Does Heat Treatment Kill Mould?
25 Aug 2014
Mould is a term that means many things to pallet users. It could be a fungus growing on the surface and degrading the wood. Or it may be just dust or pollen. Some types of mould are not detectable by the naked eye, while others produce a marked discolouration of the wood.
To thrive, mould needs four things: oxygen from the atmosphere, a suitable temperature, a source of food (meaning the wood), and moisture. Of these, the pallet user can only really control the moisture. Some fungi are capable of growing even in cool conditions.
Wooden pallets are made using green or fresh wood that is still moist. Over time, the moisture content of the wood does fall to around 20 per cent. However, mould fungi are able to grow into the wood over this period. If pallets are stored outdoors, rain and moisture in the atmosphere will increase the moisture content and encourage mould growth.
Leave to Dry
The solution to this problem is to allow the wood to dry over a period of about two weeks in a reliable indoor airflow and in an environment protected from the weather. This airflow has to be constant and uniform though the batch of wood, meaning that the pallets should be spaced adequately. If the airflow is not uniform, the mould will attack again.
Many businesses claim that they have neither the time nor the space for such an extended wood treatment. Pallets have to be reused as soon as they are returned from an earlier job. So the challenge is to find another method of protecting the wood.
There are a number of specialised chemicals that can be applied to the wood as soon as it is sawn that will limit mould and other fungi. However, many pallets users are unhappy about chemical treatment, especially if the pallets are being used for sensitive goods.
Some plant extracts are able to limit mould attack on newly sawn wood. Cinnamon leaf oil is one such substance. But this has to be dispersed in ethanol prior to application on the wood. Some food-grade pallet users would not welcome this combination.
In general, essential oils can control mould on wood but they have to be dispersed in some form of organic solvent rather than water. This in turn creates a risk. Chitosan, a derivative of shrimp and seafood farming, is one substance that works as a mould inhibitor, but it has not been widely used for wood protection.
Pallet manufacturers can at least limit the risk of mould formation by ensuring that the wood they use is fresh and is not stored over a long period.
The pallet user should try to keep pallets as dry as possible. If it is commercially possible to protect the wood with a mild fungicide, this should be done.