This project was initiated to provide technical assistance to the Alberta wood drying industry. The specific objective was to identify opportunities to improve product quality through modification of the drying schedules. Seven mills representing almost 50% of the solid, softwood lumber production in the province were selected for the project. All mills provided a great deal of cooperation and commitment to the project was excellent. In general, lumber drying operations in Alberta are in good physical condition and operating personnel have a sound knowledge of basic drying concepts.
In general, drying schedules were found to be quite harsh. the specific concerns at most mills related to too rapid a heat-up rate and extremely low relative humidity at the end of the drying cycle. Most of the schedule modification called for more gradual and controlled heat-up rates with higher wet-bulb temperatures. The objective of this modification is to avoid setting up conditions othat promote variability in moisture content from board to board. Higher relative humidity is required at the end of the drying cycle to avoid over-drying faster drying boards. Achieving a reduction in final moisture content variability and a higher overall average moisture content should be the objective of drying schedule modifications.
Mill visits were used not only to review drying schedules but also to conduct a brief inspection of drying practices and equipment. It would be unproductive to identify schedule modifications if there were obvious shortcomings in other areas of the operation that would make it difficult to implement or over-shadow the effect. The primary concern with drying equipment is the leakiness of the structures. A common recommendation to mills was to tighten up kiln doors and walls in order to retain more moisture in the kiln environment. Another area of concern was related to lumber handling operations. Most problems in this area could be addressed through educating and training staff working at stackers, handling material in the yard, or preparing loads for the kiln.
Logging and log storage practices at all of the mills visited has a serious and detrimental impact on the drying operations. At most times of the year, operators are having to deal with a wood supply that has a mix of initial moisture content conditions. Most mills seem to manage the small percentage of balsam fir in their mix effectively. Some future gains may be achieved through refined presorting techniques that take into account initial MC variability as well as differing drying characteristics between species.
Over 0.5 million bone-dry tons of bark residues are produced annually in Alberta. Stricter regulations are now being invoked by environmental agencies with regard to disposal of bark residues by landfilling or burning in beehive burners. Hence it is highly important to find alternate uses for bark waste in the form of higher-valued products. The present study describes the manufacture of bark boards, using high-temperature pressing, without the addition of synthetic adhesives. Internal bond strength and linear expansion values for spruce and pine bark boards fell within the range of requirements for the grades of interior particleboards in the CAN 3-0188.1-M-78 standard (Interior Mat-formed Wood Particleboard). Although the bending strength values for the bark boards were below the bending requirements in the CAN 3-0188.1-M-78 Standard, the requirements could easily be met by applying thin overlays to the bark boards. This would also enhance their appearance. The boards exhibited excellent durability properties when tested using a 2-hour boil test. An important environmental advantage of bark board would be the absence of formaldehyde emission since the board is made without urea formaldehyde resin. It is likely that volatile organic compounds (VOC's) would be emitted in the high-temperature bark board pressing process and these would need to be controlled or trapped in some way, possibly by passage through a biofilter using bark as a medium.