Paulownia Wood Board Testing

Tung wood board testing is conducted in accordance with relevant standards and industry specifications. Scientific testing and analysis are performed on dimensional and appearance defect testing, moisture content determination, physical and mechanical property testing, formaldehyde emission testing, surface paint film performance testing, and insect and corrosion resistance evaluation, objectively assessing the product quality grade. A detailed test report is issued within 7-10 working days, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Dimensional and appearance defect testing: Mainly inspects the length, width, thickness and tolerances of the board to determine whether they conform to contractual or standard requirements. It also checks whether the surface contains natural defects such as live knots, dead knots, decay, cracks, wormholes, bark pockets and discoloration, as well as processing defects such as missing edges, warping, twisting and wavy bowing, which directly affect the grade and yield of the board.

Moisture content determination: The moisture content of tung wood board is a core quality indicator that directly affects the stability of subsequent processing and the durability of finished products. Testing is usually carried out under constant temperature and humidity conditions using the oven-drying method or a resistance-type moisture meter. The moisture content must be compatible with the equilibrium moisture content of the place of use to prevent the board from drying shrinkage, wet swelling, cracking or deformation in service.

Physical and mechanical property testing: Evaluates the basic load-bearing and deformation capacity of tung wood as a material. Key items include density, drying shrinkage rate, wet swelling rate, compressive strength parallel to grain, bending strength and modulus of elasticity in bending. Tung wood is light and soft with low density and moderate mechanical strength; these data provide a scientific basis for its application in packaging, musical instruments, models and other specific fields.

Formaldehyde emission testing: If adhesives are used in the production of tung wood board (e.g., plywood or finger-jointed board), formaldehyde emission testing must be carried out in accordance with national standards. Common methods include the desiccator method, the perforation extraction method or the 1 m³ chamber method, corresponding to different product types and limit requirements (e.g., E1 grade, ENF grade). This is a key mandatory item related to indoor environmental safety.

Surface paint film performance testing: For tung wood boards that have been coated, the quality of the paint film needs to be evaluated. Test items include paint film adhesion (cross-cut method), abrasion resistance, resistance to dry heat, resistance to cold liquids (such as vinegar and alcohol), resistance to cigarette burning, and gloss, to determine the durability and service performance of the surface decorative layer.

Insect and corrosion resistance evaluation: Tung wood itself has a certain resistance to insect attack, but for special applications (such as export packaging and outdoor components), artificial accelerated aging tests or biological attack tests may be required to evaluate its natural resistance grade, or to verify whether the preservative retention and penetration after preservative treatment (e.g., pressure impregnation) meet the requirements.

Testing Scope

Rough sawn timber and sawn timber: Refers to wany-edged or square-edged boards directly sawn from tung wood logs, representing the most basic form of tung wood circulation. Testing mainly focuses on natural defect grade, dimensional specifications, moisture content and the presence of internal decay, and is used for preliminary grading and pricing, commonly found in primary timber markets or as upstream material for custom processing.

Kiln-dried boards: Tung wood boards processed in an artificial drying kiln, whose moisture content is effectively and uniformly controlled. Testing focuses on verifying drying quality, including whether the final moisture content meets requirements, drying uniformity, and whether improper drying processes have caused internal cracks, surface checks, warping and other drying defects, to ensure material processing stability.

Finger-jointed laminated timber: Long boards or wide panels formed by longitudinally gluing short tung wood pieces through sawtooth joints. In addition to basic physical properties, the testing scope focuses on finger-joint strength testing (bending or tension) and bonding strength testing, to ensure that the mechanical performance at the joint is not lower than that of the wood itself, while strictly testing its formaldehyde emission.

Tung wood plywood and blockboard: Multi-layer wood-based panels made with tung wood veneer or tung wood strips as the core and surface panels. Testing must comply with the corresponding wood-based panel standards, covering bonding strength, modulus of rupture, modulus of elasticity, moisture content, formaldehyde emission and surface veneer quality defects, and is widely used in furniture manufacturing and interior decoration.

Tung wood board for export packaging: Used for packaging boxes of precision instruments, handicrafts and other export items. In addition to routine items, special attention must be paid to compliance with international phytosanitary standards (such as ISPM 15), including fumigation treatment certification and marking inspection, to prevent the cross-border spread of pests, and to evaluate its cushioning and shock resistance.

Special tung wood board for musical instruments: Mainly used for making soundboards of national musical instruments such as guzheng and pipa. Testing requirements are extremely strict. Acoustic performance screening of the wood in specific parts (such as the soundboard) is required, including testing of dynamic modulus of elasticity, sound radiation quality constant and vibration decay modes, so as to select "instrument wood" with excellent resonance performance.

Testing Methods

Moisture content determination - oven-drying method: This is the arbitration and reference method. A wood block of approximately 20 mm × 20 mm × 20 mm is cut from the specimen and weighed immediately (accurate to 0.001 g) as the wet mass, then dried in an oven at (103 ± 2) ℃ to constant weight and weighed again to obtain the oven-dry mass. The absolute moisture content is calculated from the mass difference, giving accurate and reliable results.

Dimension and defect inspection - manual and instrument combined method: Steel tape measures, vernier calipers and micrometers are used to measure length, width, thickness and warpage. Appearance defects are determined, measured and recorded by visual inspection and hand feeling, with the aid of probes and magnifiers where necessary, in accordance with national standards (such as GB/T 4823) or the grade standards agreed between the buyer and seller, and the board is graded according to the most severe defect.

Formaldehyde emission testing - 1 m³ chamber method: This is the arbitration method simulating a real indoor environment. A specimen with a surface area of 1 m² is placed in a climate chamber with strictly controlled temperature, humidity and air exchange rate. Air in the chamber is periodically extracted and passed through an absorption bottle containing distilled water, where formaldehyde is absorbed. The formaldehyde concentration in the absorption solution is determined by the acetylacetone spectrophotometric method, and the formaldehyde emission per unit area and unit time is finally calculated.

Mechanical property testing - universal testing machine method: Standard test pieces are prepared according to national standards (such as GB/T 1936.1) and loaded at a constant rate on a universal testing machine. The load-deformation curve is recorded through load cells and displacement sensors, and data such as bending strength, modulus of elasticity in bending and compressive strength parallel to grain are automatically calculated and output. The whole process is computer-controlled to ensure accuracy.

Bonding strength determination - tensile shear method: Applicable to finger-jointed timber and plywood. Specimens of specific shapes (such as short test strips for finger-jointed timber, and test pieces of two glued veneers for plywood) are made and subjected to tensile shear testing on a universal testing machine. The maximum load at failure is recorded, and the shear strength per unit bonded area is calculated to evaluate the performance of the adhesive and the quality of the gluing process.

Acoustic performance screening - dynamic method (tapping method): Used for rapid preliminary screening of wood for musical instruments. The board specimen is freely suspended and its free vibration is excited by tapping with an impact hammer. The vibration signal is received by a high-precision pickup and input into a spectrum analyzer. By analyzing the fundamental frequency, resonance peaks and other spectral characteristics, acoustic parameters such as dynamic modulus of elasticity and logarithmic decrement of the material are quickly calculated, enabling non-destructive grading.

Testing Standards

Domestic Standards:

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

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

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

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

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

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

Electronic balance and electric blast drying oven: Core equipment for moisture content determination. The electronic balance needs to provide high precision of 0.001 g to ensure accurate weighing. The electric blast drying oven must be able to precisely control (103 ± 2) ℃ with uniform internal air circulation to ensure uniform heating of the specimen to an oven-dry state. The two work together to complete the moisture content determination by the reference method.

Universal testing machine: Key equipment for all mechanical property tests. It should have sufficient load capacity (usually above 50 kN) and accuracy class, be equipped with various special fixtures (such as bending, compression and shear fixtures), and be computer-controlled for loading rate, data acquisition and report generation. It is the core instrument for evaluating the load-bearing capacity of tung wood.

1 m³ formaldehyde climate chamber and spectrophotometer system: A high-end system for accurate determination of formaldehyde emission. The climate chamber must precisely control temperature (23 ℃ or otherwise specified), relative humidity (45% or otherwise specified), air exchange rate (1.0 times/h) and air flow rate. The collected formaldehyde absorption solution is measured with a spectrophotometer at a wavelength of 412 nm to determine absorbance, and quantified through a standard curve. The whole system requires extremely high performance.

Precision dimensional measuring tool set: Including digital vernier calipers (accuracy 0.01 mm), external micrometers, steel tape measures, feeler gauges, universal bevel protractors and a flatness inspection platform. It is used to comprehensively measure the geometric dimensions, diagonal difference, warpage, wavy bowing height and other parameters of the board, providing precise data for dimensional tolerance and form tolerance assessment.

Moisture meter: Including resistance-type pin moisture meters and near-infrared non-destructive moisture meters. The resistance-type moisture meter indirectly reflects moisture content by measuring the electrical resistance of wood. It is fast and convenient, suitable for rapid large-scale on-site screening, but needs to be calibrated for tung wood species. The near-infrared moisture meter uses spectroscopic technology to achieve faster non-destructive testing.

Spectrum analyzer and vibration excitation/acquisition system: Professional equipment for acoustic property testing of tung wood. It includes an impact hammer (with force sensor), high-sensitivity accelerometers or microphones, a data acquisition card and professional spectrum analysis software. Through modal analysis or the tapping method, the vibration spectrum of the specimen is obtained, and key acoustic parameters such as dynamic modulus of elasticity and acoustic radiation damping are calculated, enabling scientific screening of wood for musical instruments.