The natural durability of western red cedar cannot be entirely explained by the presence of the thujaplicins – the only extractives identified with significant direct fungal toxicity. However, other extractives may contribute to the natural durability of western red cedar through interactions with the thujaplicins. Plicatic acid is the most abundant extractive in western red cedar and it is also a strong radical scavenger and metal chelator. To identify any interactions between plicatic acid and beta-thujaplicin, the effect of plicatic acid on the inhibition of fungal growth by beta-thujaplicin was determined using a micro-bioassay. Increased fungal growth was observed in some samples treated with plicatic acid. However, in most samples plicatic acid did not affect the ability of beta-thujaplicin to inhibit the growth of decay fungi in this agar-based bioassay.
A study was carried out to characterize the raw materials and their corresponding wood fibres produced in an industrial MDF mill. Six raw wood materials with the typical mixture of softwood and hardwood species used in the mill and six fibre samples were collected. The characterization was carried out to test the pH, acid buffer capacity and UF resin gel time in the presence of wood flours either from raw wood or wood fibres. The conclusions are made based on the testing results:
Variations of pH, acid buffer capacity and UF resin gel time (in the presence of wood) existed between different batches of raw wood materials and wood fibres.
There was no obvious linear correlation between raw wood and its corresponding wood fibre in terms of their pH, acid buffer capacity and the gel time of UF resin.
With the six wood fibre samples studied, there was no obvious correlation between pH and acid buffer capacity, or between pH and UF resin gel time. This suggests that pH would not be a good indicator to predict the UF resin reactivity with various wood fibres.
To some extent, a linear correlation existed between the acid buffer capacity of the wood fibre and the gel time of UF resin. However, it would not be practical to use the acid buffer capacity to predict the UF resin reactivity with wood fibre due to the tedious test procedure, which is a result of the technology currently used.
However, with limited test samples and within a short period of time (six wood / fibre samples within 12 days), no large variations were observed for pH, acid buffer capacity and gel time. Further study might be needed if the raw material differences for a longer time period and the seasonal effect are required.