An accurate and inexpensive method developed for estimating chip brightness involves a two-stage grinding of air-dried chips to powders with small particle sizes and narrow size distributions, and measurement of ISO brightness of the resulting powders. Using this method, ISO brightness values of 20 mill or pilot-plant thermomechanical pulps (TMP) can be linearly correlated, with an R~2 value of 0.885, to ISO brightness of the mill or pilot-plant chips. Analyses of chip and TMP samples taken from a TMP mill every month for one year show that both the chip and TMP brightness values are the lowest in July.
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