What happens when wood is treated with gaseous ozone?
Treating wood with gaseous ozone (O₃) primarily induces oxidation reactions that affect the wood’s biological, chemical, and— to a lesser extent—physical properties. The key mechanisms and effects are outlined below.
1. Fundamental chemical mechanisms
Ozone is a highly powerful oxidizing agent. When it comes into contact with wood, it reacts mainly with:
- Lignin (the primary aromatic component of wood)
- Extractives (tannins, resins, phenolic compounds)
- To a lesser extent, cellulose and hemicellulose
These reactions result in:
- Cleavage of aromatic double bonds
- Formation of carbonyl, carboxyl, and peroxide groups
- Partial depolymerisation of lignin
2. Biological effects
a) Disinfection and biocidal action
Ozone:
- Inactivates bacteria, fungi, moulds, and spores
- Eliminates certain insects and larvae
- Neutralises odours of biological origin
This makes ozone particularly valuable for wood preservation and sanitary treatment.
3. Effects on wood appearance
a) Colour modification
- Frequent bleaching or lightening
- Reduction of yellowish or dark brown tones
- Results vary depending on wood species (softwoods vs hardwoods)
This effect is caused by the oxidation of lignin chromophores.
4. Effects on surface properties
a) Increased surface energy
- Improved wettability
- Potential enhancement of adhesion for:
- adhesives
- varnishes
- surface coatings
b) Chemical surface activation
- Introduction of polar functional groups
- Facilitates subsequent treatments such as bonding or impregnation
5. Mechanical and structural effects
- Moderate treatments: little to no impact on mechanical strength
- Excessive or prolonged exposure:
- Surface embrittlement
- Localised reduction in strength
- Degradation of lignin affecting structural cohesion
Precise control of ozone concentration and exposure time is therefore essential.
6. Environmental and health considerations
Advantages
- No persistent toxic residues
- Ozone naturally decomposes into oxygen
- Viable alternative to conventional chemical biocides
Constraints
- Ozone is hazardous to human health (respiratory irritation)
- Requires sealed treatment environments and controlled ventilation
- Strict monitoring of exposure levels is mandatory
7. Typical Applications
- Disinfection of reclaimed or heritage wood
- Odour removal (flood-damaged, smoke-exposed, or stored wood)
- Surface pre-treatment prior to bonding or finishing
- Research into chemical modification of wood
Treating wood with gaseous ozone involves controlled surface oxidation, enabling effective disinfection, colour modification, and chemical activation, while requiring careful process control to avoid structural degradation.