UK Study Identifies Best Practices & Key Lessons for Drying Pallets Manufactured from Non-kiln Dried Timber
Fight Mold: European pallet association conducts extensive drying study to prevent mold and stain growth on wooden pallets. Research finds best practices and key lessons.
Date Posted: 7/1/2014
Due to the increase in demand from customers for eliminating mold and stain on pallets using kiln drying, and for sound science to back up claims made by European pallet producers, industry leaders recently responded by releasing the results of the largest study of its kind.
The Timber Packaging and Pallet Confederation (TIMCON), the national pallet association in the United Kingdom, has been very active in commissioning an in-depth pallet drying project in response to reports from members concerning issues with stain and mold. TIMCON has also issued a “TIMCON Best Practice Guide to Timber Stain & Mold” for users of wooden pallets and has recently drawn up a protocol for pallet manufacturers for kiln drying of assembled pallets.
This new guide is very important and ground breaking work as mold can be a concern to pallet users, and there is limited scientific research available about this complicated subject. The research was led by Ivor Davies (Ph.D.) of Edinburgh Napier University Forest Products Research Institute (FPRI) and has resulted in drying specifications and quality control measures to allow for standard moisture content levels based on best practices.
The research in the UK is limited to Sitka spruce timber species, and it looked at 1,360 pallets from 18 kiln batches. Although there are some variance from species to species, the idea was to conduct research on a common species to develop baseline understanding that could be applied throughout Europe.
Arthur Jenkinson, who worked with TIMCON to coordinate the research, said, “The study found that the actual moisture content of the pallets varied greatly even though the kiln settings were standardized.”
He added, “There was a high range of moisture content, and a probability of mold forming on the wetter parts of the pallets in certain environments.” This tendency to have the moisture content vary greatly even on a single pallet is one of the reasons why TIMCON discourages offering guarantees. It has developed a three tiered approach that can help companies offer ranges of service depending on the amount of time the pallets are dried in the kilns.
John Dye works for Scott Pallets, one of the largest pallet companies in Europe, and as president of TIMCON has been involved in the study. Dye said, “To us mold is a challenge, but it is a challenge that we as an industry have always maintained we can meet, and now we have the scientific data to back this up.”
When it comes to making claims that are hard to back up, it is believed that on occasion pallet companies in the UK, as well as the United States, have been responding to customer pressure by guaranteeing mold free pallets and a set maximum moisture content for every pallet.
Dye warned that manufacturers making these claims were potentially causing harm to the industry because it has always been believed that it has been nearly impossible to guarantee that all the components of a manufactured pallet will have the same moisture content level. And now this report scientifically backs this up, yet more importantly, it shows that pallets dried using best practice guidelines can keep the potential variances to a minimum.
Dye explained, “When you kiln dry pallets, you can get wet zones. Pallets sit on top of each other and can potentially foster mold in those areas. It is important to keep pallets off the dry kiln floor.”
Study Results and Conclusions
The UK study has come up with various quality levels that are based on average moisture content not the condition of any one pallet or any one spot on a pallet. The various service levels differ in the moisture content range, amount of time spent air drying, and the performance level. See chart 1 for more information. .
Pallets in the new study were allowed to air dry under well-ventilated, covered storage for 14 days prior to being placed in a kiln. Jenkinson said, “Because we air dried pallets first, the moisture content of the undried timber was conditioned reducing variability with the added benefit of reducing kiln operating time by an average of 35%
Then pallets were dried in the kiln to various schedules between 19-25 hours to reach targeted moisture contents ranging from 15-22% moisture content. Pallets were then removed and allowed to cool down for two days before being tested with a moisture meter. Throughout the process, pallets were stored under cover to prevent rewetting.
Jenkinson commented, “Proper storage is critical to make sure that moisture content is kept to the desired levels. That is why simply using kiln drying lumber may not be an effective solution because if it is allowed to be stored or transported outdoors, the drying process can be rendered ineffective due to rewetting.”
The survey led to the development of best practices for the entire process including how to take moisture measurements. Jenkinson stated that they discovered they made the best readings if measurements were taken in at least five points in wet and dry zones.
Readings could vary widely even in the same kiln run or on the same pallet depending on the environmental conditions, temperature, humidity, moisture content, placement of pallets, type of kiln, wood species, etc.
When looking at current practices, the study found that existing procedures was usually not sufficient to make 100% guarantees. Jenkinson explained, “Current practices in Europe actually fell around the common standard or somewhere between common standard and standard plus depending on the levels of controls used by each manufacturer.” However it should be noted that some pallet manufacturers have been working closely with their customers and in many cases were following many of the guidelines in the best practice document already.
Dye said, “We published the users best practice guidelines to help and make users of pallets aware of the importance and their responsibility for proper handling and storage of the pallets after delivery. For example, there is no point in premium dried pallets if they are going to be off loaded and stored outside.”
Best practices include storing pallets inside in a space that encourages air flow in some cases using fans or the appropriate level of spacing between pallet stacks, and rotating stock so the first pallet in is the first pallet out.
Looking at best practices, Dye commented, “The study has shown that the best way to do this is to air dry the pallets before putting them in the kiln.”
Mold Treatment & Prevention Strategies
Pallet companies can take steps to reduce moisture content variance. There are a number of options. The first starts with drying pallet longer to reduce moisture content.
Niels Jorgensen, president of Kiln-direct.com, said, “Most of the kilns that we see dry pallets run about 200 degrees Fahrenheit and go between 12-36 hours depending on how dry they want it. After about 16 hours, the pallets lose about 12 lbs. of water for an average GMA pallet. This is the standard that we are seeing among customers. Most need 12-18 hours to get the moisture content low enough to prevent most mold.”
Another strategy is to use large fans and appropriate spacing to allow pallets to air dry in storage. This is a best practice that should be followed by both pallet suppliers and users alike. Storing pallets inside where they will not get rained on is a smart move to keep the moisture content low. One innovative company has developed an approach that retrofits trailers to encourage air flow as a load of pallets is moving down the road. You can find out more information at www.aftstrailers.com.
There are chemical products that can be used to prevent mold growth. ISK Biocides has become one of the most popular companies because its PQ-80 product is approved for food contact. For more information on ISK call 800-238-2523.
A different chemical approach is X-Mold, which basically encapsulates the wood preventing oxygen from getting to the mold spores. X-Mold still exists although it is not as visible in the industry as it once was.
And a new company to target the pallet industry is Osmose Inc. Michael Pompeo, director of technical development at Osmose. He said, “Performance of these products is affected by the temperature and humidity of where the wooden pallet is stored.”
Osmose is now offering Cellbrite to the U.S. market after it has been used successfully in Europe for wooden packaging that comes in contact with food and other sensitive products. It protects against mold growth and blue stain.
When it comes to applying chemicals, you can either use dip tanks or spray applications. More automated processes help improve performance and reduce the waste of chemicals. Some pallet companies even use hand application methods for small lots with a hand sprayer. But this tends to waste chemicals and cost more in the long run.
TIMCON members who want to receive certain designations will be required to submit their drying data to ensure that they are meeting the technical specification so that they can claim that they are meeting the TIMCON standard. The Essential Guide Pack including Dry Specification Guide will soon be provided free of charge to TIMCON members. In addition, a guide for pallet users has also been developed and is currently available.
TIMCON is making its complete pallet drying Essential Guide Pack available to members only. U.S. pallet companies can join TIMCON to obtain access to this material. A general overview of best practices has been prepared for pallet users. You can download a copy of the information from www.palletenterprise.com. Look for “TIMCON Best Practices Guide for Timber Stain and Mold.”
For more information on the research, contact TIMCON at John.Dye@scott-pallets.com or visit www.timcon.org.
Service Levels Offered in the UK Model
• Kiln dried 15-17% target moisture content
• Air dry for 14 days
• Formal Quality Control procedures employed (Essential Guide Pack)
• Target Acceptable Quality Level ≥ 90% conformance
• Kiln dried for 18-22% target moisture content
• Air dry for 14 days
• Formal Quality Control procedures employed (Essential Guide Pack)
• Target Acceptable Quality Level ≥ 80% conformance
• Kiln dried 18-22% target moisture content
• No Air dry or formal quality control
• Target Acceptable Quality Level – conformance unpredictable
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