Preservative-treated Wood Testing

Preservative-treated wood testing mainly conducts scientific testing and analysis on wood preservative retention testing, preservative penetration testing, mechanical property testing, dimensional stability testing, decay resistance performance, weather resistance and aging performance testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Wood preservative retention testing: This is a core testing item used to determine whether the content of active ingredients of the preservative in the wood reaches the specified standard. By sampling different parts of the wood and analyzing the concentration of its active ingredients (such as copper, quaternary ammonium salts and azoles), it ensures that the preservative has deeply, uniformly penetrated and fixed to provide long-term protection. This is the primary indicator for judging whether the preservative treatment is qualified.

Preservative penetration testing: This item evaluates the depth and uniformity of preservative penetration into the wood. Through chemical color development methods or physical measurement methods, the penetration of the preservative along the wood grain direction and on the cross-section is checked. Sufficient penetration is key to ensuring that both the heartwood and sapwood of the wood are effectively protected, especially for members in direct contact with the ground, which require deeper penetration.

Mechanical property testing: Evaluates whether the preservative treatment process (such as high-pressure vacuum impregnation) has a negative impact on the original mechanical strength of the wood. Main test items include bending strength, modulus of elasticity in bending, compressive strength parallel to grain and hardness. It ensures that preservative-treated wood can still carry the design load while meeting durability requirements, safeguarding structural safety.

Dimensional stability testing: Tests the dimensional change rate of preservative-treated wood under dry-wet cycling environments, such as the swelling and shrinkage coefficients of width, thickness and volume. It evaluates whether the preservative treatment affects the hygroscopicity of the wood, which is crucial for outdoor paving, connection joint design, and preventing cracking and warping deformation.

Decay resistance (laboratory) testing: Through laboratory accelerated decay tests, the resistance of preservative-treated wood to specific decay fungi (such as white rot fungi and brown rot fungi) and wood-boring insects is evaluated. Usually, treated specimens and control wood blocks are placed in a specific fungal culture environment, and the mass loss rate is regularly observed and compared to scientifically quantify its decay prevention effectiveness.

Weather resistance and aging performance testing: Simulating outdoor natural environments, artificial accelerated aging tests (such as xenon arc aging, UV irradiation and water spray cycles) are used to evaluate the color change, surface chalking, cracking and preservative loss of preservative-treated wood. This item concerns the appearance retention and performance decay of the product under long-term sun and rain exposure.

Hazardous substance release testing: Tests hazardous substances that may be released from preservative-treated wood into the environment, such as the leaching amount of heavy metals (arsenic, chromium and copper), or the release level of volatile organic compounds (VOC). This item concerns environmental protection and human health, and is an important basis for green building material evaluation.

Testing Scope

CCA (copper-chromium-arsenic) treated wood: This is a traditional high-efficiency preservative-treated wood. The testing focus is on the retention and penetration of arsenic, chromium and copper elements, as well as the risk of heavy metal leaching. Due to its environmental sensitivity, testing must strictly follow relevant environmental regulations, and it is currently mostly limited to specific industrial uses.

ACQ (alkyl ammonium compound) treated wood: As one of the main environmentally friendly substitutes for CCA, the testing core is the retention of copper and quaternary ammonium salts. Attention should be paid to its characteristic of corroding metal connectors, as well as its fixation effect and leaching resistance in different wood species (such as southern pine and Mongolian Scots pine).

CuAz (copper azole) treated wood: Another mainstream environmentally friendly preservative-treated wood. Test items include the content of copper and azole preservatives (such as tebuconazole and propiconazole). Its testing needs to evaluate the leaching resistance of the azole components and the broad-spectrum inhibitory effect against different fungal species.

Borate-treated wood: Mainly used for indoor or moisture-proof environments. The testing focus is the retention of boron. Borates are easily soluble in water, so their leaching resistance testing is particularly important, and they are not suitable for long-term wet or direct water-contact outdoor applications.

Micronized wood (thermally treated wood): Although not chemically preserved, it is a durability-modified wood. The testing scope includes its equilibrium moisture content, dimensional stability, decay resistance grade and the mechanical strength changes caused by the heat treatment process. Biological decay resistance tests are needed to verify its durability improvement effect.

Carbonized wood: Deeply thermally modified wood. Testing needs to pay attention to its carbonization layer depth, surface hardness, hygroscopicity, decay resistance and significant decline in mechanical properties (especially impact strength). Color uniformity and surface cracks are also important appearance testing items.

Preservative-treated wood for different uses: Targeted testing is carried out according to the use environment grade (such as above ground, in contact with ground, submerged in fresh water or seawater). For example, seawater-use preservative-treated wood needs additional testing of resistance to marine boring organisms (shipworms and gribbles), which has the most stringent requirements.

Testing Methods

Chemical titration and spectroscopic methods: Used for quantitative analysis of preservative retention. For example, atomic absorption spectroscopy (AAS) or inductively coupled plasma optical emission spectrometry (ICP-OES) precisely determines the content of metal elements such as copper, chromium and arsenic; high-performance liquid chromatography (HPLC) can be used to analyze organic preservative components (such as azoles).

Color development indicator method: Used for rapid and intuitive determination of preservative penetration. For example, chrome azurol S reagent reacts with copper ions to develop color, or diphenylcarbazide reacts with chromium ions to develop color, directly observing the distribution and depth of the colored area on the cross-section or longitudinal section of the wood to judge whether penetration meets the requirements.

Laboratory culture method for wood decay fungi: In accordance with national standards (such as GB/T 13942.1), preservative-treated wood specimens and specific decay fungi (such as Postia placenta) are co-cultured under constant temperature and humidity conditions for a certain period (usually 12-16 weeks). After the test, the specimens are dried and weighed, and the mass loss rate is calculated to evaluate the decay resistance grade.

Laboratory bioassay method for termites: In a controllable experimental device, preservative-treated wood specimens are exposed to a certain number of termites (such as Coptotermes formosanus). After a specified time, the extent of the specimens being eaten is checked to evaluate their termite resistance, usually classified into anti-boring grades.

Artificial accelerated aging test method: Using a xenon arc aging test chamber or UV aging chamber to simulate climate factors such as sunlight, rain and dew, cyclic irradiation and spraying are carried out on preservative-treated wood samples. The color change (using a colorimeter), surface morphology and preservative loss of the samples are regularly evaluated to accelerate the assessment of their outdoor durability.

Standard mechanical property test methods: Completely in accordance with national standards for wood mechanical property testing. For example, bending strength testing is carried out in accordance with GB/T 1936.1, and compressive strength parallel to grain testing in accordance with GB/T 1935, ensuring the uniformity and comparability of test conditions, specimen dimensions and loading speed.

Hazardous substance leaching test method: Simulating the actual service environment, the extraction method is adopted (such as soaking the specimen in deionized water under certain conditions), and then instruments such as AAS and ICP-MS are used to analyze the concentration of heavy metal ions in the extraction solution, evaluating the potential pollution risk to soil and water bodies.

Testing Standards

Domestic Standards:

1. GB/T 1936.1-2009, Method of testing in bending strength of wood

2. GB 18580-2025, Indoor decorating and refurbishing materials — Limit of formaldehyde emission of wood-based panels and finishing products

3. GB/T 17657-2022, Test methods of evaluating the properties of wood-based panels and surface decorated wood-based panels

4. GB/T 1931-2009, Method for determination of moisture content of wood

5. GB/T 4823-2013, Defects in sawn timber

International Standards:

1. ISO 12460-1, Determination of formaldehyde emission of wood-based panels — Part 1: 1 m³ chamber method

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Atomic absorption spectrometer (AAS) and inductively coupled plasma spectrometer (ICP-OES/ICP-MS): Core equipment for testing the retention of metal elements (Cu, Cr, As, B, etc.) in preservative-treated wood. They feature high sensitivity, good accuracy and the ability to determine multiple elements simultaneously or sequentially, meeting the strict requirements of the standards for quantitative analysis of trace elements.

High-performance liquid chromatograph (HPLC) and gas chromatography-mass spectrometry (GC-MS): Used to test the active ingredients of organic preservatives, such as quaternary ammonium salts in ACQ and tebuconazole in CuAz. These devices can separate, qualitatively and quantitatively analyze complex organic compounds, evaluating their content and degradation condition.

Constant temperature and humidity incubator and biological safety cabinet: Essential equipment for wood decay resistance and termite resistance tests. The incubator can precisely control temperature (usually 28±2 ℃) and humidity (75±5%), providing an optimal growth environment for decay fungi or termites; the biological safety cabinet ensures the safety of the operation process and prevents microbial leakage.

Mechanical testing machine (universal material testing machine): Used to complete all mechanical property tests, including bending, compression, tension and shear tests. The equipment is equipped with different fixtures and sensors, can precisely control the loading rate and record the load-displacement curve, thereby calculating various strengths and moduli of elasticity.

Xenon arc aging test chamber and UV aging test chamber: Key equipment for artificial accelerated aging tests. The xenon arc lamp can simulate full-spectrum sunlight, which is closer to the real outdoor environment; the UV aging chamber mainly strengthens the influence of the ultraviolet band. Both can be programmed to control light, dark and spray cycles to accelerate the material aging process.

Colorimeter and microscope: The colorimeter is used to quantitatively evaluate the color change of preservative-treated wood before and after aging or between different batches (L*, a*, b* values). Stereo microscopes or electron microscopes are used to observe the surface microscopic morphology of the wood, the crystalline state of preservatives, the details of fungal erosion or insect boring holes.

Precision electronic balance and drying oven: Basic but crucial equipment. The precision electronic balance (accuracy 0.001 g) is used to weigh the specimens before and after the decay resistance test to calculate the mass loss rate. The forced-air drying oven is used to dry the wood specimens to the absolutely dry state, and is the standard equipment for determining moisture content and oven-dry weight.