The first tape measures were simply strips of leather with regular markings; the earliest known recorded use was by that of the ancient Romans. A tape measure can be seen in many different lengths, shapes and sizes. Certain professions, like seamstresses, require flexible measuring tapes made of fiberglass or cloth, while site surveyors require extra long tape measures for plotting out property.
This is accomplished by dissolving lignin in a cooking liquor, so that it may be washed from the cellulose ; this preserves the length of the cellulose fibres. Paper made from chemical pulps are also known as wood-free papers —not to be confused with tree-free paper ; this is because they do not contain lignin, which deteriorates over time.
The microscopic structure of paper: Micrograph of paper autofluorescing under ultraviolet illumination. There are three main chemical pulping processes: The kraft processinvented in the s and first used in the s, is now the most commonly practiced strategy, one of its advantages is the chemical reaction with lignin, that produces heat, which can be used to run a generator.
Most pulping operations using the kraft process are net contributors to reading writing and arithmetic vinyl siding electricity grid or use the electricity to run an adjacent paper mill. Another advantage is that this process recovers and reuses all inorganic chemical reagents.
Soda pulping is another specialty process used to pulp strawsbagasse and hardwoods with high silicate content. Mechanical pulping There are two major mechanical pulps: In the TMP process, wood is chipped and then fed into steam heated refiners, where the chips are squeezed and converted to fibres between two steel discs.
In the groundwood process, debarked logs are fed into grinders where they are pressed against rotating stones to be made into fibres. Mechanical pulps have rather short fibres, thus producing weak paper.
Although large amounts of electrical energy are required to produce mechanical pulp, it costs less than the chemical kind. De-inked pulp Paper recycling processes can use either chemically or mechanically produced pulp; by mixing it with water and applying mechanical action the hydrogen bonds in the paper can be broken and fibres separated again.
Most recycled paper contains a proportion of virgin fibre for the sake of quality; generally speaking, de-inked pulp is of the same quality or lower than the collected paper it was made from.
There are three main classifications of recycled fibre:. Such out-of-specification paper is not sold and is therefore often not classified as genuine reclaimed recycled fibre, however most paper mills have been reusing their own waste fibre for many years, long before recycling became popular.
Additives Besides the fibres, pulps may contain fillers such as chalk or china clay which improve its characteristics for printing or writing. Producing paper Main articles: Paper machine and papermaking The pulp is fed to a paper machine where it is formed as a paper web and the water is removed from it by pressing and drying.
Pressing the sheet removes the water by force; once the water is forced from the sheet, a special kind of felt, which is not to be confused with the traditional one, is used to collect the water; whereas when making paper by hand, a blotter sheet is used instead.
Drying involves using air or heat to remove water from the paper sheets.
In the earliest days of paper making, this was done by hanging the sheets like laundry; in more modern times, various forms of heated drying mechanisms are used. On the paper machine, the most common is the steam-heated can dryer.
Finishing The paper may then undergo sizing to alter its physical properties for use in various applications.
Paper at this point is uncoated. Coated paper has a thin layer of material such as calcium carbonate or china clay applied to one or both sides in order to create a surface more suitable for high-resolution halftone screens.
Uncoated papers are rarely suitable for screens above lpi. Coated or uncoated papers may have their surfaces polished by calendering. Coated papers are divided into matte, semi-matte or silk, and gloss.Agree disagree essay example jay reading essay writing music my life?
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