Mold on pallets can be serious business. In recent years, Starbucks went after a company that supplied it with wood pallets that were used to ship and store coffee beans. Starbucks claimed that mold on the pallets contaminated several million dollars’ worth of coffee beans that had to be destroyed and initiated a $5.3 million lawsuit.
In another incident that occurred just a year earlier, Johnson & Johnson and Pfizer recalled product that had developed a noxious odor. Both companies pointed to wooden pallets shipped from Puerto Rico. In both cases, the cause was linked to a chemical treatment applied to wood in order to prevent mold.
The key to controlling — preventing — mold on wood, experts agree, is the moisture content of the wood. Wood with a moisture content below 20% will not support mold, mildew, decay, or fungus, according to the Virginia Tech Center for Packaging &d Unit Load Design (The Center).
Yet, despite scientific evidence showing that level of moisture content greatly limits mold growth, it still does not guarantee that mold will not occur. It is possible, if the right conditions exist, that some remaining moisture in the wood can come to the surface, and if it accumulates, mold can occur. If the wood becomes wet from some other source — rain, for example — mold also can grow.
Still, wood that is dry below 20%, and kept dry, is still the best inhibitor of mold.
Ralph Rupert, manager of unit load technology for Millwood, noted a widely held misconception about heat-treatment – that the process prevents mold on wood.
Speaking during a panel discussion on the issue of mold on pallets at the National Wooden Pallet and Container Association annual meeting several years ago, and as reported by the NWPCA, he remarked, “While heat treatment may kill existing mold spores on the surface of the wood, its intended purpose is to kill insects and does not prevent future spores from growing, so post heat-treated material is not immune.”
He went to point out that since the heat-treatment process pulls out internal moisture to the surface of the wood, it can actually lead to more favorable conditions that allow mold to occur.
Mold spores are everywhere. If they have sufficient moisture, the right temperature, and a food source, they can germinate in 24-to-48 hours if exposed to proper moisture, temperature and a food source. Wood is a food source for mold, which has a fairly broad temperature range for occurring, so moisture becomes the controlling factor to prevent mold.
Kiln drying can reduce the wood moisture content below 20 %, but it’s likely impractical because of the cost. Also, mold can still occur on kiln-dried wood if the material gets wet.
Another option is to treat the wood with chemicals that prevent mold from growing.
Michael Pompeo, director for technical development for Osmose Inc., which offers products for protecting wood, participated in the panel with Ralph. There are several major suppliers of moldicides in the United States, he noted. These type of products can be applied to wood with dipping or spraying systems.
“These formulations tend to be a mixture of several active ingredients and they are all EPA registered pesticides,” he said during the panel. “A few substances are approved or exempted by the FDA as safe to use for food contact application, and they are known as Copper-8 and potassium sorbate. Potassium sorbate is in fact a food additive that functions as a preservative/moldicide.”
The effectiveness of these products depends on the type of chemical formulation as well as environmental conditions, noted Michael. He recommended consulting with an expert in wood preservation products as well as conducting field trials to determine how long a treatment will protect the wood. Effectiveness of treatments can range from a few weeks to a few months or longer, he indicated.
In a research paper about mold and wood, Jeff Morrell, a professor of wood science and engineering at Oregon State University, also recommended field testing applications. However, he also noted that many pallet-using companies do want pallets made of chemically-treated wood because of concerns about chemical contamination of their product.
Probably, the most popular fungicides to control mold on wood contain copper-8-quinolinolate or chlorothalonil. The leading brand is PQ-80 offered by ISK Biocides Inc. This product is approved for use in food and pharmaceutical applications. It has been widely used by industry for more than 80 years to control mold. For more information, visit ww.iskbiocides.com or call 800-238-2523.
Pallet Machinery Group (PMG) is offering a new solution for treating pallets called WoodLock Bio-Shield. The developer of the product, Jim Stanley, was in coatings formulations for years. He designed the product to treat homes to inhibit mold growth. It has been reformulated to work on pallets and lumber. The biggest advantage of the WoodLock Bio-Shield is longevity. It is a mold inhibiting solution that is not water soluble and can handle thousands of wet/dry cycles. Stanley suggested the product can last 2-4 months or longer. WoodLock Bio Shield is formulated with an acrylic co-polymer that exhibits an ionic bond with the anti-microbial and mechanically bonds to the wood. Depending on the volume, PMG stated that WoodLock Bio-Shield costs 4-5 cents per pallet to treat. It is available now for application and a number of active trials are going on right now in the industry.
Stanley explained, “The WoodLock Bio-Shield inhibits mold growth by stopping the gestation of the mold spores.” It has a zone of inhibition up to 2-3 mm away ensuring that nearby areas are protected even if you don’t get complete coverage. The active ingredient is an EPA-registered product that is non-toxic, benign and won’t leach in to the environment, according to PMG. To find out more information on WoodLock Bio-Shield, call PMG at 540-644-9220.
For pallets where chemical exposure is less of a concern, the Center recommends periodically applying a bleach solution to the lumber. Another option to kill or remove mold is to spray or dip the pallet or lumber in a solution of two parts water and one part of a household detergent. The solution will be effective for 3-5 days.
Morrell of Oregon State University recommends that pallet manufacturers use freshly sawn wood that should not be stored for long periods of time; the longer it is stored, the higher the risk it will develop mold. Also, do not store heat-treated wood in conditions that inhibit drying; create good air flow to allow the surface of the wood to dry. It is important to keep pallets or lumber away from any sources of mold spores, such as decaying wood. Simple good housekeeping practices can reduce the presence of mold spores in the air.
The three NWPCA panelists also made the point about proper storage conditions to prevent mold, which will occur on just about anything if the environment is moist and there is little or no air flow. For example, trailers should be unloaded quickly, and wood should be stored in ventilated areas to promote drying and to inhibit mold from occurring. Slight air velocity of a few feet per second can help prevent mold.
One great solution developed by a pallet guy is the Air Flow Trailer System (AFTS), which supplies kits designed to improve the air flow through a trailer. Testing at Virginia Tech has demonstrated that AFTS-equipped trailers can reduce the moisture content of lumber down to 12%. Literally, you can store pallets in trailers instead of sheds and reduce moisture content while the load is traveling down the road. AFTS uses regular trailers that are modified with vents and fans. It is an ideal way to solve mold developing on pallets during delivery. And it accomplishes all of this for a minimum investment and no chemicals. Find out more at www.aftstrailers.com or call 262-677-9033.
Pallets or lumber stored outside should be covered to prevent exposure to rain and also should allow air circulation. And they should be stored elevated, above the floor or ground.
Communication with customers is important, too. Educate your customers about what conditions will enable mold growth, and what they can do about it. This will help them better understand the problem and how their actions might make it worse.
