Knowledge of pH and buffering capacity of raw fiber materials is important for understanding the effects of raw material on the curing rate of urea formaldehyde (UF) resin, used for panel manufacturing, especially with some less-desirable wood materials such as bark, top, and commercial thinnings.
The effects of pH and buffering capacity as well as catalyst content on the gel time of UF resin were investigated. The results obtained from this study indicate that bark has a lower pH value as well as higher acid and alkaline buffering capacities than wood of the same species due to their extractives. The pH values of the raw fiber materials studied decrease with increased absolute and relative acid buffering capacity due to the increased absolute acidity mass in the solution.
At lower levels of added catalyst, the effect of raw material pH on UF resin gel time is significant, while it is insignificant at higher catalyst contents. This may be due to the acidity of wood, which is the main acid catalyst source of the mixture at lower levels of added catalyst, while at higher levels, catalyst is the main source. With higher catalyst contents, all studied raw materials mixed with UF resin result in a longer gel time than does UF resin alone.
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