Alkaline copper quaternary, usually abbreviated ACQ, is a type of water-based

wood preservative Wood easily degrades without sufficient preservation. Apart from structural wood preservation measures, there are a number of different chemical preservatives and processes (also known as "timber treatment", "lumber treatment" or "pressure treat ...

product containing a

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...

copper(II) complex and

quaternary ammonium In chemistry, quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure , R being an alkyl group or an aryl group. Unlike the ammonium ion () and the primary, secondary, or tertiary ammonium cations ...

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloalk ...

- or

aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used as ...

-substituted compounds ("quats"). Thus the product was originally called ammoniacal copper/quaternary ammonium.

Composition

Copper complex

The copper in the preparation is in the form of a soluble complex with

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

or an

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...

such as

ethanolamine Ethanolamine (2-aminoethanol, monoethanolamine, ETA, or MEA) is an organic chemical compound with the formula or . The molecule is bifunctional, containing both a primary amine and a primary alcohol. Ethanolamine is a colorless, viscous liquid wit ...

. In any case, the copper content is usually expressed as a weight percentage of the amount of

copper oxide Copper oxide is a compound from the two elements copper and oxygen. Copper oxide may refer to: * Copper(I) oxide (cuprous oxide, Cu2O) * Copper(II) oxide Copper(II) oxide or cupric oxide is an inorganic compound with the formula CuO. A black so ...

that would account for the copper present. As a copper carrier, ammonia has the advantage that it will penetrate difficult-to-treat Western species better than other waterborne preservatives. Otherwise ethanolamine is preferred as copper carrier.

Quaternary ammonium cations

Quaternary ammonium cation In chemistry, quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure , R being an alkyl group or an aryl group. Unlike the ammonium ion () and the primary, secondary, or tertiary ammonium cations ...

DDA

The quaternary ammonium cation in some formulations is didecyldimethylammonium (DDA) . DDA is commercially produced as the carbonate, under the trade name "Carboquat". The carbonate is used instead of the chloride to reduce corrosion of the treatment equipment. DDA carbonate is non-volatile and highly soluble in water, with near zero

octanol-water partition coefficient The ''n''-octanol-water partition coefficient, ''K''ow is a partition coefficient for the two-phase system consisting of ''n''-octanol and water. ''K''ow is also frequently referred to by the symbol P, especially in the English literature. It is a ...

ADBA

Another quaternary ammonium cation used in some formulations is alkyldimethylbenzylammonium (ADBA). The formula is , where ''n'' varies between 8 and 18.

Counterions

Both the copper complex and the quats are positive

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by con ...

. The

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s (the

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s that balance their positive charges) are typically

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochemic ...

Standard formulations

Formulations of ACQ differ in the "carrier" (complexing agent for copper), either ammonia or ethanolamine; and on the quaternary ammonium cation present. Types registered in the US and

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

: * ACQ-A: copper-ethanolamine (50% CuO equivalent), and DDA chloride (50%). * ACQ-B: copper-ammonia (66.7% CuO) and DDA chloride (33.3%). Not currently registered for use in Canada. * ACQ-C: copper-ammonia and/or copper-ethanolamne (66.7% CuO) and ADBA chloride (30%). * ACQ-D: copper-ethanolamine (66.7% CuO) and DDA chloride or carbonate (33.3%). The ACQ Type D formulation also contains two moldicides: 2-methyl-4- isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one. The ammonia carrier ACQ-B improves its ability to penetrate into wood that is difficult to treat, like some US Western lumber. The formulations with ethanolamine, especially ACQ-D, are generally used for easier woods (such as

southern pine Southern may refer to: Businesses * China Southern Airlines, airline based in Guangzhou, China * Southern Airways, defunct US airline * Southern Air, air cargo transportation company based in Norwalk, Connecticut, US * Southern Airways Express, ...

) because it provides a more uniform surface appearance.

Mechanism of action

During the wood treatment process, the water-soluble copper and the quaternary ammonium cations are immobilized by the formation of stable insoluble compounds with

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

, and

hemicellulose A hemicellulose (also known as polyose) is one of a number of heteropolymer, heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all embryophyte, terrestrial plant cell walls.Scheller HV, Ulvskov H ...

and other wood components. The copper is the primary

bactericide A bactericide or bacteriocide, sometimes abbreviated Bcidal, is a substance which kills bacteria. Bactericides are disinfectants, antiseptics, or antibiotics. However, material surfaces can also have bactericidal properties based solely on thei ...

and

fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

agent. The quaternary ammonium cation is added to prevent growth of copper-tolerant bacteria, fungus, and mold, as an

insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...

Use

ACQ is applied at a timber treatment plants by industrial vacuum-pressure impregnation. Bunks of dried lumber are loaded into a long (up to 150') cylindrical container, seven feet in diameter. The bunks ride on a rail system at the bottom of the cylinder. Once filled, the container is subjected to a hard vacuum, drawing all the air and any remaining moisture out of the wood. Then, the cylinder is filled nearly full of the ACQ solution and a pressure of 150PSI is applied for several hours to force the solution completely into the wood. After the solution has been pumped out, a vacuum is applied again, to remove excess solution from the wood. 2022-4-13 Bunk sizes: 2×4 have 294 pcs, 2×6 have 189 pcs, 2×8 YP have 96 pcs, 2×10 YP have 80 pcs, and 2×12 YP have 64 pcs. (YP= Yellow Pine) The lumber is usually eight, twelve, or sixteen feet long, but can be longer. The ACQ-C product is normally shipped from manufacturer as a concentrated solution that is diluted at the wood treatment plant. ACQ-D and ACQ-A are shipped as two separate solutions that are mixed and diluted at the latter. In the US and other countries, ACQ is registered for use on lumber, timbers, landscape ties, fence posts, building and utility poles, land, freshwater and marine pilings, sea walls, decking, wood shingles, and other wood structures.

Treated wood color

Wood treated with ACQ has greenish-brown color which may fade to brown, and may have a slight ammonia odor until the wood dries.

Safety

In the treated wood, the copper is relatively harmless and not an environmental or health concern. DDA chloride is approved as

germicide An antiseptic (from Greek ἀντί ''anti'', "against" and σηπτικός ''sēptikos'', "putrefactive") is an antimicrobial substance or compound that is applied to living tissue/skin to reduce the possibility of infection, sepsis, or putre ...

, and

algicide Algaecide or algicide is a biocide used for killing and preventing the growth of algae, often defined in a loose sense that, beyond the biological definition, also includes cyanobacteria ("blue-green algae"). An algaecide may be used for controlled ...

for

disinfectant A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than st ...

products that have been used for decades in hospitals and other commercial and industrial establishments. ADBA chloride has been used in commercial products in the US since 1947. A registration standard was issued by EPA in 1985. One disadvantage of ACQ is that significant amounts of air pollution, in the form of ammonia, are released from treatment plants and freshly treated wood in storage yards. While the CCA components are far more toxic in a weight basis, being non-volatile solids they can be effectively contained.

Fastener corrosion

The copper in ACQ treated wood accelerates corrosion of galvanized steel fasteners (such as nails and screws) 10 times or more in comparison with CCA-treated wood.

Stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...

(AISI 316) is not affected.

Aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

and Galvalum fasteners should be avoided. One should use fasteners made of hot-dipped galvanized steel, copper, or stainless steel.

History

ACQ technology was developed and patented in Canada and improved in the U.S. It has been in commercial production in Europe, Japan and the U.S. since the late 1980s. Wood products treated with ACQ preservative were commercially produced in Canada for the first time in 2004. ACQ became a widely used wood preservative after concerns were raised about possible environmental contamination by

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...

and

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...

from wood treated with

chromated copper arsenate Chromated copper arsenate (CCA) is a wood preservative containing compounds of chromium, copper, and arsenic, in various proportions. It is used to impregnate timber and other wood products, especially those intended for outdoor use, in order to pr ...

(CCA), through contact (especially in

playground A playground, playpark, or play area is a place designed to provide an environment for children that facilitates play, typically outdoors. While a playground is usually designed for children, some are designed for other age groups, or people ...

s), leaching, sawing and sanding, or burning. These concerns led to the virtual banning of CCA for residential purposes by the US EPA, in 2003-2004. Chemical Specialties, Inc (CSI, now Viance) received

U.S. Environmental Protection Agency The Environmental Protection Agency (EPA) is an Independent agencies of the United States government, independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon pro ...

’s

Presidential Green Chemistry Challenge Award Green chemistry, also called sustainable chemistry, is an area of chemistry and chemical engineering focused on the design of products and processes that minimize or eliminate the use and generation of hazardous substances. While environmental che ...

in 2002 for commercial introduction of ACQ.

References

Gareth Kear, Hăi-ZhènWú, Mark S. Jones (2009): "Weight loss studies of fastener materials corrosion in contact with timbers treated with copper azole and alkaline copper quaternary compounds". ''Corrosion Science'', volume 51, issue 2, pages 252-262. Preservative-Treated Wood and Alternative Products in the Forest Service
USDA, United States Forest Service, online report. Accessed on 2019-04-20. C A Cushing, R Golden, Y W Lowney, S E Holm (2007):
Human Health Risk Evaluation of ACQ-Treated Wood
. ''Journal Human and Ecological Risk Assessment'', volume 13, issue 5, pages 1014-1041. {{doi, 10.1080/10807030701506173 ACQ (Alkaline Copper Quaternary) Wood Preservative and Fasteners - Are They Compatible?
Fasteners Eurasia website. Accessed on 2019-04-20. Chapter G – Alkaline Copper Quaternaryernary (ACQ) Wood Preservation Facilities
Environment and Climate Change Canada website. Accessed on 2019-04-20. Jonathan Chen and others (2006):
Reregistration Eligibility Decision for Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC)
. Report EPA739-R-06-009, US EPA, Dept of Prevention, Pesticides, and Toxic Substances. Abraham S. C. Chen (1994):
Evaluating ACQ as an Alternative wood Preservative System
. Report APA/600/SR-94/036, US EPA, Risk Reduction Engineering Laboratory. James (Scott) Groenier, Stan Lebow (2006):
Preservative-treated wood and alternative products in the Forest Service
. Missoula, MT : U.S. Dept. of Agriculture, Forest Service, Technology & Development Program, 2006: iv, 44 pages. Accessed on 2021-07-02.

External links

* ttp://www.epa.gov/oppad001/reregistration/cca/acq.htm Information from the U.S. Environmental Protection Agencybr>Alkaline Copper Quaternary - Safety Data Sheet
Wood