Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
Water Retention Value
The water retention value (WRV) test provides an indication of fibers' ability to take up water and swell. The WRV is also highly correlated to the bonding ability of kraft fibers. The test is carried out by placing a pad of moist fibers in a centrifuge tube that has a fritted glass filter at its base. The centrifuge is accelerated at 900g to remove water from the outside surfaces and lumens of the fiber (a higher force is used according to some European standards). The remaining water is believed to be associated with submicroscopic pores within the cell wall. The centrifuged fiber pad is weighed, dried at 105 degrees Centigrade, and then reweighed. The WRV value equals the ratio of the water mass to the dry mass. The WRV value of a papermaking furnish tends to increase with increasing refining and increasing pH. The WRV value tends to decrease when kraft fibers are dried and reslurried.
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