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Bleaching of wood pulp is the chemical processing of wood pulp to lighten its color and whiten the pulp. The primary product of wood pulp is paper , for which whiteness (similar to, but distinct from brightness) is an important characteristic. [ 1 ]
Chemical pulping involves dissolving lignin in order to extract the cellulose from the wood fiber. The different processes of chemical pulping include the Kraft process, which uses caustic soda and sodium sulfide and is the most common; alternatively, the use of sulfurous acid is known as the sulfite process, the neutral sulfite semichemical is treated as a third process separate from sulfite ...
A precursor to the soda pulping process was the paper making process developed by Matthias Koops in 1801 which involved washing wood shavings in limewater, adding soda crystals and then boiling the mixture. [2] Soda pulping was one of the first chemical pulping methods and was invented in 1851 by Burgess (United States) and Watts (England).
Wet pulp is loaded in the port in Umeå, Sweden in 1967. Mechanical pulp is very different from the pulp produced in the chemical processes (the sulfite process and the Kraft process). The chemical methods gives paper with higher strength and pulp that can be bleached further than the mechanical pulps.
Recycling of used paper before the industrialisation of paper production, rag paper was recycled to make low-grade board. A process for removing printing inks from recycled paper was invented by German jurist Justus Claproth in 1774. [2] He practiced together with German paper producer Johann Engelhard Schmid. Today this method is called deinking.
Dissolving pulp is mainly produced chemically from pulpwood in a process that has a low yield (30 - 35% of the wood). This makes up of about 85 - 88% of the production. [2] Dissolving pulp is made from the sulfite process or the kraft process with an acid prehydrolysis step to remove hemicelluloses. For the highest quality, it should be derived ...
The pulp produced up to this point in the process can be bleached to produce a white paper product. The chemicals used to bleach pulp have been a source of environmental concern, and recently the pulp industry has been using alternatives to chlorine, such as chlorine dioxide, oxygen, ozone and hydrogen peroxide.
The Kappa number estimates the amount of chemicals required during bleaching of wood pulp to obtain a pulp with a given degree of whiteness. Since the amount of bleach needed is related to the lignin content of the pulp, the Kappa number can be used to monitor the effectiveness of the lignin-extraction phase of the pulping process.