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The kraft process (also known as kraft pulping or sulfate process) is a process for conversion of wood into wood pulp, which consists of almost pure cellulose fibres, the main component of paper. The kraft process involves treatment of wood chips with a hot mixture of water, sodium hydroxide (NaOH), and sodium sulfide (Na 2 S), known as white ...
Fibres in wood pulp. The timber resources used to make wood pulp are referred to as pulpwood. [17] While in theory any tree can be used for pulp-making, coniferous trees are preferred because the cellulose fibers in the pulp of these species are longer, and therefore make stronger paper. [18]
Wood pulp for sack paper is made from softwood by the kraft process. The long fibers provide the paper its strength and wet strength chemicals are added to even further improve the strength. Both white and brown grades are made. Sack paper is then produced on a paper machine from the wood pulp. The paper is microcrepped to give porosity and ...
This, along with the ability of the kraft process to accept a wider variety of types of wood and produce stronger fibers [4] made the kraft process the dominant pulping process starting in the 1940s. [3] Sulfite pulps now account for less than 10% of the total chemical pulp production [3] and the number of sulfite mills continues to decrease ...
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 ...
Mechanical pulp can also be bleached to increase the brightness, but retaining the lignin in the pulp. [1] Industrial mechanical pulping started in the 1840s with groundwood pulping, producing the pulp from grinding. This made wood fibers the main raw material in paper, instead of textile fibers.
Tissue pulp: This is the most common type of wood-free paper. It is made from wood pulp that has been treated with chemicals to remove the lignin. Lignin is the natural adhesive that holds wood fibers together. [29] Non-wood pulp: This is a type of wood-free paper that is made from non-wood materials, such as cotton, hemp, linen, and bamboo. [16]
Most kraft pulp mills use recovery boilers to recover and burn much of the black liquor they produce, generating steam and recovering the cooking chemicals (sodium hydroxide and sodium sulfide used to separate lignin from the cellulose fibres needed for papermaking). This has helped paper mills reduce problems with water emissions, reduce their ...
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