Wood preservation facilities, alkaline copper quaternary: chapter G-1

1. Production and Use

There are four formulations of alkaline copper quaternary (ACQ) preservative: Type A, Type B, Type C and Type D. Type A, Type C and Type D are currently registered for use in Canada. The different formulations allow flexibility in achieving compatibility with different wood species and end use applications. All ACQ types contain two active ingredients, which may vary within the following limits: copper ethanolamine complex or basic copper carbonate, which is the primary fungicide and insecticide; and a quaternary ammonium compound (quat), which provides additional fungicide and insect resistance properties. All ACQ types contain copper and quat at either 2:1 or 1:1 ratio CuO to quat. (1).

• ACQ-A: ACQ type A is copper dissolved in ethanolamine with didecyl dimethyl ammonium chloride (DDAC) as the quat. ACQ-A contains 50% copper oxide and 50% quat.
• ACQ-B: Not currently registered for use in Canada.Was primarily used for the treatment of western wood species such as Douglas Fir because its ammonia carrier solution allows the ACQ to penetrate into these difficult-to-treat species. This formulation contains 66.7% copper oxide and 33.3% DDAC as the quat. Wood treated with ACQ-B has a dark greenish brown colour that fades to a lighter brown and may have a slight ammonia odour until dry. ACQ-B is no longer use in Canada and is excluded from the CSA O80 Series of Standards.
• ACQ-C: It contains 66.7% copper oxide and 33.3% quat as alkyldimethylbenzyl-ammonium chloride (ADBAC). Ammonia and/or ethanolamine can be used as the carrying solution in this formulation. Wood treated with ACQ-C varies in colour that ranges between that of type B and type D. Most wood-preservation facilities in Canada use the ACQ-C formulation.
• ACQ-D: ACQ-D contains 66.7% copper oxide and 33.3% quat as didecyl dimethyl ammonium chloride (DDAC) or carbonate/bicarbonate (DDACB). Type D differs from type B in that it uses an ethanolamine carrier solution rather than ammonia. Type D differs from type A in the proportion of quat and copper oxide. Wood treated with ACQ-D has a lighter greenish brown colour with little odour (2).

The term “alkaline” is used generally to describe either ammonia or ethanolamine formulations. With either carrier, the formulation is completed by the addition of copper oxide and quaternary ammonium compound to water. ACQ is a technology that was developed in Canada and further advanced 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 replaced chromated copper arsenate (CCA) at many plants due to restrictions on residential uses of CCA-treated wood. In 2012, 22 Canadian facilities were using ACQ, and 8 were using it as the sole preservative (3).

The ACQ-C preservative is shipped in tanker trucks to wood preservation facilities as a premixed concentrated solution of 14.14% active ingredients (as CuO) that is then made into a ready-to-use working-strength solution by adding a known quantity of water in a mix tank.

The ACQ-C preservative is shipped in tanker trucks to wood preservation facilities as a premixed concentrated solution that is then made into a ready-to-use working-strength solution by adding a known quantity of water in a mix tank.

ACQ-D and ACQ-A preservative are shipped as two premixed solutions that are then mixed together at the facility. The preservative is prepared by adding a known quantity of amine copper to a measured amount of water in a mix tank. Quat is then added to achieve a copper-to-quat ratio of 2:1 by weight for ACQ-D and 1:1 by weight for ACQ-A, in the working solution. The quaternary (quat) component is shipped in totes at concentrations of about 43% to 50% and the copper ethanolamine complex as an 11.25% CuO concentrate. The copper ethanolamine concentrate can also be used for make-up to balance the solution.

The use of Ammonium Hydroxide concentrate can sometime be use to top up the ACQ solution or concentrate if the ammonia levels get low.

ACQ is suited for treatment of all commercially used tree species and can be applied to those species that are refractory and difficult to impregnate. ACQ is suitable for above-ground and ground contact in the categories described in Table 1. It is often used where environmental sensitivities exist for the intended use of the treated wood product (4).

Single-cylinder preservation plants sometimes use more than one preservative. This is not recommended with ACQ as an ongoing practice, but can be done if appropriate precautions are taken and strictly followed. ACQ solutions are basic in pH, while others, such as CCA, are acidic. This situation dictates complete flushing of one preservative from the cylinder, piping, and all sumps and collection areas before introduction of the other preservative. One of ACQ's advantages is that it is free of ingredients such as arsenic and chromium. This environmental and operational advantage may be lost if ACQ is mixed with the components of other preservatives.
The CSA O80 Series of Standards specifies requirements related to the preservation and fire retardance of wood through chemical treatment (pressure), which includes ACQ-treated products. (5) Treatment conditions must be calibrated to yield the target retention levels described on the pesticide label.