The effect of moisture content on wood panels

Different industries have their own professional terminology. To understand an industry, you can start with its terminology. This article will be divided into several special issues to guide you through the various professional terms in the board industry. Today, let's decipher the term "moisture content".

▲ Logs awaiting processing

Ⅰ What is "moisture content"?

Under normal circumstances, boards or wood products contain a certain amount of moisture. In my country, the moisture content of wood is defined as the percentage of the weight of the wood containing moisture to the weight of the dried wood.

The formula for calculating moisture content is as follows:

W = (Gs - Ggo) / Ggo × 100%

Where: W-Absolute moisture content of wood

Gs – Weight of wet wood

Ggoo - Weight of Oven-Dry Material

Ⅱ What impact does "moisture content" have on the quality of boards?

During daily use, our furniture may exhibit deformation, cracking, warping, bulging, and other phenomena. These are primarily caused by excessively high or low moisture content in the boards and their products. Only when the moisture content in the boards reaches a balanced state can these issues be effectively avoided.

Ⅲ What is the effect of "moisture content" on formaldehyde release?

Formaldehyde (fHCHO) is a colorless, easily soluble, and irritating gas. It has become the leading indoor air pollutant in my country. It can be absorbed through the respiratory tract, and its aqueous solution, formalin, can be absorbed through the digestive tract, negatively impacting human health. When the concentration in indoor air is 0.1 mg/m³, it produces an unpleasant odor and discomfort; 0.5 mg/m³ can irritate the eyes and cause tearing; 0.6 mg/m³ can cause throat discomfort or pain; higher concentrations can cause nausea, vomiting, coughing, chest tightness, wheezing, and even emphysema; and a concentration of 30 mg/m³ can lead to immediate death. The moisture content of the board after gluing also affects the formaldehyde release from engineered wood products. Under the same conditions, the higher the moisture content, the greater the formaldehyde release from the board.

IV. What is the appropriate moisture content?

V. How are Cornell boards made?

In conclusion, the importance of moisture content to a good board is evident. So, what processes are used to control the moisture content of the board?

1. Natural air drying + kiln drying

To achieve a relatively balanced and stable moisture content, the drying process of the boards combines natural air drying with constant temperature kiln drying.

▲Air dry

▲Constant Temperature Drying Kiln

2. Multiple conditioning treatments to stabilize moisture content

Before processing, logs undergo a curing period to allow them to adapt to the humidity of the local air, making them easier to process later. During the processing, they will also undergo several curing stages. After the finished products are produced in the factory and shipped to warehouses and stores in various locations, they will also undergo a curing period to allow the boards to adapt to the local environment and achieve a balanced moisture content.

▲ Curing process of billet

▲ Finished board storage and conditioning process

VI. Can the "moisture content" meet the standard through the above process?

▲National standard for moisture content of wood-based panels

▲ Actual measurement of the moisture content of the board material