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Tune in to clean wood

New radio wave technology heats up forest industry

With the same technology that carries tunes through the airwaves into your old AM/FM radio, Stavros Avramidis decontaminates wood. It’s a new solution to an old problem.

“We’ve found a greener and less toxic way to pasteurize logs and wood,” says the professor of Wood Science in the Faculty of Forestry.

Thousands of microorganisms, fungi, insects and worms live in and on trees. If these tiny creatures get sent abroad on a piece of wood, they can wreak havoc on foreign forests.

Dutch elm disease devastated European and North American elm trees after fungi from Asia was introduced to these regions in the early 20th century. The European and North American elm trees had no built-up resistance to the fungi and it swiftly infected trees across both continents.

Preventing the next Dutch elm diseases

Now countries must adhere to the International Plant Protection Convention, a treaty implemented in 1952 by the Food and Agriculture Organization (FAO) of the United Nations to prevent the international spread of pests and plant diseases.

To prepare B.C.’s logs and wood products for export, the forest industry uses two methods: thermal treatment and fumigation with methyl bromide.

Thermal treatment is like pasteurization – it involves heating wood to 56°C for 30 minutes. This process can take longer than a day and eats up a lot of energy.

“It’s like cooking a turkey at Thanksgiving; it takes a long time for the centre of the turkey to reach the right temperature.”

This method is also problematic because B.C. exports a lot material that is still green or wet. If the wood hasn’t been processed and dried, heating it up causes it to crack and develop stresses.

The only other method is fumigation where wood is bathed in a toxic chemical known as methyl bromide for 16 hours. Avramidis says this treatment is going out of style – it is bad for the environment and people don’t want to live in houses built out of a material that has been soaked in toxic chemicals.

An alternative to thermal heat

For years, Avramidis has used a process known as vacuum dielectric heating to dry wood. Dielectric heating sends electric waves through a material at a speed that causes water molecules in the material to vibrate and rotate and that molecular commotion with the help of friction result in significant heat generation. If this sounds familiar, it is. Dielectric heating is essentially what happens to food in a microwave oven. Four years ago, Avramidis was awarded an NSERC Strategic Project Grant to investigate the possibility of dielectric heating as a tool for pasteurizing wood products for exports.

“We wanted to find a fast method that didn’t waste energy and had little effect on the moisture and quality of the materials,” said Avramidis. “We also needed a system that could pasteurize the wood in big batches like we do now in drying.”

Electric waves travel through the typical household power bar at a frequency of 50 cycles per second. In microwaves, electric waves are travelling at billions of cycles of seconds. Many of Avramidis’ colleagues use microwaves to pasteurize food and plant matter that is being exported.

For wood, microwaves travel too quickly. The faster a wave moves, the smaller it becomes. Microwaves are too small to penetrate dense material like wood. Instead, Avramidis has been using radiowaves, which oscillate at about 2 to 20 million cycles per second.

Radiowaves a break through

“The biggest challenge is designing the technology for the process. With radiowaves you have to continuously ‘tune’ the frequency and energy of the waves, just like you would adjust an AM radio as you drive through a mountain range.”

Avramidis found radiowaves to be a successful solution. He says the process, known as radio-frequency heating, only takes two to three hours regardless of product thickness and the wood maintains its moisture. No damage to expensive logs or timbers is noticed.

In April, he heard from the FAO that dielectric heating has been approved as a new sterilization process for pallets of processed and dried wood. The next step will be to get forest companies to test the process on a commercial level and to try to improve the tuning system. Avramidis is also hoping the FAO will one day approve the process for green wood exports.

Source: UBC News

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