Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
The wet strength of paper is evaluated by taking a dry piece of paper, wetting it with a standard test fluid for a set amount of time, and then measuring the strength. The burst test is often used because of the ease and speed of testing. Wet tensile tests are also common, depending on the type of paper grade. One of the rules of thumb that papermakers use to evaluate wet strength is the ratio of wet strength to dry strength, e.g. the "percent wet over dry." A true wet-strength paper grade has been defined by various writers to have a wet strength that is at least 10% or 15% of its dry strength. Wet strength can be achieved by treating the furnish with a reactive polymeric material such as polyamidoamine-epichlorohydrin (PAAE, for alkaline papermaking), melamine-formaldehyde or urea formaldehyde resins (MF or UF for acidic papermaking), or glyoxylated polyacrylamide for temporary wet-strength of some tissue products.
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