Paper is a thin material used for printing, writing, converting into books, magazines etc. Paper is derived from wood by the process of pulping. Pulping equipment is used for the process of pulping. After pulping, the cellulose fibers are washed and dried on planes to form rolls of paper. These then undergo a process called paper conversion and then are sent to markets.
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There are many methods which can be employed for pulping. Some of them are mechanical pulping, thermomechanical pulping, chemithermomechanical pulping, chemical pulping, recycled pulping, organosolv pulping etc.
Stone pulp is made by grinding wood called bolts using grindstones which are embedded with silicon carbide or aluminum oxide. Before grinding if the wood is steamed, it is called pressure ground wood pulp. Refiner plates are used recently for grinding rather than grindstones. If these refiner plates are used for grinding, they are called refined mechanical pulp and if the wood chippings are steamed while refining process, the pulp is called thermomechanical pulp.
Thermomechanical pulp uses two stages for processing. The first stage involves removing the bark from the tree wood collected, cut into wood chippings. These are hen crushed using grinders and subjected to heat which produces water vapor due to the moisture content inside it. This process separates out the fibers. If there are any clumps, it is reprocessed.
In chemithermomechanical pulping, chemicals like sodium carbonate, sodium hydroxide and sodium sulphite are penetrated into the wood chippings. The equipment used for this process is similar to the equipment used for mechanical pulping. The other conditions, such as heat applied is lower as compared to the conditions in chemical pulping.
In chemical pulping, vessels called digesters are used where chemicals and wood is combined and heated to break down the lignin. By doing this, the cellulose fibers will separate out. Recycled pulp is the pulp obtained from recycled pulping. This is alternately called deinked pulping. Recycled paper is used for pulping in this method. The recycled paper is processed using chemicals to remove the ink and other contaminants. Newsprint, toilet paper and facial tissues contain deinked pulp.
In organosolv pulping, organic solvents are used above temperatures of 140 degree Celsius for breaking down lignin and hemicellulose to soluble materials. The substance used for pulping can be recovered from distillation. The organic solvent is used, primarily to make the lignin soluble. Commonly used organic solvents are ethanol, formic acid, methanol, acetic acid etc.