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New Pallet Treatment Options Loom on Horizon
Will Vacuums, Microwaves or Radio Frequency Treatment Be the Next Big Thing?

By Chaille Brindley
Date Posted: 3/1/2005

As international governments work toward synchronizing phytosanitary (plant health) standards around the world, researchers are looking for the next break-through treatment technology. They hope to discover technology that might lower treatment costs or eliminate a major drawback of the current methods – heat treatment and methyl bromide fumigation. There are a number of innovative research projects going on around the country right now. Two of the more promising ideas include vacuum treatment and microwave/radio frequency treatment.

            While none of these technologies are ready to market yet, research indicates the processes do work and could provide unique benefits. It could take years for them to be recognized as allowable options under the new international standard (ISPM-15) if it ever happens. But in the meantime, these emerging technologies point to the future and could fit in some niche treatment applications today.


Vacuum Treatment

Virginia Tech has pioneered the vacuum technology under the direction of Dr. Marshall (Mark) White and Zhangjing Chen. Known as the leading voice on pallet design research, Dr. White believes that the vacuum technology shows promise, especially for the treatment of pallet components, lumber and cants.

“You can sanitize large volumes of raw material very easily with the vacuum process,” said Mark. The process kills pests by removing the moisture from their bodies until they die. Dead piled timbers, lumber or pallet components can be put into any kind of sealable container, such as a vacuum tube, flexible sack or even certain shrink wraps. Then a low pressure is applied until the moisture is removed from the pests. Although the vacuum removes enough moisture to kill the pests, it does not significantly remove moisture from the wood itself or cause any noticeable lumber degrade, said Mark.

The process (using flexible containers) is not really designed for finished pallets because the vacuum of 20 mm of mercury would crush the pallets, whereas it doesn’t have any real structural impact on solid wood itself. Pallets could be vacuum treated in cylinders.

Major advantages of the vacuum technology are that it consumes little energy, eliminates the need for a heating system, does not release ozone depleting chemicals, and maintains the original color and strength of treated wood. Mark estimates that the energy costs to power the pump would be only $1,225 per year for treating 4.2 million board feet of pallet cants, lumber or parts.

The only equipment needed are vacuum pumps (which are readily available and can be purchased for around $10,000 apiece), some type of large flexible containers, a forklift, and some basic maintenance tools. Based on Virginia Tech’s calculations, the cost to treat lumber would be very competitive to existing treatment technologies if not cheaper. “The economics are there,” said Mark.

The major disadvantage of the technology is the time it takes to treat raw materials and the fact that it has not been certified under the international standard. The process is much longer than heat treatment. Virginia Tech’s research indicates that it will take 24 hours to treat and kill pests in lumber with a low-power vacuum. However, based on board feet per hour, this vacuum technology is significantly more productive than heat-treatment.

            As an emerging technology, Virginia Tech would need to get the technology recognized by the International Plant Protection Convention (IPPC) as a viable treatment alternative under the new international standard before it became attractive to most pallet or lumber companies. Currently, researchers are working to commercialize the product and present their research to the international community for consideration. The research was scheduled to be discussed during a meeting of the international quarantine research group of IPPC in late February.

Virginia Tech is already getting calls about the technology from people concerned about treating with heat due to the temperature sensitive nature of some wood items. For example, the technology could be used to kills bugs in antique furniture, which could be damaged if exposed to extreme heat.

While the vacuum technology will not be on the shelf in the near future, it could become a reality sooner than you think. It is at least something to consider for those looking at treating lumber or pallet components.


Microwave Technology

            If you thought microwaves are only for TV dinners, then think again. Microwaves have been used for a number of commercial applications, such as drying of coatings, snack food processing, rubber vulcanization, mold drying and chemical waste processing. The Wood Products Program at Penn State University’s School of Forest Resources is researching microwave and radio frequency treatment for wood packaging material. The project is being spearheaded by Dr. John Janowiak and Kelli Hoover (department of entomology).

            Penn State’s research is showing that microwaves can quickly kill insect and pests in wood. When 60 degrees Celsius is applied using a microwave, most pests are killed while the wood remains structurally undamaged. Penn State used Red Pine, which is known for having high moisture content.

The relative moisture content of the surrounding wood has a big impact on the treatment time. Once the wood reaches the desired temperature, pests are killed relatively quickly. John said, “They get cooked in a matter of seconds.” In general, microwaves do not take anywhere near as long as heat treatment to sterilize wood, this is particularly true if the wood has a low moisture content.    

Since the technology works so quickly, John envisions microwaves being a good solution for those looking to treat high volumes of pallets or lumber in a short period of time. The technology could even be used where the lumber/packaging is continuously fed through a microwave tunnel.

The two major questions about the microwave technology are the shadow effect and equipment costs. John said, “We don’t really know what the cost of the microwave equipment will be.” Everything that is currently being used to test the technology has been custom made. If the technology were to ever takeoff, it could be feasible for a major microwave manufacturer to develop cost effective treatment equipment.     

And the other major concern about microwave technology is something known as shadowing. Microwaves do not heat evenly because there tend to be blind spots. The microwaves emanate from the source and may not effectively hit every area. This is why most conventional household microwaves have turntables to foster more even heating. A tunnel design could help reduce the shadowing effect, which would tend to be greater in a big chamber design where there would naturally be more blind spots.

Radio frequency treatment is another possible solution to the shadowing effect. Radio frequency does not have the shadowing problem and offers some of the same advantages as microwaves.

The Pallet Enterprise will publish more on these technologies as they develop. For many pallet companies, waiting around for new technology to emerge is something they simply just cannot do. Existing methods, such as heat treatment and methyl bromide fumigation, offer cost effective, certified processes. Will these new technologies take over someday? Who knows? But it is interesting to see what may be viable options for the future.


Do’s & Don’ts for Heat Treatment


            Heat treatment is being done by many pallet and lumber companies across the country. There is a significant amount of research and technical assistance out there for companies looking to use heat treatment. Equipment manufacturers, major forest products programs at various universities, inspection agencies and other experts are good sources for technical information on the art of heat treating.

            Below are some ideas and tips to consider when using heat treatment technology to sterilize pallets. They are based on research and presentations by Dr. Brian Bond of Virginia Tech.


  • Mold will grow on wood that has 20% moisture content or greater. Heat treatment is not the same as killing mold. Pallets or lumber that have just been treated can release a tremendous amount of moisture into the air. You don’t want moisture coming off pallets to condense back onto the pallet or treating structure. Thus, it is best to let lumber air dry before putting the product into a trailer or other enclosed area. This will help prevent mold from developing on the pallets or lumber.
  • If you want to heat treat and eliminate mold, then you would need to dry the lumber using a kiln. This can take five or six days. It can be done faster but not without the possibility of causing lumber degrade.
  • Unless done properly, removing moisture from the lumber can cause lumber degrade, such as splitting and cracking.
  • In a finished pallet, if no splitting occurs at a nail or the amount of shrinking does not expose any of a nail, it is not a significant strength or degrade concern for the pallet.  
  • According to research by Dr. Bond, if you disregard the warm-up time, heat treating takes three times longer than steam heating. Research indicates that steam treatment does not cause any significant moisture loss or lumber degrade.
  • Steam can be very hard on a kiln or other treatment structure. It can be very corrosive and impact the lifespan of your treatment chamber as well as increase fuel costs.
  • Humidity helps with the treatment process, but it is not absolutely necessary to do the job. Adding humidity with a small boiler or mystifier reduces treatment times.
  • When looking at treatment options, consider the heating source and the amount of heat it generates. Remember that the more BTUs a device outputs, the faster the treatment time.
  • When evaluating treatment processes, investigate the air flow of the device because proper air flow is critical for treatment.
  • Black iron stains are normal when wood and metal come into contact. Nails or metal banding can cause such discoloration. It is not a degrade or defect and should not be considered a factor for your customers.

      For more information, visit the pallet phytosanitation portal developed by the Lousiana State University Ag Center at www.agctr.lsu.edu/enr/palletsanitation/index.asp or visit our treatment resource page at www.palletenterprise.com/pests.


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