecules act as wetting agents which induce better penetration by both oil-based and water-based preservatives and permit the wood system to be thoroughly wetted before the application of preservative.
  • the less soluble material such as poly-saccharides were hydrolysed to sugars and removed along with starches from the system. Residual oils floated out of the wood system and alkyl-aryl compounds formed by condensation of precursors of the lignin manufacture formed and being soluble moved out of the system. The wood was thoroughly wetted and became completely waterlogged and was allowed to stand and cool.
  • the water containing the extracts from the substrate of the wood being treated was removed and replaced by a preserving solution comprising a bath of a solution containing copper ions, arsenic acid ions, chromic acid ions such that the acid copper arsenate equilibrium became established.
  • the bath was once again brought to the boil and allowed to cool. Convection currents set up within the wood system replace the sulphuric acid solution with preservative solution which then diffused throughout the wood system.
  • the wood was allowed to stand and cool so that the ions diffused throughout the wood system.
  • the wood was inserted into a cylinder and oil-borne preservative containing a high level of tar acids and bases at least 20% was introduced to the system.
  • a pressure of five atmospheres was applied order to assist the infusion.
  • a vacuum was applied after a period of time and the oil carrier removed from the system.
  • the butt end of the post or pole can be stood upright in a bath of an oil-borne carrier such as a lignin tar or high tar acid creosote and brought to the boil.
  • an oil-borne carrier such as a lignin tar or high tar acid creosote and brought to the boil.
  • the water in the butt of the post or pole is evaporated and ejected from the system, on cooling the atmospheric pressure forces the oil carrier into the wood system and thoroughly encapsulates the wood.
  • the chromic acid ion absorbs into the wood-substance, preferentially the lignin.
  • the pH in the system inside the wood rises and the chromium of Valency 6, is reduced to Valency 3 to permit the fixation of basic copper arsenate.
  • the preliminary step is to establish the acid copper arsenate equilibrium within the wood system, and is achieved by water-logging the wood in acid solution to reduce the pH within the wood to less than 2.8, at which point copper chrome arsenate is the stable equilibrium.
  • the equations are as follows:-
  • chromic acid ion is included in the formulation to ensure that the arsenic acid ion, freed by the fixation of the basic copper arsenate, is fixed as tertiary chromium arsenate which is a recognised insecticide.
  • a typical formulation is as follows:- ( a) 4.CuSo 4 .5H 2 ) + As 2 0 5 .5H 2 0
  • the solution can be prepared by adding to 1000 litres of water:-
  • the pH in the wood system is below 2.8, the fixation reactions are self controlled.
  • the pH of the solution must be kept below 2 by adding copper sulphate and arsenic pentoxide.

Landscapes

  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Forests & Forestry (AREA)
  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Chemical And Physical Treatments For Wood And The Like (AREA)

Abstract

Un procede de conservation du bois avec un agent de conservation porte soit par de l'eau soit par de l'huile comprend une etape de conditionnement dans laquelle les extractifs dans le systeme du bois sont enleves avant l'etape de conservation. Le bois est place dans un bain d'acide chauffe pour sortir par diffusion les extractifs solubles a l'eau puis il est soumis a un vide de maniere a reduire le point d'ebullition de l'eau emprisonnee dans le bois de maniere a ce que la vapeur ainsi produite refoule l'eau residuelle restant dans les cellules du bois.
PCT/AU1981/000172 1980-11-26 1981-11-26 Procede de conservation du bois WO1982001848A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
BR8108888A BR8108888A (pt) 1980-11-26 1981-11-26 Processo de preservacao da madeira
AU78097/81A AU7809781A (en) 1980-11-26 1981-11-26 Wood preservation process
FI822602A FI822602A0 (fi) 1980-11-26 1982-07-23 Traeimpregneringsfoerfarande

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU6644/80801126 1980-11-26
AUPE664480 1980-11-26

Publications (1)

Publication Number Publication Date
WO1982001848A1 true WO1982001848A1 (fr) 1982-06-10

Family

ID=3768852

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/AU1981/000172 WO1982001848A1 (fr) 1980-11-26 1981-11-26 Procede de conservation du bois

Country Status (4)

Country Link
EP (1) EP0065548A4 (fr)
JP (1) JPS57501949A (fr)
BR (1) BR8108888A (fr)
WO (1) WO1982001848A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0191446A1 (fr) * 1985-02-14 1986-08-20 Dr. Wolman GmbH Mélange de sel contenant du cuivre et du chrome pour protéger le bois

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101143535B1 (ko) * 2007-06-25 2012-05-09 아우토리브 디벨롭먼트 아베 좌석 벨트용 저마찰 조성물 및 그러한 조성물로 코팅된 좌석 벨트

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU1099170A (en) * 1969-02-05 1971-08-05 William Tack George Improvements in or relating to multi salt wood preservatives
AU1324276A (en) * 1976-04-22 1977-10-13 Hoppers Company, Inc Chromated copper arsenate wood preservative compositions
AU5288479A (en) * 1978-11-27 1980-05-29 Schroder, J.G. And Schroder, J.A. Preservation of wood

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB314380A (fr) * 1928-06-26 1930-05-22 Grubenholzimpraegnierung Gesellschaft Mit Beschraenkter Haftung
US3080212A (en) * 1961-12-12 1963-03-05 Koppers Co Inc Treatment of wood with hot chromated copper arsenate solutions

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU1099170A (en) * 1969-02-05 1971-08-05 William Tack George Improvements in or relating to multi salt wood preservatives
AU1324276A (en) * 1976-04-22 1977-10-13 Hoppers Company, Inc Chromated copper arsenate wood preservative compositions
AU5288479A (en) * 1978-11-27 1980-05-29 Schroder, J.G. And Schroder, J.A. Preservation of wood

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP0065548A4 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0191446A1 (fr) * 1985-02-14 1986-08-20 Dr. Wolman GmbH Mélange de sel contenant du cuivre et du chrome pour protéger le bois

Also Published As

Publication number Publication date
EP0065548A1 (fr) 1982-12-01
JPS57501949A (fr) 1982-11-04
BR8108888A (pt) 1982-10-26
EP0065548A4 (fr) 1983-03-29

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