Paper

Paper is a thin sheet material produced by

mechanically or chemically processing cellulose Paper
fibres derived from wood, rags, grasses,
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
CE,[1] by the Han court eunuch Cai Lun,
although the earliest archaeological fragments of
paper derive from the 2nd century BCE in Paper products: book, toilet paper, ruled paper,
China.[2] carton, egg box
Material type Thin material
Although paper was originally made in single
Physical properties
sheets by hand, today it is mass-produced on
large machines—some making reels 10 metres Density (ρ) From 10 gsm to 3000 gsm
wide, running at 2,000 metres per minute and up
to 600,000 tonnes a year. It is a versatile material with Paper
many uses, including printing, painting, graphics,
signage, design, packaging, decorating, writing, and
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.
"Paper" in Traditional (top) and Simplified
(bottom) Chinese characters
History Traditional Chinese 紙
The oldest known archaeological fragments of the
Simplified Chinese 纸
Transcriptions
immediate precursor to modern paper date to the 2nd
century BCE in China. The pulp papermaking process Standard Mandarin
is ascribed to Cai Lun, a 2nd-century CE Han court Hanyu Pinyin zhǐ
eunuch.[2] IPA [ʈʂɨ̀]
Yue: Cantonese
It has been said that knowledge of papermaking was
passed to the Islamic world after the Battle of Talas in Yale Romanization jí
751 CE when two Chinese papermakers were captured Jyutping zi2
as prisoners and used to extract 'the secrets' of Southern Min
papermaking. Although the veracity of this story is Hokkien POJ choá
uncertain, paper started to be made in Samarkand soon Tâi-lô tsuá
after.[3] In the 13th century, the knowledge and uses of
paper spread from the Middle East to medieval Europe, where
the first water-powered paper mills were built.[4] Because
paper was introduced to the West through the city of
Baghdad, it was first called bagdatikos.[5] 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.[6]

Early sources of fibre

Before the industrialisation of paper production the most Hemp wrapping paper, China, c. 100
BCE
common fibre source was recycled fibres from used textiles,
called rags. The rags were from hemp, linen and cotton.[7] A
process for removing printing inks from recycled paper was invented by German jurist Justus Claproth in
1774.[7] 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 ragpickers.[7]

Etymology
The word paper is etymologically derived from Latin papyrus, which comes from the Greek πᾰ́πῡρος
(pápūros), the word for the Cyperus papyrus plant.[8][9] Papyrus is a thick, paper-like material produced
from the pith of the Cyperus papyrus plant, which was used in ancient Egypt and other Mediterranean
cultures for writing before the introduction of paper.[10] Although the word paper is etymologically
derived from papyrus, the two are produced very differently and the development of the first is distinct
from the development of the second. Papyrus is a lamination of natural plant fibre, while paper is
manufactured from fibres whose properties have been changed by maceration.[2] 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.[11]

Papermaking

Chemical 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 papers (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 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.

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
The microscopic structure of paper: Micrograph of paper
chemical reagents. Soda pulping is another
autofluorescing under ultraviolet illumination. The
specialty process used to pulp straws, bagasse individual fibres in this sample are around 10 μm in
and hardwoods with high silicate content. diameter.

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 – 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 – 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).[12]
Postconsumer waste – 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 – either digitally or by more conventional means such as
lithography or rotogravure – 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,[13] which improve its
characteristics for printing or writing.[14] 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
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. When making paper by hand, a blotter sheet is used
instead.
Paper mill in Mänttä-Vilppula, Finland

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 93 °C (200 °F) 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
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 calendering. 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 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 Lower quality paper (used to print the
book in 1991) with visible bits of wood
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, watermarks 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.[15]

Applications
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
For storing information: book, notebook, graph
paper, punched card, photographic paper Paper money from different countries

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, 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 towels, facial tissue.
For food utensils and containers: wax paper, paper plates and paper cups, beverage
cartons, tea bags, condiments, food packaging, coffee filters, cupcake cups.
For construction: papier-mâché, origami paper, paper planes, quilling, paper honeycomb,
sandpaper, used as a core material in composite materials, 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 petabytes.[16] 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.[16]

Paper has a major role in the visual arts. It is used by itself to form two- and three-dimensional shapes
and collages.[17][18] It has also evolved to being a structural material used in furniture design.[19]
Watercolor paper has a long history of production and use.

Types, thickness and weight

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.[20] Paper
may be between 0.07 and 0.18 millimetres (0.0028 and
0.0071 in) thick.[21]

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 lb, 8.5 in Card and paper stock for crafts use
× 11 in (216 mm × 279 mm) paper weighs 5 pounds because comes in a wide variety of textures and
[22] colors.
it has been cut from larger sheets into four pieces. In the
United States, printing paper is generally 20 lb, 24 lb, 28 lb,
or 32 lb at most. Cover stock is generally 68 lb, and 110 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/m2 or usually gsm) of the paper. Printing paper is generally between 60 gsm and
120 gsm. Anything heavier than 160 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 sizes based on 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 mm). A1 is half the size of a sheet of A0 (i.e., 594 mm × 841 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 250 kg/m3 (16 lb/cu ft) for tissue paper to 1 500 kg/m3 (94 lb/cu ft) for
some specialty paper. Printing paper is about 800 kg/m3 (50 lb/cu ft).[23]

Paper may be classified into seven categories:[24]

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 papers, Japanese paper and
tissues, all characterized by lack of grain direction.
Specialty papers including cigarette paper, toilet tissue, and other industrial papers.
Some paper types include:

Bank paper
Banana paper
Bond paper
Book paper
Coated paper: glossy and matte surface
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

Paper stability
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,[25] 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.[26] The cellulose
fibres that make up paper are hydrolyzed by acid, and the
presence of alum eventually degrades the fibres until the A book printed in 1920 on acidic paper,
acidic paper disintegrates in a process known as "slow fire". now disintegrating a hundred years later.
Documents written on 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 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,[27] which is why newsprint and
other mechanical paper yellows with age. Paper made from bleached kraft or 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.[28] 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.[29]

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 paperback books.

Environmental impact
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 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 forests accounts for less than 10% of wood
pulp,[30] 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 million tons of paper waste per year in the United States alone.[31] The average office worker in
the US prints 31 pages every day.[32] Americans also use in the order of 16 billion paper cups per year.

Conventional bleaching of wood pulp using elemental chlorine produces and releases into the
environment large amounts of chlorinated organic compounds, including chlorinated dioxins.[33] 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.[34]

The paper pulp and print industries emitted together about 1% of world greenhouse-gas emissions in
2010[35] and about 0.9% in 2012.[36]

Current production and use

In the 2022−2024 edition of the annual "Pulp and paper capacites survey", the Food and Agriculture
Organization of the United Nations (FAO) reports that Asia has superseded North America as the top
pulp- and paper-producing continent.[37]

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.[37]

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.[37] Data from FAO suggest that it has
been even further boosted by COVID-19-related lockdowns.[38]

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
biodegradable and can also be recycled with ordinary paper.[39]

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.[40]

Also, synthetics such as Tyvek and Teslin have been introduced as printing media as a more durable
material than paper.
See also
Arches paper Paper and ink testing
Buckypaper Paper armour
Continuous form paper (or "continuous Paper chemicals
stationery") Paper clip
Deinked pulp Paper craft
Environmental impact of paper Parchment paper, which emulates the
Fibre crop texture of animal-based parchment
Graphene oxide paper Roll hardness tester
Lokta paper Seed paper
Mass deacidification Stone paper

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General references
Burns, Robert I. (1996). "Paper comes to the West, 800–1400". In Lindgren, Uta (ed.).
Europäische Technik im Mittelalter. 800 bis 1400. Tradition und Innovation (4th ed.). Berlin:
Gebr. Mann Verlag. pp. 413–422. ISBN 978-3-7861-1748-3.
Monro, Alexander (2016), The Paper Trail: An Unexpected History of a Revolutionary
Invention, Alfred A. Knopf
Tsien, Tsuen-Hsuin (1985). Needham, Joseph (ed.). Paper and Printing. Science and
Civilisation in China, Chemistry and Chemical Technology. Vol. V (part 1). Cambridge
University Press.
"Document Doubles" in ARCHIVED – Introduction – Detecting the Truth. Fakes, Forgeries
and Trickery – Library and Archives Canada (http://www.collectionscanada.ca/forgery/index-
e.html) Archived (https://web.archive.org/web/20170412144206/http://www.collectionscanad
a.ca/forgery/index-e.html) 12 April 2017 at the Wayback Machine, a virtual museum
exhibition at Library and Archives Canada

Further reading
Kurlansky, Mark (2016). Paper: Paging External videos
Through History. W. W. Norton & Company.
ISBN 9780393239614. Discussion with Mark Kurlansky on Paper:
Paging Through History, June 12, 2016 (http
May, Steven W. 2023. English Renaissance
Manuscript Culture: The Paper Revolution. s://www.c-span.org/video/?410275-7/mark-kurl
Oxford: Oxford University Press. ansky-discusses-paper), C-SPAN
Monro, Alexander (2013). The Paper Trail: An
Unexpected History of the World's Greatest
 Invention. London: Allen Lane. ISBN 9781846141898. OCLC 1040764924 (https://search.w
orldcat.org/oclc/1040764924).
"Paper Brightness, Whiteness & Shade: Definitions and Differences" (https://colorwise.com/
blog/paper-brightness-whiteness-shade-definitions-differences/) by David Rogers (June 26,
2015)

External links
Technical Association of the Pulp and Paper Industry (http://www.tappi.org) (TAPPI) official
website
The Arnold Yates Paper collection at University of Maryland Libraries
"How is paper made?" (https://www.straightdope.com/columns/read/2231/how-is-paper-mad
e/) at The Straight Dope, 22 November 2005
Thirteen-minute video on modern paper production system (https://www.youtube.com/watc
h?v=E4C3X26dxbM), from Sappi

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