Drainage Aids

The rate at which water is released from a wet paper web can be increased by chemical treatment. Such chemical treatments are believed to function in one or more of the following ways: (a) by retaining fiber fines onto the surfaces of long fibers so that they are not able to move into positions where they block drainage channels in the wet web; (b) by increasing first-pass retention of fines in general; (c) by causing fibrils at the fiber surface to lie down onto the fiber surface, creating a more streamlined path for water to flow past them; (d) by creating a more bulky, porous structure of the wet paper web; and (e) possibly decreasing the water retention in the fiber walls or in polymeric gels consisting of hemicellulose or additives at the fiber surface.