Wood drying is one of the most important stages in preparing raw material for the production of wooden pallets, transport crates, and other wooden packaging elements. It is a technological process that determines the quality, durability, and dimensional stability of wood products. Proper moisture removal is crucial both for mechanical performance and for meeting phytosanitary requirements, especially in the context of IPPC certification (ISPM 15).
Without proper drying, wood remains dimensionally unstable and susceptible to deformation, cracking, and microbial growth. In industrial and logistics applications, such properties are unacceptable. Therefore, every modern production line for EUR pallets or pallet collars uses wood with a defined and controlled moisture content. This article explains the technical aspects of the drying process, its importance for pallet construction, and the relationship between thermal parameters, moisture content, and final product quality.
Why is wood moisture content so important?
Wood moisture content—defined as the ratio of water mass to oven-dry mass—is one of the key parameters influencing its physical and mechanical properties. Freshly cut wood may contain 50–100% moisture relative to dry mass, while industrial applications typically require 18–22% for transport pallets and 8–12% for structural or furniture components.
Moisture content affects:
- Dimensional stability – overly wet wood shrinks during use, causing deformation,
- Product weight – wet pallets are heavier, increasing transport costs,
- Biological durability – high moisture promotes mold and fungal growth,
- Mechanical properties – overly dry wood may crack or break under dynamic loads.
For this reason, moisture control is a key element of every pallet production line and IPPC wooden crate manufacturing process.
Wood drying methods: natural and kiln drying
There are two primary methods for reducing wood moisture content: natural air drying and kiln drying. The choice depends on wood species, required quality, and final application.
Natural (air) drying
This method involves storing wood outdoors for several months, relying on natural air circulation and temperature differences. While low-cost, it has significant limitations: dependence on weather conditions, uneven moisture distribution, and inability to achieve moisture levels below 18–20%. Therefore, it is insufficient for IPPC pallet production.
Kiln drying
Kiln drying takes place in insulated chambers with precisely controlled temperature, humidity, and airflow. It is significantly faster (days instead of months) and allows both moisture reduction and phytosanitary heat treatment (HT) in a single process. Modern kilns use automated control systems based on temperature and moisture sensors placed in both the chamber and the wood.
Chamber kiln design and operating principle
A chamber kiln consists of an insulated enclosure, heating system, circulation fans, heat exchangers, and a control and sensor system. Air ducts ensure uniform airflow through stacked wood.
Main components include:
- Drying chamber – insulated structure resistant to heat and moisture,
- Fans – ensure forced air circulation,
- Heaters or heat exchangers – steam, hot water, or gas-powered,
- Control system – automatically regulates and records parameters,
- Airflow reversal system – equalizes moisture distribution.
Stages of wood drying – step by step
- Preheating – heating wood to approx. 60–70°C at high humidity (90–95%),
- Main drying – intensive moisture removal at 70–90°C and 60–70% humidity,
- Stabilization – equalizing moisture gradients,
- Cooling and conditioning – gradual cooling to hygroscopic equilibrium.
Drying parameters
| Stage | Temperature [°C] | Relative Humidity [%] | Average Duration |
|---|---|---|---|
| Preheating | 60–70 | 90–95 | 4–6 h |
| Main drying | 70–90 | 60–70 | 24–48 h |
| Stabilization | 60–70 | 70–80 | 6–12 h |
| Cooling | 40–50 | 80–90 | 4–6 h |
For ISPM 15 compliance, the wood core must reach 56°C for at least 30 minutes. These values are automatically recorded and archived as the basis for IPPC certification.
Summary
Wood drying is fundamental to the quality and durability of pallets, crates, and pallet collars. Properly controlled kiln drying ensures dimensional stability, biological resistance, and full compliance with IPPC and ISPM 15 requirements, while modern technology minimizes energy use and environmental impact.