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[[Image:ManilaPaper.jpg|thumb|A stack of [[manila paper]]]]
{{wiktionary|paper}}
{{commonscat}}
'''Paper''' is a thin material mainly used for writing upon, printing upon or for packaging. It is produced by pressing together moist [[fiber]]s, typically [[cellulose]] pulp derived from [[wood]], [[rags]] or [[grass]]es, and drying them into flexible sheets.

Paper is a versatile material with many uses. Whilst the most common is for [[writing]] and [[printing]] upon, it is also widely used as a [[packaging]] material, in many [[cleaning]] products, in a number of industrial and construction processes, and occasionally as a [[Edible paper|food ingredient]], particularly in Asian cultures.

==History==
{{Main|History of paper}}
{{See|Science and technology of the Han Dynasty|List of Chinese inventions}}
The word paper derives from the Greek term for the [[ancient Egypt]]ian writing material called [[papyrus]], which was formed from beaten strips of [[Cyperus papyrus|papyrus plants]]. The immediate predecessor to modern paper is believed to have originated in China in approximately the 2nd century AD, although there is some evidence for it being used before this date.{{fact|date=February 2010}} [[Papermaking]] is considered to be one of the ''[[Four Great Inventions of Ancient China]]'', since the first pulp papermaking process was developed in [[China]] during the early 2nd century AD by [[Han Dynasty|the Han]] court eunuch [[Cai Lun]]. China used paper as an effective and cheap alternative to silk, letting them sell more silk, leading to a [[Golden Age]]. 

The use of paper spread from China through the [[Muslim world|Islamic world]] and entered production in [[medieval Europe]] in the 13th century, where the first water-powered [[paper mill]]s were built and mechanization of papermaking began.<ref name="Burns 1996, 417f.">{{harvnb|Burns|1996|pp=417f.}}</ref> The industrial production of paper in the early 19th century caused significant cultural changes worldwide, allowing for relatively cheap exchange of information in the form of letters, newspapers and books for the first time. In 1844, both Canadian inventor [[Charles Fenerty]] and German inventor F.G. Keller had invented the machine and process for pulping wood for the use in paper making.<ref>[http://www.charlesfenerty.ca/book.html Burger, Peter]. ''Charles Fenerty and his Paper Invention''. Toronto: Peter Burger, 2007. ISBN 978-0-9783318-1-8 pp.25-30</ref> This would end the nearly 2000-year use of pulped rags and start a new era for the production of newsprint and eventually all paper out of pulped wood.

==Papermaking==
[[Image:PaperAutofluorescence.jpg|thumb|300px|right|The microscopic structure of paper: [[Micrograph]] of paper [[autofluorescence|autofluorescing]] under [[ultraviolet]] illumination. The individual fibres in this sample are around 10 [[micrometre|µm]] in diameter.]]
{{Main|Papermaking}}

===Chemical pulping===
{{Main|kraft process|sulfite process|soda pulping}}

The purpose of a [[chemical pulping process]] is to break down the chemical structure of [[lignin]] and render it soluble in the cooking liquor, so that it may be washed from the [[cellulose]] fibers. Because lignin holds the plant cells together, chemical pulping frees the fibres and makes pulp. The pulp can also be [[bleaching of wood pulp|bleached]] to produce white paper for [[printing]], [[painting]] and [[writing]]. Chemical pulps tend to cost more than [[mechanical pulp]]s, largely due to the low yield, 40–50% of the original wood. Since the process preserves fibre length, however, [[chemical pulp]]s tend to make stronger paper. Another advantage of chemical pulping is that the majority of the heat and [[electricity]] needed to run the process is produced by burning the [[lignin]] removed during pulping. 

Paper made from chemical pulps are also known as [[wood-free paper]]s. Not to be confused with [[tree-free paper]].

The [[Kraft process]] is the most commonly practiced strategy for pulp manufacturing and produces especially strong, unbleached papers that can be used directly for bags and boxes but are often processed further, e.g. to make [[corrugated cardboard]].

===Mechanical pulping===
There are two major mechanical pulps, [[thermo mechanical pulp]] (TMP) and [[groundwood pulp]] (GW). In the TMP process, wood is chipped and then fed into large steam-heated refiners where the chips are squeezed and fibreized between two steel discs. In the [[groundwood process]], debarked logs are fed into grinders where they are pressed against rotating stones and fibreized. Mechanical pulping does not remove the [[lignin]], so the yield is very high, >95%, but also causes paper made from this pulp to yellow and become brittle over time. Mechanical pulps have rather short fibre lengths and produce weak paper. Although large amounts of [[electrical energy]] are required to produce mechanical pulp, it costs less than chemical pulp.

===Deinked pulp===
{{Main|deinking}}

[[Paper recycling]] processes can use either chemical or mechanical pulp. By mixing 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 in the interests of quality. Generally deinked pulp is of the same quality or lower than the collected paper it was made from.

There are three main classifications of recycled fibre:.
* Mill Broke or Internal Mill Waste — this incorporates any substandard or grade-change paper made within the paper mill which then goes back into the manufacturing system to be repulped back into paper. 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 recycling their own waste fibre for many years, long before recycling become popular.
* Preconsumer Waste — this is offcuts and processing waste, such as guillotine trims and  envelope blank waste. This waste is generated outside the paper mill and could potentially go to landfill, and is a genuine recycled fibre source.  Also includes de-inked preconsumer (recycled material that has been printed but did not reach its intended end use, such as waste from printers and unsold publications).<ref>[http://www.nrdc.org/ Natural Resource Defense Council]</ref>
* Postconsumer waste — this is fibre from paper which has been used for its intended end use and would include office waste, magazine papers and newsprint. As the vast majority of this paper has been printed (either digitally or by more conventional means such as litho or gravure), it will either be recycled as printed paper or go through a deinking process first.

Recycled papers can be made from 100% recycled materials or blended with virgin pulp. They are (generally) not as strong nor as bright as papers made from virgin pulp.

===Additives===
Besides the fibres, pulps may contain fillers such as [[chalk]] or [[china clay]], which improve the characteristics of the paper for printing or writing. Additives for [[sizing]] purposes may be mixed into the pulp and/or applied to the paper web later in the manufacturing process. The purpose of sizing is to establish the correct level of surface absorbency to suit the ink or paint.

===Producing paper===
{{Main|Papermachine|handmade paper}}
{{Also|Air-laid paper}}

The [[Pulp (paper)|pulp]] is feed 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, felt (not to be confused with the traditional [[felt]])  is used to collect the water. When making paper by hand, a blotter sheet is used.

Drying involves using air and or heat to remove water from the paper sheet. In the earliest days of papermaking this was done by hanging the paper 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. These dryers can heat to temperatures above 200°F (93°C) and are used in long sequences of more than 40 cans. The heat produced by these can easily dry the paper to less than 6% moisture.

===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 150 lpi.) Coated or uncoated papers may have their surfaces polished by [[calender]]ing. Coated papers are divided into matte, semi-matte or silk, and gloss. Gloss papers give the highest [[optical density]] in the printed image.

The paper is then fed onto reels if it is to be used on web printing presses, or cut into sheets for other printing processes or other purposes. The fibres in the paper basically run in the machine direction. Sheets are usually cut "long-grain", i.e. with the grain parallel to the longer dimension of the sheet.

All paper produced by paper machines as the [[Fourdrinier machine]] are wove paper, i.e. the wire mesh that transports the web leaves a pattern that has the same density along the paper grain and across the grain. Textured finishes, [[watermark]]s and wire patterns imitating hand-made ''laid'' paper can be created by the use of appropriate rollers in the later stages of the machine.

Wove paper does not exhibit "laidlines", which are small regular lines left behind on paper when it was handmade in a mould made from rows of metal wires or bamboo. Laidlines are very close together. They run perpendicular to the "chainlines", which are further apart. Handmade paper similarly exhibits "deckle edges", or rough and feathery borders.<ref>"Document Doubles" in [http://www.collectionscanada.ca/forgery/002035-500-e.html Detecting the Truth: Fakes, Forgeries and Trickery], a virtual museum exhibition at Library and Archives Canada</ref>

==Applications==
[[Image:Paper cutter 1.jpg|thumb|left|180px|A [[Paper cutter]]]]
*To write or print on: the piece of paper becomes a [[document]]; this may be for keeping a record (or in the case of printing from a computer or copying from another paper: an additional record) and for [[communication]]; see also [[Reading (activity)|reading]]. 

Paper can be produced with a wide variety of properties, depending on its intended use.<ref>{{cite web|url=http://www.paperonweb.com/grade11.htm|title=Grades and uses of paper|accessdate=2007-10-12}}</ref>
*'''To represent a value:''' [[paper money]], [[bank note]], [[cheque]], [[security]] (see [[Security paper]]), [[voucher]] and [[ticket]]
*'''For [[Data storage device|storing information]]''': [[book]], [[notebook]], [[magazine]], [[newspaper]], [[art]], [[zine]], [[letter (message)|letter]]
**for personal use: [[diary]], note to remind oneself, etc.; for temporary personal use: scratch paper
**for [[communication]] to someone else:
*** by transportation of the paper from the place where it is written or printed to the place where it is read: delivered by sender, transported by a third party (e.g. in the case of [[mail]]), or taken by the receiver
***by writing at the same place as where it is read:
****if sender and receiver are not there at the same time, in the case of a posted notice
****if sender and receiver are both present, but use paper for illustration, or if communication by talking is not suitable:
*****because one is [[Muteness|mute]] or the other is [[deaf]]
*****to avoid other people hearing it, because it is secret, or in order not to disturb them
*****in a noisy environment
*'''For packaging:''' [[corrugated box]], [[paper bag]], [[envelope]], [[wrapping tissue]], [[Charta emporetica]] and [[wallpaper]]
*'''For cleaning:''' [[toilet paper]], [[handkerchief]]s, [[paper towel]]s, [[facial tissue]] and [[cat litter]]
*'''For construction:''' [[papier-mâché]], [[origami]], [[paper plane]]s, [[quilling]], Paper [[honeycomb]], used as a core material in [[composite material]]s, [[paper engineering]], [[construction paper]] and [[paper clothing]]
*'''Other uses:''' [[emery paper]], [[sandpaper]], [[blotting paper]], [[litmus paper]], [[universal indicator]] paper, [[paper chromatography]], [[electrical insulation paper]] (see also [[dielectric]]s and [[permittivity]]) and [[filter paper]]

==Types, thickness and weight==
[[Image:Coloured, textured craft card.jpg|thumb|right|Card and paper stock for [[craft]] use comes in a wide variety of textures and colors.]]

{{Main|Paper size|Paper density}}

The thickness of paper is often measured by caliper, which is typically given in thousandths of an inch.<ref>[http://www.casepaper.com/calc_chart_caliper.htm "Paper Thickness Chart", Case Paper Company Inc.]</ref>  Paper may be between {{convert|0.07|mm|in}} and {{convert|0.18|mm|in}} thick.<ref>[http://hypertextbook.com/facts/2001/JuliaSherlis.shtml "Thickness of a Piece of Paper", HyperTextbook.com]</ref>

Paper is often characterized by weight. In the United States, the weight assigned to a paper is the weight of a ream, 500 sheets, of varying "basic sizes", before the paper is cut into the size it is sold to end customers. For example, a ream of 20&nbsp;lb, {{convert|8.5|x|11|in|mm|0|abbr=on}} paper weighs 5 pounds, because it has been cut from a larger sheet into four pieces.<ref> McKenzie, Bruce G., ''The Hammermill Guide to Desktop Publishing in Business'', p. 144, Hammermill Papers, 1989.</ref> In the United States, printing paper is generally 20&nbsp;lb, 24&nbsp;lb, or 32&nbsp;lb at most. [[Cover stock]] is generally 68&nbsp;lb, and 110&nbsp;lb or more is considered [[card stock]].

The  {{convert|8.5|x|11|in|mm|1|abbr=on}} size stems from the original size of a vat that was used to make paper.{{Citation needed|date=March 2009}}  At the time, paper was made from passing a fiber and water slurry through a screen at the bottom of a box.  The box was {{convert|17|in|mm|1|abbr=on}} deep and {{convert|44|in|mm|1|abbr=on}} wide.  That sheet, folded in half in the long direction, then twice in the opposite direction, made a sheet of paper that was exactly  {{convert|8.5|x|11|in|mm|1|abbr=on}}.

In Europe, and other regions using the [[ISO 216]] paper sizing system, the weight is expressed in grammes per square metre (g/m<sup>2</sup> or usually just g) of the paper. Printing paper is generally between 60 g and 120 g. Anything heavier than 160 g is considered card. The weight of a ream therefore depends on the dimensions of the paper and its thickness.

The sizing system in Europe is based on common width to height ratios for different paper sizes. The largest standard size paper is A0 (A zero). Two sheets of A1, placed upright side by side fit exactly into one sheet of A0 laid on its side. Similarly, two sheets of A2 fit into one sheet of A1 and so forth. Common sizes used in the office and the home are A4 and A3 (A3 is the size of two A4 sheets).

The [[density]] of paper ranges from {{convert|250|kg/m3|lb/ft3|0|abbr=on}} for tissue paper to {{convert|1500|kg/m3|lb/ft3|0|abbr=on}} for some speciality paper. Printing paper is about {{convert|800|kg/m3|lb/ft3|0|abbr=on}}.<ref>{{cite web|url=http://www.paperonweb.com/density.htm|title=Density of paper and paperboard|publisher=PaperOnWeb|accessdate=2007-10-31}}</ref>

Some paper types include:
{{multicol}}
*[[Bank paper]]
*[[Banana paper]]
*[[Bond paper]]
*[[Book paper]]
*[[Coated paper]]: glossy and matte surface
*[[Construction paper|Construction paper/sugar paper]]
*[[Cotton paper]]
*[[Electronic paper]]
{{multicol-break}}
*[[Fish paper]] ([[vulcanized]] fibres for electrical insulation)
*[[Inkjet paper]]
*[[Kraft paper]]
*[[Laid paper]]
*[[Leather paper]]
*[[Mummy paper]]
*[[Sandpaper]]
{{multicol-break}}
*[[Tyvek paper]]
*[[Wallpaper]]
*[[Washi]]
*[[Waterproof paper]]
*[[Wax paper]]
*[[Wove paper]]
*[[Xuan paper]]
{{multicol-end}}

==The future of paper==
Some manufacturers have started using a new, significantly more environmentally friendly alternative to expanded plastic packaging made out of paper, known commercially as paperfoam.  The packaging has very similar mechanical properties to some expanded plastic packaging, but is biodegradable and can also be recycled with ordinary paper.<ref>[http://www.paperfoam.com/ PaperFoam Carbon Friendly Packaging]</ref>

With increasing environmental concerns about synthetic coatings (such as [[PFOA]]) and the higher prices of hydrocarbon based petrochemicals, there is a focus on [[zein]] (corn protein) as a coating for paper in high grease applications such as popcorn bags.<ref>[http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=WO2006002346&F=0 Barrier compositions and articles produced with the compositions cross-reference to related application]</ref>

Also, synthetics such as [[Tyvek]] and [[Teslin]] have been introduced as printing media as a more durable material than paper.

==See also==
{{multicol}}
*[[Arches paper]]
*[[Buckypaper]]
*[[Deinked pulp]]
*[[Graphene Oxide Paper]]
*[[Origami]]
*[[Paper and ink testing]]
{{multicol-break}}
*[[Paper engineering]]
*[[Paper recycling]]
*[[Paper size]]
*[[Paper towels]]
*[[Papier-mâché]]
{{multicol-break}}
*[[Papier]] "paper" in French or German
*[[Roll hardness tester]]
*[[Security paper]]
*[[Seed paper]]
*[[Toilet paper]]
{{multicol-end}}

==References and notes==
{{Reflist}}
*{{Cite book
 | last = Burns
 | first = Robert I.
 | editor-last = Lindgren 
 | editor-first = Uta 
 | contribution = Paper comes to the West, 800−1400
 | title = Europäische Technik im Mittelalter. 800 bis 1400. Tradition und Innovation
 | edition = 4th
 | year = 1996
 | publisher = Gebr. Mann Verlag
 | location = Berlin 
 | isbn = 3-7861-1748-9
 | pages = 413–422
 | ref = harv
 | postscript = <!--None-->
}}
*Needham, Joseph (1986). ''Science and Civilization in China: Volume 5, Chemicals and Chemical Technology, Part 1, Paper and Printing''. New York: [[Cambridge University Press]], 1985.  (also published in Taipei: Caves Books, Ltd., 1986.)
::also referred to as:
*Tsien, Tsuen-Hsuin, '"Paper and Printing," vol. 5 part 1 of Needham, Joseph ''Science and Civilization in China:''.  Cambridge University Press, 1986. ISBN 0521086906.  (also published in Taipei: Caves Books, Ltd., 1986.)
*"Document Doubles" in [http://www.collectionscanada.ca/forgery/ Detecting the Truth: Fakes, Forgeries and Trickery], a virtual museum exhibition at Library and Archives Canada

==External links==
*[http://www.tappi.org TAPPI] Technical Association of the Pulp and Paper Industry
*[http://www.straightdope.com/mailbag/mpapermaking.html ''How is paper made?''] at The [[Straight Dope]], 22 November 2005
*[http://internationalpaper.com/Our%20Company/Learning%20Center/How%20Paper%20Is%20Made.html How Paper Is Made]
*[http://www.gpo.gov/acquisition/paperspecs.htm United States Government Printing Office: Government Paper Specification Standards]
*[http://www.ecopaper.com/bananapaper/howitsmade How Organic Paper is Made]

[[Category:Paper| ]]
[[Category:Printing materials]]
[[Category:Papermaking]]
[[Category:Writing media]]
[[Category:Materials]]
[[Category:Stationery]]
[[Category:Art materials]]
[[Category:Paper art]]

[[Category:Chinese inventions]]
[[Category:Traditional Chinese objects]]
[[Category:Packaging materials]]

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