This study was conducted to evaluate how wood harvest seasons (winter, spring, summer, fall), species (single, mixture), divisions of the stem (sapwood, heartwood), and test methods (cold water extraction, hot water extraction) affect wood chemical characteristics. Ten wood species, normally used for manufacturing particleboard, medium density fiberboard (MDF), and oriented strand board (OSB), were characterized for pH, buffer capacity (acid, base), acid content (total, soluble, bound), and solubility (water, ethanol-toluene).
First, it was observed that wood harvest season affected the chemical properties of jack pine, black spruce, white spruce, and balsam fir. The extent of seasonal influence on wood chemical properties depended on individual species. In general, wood harvested in fall and summer yielded lower pH values than wood harvested in winter and spring. Winter-harvested balsam fir had significantly higher acid buffer capacity (followed by summer and spring) than other species during the same seasons. Most species yielded higher total and soluble acid contents when harvested in summer compared with winter, and yielded higher water solubility when harvested in winter compared with summer. Higher ethanol-toluene solubility and lower levels of bound acid were observed for jack pine and black spruce, respectively, compared with other species harvested in winter and/or summer seasons.
The wood chemical properties of spruce (black and white), jack pine, and balsam fir (SPF) mixes did not follow the “ideal mixture behaviour” predicted by simply averaging values for individual species (only winter season was examined). This phenomenon could be attributed to the interaction between chemical compounds of wood extractives of the different wood species. Such interactions would either offset or reinforce each other in terms of wood chemical properties between different wood species. An increase in the percentage of balsam fir (from 20 to 60%) in the SPF mix increased pH, acid buffer capacity, and soluble acid content, but decreased the bound acid content. A higher spruce content in the SPF mix resulted in lower water solubility and lower ethanol-toluene solubility.
Wood pH and buffer capacity differed between sapwood and heartwood for SPF species (only fall harvest season was examined). All species except for balsam fir had higher pH and lower acid buffer capacity for heartwood than for sapwood. Sapwood and heartwood yielded higher pH and acid buffer capacity than the whole tree of each species. Differences in wood pH and base buffer capacity between sapwood and heartwood were also observed for five hardwood species and one softwood species—southern yellow pine (only fall harvest season was examined). Aspen and white birch heartwood had higher pH values than the sapwood, while yellow birch, red maple, southern yellow pine (SYP), and sweet gum heartwood had lower pH values than the sapwood. Heartwood and sapwood had an opposite effect on wood base buffer capacity than they did on pH value for these species.
In jack pine, wood chemical characteristics such as pH and acid buffer capacity were influenced by extraction time and temperature, wood quantity in titration, and wood particle size. Increased extraction time and decreased particle size in hot water extraction resulted in slightly lower pH values and a higher acid buffer capacity. Increased extraction time and decreased particle size in cold water extraction seemed to slightly decrease both wood pH values and acid buffer capacity. However, compared to extraction temperature, extraction time and particle size (between 60 and ¼ meshes) had much less influence on wood chemical properties. Hot water extraction resulted in lower pH values and acid buffer capacities than with cold water extraction; this was attributed mainly to different water temperatures (100oC vs. ambient condition) and quantities of wood (25 vs. 3 g of OD wood flour) used in extraction. In addition, hot water extraction might yield more acidic soluble materials than cold water extraction.