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Timber decking and Wood pulp
In architecture, a deck is a flat surface capable of supporting weight, similar to a floor but typically constructed outdoors and usually connected to a building. The term is a generalization of decks as found on ships.
Wood or timber "decking" can be used in a number of ways - as part of garden landscaping, to extend living areas of houses, and as an alternative to stone based features such as patios. Decks are made from treated lumber, teak, mahogany and other hardwoods and recycled planks made from PET plastic.A deck of a house is generally a wooden platform built above the ground and connected to the main building. It is generally enclosed by a railing for safety. Access may be from the house through doors and from the ground via stairs. Residential decks can be constructed over steep areas or rough ground that is otherwise unusable. Decks can also be covered by a canopy or pergola to control sunlight.
Larger buildings may also have decks on the upper floors of the building which may be open to the public as observation decks. A deck is the surface used to construct a boardwalk over sand on barrier islands.Wood pulp is the most common material used to make paper. The timber resources used to make wood pulp are referred to as pulpwood. Wood pulp generally comes from softwood trees such as spruce, pine, fir, larch and hemlock, but also some hardwoods such as eucalyptus and birch.
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Wood pulp is made in several stages:
First the bark is removed from the wood. This can be done with or without water (wet stripping). The bark is generally recovered to use as fuel in the pulp and paper making process.The cellulose fibers that keep the wood together are then separated. This can be done in a number of ways:
The wood can be crushed with grinders (huge grindstones) and then soaked in water to produce ground wood (GW). Mechanical pulps are used for products that require less strength, such as newsprint and paperboards.
The wood can be crushed with refiners using steam at high pressures and temperatures to produce
thermo mechanical pulp (TMP). TMP differs in quality from ground
wood.
In addition to the refiners, chemicals can be used to break up the cellulose fibres. Pulp produced this way is known as chemithermomechanical pulp (CTMP). GW, TMP and CTMP are all considered as mechanical pulps. The mechanical pulps tend to turn yellow in time, because of the binding material, lignin, in the pulp.
Chemical pulp is produced by combining wood chips and chemicals in huge vats known as digesters. The effect of the heat and the chemicals dissolves the lignin, that binds the cellulose fibers together, without breaking the wood
fibers. The fluid that contains lignin and other dissolved material is then dried and used as fuel. Chemical pulp is used for materials that need to be stronger or combined with mechanical pulps to give a product different characteristics. Chemical pulps include kraft pulp (or sulphate pulp).
Pulp can also be made out of waste paper and paperboard. Recycled pulp is most often used to make paperboard, newsprint or sanitary paper.
Research is under way to develop biological pulping, similar to chemical pulping but using certain species of fungi that are able to break down the unwanted lignin, but not the cellulose
fibers. This could have major environmental benefits in reducing the pollution associated with chemical pulping.
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 oxygen, ozone and hydrogen peroxide.
The pulp mixture is now sent to the paper machine, where it is shaped and dried.
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History
Using wood to make paper is a fairly recent innovation. In the 1800s, fiber crops such as linen fibers were the primary material source, but a shortage led to experimentation with other materials. Around 1850, a German named Friedrich Gottlob Keller crushed wood with a wet grindstone to obtain wood pulp. Further experimentation by American chemist C.B. Tilghman and Swedish inventor C.F. Dahl enabled the manufacture of wood pulp using chemicals to break down the fibers. The use of wood pulp (and the introduction of steam power to the printing and paper making processes) led to cheaper paper and to the arrival of a new literary genre which we would later coin pulp fiction but were known to their contemporaries as dime novels or penny dreadful.
Environmental impact
The major environmental impacts of wood pulping come from its impact on forest resources and from its waste by-products.
The number of trees consumed depends on the type of paper, whether made by using the ground wood process or the Kraft process. It has been estimated that based on a mixture of softwoods and hardwoods 40 feet tall and 6-8 inches in diameter, it would take a rough average of 24 trees to produce a ton of printing and writing paper, using the Kraft chemical (free sheet) pulping process. On the assumption that the ground wood process is about twice as efficient in using trees, it takes about 12 trees to make a ton of ground wood and newsprint.classical Greek architecture Origin of the Gujarati language Computer keyboard diamonds Furniture
When the paper is bleached with elemental chlorine, byproducts such as chlorinated compounds such as dioxins and furans are formed, and in high pulping areas such as British Columbia, high concentrations of these contaminates led to the closures of some fisheries in 1992. However, improvements in technology have either eliminated the use of elemental chlorine through Elemental Chlorine Free (ECF) or Totally-Chlorine Free (TCF) technology these technologies reduced the amount of chlorinated compounds released into the environment. Elemental Chlorine Free technology utilizes chlorine dioxide (ClO2) in place of chlorine (Cl2). Total chlorine free bleaching utilizes no chlorine in the bleaching process.The wastewater effluent can also be a major source of pollution, containing lignin's from the trees, high biological oxygen demand (BOD) and dissolved organic carbon (DOC), along with alcohols, chlorates, heavy metals, and chelating agents. Reducing the environmental impact of this effluent is accomplished by closing the loop and recycling the effluent where possible, as well as employing less damaging agents in the pulping process.
In the Kraft process, the largest volume byproduct from the pulping process is weak black liquor. This liquor contains the pulping chemicals and the lignin from the trees. The lignin is high in heat content, so this weak black liquor (about 15% solids) is concentrated into heavy black liquor (usually 68% to 75% solids) by use of multiple effect evaporation. Multiple effect evaporation is a process in which one pound of steam is used to boil 4.5 to 5.5 pounds of water. The heavy black liquor is burned in a recovery boiler and the chemicals fall to the bottom of the boiler in a semi-liquid state called smelt. The smelt then flows out of the boiler and is dissolved in water or weak wash to form green liquor. The green liquor is then clarified. Quick lime (CaO) is added to the clarified green liquor to convert a majority of the sodium carbonate (Na2CO3) to sodium hydroxide (NaOH). The green liquor with the quick lime is then clarified and the resulting liquid is white liquor. The white liquor is used as pulping chemicals and the process begins again. The spent lime (CaCO3) is then calcined at approximately 1800 degrees Fahrenheit (1000 degrees Celsius) to yield quick lime to be used again in the clarified green liquor.High-definition television history of art history of brutalist information and analog signals internal combustion engine
Paper made from wood pulp can typically be recycled four to seven times before the fibers become too short. To solve this problem recycled paper is usually mixed with virgin wood pulp to ensure a high quality paper.
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