TM Wood

Thermal modification of timber

Thermal modification (TM) of wood is achieved by heating wood up to 230C in the absence of oxygen. The TM process results in removal of cellulose, the chemical on which micro-organisms feed in the process of making the wood decay. TM wood is lighter, hydrophobic, and has a low equilibrium moisture content, qualities that provide increased external durability. The TM wood is less strong and not suited to structural applications.

Benefits of TM wood

With the increased durability of TM wood we can use our regular ash eucalypts, which typically are well suited to interior use, for cladding or decking. In addition, because TM wood has a rich dark colour, it may be used for interior uses to achieve the desired wood colour.

How to make TM wood

Most TM processes use steam to conduct the heat and exclude oxygen. An alternative approach, called Oil Heat Treatment (OHT), was developed in Germany in the 1980s which used linseed oil as the medium to conduct heat.

An advantage of OHT is that one avoids dealing with steam process which can have demanding obligations for safety and require regular inspection. To explore OHT we deep fried E. nitens samples in heated recycled canola oil and learned that nitens can handle 230C without splitting.

Now we are constructing a large-scale TM plant, able to process two pallets of timber at as time. A 300kW wood fired furnace will be used to heat thermal oil to conduct heat to the process vessel. The thermal oil will run through heat exchanger pipes at the bottom of the process vessel which contains recycled canola oil. The pallets of wood will be placed in the process vessel with specially designed lifting frames.

Acknowledgment

This development was assisted by funding from the Forest Service, Te Uru Rakau, and their Wood Processing Growth Fund (Catalyst grant).