NATURAL DIRT IN WOOD CHIPS

The purpose of this method is to estimate the amount of natural (wood-derived) dirt in chips. The amount of dirt in the chips may be reflected in the level of dirt in the finished pulp or in bleaching and screening steps needed to produce an acceptable product. The determination is made by examining and classifying chips into categories defined by the ultimate contribution to dirt levels in the final product. For sulfite pulps from certain species, a dirt contribution values table (Table 1) is provided, which allows the results to be expressed in terms of an index based on square millimeters or equivalent area of black dirt. (See TAPPI T 213 “Dirt in Pulp.”)