View source for Paper

{{short description|Material for writing, printing, etc.}}
{{Other uses}}
{{pp-semi-indef}}
{{pp-move-indef}}
{{Use dmy dates|date=August 2014}}
{{Infobox material
| name = Paper
| image = File:Various products made from paper.JPG
| image_size = 280px
| alt = 
| caption = Paper products: [[book]], [[toilet paper]], [[ruled paper]], [[carton]], [[egg box]]
| type = Thin material
| density = From 10 [[Grammage|gsm]] to 3000 gsm
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| abrasive_resistance_note = 
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| gas_perm_temp = 20 °C
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}}
{{Infobox Chinese
|pic=Paper (Chinese characters).svg
|piccap="Paper" in Traditional (top) and Simplified (bottom) Chinese characters
|picsize=55px
|s=纸
|t=紙
|p=zhǐ
|mi={{IPAc-cmn|zh|^|3}}
|lmz=tsy<sup>5</sup>
|j=zi2
|y=jí
|poj=choá
|tl=tsuá
}}
'''Paper''' is a thin sheet [[material]] produced by mechanically or chemically processing [[cellulose]] [[fibre]]s derived from [[wood]], [[Textile|rags]], [[poaceae|grasses]], [[Feces#Other uses|herbivore dung]], or other vegetable sources in [[water]]. Once the water is drained through a fine mesh leaving the fibre evenly distributed on the surface, it can be pressed and dried. 

The papermaking process developed in east Asia, probably [[China]], at least as early as 105 [[Common Era|CE]],<ref>Hogben, Lancelot. "Printing, Paper and Playing Cards". Bennett, Paul A. (ed.) ''Books and Printing: A Treasury for Typophiles''. New York: The World Publishing Company, 1951. pp. 15–31. p. 17. & Mann, George. ''Print: A Manual for Librarians and Students Describing in Detail the History, Methods, and Applications of Printing and Paper Making''. London: Grafton & Co., 1952. p. 77</ref> by the [[Han Dynasty|Han]] court [[eunuch]] [[Cai Lun]], although the earliest archaeological fragments of paper derive from the 2nd century BCE in China.<ref name="Tsien-1985">{{Harvard citation no brackets|Tsien|1985|p=38}}</ref> 

Although paper was originally made in single sheets by hand, today it is mass-produced on large machines—some making reels 10 metres wide, running at 2,000 metres per minute and up to 600,000 tonnes a year.{{citation needed (lead)|date=March 2024}} It is a versatile material with many uses, including [[printing]], painting, graphics, signage, design, packaging, decorating, [[writing]], and [[Housekeeping|cleaning]]. It may also be used as filter paper, wallpaper, book endpaper, conservation paper, laminated worktops, toilet tissue, currency, and security paper, or in a number of industrial and construction processes.

==History==
{{Main| History of paper}}
[[File:Chinese hemp paper western han.jpg|thumb|[[Hemp]] [[wrapping paper]], China, {{circa|100}} BCE]]
The oldest known archaeological fragments of the immediate precursor to modern paper date to the 2nd century BCE in [[China]]. The pulp papermaking process is ascribed to [[Cai Lun]], a 2nd-century CE [[Han Dynasty|Han]] court [[eunuch]].<ref name="Tsien-1985" />

It has been said that knowledge of papermaking was passed to the Islamic world after the [[Battle of Talas]] in 751 CE when two Chinese papermakers were captured as prisoners and used to extract 'the secrets' of papermaking. Although the veracity of this story is uncertain, paper started to be made in [[Samarkand]] soon after.<ref>{{cite book |url= https://books.google.com/books?id=7qseCAAAQBAJ&pg=PA66 |title=The Perfection of the Paper Clip: Curious Tales of Invention, Accidental Genius, and Stationery Obsession|first= James |last=Ward |publisher=Atria Books |date=2015|isbn= 978-1476799865 }}</ref> In the 13th century, the knowledge and uses of paper spread from the [[Middle East]] to [[medieval Europe]], where the first water-powered [[paper mill]]s were built.<ref name="Burns-1996">{{Harvard citation no brackets|Burns|1996|pp=417f.}}</ref> Because paper was introduced to the West through the city of [[Baghdad]], it was first called ''bagdatikos''.<ref>Murray, Stuart A. P. ''The Library: An illustrated History''. Skyhorse Publishing, 2009, p. 57.</ref> In the 19th century, industrialization greatly reduced the cost of manufacturing paper. In 1844, the Canadian inventor [[Charles Fenerty]] and the German inventor [[Friedrich Gottlob Keller]] independently developed processes for pulping wood fibres.<ref>{{Cite book|url=http://www.charlesfenerty.ca/book.html|title=Charles Fenerty and his paper invention|last=Burger|first=Peter|date=2007|publisher=Peter Burger|location=Toronto|isbn=978-0-9783318-1-8|oclc=173248586|pages=25–30|access-date=19 May 2009|archive-url=https://web.archive.org/web/20090419054253/http://www.charlesfenerty.ca/book.html|archive-date=19 April 2009|url-status=live}}</ref>

==Early sources of fibre==
{{see also|wood pulp|deinking|pulpwood}}

Before the industrialisation of paper production the most common fibre source was recycled fibres from used textiles, called rags. The rags were from [[hemp]], [[linen]] and [[cotton]].<ref name="Göttsching-2000">{{Cite book|title=Recycling fiber and deinking|last1=Göttsching|first1=Lothar|last2=Gullichsen|first2=Johan|last3=Pakarinen|first3=Heikki|last4=Paulapuro|first4=Hannu|last5=Yhdistys|first5=Suomen Paperi-Insinöörien|author6=Technical Association of the Pulp and Paper Industry|date=2000|publisher=Fapet Oy|location=Finland|isbn=978-952-5216-07-3|oclc=247670296|pages=12–14}}</ref> A process for removing printing inks from [[recycled paper]] was invented by German jurist [[Justus Claproth]] in 1774.<ref name="Göttsching-2000" /> Today this method is called [[deinking]]. It was not until the introduction of [[wood pulp]] in 1843 that paper production was not dependent on recycled materials from [[ragpicker]]s.<ref name="Göttsching-2000" />

==Etymology==
{{Further|Papyrus}}

The word ''paper'' is etymologically derived from [[Latin]] {{lang|la|papyrus}}, which comes from the [[Ancient Greek language|Greek]] {{lang|grc|πᾰ́πῡρος}} ({{lang|grc-Latn|pápūros}}), the word for the {{Lang|la|[[Cyperus papyrus]]}} plant.<ref>[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dpa%2Fpuros πάπυρος] {{Webarchive|url=https://web.archive.org/web/20130616223117/http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dpa%2Fpuros |date=16 June 2013 }}, Henry George Liddell, Robert Scott, ''A Greek–English Lexicon'', on Perseus</ref><ref>{{Cite dictionary |url=http://www.lexico.com/definition/papyrus |archive-url=https://web.archive.org/web/20200129101010/https://www.lexico.com/definition/papyrus |url-status=dead |archive-date=29 January 2020 |title=papyrus |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}}</ref> [[Papyrus]] is a thick, paper-like material produced from the pith of the ''{{Lang|la|Cyperus papyrus}}'' plant, which was used in [[ancient Egypt]] and other [[History of the Mediterranean region|Mediterranean]] cultures for [[history of writing|writing]] before the introduction of paper.<ref>{{Cite Dictionary.com|papyrus|access-date=20 November 2008}}</ref> Although the word ''paper'' is etymologically derived from ''papyrus'', the two are separate technological developments that use different materials and production methods. Papyrus is a lamination of natural plant fibre, while paper is manufactured from fibres whose properties have been changed by maceration.<ref name="Tsien-1985" /> Papyrus has several downsides that eventually caused it to be replaced by other writing mediums such as [[parchment]] and paper. It was geographically limited to a plant primarily grown in Egypt and was both more expensive and laborious to produce compared to paper. It was also more fragile and sensitive to moisture, making it prone to break apart in damp conditions.{{sfn|Monro|2016|p=20-23, 34, 210}}

==Papermaking==
{{Main| Papermaking}}

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

To make pulp from wood, a [[chemical pulping process]] separates [[lignin]] from [[cellulose]] fibre. A cooking liquor is used to dissolve the lignin, which is then washed from the cellulose; this preserves the length of the cellulose fibres. Paper made from chemical pulps are also known as [[wood-free paper]]s (not to be confused with [[tree-free paper]]); this is because they do not contain lignin, which deteriorates over time. The pulp can also be [[bleaching of wood pulp|bleached]] to produce white paper, but this consumes 5% of the fibres. Chemical pulping processes are not used to make paper made from cotton, which is already 90% cellulose.

[[File:PaperAutofluorescence.jpg| thumb|upright=1.35|right|The microscopic structure of paper: [[Micrograph]] of tissue paper [[autofluorescence|autofluorescing]] under [[ultraviolet]] illumination. The individual fibres in this sample are around 10 [[micrometre|μm]] in diameter.]]

There are three main chemical pulping processes: the [[sulfite process]] dates back to the 1840s and was the dominant method before the second world war. The [[kraft process]], invented in the 1870s and first used in the 1890s, is now the most commonly practised strategy; one of its advantages is the chemical reaction with lignin produces heat, which can be used to run a generator. Most pulping operations using the kraft process are net contributors to the 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 [[straw]]s, [[bagasse]] and [[hardwoods]] with high [[silicate]] content.

===Mechanical pulping===
There are two major mechanical pulps: thermomechanical pulp (TMP) and groundwood pulp (GW). 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 pulping does not remove the [[lignin]], so the yield is very high, > 95%; however, lignin causes the paper thus produced to turn yellow and become brittle over time. 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:
* Mill broke or internal mill waste&nbsp;– This incorporates any substandard or grade-change paper made within the paper mill itself, which then goes back into the manufacturing system to be re-pulped 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 reusing their own waste fibre for many years, long before recycling became popular.
* Preconsumer waste&nbsp;– This is offcut and processing waste, such as guillotine trims and envelope blank waste; it is generated outside the paper mill and could potentially go to landfill, and is a genuine recycled fibre source; it includes de-inked preconsumer waste (recycled material that has been printed but did not reach its intended end use, such as waste from printers and unsold publications).<ref>{{Cite web |url=http://www.nrdc.org/ |title=Natural Resource Defense Council |access-date=20 February 2008 |archive-url=https://web.archive.org/web/20110224024346/http://www.nrdc.org/ |archive-date=24 February 2011 |url-status=live }}</ref>
* Postconsumer waste&nbsp;– This is fibre from paper that has been used for its intended end use and includes office waste, magazine papers and newsprint. As the vast majority of this material has been printed&nbsp;– either digitally or by more conventional means such as lithography or rotogravure&nbsp;– it will either be recycled as printed paper or go through a de-inking process first.

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

===Additives===
Besides the fibres, pulps may contain fillers such as [[chalk]] or [[china clay]],<ref>{{Cite book|url=https://books.google.com/books?id=SHiQAAAAIAAJ&q=pulps+may+contain+fillers+such+as+chalk+or+china+clay|title=Appropriate Technology|date=1996|publisher=Intermediate Technology Publications.| language=en}}</ref> which improve its characteristics for printing or writing.<ref>{{Cite book|url=https://books.google.com/books?id=zp0_a909uyIC&q=Besides+the+fibres,+paper+pulps+may+contain+fillers+such+as+chalk+or+china+clay,+which+improve+its+characteristics&pg=PA203|title=Applications of Wet-End Paper Chemistry|last1=Thorn|first1=Ian|last2=Au|first2=Che On|date=2009-07-24|publisher=Springer Science & Business Media|isbn=978-1-4020-6038-0|language=en|bibcode=2009aowp.book.....T}}</ref> Additives for [[sizing]] purposes may be mixed with it or applied to the paper web later in the manufacturing process; the purpose of such sizing is to establish the correct level of surface absorbency to suit ink or paint.

===Producing paper===
{{Main|Paper machine|papermaking}}
[[File:Mäntän paperitehdas 1.JPG|thumb|Paper mill in [[Mänttä-Vilppula]], [[Finland]]]]
The [[Pulp (paper)|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. 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 papermaking, 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. These can reach temperatures above {{convert|200|F|C||order=flip}} and are used in long sequences of more than forty cans where the heat produced by these can easily dry the paper to less than six percent moisture.

===Finishing===
[[File:20221129 low quality paper.jpg|thumb|Lower quality paper (used to print the book in 1991) with visible bits of wood]]
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. [[Continuous stationery|Continuous form paper]] (or continuous stationery) is cut to width with holes punched at the edges, and folded into stacks.

====Paper grain====
All paper produced by paper machines such 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>[http://www.collectionscanada.gc.ca/forgery/index-e.html "ARCHIVED – Introduction – Detecting the Truth. Fakes, Forgeries and Trickery – Library and Archives Canada"] {{Webarchive|url=https://web.archive.org/web/20180802065857/http://www.collectionscanada.gc.ca/forgery/index-e.html |date=2 August 2018 }} in a virtual museum exhibition at Library and Archives Canada</ref>

==Applications==
[[File:Money poster.JPG|thumb|right|Paper money from different countries]]
Paper can be produced with a wide variety of properties, depending on its intended use.
===Published, written, or informational items===

* '''For representing value''': [[paper money]], [[bank note]], [[cheque]], [[security]] (see ''[[security paper]]''), [[voucher]], [[Ticket (admission)|ticket]]
* '''For [[Data storage device|storing information]]''': [[book]], [[notebook]], [[graph paper]], [[punched card]], [[photographic paper]]
* '''For published materials, publications, and reading materials:''' books, newspapers, magazines, posters, pamphlets, maps, signs, labels, advertisements, billboards.
* '''For individual use''': [[diary]], notebooks, writing pads, memo pads journals, planners, note to remind oneself, etc.; for temporary personal use: scratch paper
* '''For business and professional use:''' copier paper, ledger paper, typing paper, computer printer paper. Specialized paper for forms and documents such as invoices, receipts, tickets, vouchers, bills, contracts, official forms, agreements. 
* '''For [[communication]]''': between individuals and/or groups of people: [[letter (message)|letter]], post cards, airmail, telegrams, [[newsprint]], [[card stock]]
* '''For organizing and sending documents''': envelopes, file folders, packaging, pocket folders, partition folders. 
* For artistic works and uses; drawing paper, pastels, water color paintings, [[sketch pads]], [[charcoal drawings]], 
* For special printed items using more elegant forms of paper; stationery, parchment,

===Packaging and industrial uses===
* '''For packaging''': [[corrugated box]], [[paper bag]], [[envelope]], [[wrapping paper]], [[paper string]]
* '''For cleaning''': [[toilet paper]], [[paper towel]]s, [[facial tissue]].
* '''For food utensils and containers:''' [[wax paper]], [[paper plate]]s and paper cups, [[beverage cartons]], tea bags, condiments, [[food packaging]], coffee filters, cupcake cups. 
* '''For construction''': [[papier-mâché]], [[origami paper]], [[paper plane]]s, [[quilling]], [[paper honeycomb]], [[sandpaper]], used as a core material in [[composite material]]s, [[paper engineering]], [[construction paper]], [[paper yarn]], and [[paper clothing]]
* '''For other uses''': [[emery paper]], [[blotting paper]], [[litmus paper]], [[universal indicator]] paper, [[paper chromatography]], [[electrical insulation paper]] (see also [[fishpaper]]), [[filter paper]], [[wallpaper]]

It is estimated that paper-based storage solutions captured 0.33% of the total in 1986 and only 0.007% in 2007, even though in absolute terms the world's capacity to store information on paper increased from 8.7 to 19.4 [[petabyte]]s.<ref name="Hilbert-2011">[https://www.science.org/doi/10.1126/science.1200970 "The World's Technological Capacity to Store, Communicate, and Compute Information"] {{Webarchive|url=https://web.archive.org/web/20180612163431/http://science.sciencemag.org/content/332/6025/60 |date=12 June 2018 }}, especially [https://www.science.org/doi/10.1126/science.1200970 Supporting online material] {{Webarchive|url=https://web.archive.org/web/20171018152441/http://science.sciencemag.org/content/suppl/2011/02/08/science.1200970.DC1/Hilbert-SOM.pdf |date=18 October 2017 }}, Martin Hilbert and Priscila López (2011), [[Science (journal)|Science]], 332(6025), 60–65; free access to the article through here: martinhilbert.net/WorldInfoCapacity.html {{doi|10.1126/science.1200970}}</ref> It is estimated that in 1986 paper-based postal letters represented less than 0.05% of the world's telecommunication capacity, with sharply decreasing tendency after the massive introduction of digital technologies.<ref name="Hilbert-2011"/>

Paper has a major role in the visual arts. It is used by itself to form two- and three-dimensional shapes and [[collage]]s.<ref>{{Cite news|url=https://www.arts.gov/50th/stories/lynette-schweigert|title=Lynette Schweigert|date=2015-11-05|work=NEA|access-date=2018-10-03|language=en|archive-url=https://web.archive.org/web/20181004021308/https://www.arts.gov/50th/stories/lynette-schweigert|archive-date=4 October 2018|url-status=live}}</ref><ref>{{Cite news|url=https://www.arts.gov/honors/heritage/fellows/herminia-albarr%C3%A1n-romero|title=Herminia Albarrán Romero|date=2013-01-24|work=NEA|access-date=2018-10-03|language=en|archive-url=https://web.archive.org/web/20181004021203/https://www.arts.gov/honors/heritage/fellows/herminia-albarr%C3%A1n-romero|archive-date=4 October 2018|url-status=live}}</ref> It has also evolved to being a structural material used in furniture design.<ref>{{Cite news|last=Morris|date=August–September 2018|title=Material Values, Paper|newspaper=The Economist |pages=38}}</ref> [[Watercolor paper]] has a long history of production and use.

==Types, thickness and weight==
{{Main|Paper size|Grammage|Paper density}}
[[File:Coloured, textured craft card.jpg|thumb|Card and paper stock for [[crafts]] use comes in a wide variety of textures and colors.]]
The thickness of paper is often measured by caliper, which is typically given in thousandths of an inch in the United States and in micrometres (μm) in the rest of the world.<ref>{{cite web|url=https://www.enterprise-press.com/assets/paperthickness.pdf|title=Paper Thickness (Caliper) Chart|website=Case Paper|language=en-US|access-date=2017-05-27 | archive-url = https://web.archive.org/web/20160501173425/http://www.casepaper.com/resources/charts/paper-thickness-caliper/ | archive-date = 2016-05-01}}</ref> Paper may be between {{convert|0.07|and|0.18|mm|in}} thick.<ref>{{cite web|url=http://hypertextbook.com/facts/2001/JuliaSherlis.shtml|title=Thickness of a Piece of Paper|last=Elert|first=Glenn|website=The Physics Factbook|language=en|access-date=2017-05-27|archive-url=https://web.archive.org/web/20170608160141/http://hypertextbook.com/facts/2001/JuliaSherlis.shtml|archive-date=8 June 2017|url-status=dead}}</ref>

Paper is often characterized by weight. In the United States, the weight is the weight of a ream (bundle of 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 larger sheets into four pieces.<ref>{{Cite book|title=The Hammerhill guide to desktop publishing in business|last=McKenzie|first=Bruce G.|date=1989|publisher=Hammerhill|isbn=978-0-9615651-1-4|oclc=851074844|page=144}}</ref> In the United States, printing paper is generally 20&nbsp;lb, 24&nbsp;lb, 28&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]].

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

Most commercial paper sold in North America is cut to standard [[paper size]]s based on [[United States customary units|customary units]] and is defined by the length and width of a sheet of paper.

The ISO 216 system used in most other countries is based on the surface area of a sheet of paper, not on a sheet's width and length. It was first adopted in Germany in 1922 and generally spread as nations adopted the metric system. The largest standard size paper is A0 (A zero), measuring one square metre (approx. 1189 × 841&nbsp;mm). A1 is half the size of a sheet of A0 (i.e., 594&nbsp;mm × 841&nbsp;mm), such that two sheets of A1 placed side by side are equal to one sheet of A0. A2 is half the size of a 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|comma=gaps}} for some specialty 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|access-date=31 October 2007|archive-url=https://web.archive.org/web/20071019143722/http://www.paperonweb.com/density.htm|archive-date=19 October 2007|url-status=live}}</ref>

Paper may be classified into seven categories:<ref>{{Cite book|title=The Thames and Hudson manual of bookbinding|last=Johnson|first=Arthur|date=1978|publisher=Thames and Hudson|location=London|oclc=959020143|language=en}}</ref>
* ''Printing papers'' of wide variety.
* ''Wrapping papers'' for the protection of goods and merchandise. This includes wax and kraft papers.
* ''Writing paper'' suitable for stationery requirements. This includes ledger, bank, and bond paper.
* ''Blotting papers'' containing little or no size.
* ''Drawing papers'' usually with rough surfaces used by artists and designers, including cartridge paper.
* ''Handmade papers'' including most decorative papers, [[Ingres paper]]s, [[Japanese paper]] and [[tissue paper|tissues]], all characterized by lack of grain direction.
* ''Specialty papers'' including cigarette paper, toilet tissue, and other industrial papers.

Some paper types include:
{{div col|colwidth=22em}}
* [[Bank paper]]
* [[Banana paper]]
* [[Bond paper]]
* [[Book paper]]
* [[Coated paper]]: glossy and matte surface
* [[Construction paper|Construction paper/sugar paper]]
* [[Cotton paper]]
* [[Fish paper]] ([[vulcanized]] fibres for electrical insulation)
* [[Inkjet paper]]
* [[Kraft paper]]
* [[Laid paper]]
* [[Leather paper]]
* [[Mummy paper]]
* [[Oak tag paper]]
* [[Sandpaper]]
* [[Troublewit]], specially pleated paper
* [[Tyvek paper]]
* [[Wallpaper]]
* [[Washi]]
* [[Waterproof paper]]
* [[Wax paper]]
* [[Wove paper]]
* [[Xuan paper]]
{{div col end}}

==Paper stability==
[[File:Book suffering from slow fire.jpg|thumb|A book printed in 1920 on [[acidic paper]], now disintegrating a hundred years later.]]
Much of the early paper made from wood pulp contained significant amounts of [[alum]], a variety of [[aluminium sulfate]] salt that is significantly [[acidic]]. Alum was added to paper to assist in [[sizing]],<ref name="Biermann-1993">{{Cite book|title=Essentials of pulping and papermaking|last=Biermann|first=Christopher J/|date=1993|publisher=Academic Press|location=San Diego|isbn=978-0-12-097360-6|oclc=813399142|url-access=registration|url=https://archive.org/details/essentialsofpulp0000bier}}</ref> making it somewhat water resistant so that [[inks]] did not "run" or spread uncontrollably. Early papermakers did not realize that the alum they added liberally to cure almost every problem encountered in making their product would be eventually detrimental.<ref name="Clark-1985">{{cite book |last=Clark |first=James d'A. |title=Pulp Technology and Treatment for Paper |edition=2nd |date=1985 |publisher=Miller Freeman Publications |location=San Francisco |isbn=978-0-87930-164-4}}</ref> The [[cellulose]] fibres that make up paper are [[hydrolyzed]] by acid, and the presence of alum eventually degrades the fibres until the [[acidic paper]] disintegrates in a process known as "[[slow fire]]". Documents written on [[Cotton paper|rag paper]] are significantly more stable. The use of non-acidic additives to make paper is becoming more prevalent, and the stability of these papers is less of an issue.

Paper made from [[pulp mill#The mill|mechanical pulp]] contains significant amounts of [[lignin]], a major component in wood. In the presence of light and oxygen, lignin reacts to give yellow materials,<ref>{{cite journal | last1 = Fabbri | first1 = Claudia | last2 = Bietti | first2 = Massimo | last3 = Lanzalunga | first3 = Osvaldo | year = 2005| title = Generation and Reactivity of Ketyl Radicals with Lignin Related Structures. On the Importance of the Ketyl Pathway in the Photoyellowing of Lignin Containing Pulps and Papers | journal = J. Org. Chem. | volume = 2005 | issue = 70| pages = 2720–2728 | doi = 10.1021/jo047826u | pmid = 15787565 }}</ref> which is why [[newsprint]] and other mechanical paper yellows with age. Paper made from [[bleaching of wood pulp|bleached]] [[kraft process|kraft]] or [[sulfite process|sulfite]] pulps does not contain significant amounts of lignin and is therefore better suited for books, documents and other applications where whiteness of the paper is essential.

Paper made from wood pulp is not necessarily less durable than a rag paper. The aging behaviour of a paper is determined by its manufacture, not the original source of the fibres.<ref>{{cite journal | last1 = Erhardt | first1 = D. | last2 = Tumosa | first2 = C. | year = 2005 | title = Chemical Degradation of Cellulose in Paper over 500 years | journal = Restaurator: International Journal for the Preservation of Library and Archival Material | volume = 26 | issue = 3| page = 155 | doi=10.1515/rest.2005.26.3.151| s2cid = 98291111 }}</ref> Furthermore, tests sponsored by the Library of Congress prove that all paper is at risk of acid decay, because cellulose itself produces formic, acetic, lactic and oxalic acids.<ref>
{{cite web
    | title = The Deterioration and Preservation of Paper: Some Essential Facts
    | url = https://www.loc.gov/preservation/care/deterioratebrochure.html
    | access-date = 7 January 2015
    | publisher = [[Library of Congress]]
    | quote = Research by the Library of Congress has demonstrated that cellulose itself generates acids as it ages, including formic, acetic, lactic, and oxalic acids
    | ref = refDeteriorationOfPaper
    | archive-url = https://web.archive.org/web/20150120175215/http://www.loc.gov/preservation/care/deterioratebrochure.html
    | archive-date = 20 January 2015
    | url-status=live
    }}
</ref>

Mechanical pulping yields almost a tonne of pulp per tonne of dry wood used, which is why mechanical pulps are sometimes referred to as "high yield" pulps. With almost twice the yield as chemical pulping, mechanical pulps is often cheaper. Mass-market paperback books and newspapers tend to use mechanical papers. Book publishers tend to use [[acid-free paper]], made from fully bleached chemical pulps for [[hardback]] and [[Trade paperbacks|trade paperback]] books.

== Environmental impact ==
{{Main|Environmental impact of paper|Deforestation}}

The production and use of paper has a number of adverse effects on the environment.

Worldwide consumption of paper has risen by 400% in the past 40 years{{clarify|date=November 2017}} leading to increase in [[deforestation]], with 35% of harvested trees being used for paper manufacture. Most paper companies also plant trees to help regrow forests. Logging of [[old growth forest]]s accounts for less than 10% of wood pulp,<ref name="Martin-2004">{{cite web |url=http://www.ecology.com/feature-stories/paper-chase/index.html |title=Paper Chase |access-date=21 September 2007 |last=Martin |first=Sam |date=2004 |publisher=Ecology Communications, Inc. |archive-url = https://web.archive.org/web/20070619104819/http://www.ecology.com/feature-stories/paper-chase/index.html <!-- Bot retrieved archive --> |archive-date = 19 June 2007}}</ref> but is one of the most controversial issues.

Paper waste accounts for up to 40% of total waste produced in the United States each year, which adds up to 71.6&nbsp;million tons of paper waste per year in the United States alone.<ref>{{cite web|title=General Overview of What's in America's Trash |url=http://www.epa.gov/osw/wycd/catbook/what.htm |publisher=United States Environmental Protection Agency |access-date=4 April 2012 |author=EPA |date=28 June 2006 |url-status=dead |archive-url=https://web.archive.org/web/20120105015733/http://www.epa.gov/osw/wycd/catbook/what.htm |archive-date=5 January 2012 }}</ref> The average office worker in the US prints 31 pages every day.<ref>Groll, T. 2015 [http://www.zeit.de/karriere/2015-06/papier-enerige-sparen-unternehmen In vielen Büros wird unnötig viel ausgedruckt] {{Webarchive|url=https://web.archive.org/web/20150817050102/http://www.zeit.de/karriere/2015-06/papier-enerige-sparen-unternehmen |date=17 August 2015 }}, Zeit Online, 20 June 2015.</ref> Americans also use in the order of 16&nbsp;billion [[paper cup]]s per year.

Conventional bleaching of wood pulp using elemental chlorine produces and releases into the environment large amounts of [[organochloride|chlorinated organic compounds]], including chlorinated [[Polychlorinated dibenzodioxins|dioxins]].<ref name="Health Canada DSS-1991">{{cite book |url=https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/environmental-contaminants/canadian-environmental-protection-act-priority-substances-list-assessment-report-effluents-pulp-mills-using-bleaching.html |title=Effluents from Pulp Mills using Bleaching – PSL1 |access-date=21 September 2007 |date=1991 |isbn=978-0-662-18734-9 |publisher=Health Canada DSS |archive-url=https://web.archive.org/web/20170705180453/https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/environmental-contaminants/canadian-environmental-protection-act-priority-substances-list-assessment-report-effluents-pulp-mills-using-bleaching.html |archive-date=5 July 2017 |url-status=live }} [https://www.canada.ca/content/dam/hc-sc/migration/hc-sc/ewh-semt/alt_formats/hecs-sesc/pdf/pubs/contaminants/psl1-lsp1/pulp_mill_effluents_pate_blanchie/pulp_bleaching-pate_blanchie-eng.pdf Pdf] {{Webarchive|url=https://web.archive.org/web/20170912101625/https://www.canada.ca/content/dam/hc-sc/migration/hc-sc/ewh-semt/alt_formats/hecs-sesc/pdf/pubs/contaminants/psl1-lsp1/pulp_mill_effluents_pate_blanchie/pulp_bleaching-pate_blanchie-eng.pdf |date=12 September 2017 }}</ref> Dioxins are recognized as a persistent environmental pollutant, regulated internationally by the [[Stockholm Convention on Persistent Organic Pollutants]]. Dioxins are highly toxic, and health effects on humans include reproductive, developmental, immune and hormonal problems. They are known to be carcinogenic. Over 90% of human exposure is through food, primarily meat, dairy, fish and shellfish, as dioxins accumulate in the food chain in the fatty tissue of animals.<ref>
{{cite web
    | title = Dioxins and their effects on human health
    | url = https://www.who.int/en/news-room/fact-sheets/detail/dioxins-and-their-effects-on-human-health
    | access-date = 7 January 2015
    | date = June 2014
    | publisher = [[World Health Organization]]
    | quote = More than 90% of human exposure is through food
    | ref = refDioxinsEffectsHealth
    | archive-url = https://web.archive.org/web/20180427100121/http://www.who.int/en/news-room/fact-sheets/detail/dioxins-and-their-effects-on-human-health
    | archive-date = 27 April 2018
    | url-status=live
    }}
</ref>

The paper pulp and print industries emitted together about 1% of world [[greenhouse-gas emissions]] in 2010<ref>{{cite web |title=World GHG Emissions Flow Chart 2010 |url=https://ingmarschumacher.files.wordpress.com/2013/05/asn-ecofys-2013-world-ghg-emissions-flow-chart-2010.pdf |website=Ecofys |access-date=5 July 2020 |archive-date=19 October 2020 |archive-url=https://web.archive.org/web/20201019222845/https://ingmarschumacher.files.wordpress.com/2013/05/asn-ecofys-2013-world-ghg-emissions-flow-chart-2010.pdf |url-status=live }}</ref> and about 0.9% in 2012.<ref>{{cite web |title=World GHG Emissions 2012 |url=http://www.sankey-diagrams.com/world-ghg-emissions-2012/ |website=SANKEY DIAGRAMS |date=22 February 2019 |publisher=Ecofys |access-date=5 July 2020 |archive-date=19 January 2021 |archive-url=https://web.archive.org/web/20210119044321/http://www.sankey-diagrams.com/world-ghg-emissions-2012/ |url-status=live }}</ref>

== Current production and use ==
In the 2022−2024 edition of the annual "Pulp and paper capacites survey", the [[Food and Agriculture Organization|Food and Agriculture Organization of the United Nations]] (FAO) reports that Asia has superseded North America as the top pulp- and paper-producing continent.<ref name="FAO-2023">{{Cite book |url=https://doi.org/10.4060/cc7561en |title=Sustainability by numbers: Forest products at FAO |publisher=FAO |year=2023 |location=Rome |doi=10.4060/cc7561en |language=English}}</ref>

FAO figures for 2021 show the production of graphic papers continuing its decline from a mid-2000s peak to hover below 100 million tonnes a year. By contrast, the production of other papers and paperboard – which includes cardboard and sanitary products – has continued to soar, exceeding 320 million tonnes.<ref name="FAO-2023" />

FAO has documented the expanding production of cardboard in paper and paperboard, which has been increasing in response to the spread of                e-commerce since the 2010s.<ref name="FAO-2023" /> Data from FAO suggest that it has been even further boosted by COVID-19-related lockdowns.<ref>{{Cite web |date=3 September 2021 |title=COVID-19 leads to changes in paper and paperboard production |url=https://www.fao.org/forestry/news/98965/en/ |access-date=2023-11-03 |website=www.fao.org |archive-date=3 November 2023 |archive-url=https://web.archive.org/web/20231103132409/https://www.fao.org/forestry/news/98965/en/ |url-status=live }}</ref> 

== Future ==
Some manufacturers have started using a new, significantly more environmentally friendly alternative to expanded plastic packaging. Made out of paper, and known commercially as PaperFoam, the new packaging has mechanical properties very similar to those of some expanded plastic packaging, but is [[Biodegradation|biodegradable]] and can also be recycled with ordinary paper.<ref>{{Cite web |url=http://www.paperfoam.com/ |title=PaperFoam Carbon Friendly Packaging |access-date=3 April 2006 |archive-url=https://web.archive.org/web/20060309014938/http://www.paperfoam.com/ |archive-date=9 March 2006 |url-status=live }}</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>{{Cite web |url=https://worldwide.espacenet.com/publicationDetails/biblio?CC=WO&NR=2006002346&KC=&FT=E&locale=en_EP |title=Barrier compositions and articles produced with the compositions cross-reference to related application |access-date=13 June 2018 |archive-url=https://web.archive.org/web/20181116032641/https://worldwide.espacenet.com/publicationDetails/biblio?CC=WO&NR=2006002346&KC=&FT=E&locale=en_EP |archive-date=16 November 2018 |url-status=live }}</ref>

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

== See also ==
{{columnslist|colwidth=20em|
* [[Arches paper]]
* [[Buckypaper]]
* [[continuous stationery|Continuous form paper]] (or "continuous stationery")
* [[Deinked pulp]]
* [[Environmental impact of paper]]
* [[Fibre crop]]
* [[Graphene oxide paper]]
* [[Lokta paper]]
* [[Mass deacidification]]
* [[Paper and ink testing]]
* [[Paper armour]]
* [[Paper chemicals]]
* [[Paper clip]]
* [[Paper craft]]
* [[Parchment paper]], which emulates the texture of animal-based [[parchment]]
* [[Roll hardness tester]]
* [[Seed paper]]
* [[Stone paper]]
}}

== Citations ==
{{Reflist}}

== General references ==
* {{Cite book
 | last = Burns
 | first = Robert I.
 | editor-last = Lindgren
 | editor-first = Uta|editor-link= Uta Lindgren
 | contribution = Paper comes to the West, 800–1400
 | title = Europäische Technik im Mittelalter. 800 bis 1400. Tradition und Innovation
 | edition = 4th
 | date = 1996
 | publisher = Gebr. Mann Verlag
 | location = Berlin
 | isbn = 978-3-7861-1748-3
 | pages = 413–422
}}
*{{citation|last=Monro|first=Alexander|year=2016|title=The Paper Trail: An Unexpected History of a Revolutionary Invention|publisher=Alfred A. Knopf}}
* {{Cite book |last=Tsien |first=Tsuen-Hsuin |author-link=Tsien Tsuen-hsuin |editor-first=Joseph |editor-last=Needham |editor-link=Joseph Needham |title=Paper and Printing |series=Science and Civilisation in China, Chemistry and Chemical Technology |volume=V (part 1) |publisher=Cambridge University Press |date=1985}}
* "Document Doubles" in [http://www.collectionscanada.ca/forgery/index-e.html ARCHIVED – Introduction – Detecting the Truth. Fakes, Forgeries and Trickery – Library and Archives Canada] {{Webarchive|url=https://web.archive.org/web/20170412144206/http://www.collectionscanada.ca/forgery/index-e.html |date=12 April 2017 }}, a virtual museum exhibition at Library and Archives Canada

==Further reading==
{{external media| float = right| video1 = [https://www.c-span.org/video/?410275-7/mark-kurlansky-discusses-paper Discussion with Mark Kurlansky on ''Paper: Paging Through History'', June 12, 2016], [[C-SPAN]]}} 
*{{cite book |last1=Kurlansky |first1=Mark |authorlink=Mark Kurlansky |title=Paper: Paging Through History |date=2016 |publisher=W. W. Norton & Company |isbn=9780393239614}}
*May, Steven W. 2023. ''English Renaissance Manuscript Culture: The Paper Revolution.'' Oxford: Oxford University Press.
* {{Cite book |first=Alexander |last=Monro |year=2013 |title=The Paper Trail: An Unexpected History of the World's Greatest Invention |location=London |publisher=Allen Lane |isbn=9781846141898 |oclc=1040764924}}
* [https://colorwise.com/blog/paper-brightness-whiteness-shade-definitions-differences/ "Paper Brightness, Whiteness & Shade: Definitions and Differences"] by David Rogers (June 26, 2015)

== External links ==
{{wiktionary|paper}}
{{commons category|Paper}}
* [http://www.tappi.org Technical Association of the Pulp and Paper Industry] ([[TAPPI]]) official website
* The [[hdl:1903.1/8637|Arnold Yates Paper collection]] at [[University of Maryland Libraries]]
* [https://www.straightdope.com/columns/read/2231/how-is-paper-made/ "How is paper made?"] at [[The Straight Dope]], 22 November 2005
* [https://www.youtube.com/watch?v=E4C3X26dxbM Thirteen-minute video on modern paper production system], from [[Sappi]]

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