The rags must be cut and cleaned, boiled, and beaten before they can be used by the paper mill. Other materials used in paper manufacture include bleaches and dyes, fillers such as chalk, clay, or titanium oxide, and sizings such as rosin, gum, and starch. The paper then moves onto the press section of the machine, where it is pressed between rollers of wool felt.
The paper then passes over a series of steam-heated cylinders to remove the remaining water. A large machine may have from 40 to 70 drying cylinders. The paper may be further finished by passing through a vat of sizing material. It may also receive a coating, which is either brushed on or rolled on. Coating adds chemicals or pigments to the paper's surface, supplementing the sizings and fillers from earlier in the process. Fine clay is often used as a coating.
The paper may next be supercalendered, that is, run through extremely smooth calendar rollers, for a final time. Then the paper is cut to the desired size.
The number of trees and other vegetation cut down in order to make paper is enormous. Paper companies insist that they plant as many new trees as they cut down.
Environmentalists contend that the new growth trees, so much younger and smaller than what was removed, cannot replace the value of older trees. Efforts to recycle used paper especially newspapers have been effective in at least partially mitigating the need for destruction of woodlands, and recycled paper is now an important ingredient in many types of paper production. The chemicals used in paper manufacture, including dyes, inks, bleach, and sizing, can also be harmful to the environment when they are released into water supplies and nearby land after use.
The industry has, sometimes with government prompting, cleared up a large amount of pollution, and federal requirements now demand pollutionfree paper production. The cost of such clean-up efforts is passed on to the consumer. Biermann, Christopher J. Academic Press, Bell, Lilian A. Plant Fibers for Papermaking. Liliaceae Press, Ferguson, Kelly, ed. New Trends and Developments in Papermaking. Miller Freeman, Inc. Munsell, Joel.
Chronology and Process of Papermaking, Albert Saifer Publisher, Kleiner, Art. Lamb, Lynette. This is done with a large scale version of the the wood chippers that landscaping companies use. The wood chips are placed into a giant machine that combines them with really hot water and chemicals. This helps remove air pockets so that the chips will break down into fibers more easily. Next, the wood chip and chemical mixture is moved into a pressure cooker. The wood chips spend about two hours at nearly degrees farenheit.
The combination of steam, chemicals, and pressure causes the chips to desintegrate. This leaves wood fibers, and a liquid called "black liquor. In the next step, the black liquor is removed. The remaining fiber is cleaned in a variety of ways and sometimes bleached to ensure purity. The majority of the waste in the process is black liquor - but these facilities typically operate in a "closed loop" system.
The inorganics chemicals are recovered and re-used for the next batch of paper, while the remainder of the liquid natural biomass is converted to energy to operate the plant. In most cases, these more power is generated than is needed, so this creates an environmentally friendly power source for local communities.
Papers made from chemical pulp are usually brighter, smoother, and higher quality than their mechanically pulped counterparts. The primary purpose is to take wet fibers, press them together, dry them, and then make them smooth. Pulp is mixed with water as well as additional fillers and additives and then pumped onto a belt. This belt is typically made of a mesh that encourages all of the fibers to go in one direction. Much like wood, paper has a grain direction. The orentation of the fibers on this belt dictates the "grain direction" of the paper.
This section of the paper making machine has at least one roller to push the fibers onto the belt to help make sure that the paper grain goes in the right direction. In the "Wet Press Section," the pulp moves off of the mesh belt onto a felt belt. While the felt used to be made of wool, these days synthetics are more normal. The pulp moves through a series of high pressure rollers designed to push the liquid into the felt. Once the pulp enters the "Dryer Section," it has started to take the shape of paper.
This part of the machine weaves the web of paper through a series of heated rollers. Felt belts are also used in this part of the machine to give the moisture in the paper somewhere to go. The last part of the machine is called the "Calendar Section. The more of these rollers there are, the smoother the paper will be. There are several ways to make paper glossy. These include supercalendering and coatings. Those debarked wood bolts are then chipped in a chipper if the pulping process calls for chemical digestion.
Chips are then screened for size, cleaned, and temporarily stored for further processing. In the fiber separation stage, several pulping technologies will be diverged. The chips are kept into a large pressure cooker digester , into which is added the appropriate chemicals in kraft chemical pulping. The chips are then digested with steam at specific temperatures to separate the fibers and partially dissolve the lignin and other extractives.
Some digesters operate continuously with a constant feed of chips furnish and liquor are charged intermittently and treat a batch at a time. After the digestion process, the cooked pulp is discharged into a pressure vessel. Here the steam and volatile materials are tubed off. After that, this cooked pulp is returned to the chemical recovery cycle. Fiber separation in mechanical pulping is less dramatic. Debarked logs are forced against rotating stone grinding wheels in the stone ground-wood procedure.
Refiner pulp and thermo-mechanical pulp are produced by chips. These chips are ground by passing them through rapidly rotating in both processes. In the second stage after refining, the pulp is screened, cleaned, and most of the process water is removed in preparation for paper making.
Raw pulp contains an appreciable amount of lignin and other discoloration, it must be bleached to produce light colored or white papers preferred for many products.
The fibers are further delignified by solubilizing additional lignin from the cellulose through chlorination and oxidation. These include chlorine dioxide, chlorine gas, sodium hypochlorite, hydrogen perioxide, and oxygen. Sodium Hydroxide, a strong alkali is used to extract the dissolved lignin from fibers surface.
The bleaching agents and the sequence in which they are used depend on a number of factors, such as the relative cost of the bleaching chemicals, type and condition of the pulp. Mechanical pulp bleaching varies from chemical pulp bleaching. Bleaching of mechanical pulp is designed to minimize the removal of the lignin that would reduce fiber yields.
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