Kraft

The most prevalent method of chemical pulping used in papermaking (or a term for the pulp itself).

The kraft process derived from the soda process, developed in the mid-nineteenth century that dissolved wood chips using a strong base (alkaline solution) such as lye. In 1879, sodium sulfate was added to the process, and a stronger pulp was produced. As a result, the process became known as the sulfate process, and kraft pulping is still known by that name, even though the active ingredient has since been found to be sodium sulfide. "Kraft" is a more accurate term since it is the German and Swedish word for "strength." The kraft process soon supplanted other chemical processes (such as the sulfite process) by virtue of its ability to effectively digest the wood of nearly every species of tree, its efficient heat- and chemical-recovery system which helps keep down processing costs, and the strong, high-quality pulp it produces. The addition of bleaching systems to increase the brightness and decrease the lignin content of the pulp also helped make the kraft process the most popular pulping process.

The term "kraft" is also used to refer to paper or paperboard made using unbleached pulp produced by the kraft process. Unbleached kraft pulp is generally dark brown in color and strong. Papers produced from unbleached kraft pulp include brown wrapping paper, paper bags, envelopes, etc.

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