GB1570311A

GB1570311A - Treatment of cellulosic materials

Info

Publication number: GB1570311A
Application number: GB5929/77A
Authority: GB
Original assignee: Koppers Co Inc
Current assignee: Beazer East Inc
Priority date: 1976-03-15
Filing date: 1977-02-11
Publication date: 1980-06-25
Also published as: SE7702775L; CA1085106A; DE2710530A1; AU507381B2; JPS5625362B2; DK106777A; NO770891L; AU2261277A; FI770788A7; JPS52110803A; FR2344384A1

Abstract

A wood treating impregnant is deposited in wood by a non-aqueous wood treating system that has the ability to control the distribution, to immobilize and to more permanently fix the impregnant in the wood. The wood is treated with a liquid carrier containing the impregnant and a reactive solvent so that both the impregnant and reactive solvent penetrate into the wood. The reactive solvent is soluble in the liquid carrier and the impregnant is substantially insoluble in the liquid carrier but soluble in the reactive solvent. After the impregnant, reactive solvent and liquid carrier have penetrated the wood, the reactive solvent is reacted to become a nonsolvent for the impregnant. Since the impregnant is no longer soluble in the reacted reactive solvent, the impregnant is immobilized in the wood and, therefore, is unable to bloom. After the reaction, the liquid carrier and optionally the reacted reactive solvent are recovered from the treated wood which is clean and need not be washed.

Description

(54) IMPROVEMENTS IN OR RELATING TO THE TREATMENT OF CELLULOSIC MATERIAL (71) We, KOPPERS COMPANY INC., a corporation organized under the laws of the State of Delaware, one of the United States of America, of the Koppers Building, City of Pittsburgh, Commonwealth of Pennsylvania, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to a process and to an impregnating composition for impregnating wood and other cellulosic porous materials with impregnants.

Impregnants, i.e. wood preservatives, fire retardants, dyes, water repellants and other wood-treating agents, have been added to wood for many years. The degree of penetration of the impregnant into the wood varies from treatment to treatment. The treatment that gives the maximum penetration is a pressure treatment.

In a pressure treatment a positive external pressure is applied to the wood to force an impregnating composition containing the impregnant into the pores of the wood.

In many pressure treatments it is customary to use an impregnating composition comprising an impregnant dissolved in a solvent; for example, the impregnating composition may comprise a solid organic compound dissolved in a petroleum distillate. There are certain inherent disadvantages when an impregnant is applied to the wood in such non-aqueous solutions.

One disadvantage is migration which is a phenomenon where the impregnant, after being deposited in the wood, moves to the peripheral areas of the wood due to the movement of residual solvent remaining in the wood. Another disadvantage, which is related to migration, is blooming. Blooming is a phenomenon where the impregnant deposited in the wood crystallizes out of the solvent onto the surface of the treated wood. This phenomenon is believed to be caused by the migration of the solvent in the treated wood to the surface of the treated wood and this migrating solvent brings along with it the dissolved impregnant which forms crystals on the surface of the treated wood. Since some impregnant is lost because of blooming, the amount of impregnant used to treat the wood must be greater than the amount that is desired to be retained in the wood.Apart from the waste involved, this situation leads to a problem in treating thin pieces of wood with impregnant when a volatile solvent is used. Another disadvantage is the difficulty in obtaining a treated wood that has a controlled distribution of the impregnant within the treated areas.

Attempts have been made to overcome some of these disadvantages by using antiblooming agents or by removing the scl- vents from the wood once the impregnant is in the wood Anti-blooming agents usually have a relatively high viscosity and a high solvency for the impregnant, and do not readily volatilize from the wood.

These agents may also contribute to water repellency, and act as an auxiliary solvent.

Typical anti-blooming agents that are used when the impregnant is pentachlorophenol, for example, are polypropylene glycol, trixylylphosphate, linseed oil, ester gum, long oil alkyds, and o-dichlorobenzene.

The removal of the solvent from the treated wood ostensibly leaves only the impregnant in the treated wood. Recovery of the solvent reduces the amount of blooming and makes an impregnation process more economical by saving expensive solvents that can be reused, but when the solvent is removed it brings some of the impregnant with it. Also, it is difficult to remove all of the solvent because some of the solvent is entrapped in the wood, and this leads to post-treatment blooming.

According to one aspect of the invention there is provided a process for impregnating a cellulosic porous material such - as wood with an impregnant, which process comprises impregnating the cellulosic porous material with an impregnating composition comprising an impregnant, a solvent for the impregnant which solvent comprises a compound or mixture of compounds which can be reacted in situ in the cellulosic porous material to form a nonsolvent for the impregnant, and a liquid carrier in which said solvent is soluble and the impregnant is substantially insoluble; reacting the compound or mixture of compounds of said solvent to form said non-solvent whereby the impregnant is substantially immobilized in the cellulosic porous material; and removing the liquid carrier from the cellulosic porous material.

According to another aspect of the invention there is provided an impregnating composition for use in impregnating a cellulosic porous material such as wood which impregnating composition comprises an impregnant, a solvent for the impregnant which solvent comprises a compound or mixture of compounds which can be reacted in situ in the cellulosic porous material to form a non-solvent for the impregnant, and a liquid carrier in which said solvent is soluble and the impregnant is substantially insoluble.

The impregnants used in the process and impregnating composition of this invention may be, for example, preservatives, fire retardants, dyes, water repellants, and other wood treating agents. The amount of impregnant used will generally be the amount necessary to treat the wood effectively, i.e. the amount of impregnant which suffices to impart preservative, flame retardant, dye or water repellant character, etc.

to the wood. The amount of impregnant used will vary depending upon the impregnant and the end-use of the impregnated wood. The effective amount for a particular impregnant and end-use can generally be determined by consulting the literature to determine the threshold value of that impregnant for protection of soil blocks. The effective amount is usually equal to the amount of the threshold value.

The threshold value for soil blocks may be obtained from such literature as the American Wood Preservers' Association Standards, the American Wood Preservers' Associated Journal, the British Wood Preservers' Association Standards, the Forest Product Research Society Journal, the Journal of Wood and Fiber, the Journal of the Institute of Wood Science, and Holzforschung.

The solvent used in the process and impregnating composition of this invention can comprise, for example, a non-aqueous compound or mixture of compounds that keeps the impregnant in solution and that can be reacted to form a substance in which the impregnant is substantially insoluble,- i.e. a non-solvent for the impregnant. The solvent keeps the impregnant dissolved in the three component, nonaqueous impregnating composition of impregnant, solvent and liquid carrier. The solvent is soluble in the liquid carrier while the impregnant is substantially insoluble in the liquid carrier. Examples of solvents that can be used in the invention are waterinsoluble polymerizable monomers.The amount of solvent that is needed will generally be the amount necessary to keep the impregnant solubilized before the compound or mixture of compounds constituting the or part of the solvent is or are reacted to form the non-solvent for the impregnant. The impregnant is immobilized in wood, for example, by being substantially insoluble in the non-solvent and the liquid carrier.

The liquid carrier used in the process and impregnating composition of this invention should be an inert liquid in which the solvent is soluble but the impregnant is substantially insoluble. Additionally, the liquid carrier should advantageously have a low viscosity and a high penetrating ability in wood. The amount of liquid carrier needed is at least that amount necessary to dissolve the solvent.

The impregnation of wood by the process of this invention can be carried out at atmospheric pressure or superatmospheric pressure. When a superatmospheric pressure is used, a full cell or an empty cell process may be utilized. The impregnation is carried out in such a way as to allow penetration, or impregnation, of the wood by the impregnant, the solvent and the liquid carrier.

The manner in which the compound or mixture of compounds constituting the or part of the solvent is reacted to form the non-solvent for the impregnant differs with the type of solvent used. When said compound or mixture of compounds is one or more polymerizable monomer(s) it can be reacted by subjecting the impregnated wood to high energy radiation or heat. In an addition polymerization reaction the quantity of high energy radiation or heat needed to effect polymerization may be lessened by using an initiator. The use of an initiator can avoid the possibility of the wood being damaged from the large quantity of high energy radiation or large quantity of heat needed to effect polymerization.

The initiator need not be a true catalyst because some of the initiator may take part permanently in the reaction and appear chemically combined with the resulting polymer. The initiator may undergo decomposition by heat, or decomposition as a photosensitizer under the influence of a photon for surface layer reaction, or decomposition by high-energy elementary particles, such as electrons, protons, alpha particles or neutrons. This decomposition forms a free radical which attacks the monomer in such a way as to form polymers. When the polymers are formed they constitute a non-solvent and no longer keep the impregnant in solution.

The liquid carrier is removed from the treated wood after the non-solvent has been formed. The solvent is soluble in the liquid carrier but the non-solvent may or may not be soluble in the liquid carrier.

When a solvent is used that forms a non-solvent which remains in the wood, a wood product is produced that contains the impregnant and the non-solvent. The composition used to contact the wood in order to produce such a wood product is composed of an impregnant dissolved in a solvent which is itself soluble in the liquid carrier, but the impregnant is substantially insoluble in the liquid carrier. The solvent may also include cosolvents which aid in dissolving the compound or mixture compounds from which the non-solvent is formed in the liquid carrier.

Generally, in the processes and impregnating compositions of this invention the impregnant used to treat the wood is a preservative or fire retardant. The preservative may be any of the solvent-soluble toxic preservatives which are often referred to as toxic salts. These toxic salts, of which some are not salts in the technical sense, include what is generally referred to as the oil-borne preservatives. Examples of the solvent-soluble toxic preservatives are chlorinated organic compounds, metal organic compounds and inorganic compounds.The chlorinated organic compounds include pentachlorophenol; 2,4 dinitrochlorobenzene; chloronaphthalene; 1 -chlorobetanaphthol; 2,4-chloroalphanaphthol; trichlorobenzene; tetrachlorophenol; 2,4, 5-trichlorophenol; 2,4,6-trichlorophenol; tetrachloronaphthalene; and 1,2,3,4,10,10hexachloro-6,7-exoxy- 1,4,4a,5,6,7,8,8a-ox- tahydro-1,4-endo, exo-5,8-dimethanonaphthalene which is better known as "Dieldrin".The metal organic compounds include copper naphthenate, copper resinate, copper abietinate, zinc naphthenate, zinc resinate, zinc abietinate, ethyl mercuric acetate, ethyl mercuric chloride, ethyl mercuric oleate, phenyl mercuric acetate, phenyl mercuric chloride, phenyl mercuric oleate, solubilized copper-8-quinolinolate, copper pentachlorophenol pentachlorophenol-zinc-naphthenate, sodium pentachlorophenyl, and tributyltin acetate and tributyl lead acetate and tributylin oxide.

When the solvent comprises a polymerizable monomer the monomer is a solvent for the preservative. By being a solvent for the preservative, the solvent contains the preservative and keeps the preservative in solution in the three component, nonaqueous impregnating composition comprising preservative, solvent and liquid carrier. Any polymerizable monomer that is water insoluble and a solvent for the preservative, and can undergo addition polymerization, condensation polymerization, homopolymerization, copolymerization or ionic polymerization may be used as the solvent. For example, when the preservative is pentachlorophenol, suitable polymerizable monomers include styrene, vinyl acetate, acrylonitrile, butyl acrylate, methacrylonitrile and methyl acrylate, and mixtures of these compounds such as a styreneacrylonitrile mixture.A cosolvent may be used to aid in dissolving the pentachlorophenol in the polymerizable monomer.

Good cosolvents are methanol, toluene, benzene, nitrobenzene, di- and tri-chlorobenzenes, alkylbenzenes, for example xylene hydroxybenzenes, diethyl ether, diisopropyl ether, vinyl ethyl ether, dibutyl ether, di-isobutyl ether, dibutyl ketone, diisobutyl ketone, methylisobutyl ketone, benzonitrile, decalin, tetralin, butyraldehyde, and isobutyraldehyde. When a cosolvent is used the efficiency of the process of this invention may be decreased. This decrease may result in a small amount of blooming but this small amount of blooming would still be an improvement over the prior art processes.

Examples of other combinations of specific preservatives or fire retardants and solvents that may be used include: tributylin acetate or tributyl lead acetate with, as solvent, such monomers as styrene or acrylonitrile or methacrylonitrile or mixtures of these compounds; "Dieldrin" with, as solvent, such monomers as vinyl acetate, acrylonitrile, butyl acrylate, methacrylonitrile, or methyl acrylate or mixtures of these compounds; and the fire retardant magnesium phosphate with, as solvent, acrylonitrile. An example of a three component non-aqueous impregnating composition including dibasic magnesium phosphate is a composition comprising 5% by weight magnesium phosphate, 5% by weight acrylonitrile and 899% pentane and 01% by weight benzoyl peroxide.These examples of specific preservatives and fire retardants in combination with specific polymerizable monomers, as solvents, are not limitations on the scope of this invention and it is to be understood that there can be used any combination of water-insoluble polymerizable monomer as solvent, and solvent-soluble impregnant.

For monomers that undergo addition polymerization, initiators such as peroxides, for example acetyl peroxide, benzoyl peroxide and lauroyl peroxide, or hydroperoxides, for example cumene hydroperoxide, or azo compounds, for example 2,2'bisazoisobutyronitrile may be used. These initiators decompose under the influence of heat, or high energy elementary particles such as electrons, protons, alpha particles or neutrons to form free radicals which initiate polymerization of the monomer. Certain vinyl type monomers do not respond to free-radical initiation but polymerization of these monomers, like propylene, isobutylene and most vinyl ethers, can be initiated by Friedel-Craftstype catalysts. Examples of catalysts of this type are boron trifluoride, aluminium chloride, stannic chloride and aluminium bromide with co-catalysts of water and acetic acid.Other initiators that are known to those skilled in the art may be used.

The liquid carrier used to facilitate the impregnation of wood, for example, with the solvent and the impregnant is a nonaqueous liquid in which the solvent is soluble but the impregnant is substantially insoluble. This liquid carrier should be easy to recover so it can be reused, if desired. Examples of such a liquid carrier are aliphatic hydrocarbon compounds which boil below the boiling point of water at ambient atmospheric pressure and liquify readily at ambient atmospheric temperatures when placed under elevated pressure.

For example, when pentachlorophenol is the impregnant, liquid carriers such as liquified petroleum gas, liquified propane, butane, iso-butane and pentane can be used. Pentachlorophenol may be slightly soluble in these liquid carriers, but this solubility is sufficiently insignificant for the pentachlorophenol to be considered to be substantially insoluble in these compounds.

Other examples of liquid carriers that can be used with specific impregnants include aromatic hydrocarbons, petroleum distillates and any liquid which is inert to the impregnant and solvent and in which the impregnant is insoluble.

The impregnating compositions of the invention can be added to the wood by either a full cell or empty cell process. The impregnating composition must be injected into the wood under pressure at a temperature lower than that needed to react the compound or mixture of compounds from which the non-solvent is formed. If more heat is used, said compound or mixture of compounds would react before maximum penetration of the wood could be obtained and maybe before any of the impregnant could penetrate the wood..

The empty cell procedure allows the recovery of some liquid carrier that may remain in the wood after the bulk of the liquid carrier is removed by volatilization.

This remaining liquid carrier is removed from. the wood by the expansion of a non condensable gas which is placed in the wood before the impregnant, solvent, and liquid carrier. Compressed air may be used as the non-condensable gas, but if the liquid carrier has a combustible nature, an inert gas like nitrogen is preferably used. In the empty cell procedure the wood is placed in a pressure vessel, commonly a horizontal cylinder, and an inert gas, for example nitrogen, is introduced into- the cylinder before the impregnating composition. In this manner a cushion of inert gas is formed within the wood under the impregnating composition, An impregnating composition is forced into the cylinder and into the wood. Pressures of up to 100, or even 200, pounds per square inch may be required to force the impregnating composition deep into the wood.A pressure is maintained even while the impregnating composition is removed from the cylinder. While still fully saturated with solution and under pressure, the wood is heated for a sufficient time in order to cause the compound or mixture of compounds to react to form the non-solvent. The wood may be heated by any manner known to those skilled in the art. Heating mediums that can be used include hot butane vapors or hot butane liquid or water or steam. The high pressures in the wood prevent any absorption of water and still allow the treatment to be dry. Once the compound or mixture of compounds have reacted to form the nonsolvent, vapour recovery and vacuum phases can be used to recover as much of the liquid carrier as possible. A vacuum can be applied so the compressed inert gas expands in the wood cells and forces any remaining liquid carrier out of the wood.

There is no loss of impregnant in this procedure because the impregnant is substantially insoluble in the liquid carrier and in the non-solvent which has been formed in situ. Some, all or none of the non-solvent may be removed with the liquid carrier depending upon what type of non-solvent is formed.

In the full cell procedure a high vacuum is applied initially to the pressure vessel containing the wood. An impregnating composition is added to the cylinder and surrounds the wood while the vacuum is maintained. Positive pressure is then applied to force the impregnant along with the solvent and liquid carrier into the wood.

This positive pressure step is still a modi fied. heat pressure step, i.e. the amount of -heat cannot exceed the heat required to react the compound or mixture of compounds- to form the non-solvent. If the positive pressure needed cannot be reached by using the limited amount of heat, then other methods of developing pressure must be used. The positive pressure is held to allow penetration of the wood by the impregnant, solvent and liquid carrier. The cylinder is emptied while a sufficient pressure is maintained to keep most of the penetrated impregnant, solvent, and liquid carrier in the wood. The cylinder is then heated so that the non-solvent is formed and the impregnant becomes immobilized in the wood. The cylinder is emptied of the heat transfer medium which can be any heat transfer medium known to those skilled in the art.Vapours are recovered by any manner known to those skilled in the art and a final vacuum can be applied to vaporize most of the liquid carrier from the wood.

In one embodiment of the process of this invention which can be carried out commercially to preserve wood there is used an impregnating composition comprising pentachlorophenol (sometimes identified as "penta" or PCP) as the impregnant, acrylonitrile as the solvent, and liquefied butane as the liquid carrier. The amount of pentachlorophenol which is used can vary over a wide range but it is customary to use 5% by weight of the total solution as the effective amount of pentachlorophenol for treating wood against decay. The amount of acrylonitrile required is at least that amount which will dissolve the pentachlorophenol. The amount of acrylonitrile that will dissolve a 5% amount of pentachlorophenol is at least 7% by weight of the total solution and preferably there is used an amount in the range of 8% to 12% to avoid any problem with precipitation of the pentachlorophenol.This solution may be warmed at mild conditions for short periods of time to avoid any problem of pentachlorophenol precipitation. The amount of butane used is that needed to disolve the acrylonitrile which amount is usually in the range of 79-88% by weight.

In order to polymerize the acrylonitrile at relatively moderate conditions an initiator is used. Such initiators are known in the art but the preferred initiator is lauroyl peroxide. The amount of lauroyl peroxide used is that amount needed to give favourable decomposition characteristics between 20 and 100 C. The preferred amount of lauroyl peroxide used is in the range of 005% to 080% by weight of the three component impregnating composition. An example of another initiator that may be used is the azo compound, azobis-isobutyronitrile. The decomposition rate of this azo compound is slightly lower than lauroyl peroxide at the same temperature. Con sequently, longer heating periods or higher heating temperatures may be required when azobis-isobutyronitrile is used as the initiator.

The three component impregnating '-Com-, position of about 5% by weight pentachlorophenol, from 7-12% by weight of. acry-.

lonitrile and from 005-08G% by weight lauroyl peroxide and from 79-88 - by weight butane can be applied to wood in either an empty cell or full cell procedure.

Since acrylonitrile is present in the. com- position any procedure used should be. conducted in equipment which does not.con- tain any copper or brass. Acrylonitrile cor- rodes copper and brass and once the copper is in solution it forms a red complexffi pre-.

cipitate with pentachlorophenol. This. pre-, cipitate represents a loss of pentachlorophenol from the three component-- nonaqueous impregnating composition.' The preferred procedure is a full cell proce dure. The wood to be impregnated is en-.

closed in a hermetically sealed pressure cylinder. The cylinder is purged to reduce the oxygen level to below 3% so as to avoid reaching the explosive range with butane Vacuum is then pulled on the wood to re- move all non-condensable gas from wood cells to enable as much preseryative as possible to penetrate the wood.. Any initial deposition of pentachlorophenol in the cylinder may be prevented by grst im- troducing pure butane into the cylinder until the equilibrium vapor pressure at.

boiling temperature of the impregnating composition is reached. The cylinder is, filled with the above-described three- coni- ponent non-aqueous impregnating composition which is prepared by mixing pentachlorophenol with acrylonitrile in the presence of heat to aid in the dissolution of the pentachlorophenol and then diluting this mixture with butane and then adding the polymerization catalyst. This.is the preferred order of mixing, but other mixing orders may be used. - - The pressure is then raised with an inert gas to a preferred pressure of 125 pounds per square inch.

Additional impregnating composition may be pumped into the cylinder if necessary during processing. The pressure is held until sufficient pentachlorophenol has been put into the wood. This time varies depending on whether complete or near complete penetration is desired and on what species of wood is used.

When sufficient pentachlorophenol has been put into the wood for protection against decay, the cylinder is emptied while a pressure is maintained that is greater than the vapour pressure of the butane so as to keep the impregnating composition in the wood while the cylinder is emptied. The cylinder is then filled with butane which acts as the heat transfer medium. It is filled just to cover the stem coils on the bottom of the cylinder to produce hot vapours of butane or it is filled to cover the wood to heat the wood with hot liquid.

The impregnated wood is heated to a preferred temperature in the range of from 140"F (60"C) to 185"F (85"C). At this temperature the lauroyl peroxide decomposes and initiates the polymerization of acrylonitrile. The polymerized acrylonitrile is not a solvent for the pentachlorophenol and the pentachlorophenol is substantially insoluble in butane so the pentachlorophenol is immobilized in the wood.

This immobilization allows for a more permanent deposition of pentachlorophenol in wood. Vapour recovery and vacuum phases are used to recover as much butane as possible. A vapour pump is used to remove the vapours in the cylinder. The vapour pressure is reduced at a rate that will not damage the wood. After the butane and any other gases which are contained in the impregnated wood have been evaporated, condensed, and placed in a storage tank, the cylinder is subjected to a final vacuum to remove last traces of hydrocarbons, then the cylinder is purged with inert gas to reduce hydrocarbon vapour to less than 4 percent. The cylinder is then opened and the impregnated wood removed.

An alternative embodiment is the empty cell procedure where a combustible gas is used. The wood is enclosed in a hermetically sealed cylinder, the air evacuated, and an inert gas, such as nitrogen, is introduced at a relatively low pressure, and forced into the wood. On top of this gas the three component impregnating composition of pentachlorophenol, acrylonitrile and butane impregnates the wood, resulting in a cushion of inert gas under pressure within the wood under the impregnating composition. When the above described impregnating and reacting cycle is ended, the butane is returned to a pressure storage tank. The quantity of solvent retained in the wood during full cell treatment is less than solvent retention of prior art processes which use organic solvents in full cell treatments, thus solvent recovery is enacted more quickly and the cylinder can be opened earlier.

Both the above-described full cell and empty cell procedures yield a treated wood that contains wood preserving amount of pentachlorophenol immobilized in the treated wood. The treated wood also contains the polymerized acrylonitrile. The polyacrylonitrile does not interfere with the effectiveness of the pentachlorophenol as a wood preservative, therefore the polyacrylonitrile need not be removed from the treated wood. The treated wood produced from the above-described procedures contains both pentachlorophenol and polyacrylonitrile and the surface of the treated wood is clean and need not be subjected to a washing step.

For a better understanding of the invention reference will now be made, by way of example, to the following Tables and Examples: Table 1 presents examples of impregnating compositions in accordance with the invention which can -be used in the process of the invention to treat wood.

The percentage of pentachlorophenol was maintained at 50 percent. by weight in Tests (a)gi). This percentage of pentachlorophenol is customary in the wood preserving art, but the percentage of pentachlorophenol can be varied below and above the value of 5.0 percent. Also, examples of 50% by weight formulations of other wood preservations are shown. The compositions in Table I were prepared by adding at room temperature the solvent and the preservative to the liquid carrier, then the catalyst was added and the mixture was stirred for around 0.5 hours. The impregnating composition thus obtained was clear with the consistency of the liquid carrier and with a colour ranging from yellow to brown.

Table I Impregnating Compositions Test Preservative Solvent Catalyst Liquid Carrier (a) 5.00% penta 8.00% acrylonitrile 0.20% BPO 86.80% pentane (b) 5.00% penta 11.00% acrylonitrile 0.22% LPO 83-78% butane (c) 5.00% penta 10.00% acrylonitrile 0.20% AIBN 84.80% butane (d) 5.00% penta 13.7% methacrylonitrile 0.28% LPO 81.02% pentane (e) 5.00% penta 2.0% styrene 0.20% BPO 85.80% butane 7.0% acrylonitrile (f) 5.00% penta 40.00% styrene 0.80% BPO 54.20% pentane (g) 5.00% penta 14.00% vinyl acetate 0.30% BPO 80.70% pentane (h) 5.00% penta 16.00% butyl acrylate 0.32% LPO 78.64% pentane (i) 5.00% penta 13.50% methyl acrylate 0.27% LPO 81.23% pentane (j) 5.00% 15.0% styrene 0.30% LPO 79.70% pentane tributyltin acetate (k) 5.00% dieldrin 10.0% methacrylonitrile 0.20% LPO 84.80% pentane (l) 5.00% dieldrin 15.0% vinyl acetate 0.30% LPO 79.70% pentane BPO = benzoyl peroxide;LPO = lauroyl peroxide; AIBN = 2,2'azobis-isobutyronitrile.

Example I Southern yellow pine (SYP) blocks were treated by the full cell process on a bench scale with a pressure hydrometer jar used as a treating cylinder. Three-quarter inch SYP blocks were treated with a 5% by weight penta solution using pentane as the liquid carrier and either a styrene-methanol mixture of a styrene-acrylonitrile mixture as the solvent. After an initial vacuum period, pure pentane was introduced until equilibrium vapour pressure was reached.

Enough solution was added to cover the blocks. The pressure was increased to atmospheric or 15 pounds per square inch absolute and the pressure period was maintained for 30 minutes. The impregnating composition was withdrawn and pentane added to the bottom of the cylinder making sure that it did not touch the blocks. Then, the entire apparatus was heated in a hot water bath at 700C for 24 hours. The hot pentane vapours that were generated heated the blocks to cause the reactive solvent to react. No surface crystals were visible on any blocks treated in the above described manner. Table II presents data from X-ray analysis to show penta retentions on the blocks treated in the above described manner. No surface crystals were visible on any blocks treated by this technique and blooming did not occur after treatment with this technique.The treated blocks were clean, dry, natural appearing, and did not need to be washed. Table II Retentions of inch SYP Blocks Treated with an Impregnating Composition Containing 5% Pentachlorophenol Weight Weight Weight Retention Before After After or Penta Test Treatment Impregnation Reaction chlorophenol Retention No. Solvent (gm) (gm) (gm) (%) (pcf)* 1 Styrene 4.84 8.66 - 3.95 1.26 methanol 2 Styrene 4.47 8.44 4.65 4.45 1.42 methanol 3 Styrene 4.49 8.81 4.75 4.80 1.53 methanol 4 Styrene 5.04 8.76 5.29 3.67 1.17 acrylonitrile 5 Styrene 4.63 8.42 4.85 4.07 1.30 acrylonitrile 6 Styrene 4.81 8.24 5.03 3.57 1.14 acrylonitrile * Based on oven dry weight of southern yellow pine of 32 pcf (pound per cubic foot).

Example 11 Dougias fir heartwood lumber which was end-sealed to simulate the treatment of commercial lumber was treated with the non-aqueous impregnating composition on a pilot plant scale in an 8-inch diameter cylinder. The impregnant was pentachlorophenol and the solvent was a polymerizable monomer and the liquid carrier was either butane or pentane. The boards treated with this solution had clean surfaces and an appearance of untreated wood.

The results of treating Douglas-fir lumber with such an impregnating composition are summarized in Table m. Cross-sections from each sample board were cut and retentions were determined by X-ray analysis. Table III Board Number 1 2* 3 4 5 6* Nominal Dimensions (in.) 4x4x24 4x4x24 4x4x36 2x4x24 2x4x24 2x4x24 Amount of PCP (% of total) 5.0% 4.5% 5.0% 4.5% 4.0% 4.0% Liquid Carrier butane butane butane butane butane butane Solvent ACR ACR Sty-ACR ACR Sty-ACR ACR Initiator LPO LPO BPO LPO BPO LPO Treating Schedule Initial vacuum (min. at in.Hg) 30-28 30-28 30-28 30-28 30-28 30-28 Pressure rise (min. to psi) 15-125 15-125 15-125 15-125 15-125 15-125 Pressure hold (min. at psi) 30-125 30-125 30-125 30-125 30-125 30-125 Temperature (hrs. at C) 2.25-76 1.5-79 4.0-82 4.0-82 2.0-85 3.0-82 Results Surface condition after treat- clean clean clean clean clean clean ment Retentions (pfc) 0- in. 0.48 0.39 0.55 0.31 0.38 0.30 - in. 0.53 0.30 0.55 0.33 0.35 0.33 -1 in. 0.48 0.08 0.56 0.33 0.32 * Performed by empty cell method.

ACR = acrylonitrile; Sty-ACR = styrene-acrylonitrile mixture.

LPO = Lauroyl peroxide; BPO = benzoyl peroxide.

None of the boards had crystals on their surfaces after treatment. For these boards the temperature was maintained at at least 76 C for at least 1.5 hours. This time and temperature were sufficient to react all of the reactive solvent, therefore, preventing the formation of crystals on the surface of these boards.

Example 111 Further pilot plant tests were conducted in 3ft. and 18in. diameter cylinders to determine the applicability of the process of this invention to the treatment of poles.

The impregnating composition consisted of 3-647% by weight pentachlorophenol as the impregnant, 7-12% by weight acrylonitrile as the solvent, and 83-89% by weight butane as the liquid carrier along with 0.15-0.25% by weight benzoyl peroxide as an initiator for polymerization.

In this series of tests 6ft. pole sections were treated. The total volumes of these pole sections varied between 2.5 and 3.2ft. The poles were end-sealed prior to treatment to minimize end penetration effects and simulate treatment of commercial stock. Douglas fir poles were used primarily because this species represents the most serious crystal blooming problems.

One charge of a Southern Pine pole section was treated. The results of this series of treatments are reported in Table IV. Table IV Retentions Pole inches in assay zones Sample Pressure Time Temp. Time 0- - -1 1-1- 1--2 2-2- No.1 Species PSIG Hrs. C Hrs. (pcf) 1 SYP 125 1.0 82.22 4.0 0.38 0.37 0.39 0.39 0.36 0.38 2 D.F. 125 1.0 82.22 5.0 0.69 0.70 0.79 0.74 0.63 0.31 3 D.F. 125 1.0 82.22 10.0 0.73 0.61 0.67 0.65 0.69 0.47 4 D.F. 125 1.0 82.22 6.0 0.64 0.68 0.67 0.55 0.61 0.51 5 D.F. 125 1.0 82.22 4.0 0.41 0.28 0.20 0.11 0.08 0.0 6 D.F. 125 1.0 82.22 1.0 0.56 0.22 0.13 0.11 0.02 0.006 7 D.F. 125 1.0 82.22 3.0 0.77 0.47 0.42 0.38 0.41 0.12 Pole samples 1 thru 4 were impregnated by full cell procedure.

Pole samples 5 thru 7 were impregnated by partial empty cell procedure.

Based on an average density of Douglas Fir of 28 pcf and Southern Pine of 32 pcf.

Example V Four SYP blocks (i inch) were treated with an impregnating composition of 5% by weight pentachlorophenol as the preservative, acrylonitrile as the solvent and butane as the liquid carrier. After the treatment three of the blocks were placed in ovens at temperatures ranging from 50 to 900C for up to one week. This treatment determined that there was no posttreatment blooming or crystal formation on the surface of the blocks during a one week period of observation at elevated temperatures. One block was sliced into sections and submitted for X-ray analysis of pentachlorophenol. These sections were then subjected to a leaching test. This test consisted of soaking the sections in distilled water for two hours, heating in an oven at 50 C for six hours and being at room temperature for the rest of the day.This 24 hour cycle was repeated for three weeks.

The sections were submitted for pentachlorophenol (PCP) analysis at the end of this test to: idetermine if any pentachlorophenol was lost. The results are given in Table V. - The results show that only a minor amount of PCP was lost.

Table V Original PCP Final PCP Sections Content Content Sample A % pcf % pcf 1 2.35 0.75 2.23 0.71 2 2.61 0.83 2.46 0.78 3 2-12 O68 2 06 ( > 65 4 210 067 196 063 Based on average density of dry SYP being 32 pcf.

Example Vl To show that the impregnant, here pentachlorophenol, is not rendered ineffective as a result of the process of this invention, soil block tests were performed. The soil block tests were conducted to determine the effectiveness of pentachlorophenol by exposed treated blocks to Lenzites trabea for twelve weeks. Any significant loss of weight would indicate that the blocks were decayed by the organism.

A series of soil blocks were treated with an impregnated composition consisting of pentachlorophenol, a solvent comprising a mixture of styrene-methanol in a weight ratio of 7:2 with methanol as a co-solvent, and pentane as the liquid carrier. The series was composed of three sets of blocks.

The first set was treated with an impregnating composition having a pentachlorophenol concentration of 20% by weight.

The second and third sets were treated with an impregnating composition having pentachlorophenol concentrations of 1-3% and 0.6% by weight respectively. A fourth set of blocks was treated containing the solvent but no pentachlorophenol. A fifth set of blocks were untreated and served as controls. Half of the total number of blocks in each set were subjected to the standard American Wood-Preservers' Association (A.W.P.A.) two week weathering cycle.

This cycle is described in Proceedings Sixty Ninth Annual Meeting of the American Wood-Preservers' Association, American Wood-Preservers' Association, Washington D.C., Volume 69, page 116. One of the weathered and unweathered blocks from each set was ground and analyzed by X-ray analysis for pentachlorophenol content.

Because of the variation in solution pick up for different blocks, the results from X-ray analysis could only be used as a check for approximate pentachlorophenol retentions.

Analysis of all the individual blocks for pentachlorophenol retentions were conducted at the end of the test. The remaining blocks that were not ground and analysed in each set were equilibrated at constant temperature and humidity, weighed and exposed to Lenzites trabea for 12 weeks.

After the twelve week incubation period the blocks were reweighed. Any loss in weight greater than 3% indicates attack by the decay organism. A slight increase in weight is insignificant and due to variations in moisture content of the blocks. The unattacked blocks had retentions ranging from 013 to 033 pounds per cubic foot (pcf).

Results are summarized in Table VI. Table VI Pre-exp Post-exp Retention Block Weight Weight Weight % Wt. (pcf) Post Set No. (gm) (gm) Loss Loss Weathering exp X-ray A 1 5.052 5.028 0.024 0.5 U 0.27 A 2 5.429 5.380 0.049 0.9 U 0.20 A 3 4.744 4-743 0.001 0. W 0.33 A 4 4.795 4.772 0.023 0.5 W 0.30 B 1 5.023 4.853 0.170 3.4 U 0.130 B 2 4.356 4.337 0.019 0.4 U 0.167 B 3 5.198 5.206 +0.008 +0.2 W 0.199 B 4 5.188 5.150 0.038 0.7 W 0.213 C 1 4.930 4.757 0.173 3.5 U 0.113 C 2 5.226 4.743 0.483 9.2 U 0.093 C 3 5.508 5.159 0.349 6.3 W 0.078 C 4 4.867 3.778 1.089 22.2 W 0.026 D 1 4.345 1.667 2.678 61.6 U D 2 5.499 3.452 2.047 37.2 U Control 1 4.405 2.520 1.885 42.8 U 2 4.400 1.438 2.962 67.3 U 3 4.249 1.301 2.948 69.4 W 4 4.091 2.664 1.427 34.8 W Group A-2.0%pentachlorophenol treating solution.

Group B-1.3% pentachlorophenol. Group C-0.6% pentachlorophenol.

Group D-0.0% pentachlorophenol. W = weathered.

U = unweathered.

By practising the process of this invention, and using either the empty cell or full cell procedure, good penetration, retention and uniformity of treatment are obtained and blooming is prevented or substantially reduced. Even though the process of this invention has the capability of a more uniform treatment, it still can be used to effect a gradient of concentration of the impregnant in wood. A major reason for the benefits of the process of this invention is that the impregnant is deposited in the wood by a controlled reaction. The impregnant does not attach to or deposit in the wood as the impregnant first contacts the wood. The impregnant, solvent, and liquid carrier move into the wood and, when the desired penetration is reached, the non-solvent is formed and the impregnant is deposited in the wood.

WHAT WE CLAIM IS: - 1. A process for impregnating a cellu losic porous material with an impregnant, which process comprises impregnating said cellulosic porous material with a composition comprising an impregnant, a solvent for the impregnant which solvent comprises a compound or mixture of compounds which can be reacted in situ in the cellulosic porous material to form a nonsolvent for the impregnant, and a liquid carrier in which said solvent is soluble and the impregnant is substantailly insoluble; reacting the compound or mixture of compounds of said solvent to form said nonsolvent whereby the impregnant is substantially immobilized in the cellulosic porous material; and removing the liquid carrier from the cellulosic porous material.

2. A process according to claim 1, wherein the impregnant comprises one or more preservatives and/or one or more fire retardants for wood.

3. A process according to claim 1 or 2, wherein said solvent comprises one or more polymerisable monomers.

4. A process according to claim 1, 2 or 3, wherein said solvent also contains a cosolvent to facilitate the dissolving of the impregnant in said compound or mixture of compounds.

5. A process according to claim 3, wherein after the cellulosic porous material has been treated with said composition the one or more polymerisable monomers are polymerised to form said non-solvent.

6. A process according to claim 1, 2, 3 or 4, wherein said composition contains an amount of said liquid carrier sufficient to dissolve said solvent.

7. A process according to claim 1, 2, 3, 4, 5, or 6, wherein the liquid carrier is an aliphatic or aromatic hydrocarbon which boils at a temperature below the boiling point of water at ambient atmospheric pressure, and which liquifies at ambient atmospheric temperature when placed under elevated pressure.

8. A process according to any of claims 1 to 7, wherein the liquid carrier is removed from the wood by vaporization.

9. A process according to claim 1 which comprises treating wood at a superatmospheric pressure with an impregnating composition comprising pentachlorophenol, a solvent comprising a compound or mixture of compounds selected from styrene, vinyl acetate, acrylonitrile, butyl acrylate, methacrylonitrile and methyl acrylate, a liquid carrier selected from butane and pentane in an amount at least sufficient to dissolve the solvent, and a polymerization initiator selected from benzoyl peroxide, lauroyl peroxide and azobisisobutyronitrile; heating the treated wood at a temperature at least sufficient to decompose the polymerization initiator whereby the said compound or mixture of compounds reacts to form a polymer in which the pentachlorophenol is substantially insoluble thereby immobilizing the pentachlorophenol in the wood; and removing the liquid carrier from the treated wood.

10. A process according to claim 9, wherein the wood is treated with said impregnating composition at a temperature ranging from ambient temperature up to a temperature which is less than the temperature required to decompose the polymerization initiator.

11. A process according to claim 9 or 10, wherein said solvent also contains a cosolvent to facilitate the dissolving of the pentachlorophenol in said compound or mixture of compounds.

12. An impregnating composition for use in impregnating a cellulosic porous material which composition comprises an impregnant, a solvent for the impregnant, which solvent comprises a compound or mixture of compounds which can be reacted in situ in the cellulosic porous material to form a non-solvent for the impregnant, and a liquid carrier in which the said solvent is soluble and the impregnant is substantially insoluble.

13. An impregnating composition as claimed in claim 12, wherein the impregnant comprises one or more preservatives and/or one or more fire retardants for wood.

14. An impregnating composition as claimed in claim 12 or 13 wherein said compound or mixture of compounds comprises one or more polymerisable monomers.

15. A composition as claimed in claim 14, wherein said composition includes a polymerization initiator.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. By practising the process of this invention, and using either the empty cell or full cell procedure, good penetration, retention and uniformity of treatment are obtained and blooming is prevented or substantially reduced. Even though the process of this invention has the capability of a more uniform treatment, it still can be used to effect a gradient of concentration of the impregnant in wood. A major reason for the benefits of the process of this invention is that the impregnant is deposited in the wood by a controlled reaction. The impregnant does not attach to or deposit in the wood as the impregnant first contacts the wood. The impregnant, solvent, and liquid carrier move into the wood and, when the desired penetration is reached, the non-solvent is formed and the impregnant is deposited in the wood. WHAT WE CLAIM IS: -

1. A process for impregnating a cellu losic porous material with an impregnant, which process comprises impregnating said cellulosic porous material with a composition comprising an impregnant, a solvent for the impregnant which solvent comprises a compound or mixture of compounds which can be reacted in situ in the cellulosic porous material to form a nonsolvent for the impregnant, and a liquid carrier in which said solvent is soluble and the impregnant is substantailly insoluble; reacting the compound or mixture of compounds of said solvent to form said nonsolvent whereby the impregnant is substantially immobilized in the cellulosic porous material; and removing the liquid carrier from the cellulosic porous material.

16. An impregnating composition as

claimed in claim 12, 13, 14 or 15, wherein said solvent includes a cosolvent to facilitate solution of the impregnant in said compound or mixture of compounds.

17. An impregnating composition as claimed in any one of claims 12 to 16, wherein the composition contains an amount of said liquid carrier sufficient to dissolve the solvent.

18. A composition, according to claim 12, for use in preserving wood, the composition comprising: pentachlorophenol; a solvent comprising a compound or mixture of compounds selected from styrene, vinyl acetate, acrylonitrile, butyl acrylate, methacrylonitrile and methyl acrylate; a liquid carrier selected from butane and pentane in an amount at least sufficient to dissolve the solvent; and a polymerization initiator selected from benzoyl peroxide, lauroyl peroxide and azobis-isobutyronitrile.

19. A composition as claimed in claim 18, wherein the solvent includes a cosolvent selected from ethanol, toluene, benzene, nitrobenzene di- and tri-chlorobenzenes, alkylbenzenes, hydroxybenzenes, diethyl ether, diisopropyl ether, vinyl ethyl ether, dibutyl ether, diisobutyl ether, dibutyl ketone, diisobutyl ketone, methylisobutyl ketone, benzonitrile, decalin, butyraldehyde and isobutyraldehyde, which aids in making the pentachlorophenol soluble in said compound or mixture of compounds.

20. A composition as claimed in claim 19, wherein the compositoin contains an amount of solvent sufficient to solubilize at least 20% by weight of pentachlorophenol based on the total weight of the composition.

21. A process for treating porous cellulosic materials substantially as hereinbefore described.

22. An impregnating composition according to claim 12 for treating porous cellulosic materials, substantially as hereinbefore described.

23. Wood, or other porous cellulosic material, whenever treated by a process, or with a composition, as claimed in any one of the preceding claims.