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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 ...
The pulp made by this process is known as "stone groundwood" pulp (SGW). If the wood is ground in a pressurized, sealed grinder the pulp is classified as "pressure groundwood" (PGW) pulp. Most modern mills use chips rather than logs and ridged metal discs called refiner plates instead of grindstones.
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.
Mechanical pulping is the process in which wood is separated or defibrated mechanically into pulp for the paper industry.. The mechanical pulping processes use wood in the form of logs or chips that are mechanically processes, by grinding stones (from logs) or in refiners (from chips), to separate the fibers.
In the manufacturing process, pulp is introduced into a paper machine where it is shaped into a paper web and water is extracted through pressing and drying stages. Pressing involves removing water from the sheet by applying force. This process employs a specialized type of felt, distinct from traditional felt, to absorb the water.
In 1844, Canadian Charles Fenerty and German Friedrich Gottlob Keller had invented the machine and associated process to make use of wood pulp in papermaking. [15] This innovation ended the nearly 2,000-year use of pulped rags and start a new era for the production of newsprint and eventually almost all paper was made out of pulped wood.
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 ...
After the breakdown process, fibres (composed of two kinds of cellulose) and lignin are leftover. Lignin is the glue or cement that holds the fibres in wood together. Simply putting it, wood pulp is a large amount of individual wood fibres with the lignin removed. Wood pulp is naturally between dark brown to light grey in colour.