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Paper is a commodity of thin material produced by the amalgamation of fibers, typically vegetable fibers composed of cellulose, which are subsequently held together by hydrogen bonding. While the fibers used are usually natural in origin, a wide variety of synthetic fibers, such as polypropylene and polyethylene, may be incorporated into paper as a way of imparting desirable physical properties. The most common source of these kinds of fibers is wood pulp from pulpwood trees, largely softwoods and hardwoods, such as spruce and aspen respectively. Other vegetable fiber materials including those of cotton, hemp, linen, and rice may be used.

History

The word paper comes from the Greek term for the ancient Egyptian writing material called papyrus, which was formed from beaten strips of papyrus plants. Papyrus was produced as early as 3000 BC in Egypt, and sold to ancient Greece and Rome. The establishment of the Library of Alexandria in the 3rd century BC put a drain on the supply of papyrus. As a result, according to the Roman historian Pliny (Natural History records, xiii.21), parchment was invented under the patronage of Eumenes of Pergamum to build his rival library at Pergamum. Outside of Egypt, parchment or vellum, made of processed sheepskin or calfskin, replaced papyrus as the papyrus plant requires subtropical conditions to grow.

Paper is considered to be one of the Four Great Inventions of Ancient China, as the first standard papermaking process was made in China during the early 2nd century. During the Shang (1600 BC-1050 BC) and Zhou (1050 BC-256 BC) dynasties of ancient China, documents were ordinarily written on bone or bamboo (on tablets or on bamboo strips sewn and rolled together into scrolls), making them very heavy and awkward to transport. The light material of silk was sometimes used, but was normally too expensive to consider. Indeed, most of the above materials were rare and costly. While the Han Dynasty Chinese court official Cai Lun is widely regarded to have first invented the modern method of papermaking (inspired from wasps and bees) from wood pulp in 105 AD, the 2006 discovery of specimens bearing written Chinese characters in north-west China's Gansu province suggest that paper was in use by the ancient Chinese military more than 100 years before Cai in 8 BC. Archeologically however, true paper without writing has been excavated in China dating to the reign of Emperor Wu of Han from the 2nd century BC, used for purposes of wrapping or padding protection for delicate bronze mirrors. It was also used for safety, such as the padding of poisonous 'medicine' as mentioned in the official history of the period. Although paper used for writing became widespread by the 3rd century, paper continued to be used for wrapping (and other) purposes.

Toilet paper was used in China by at least the 6th century AD. In AD 589, the Chinese scholar-official Yan Zhitui (531-591 AD) once wrote: "Paper on which there are quotations or commentaries from Five Classics or the names of sages, I dare not use for toilet purposes". An Arab traveler to China once wrote of the curious Chinese tradition of toilet paper in AD 851, writing: "They (the Chinese) are not careful about cleanliness, and they do not wash themselves with water when they have done their necessities; but they only wipe themselves with paper". Toilet paper continued to be a valued necessity in China, since it was during the Hongwu Emperor's reign in AD 1393 that the Bureau of Imperial Supplies (Bao Chao Si) manufactured 720,000 sheets of toilet paper for the entire court (produced of the cheap rice-straw paper). For the emperor's family alone, 15,000 special sheets of paper were made, in light yellow tint and even perfumed. Even at the beginning of the 14th century, during the middle of the Yuan Dynasty, the amount of toilet paper manufactured for modern-day Zhejiang province alone amounted to ten million packages holding 1000 to 10000 sheets of toilet paper each. During the Tang Dynasty (AD 618-907) paper was folded and sewn into square bags to preserve the flavor of tea. During the same period, it was written that tea was served from baskets with multi-colored paper cups and paper napkins of different size and shape. During the Chinese Song Dynasty (AD 960-1279) not only did the government produce the world's first known paper-printed money, or banknote (see Jiaozi and Huizi), but paper money bestowed as gifts to deserving government officials were wrapped in special paper envelopes.

In America, archaeological evidence indicates that paper was invented by the Mayans no later than the 5th century AD. Called amatl, it was in widespread use among Mesoamerican cultures until the Spanish conquest. In small quantities, traditional Maya papermaking techniques are still practiced today.

Paper spread slowly outside of China; other East Asian cultures, even after seeing paper, could not figure out how to make it themselves. Instruction in the manufacturing process was required, and the Chinese were reluctant to share their secrets. The paper was thin and translucent, not like modern western paper, and thus only written on one side. Books were invented in India, of Palm leaves (where we derive the name leaf for a sheet of a book). The technology was first transferred to Korea in 604 and then imported to Japan by a Buddhist priests, around 610, where fibres (called bast) from the mulberry tree were used.

After further commercial trading and the defeat of the Chinese in the Battle of Talas in 751, the invention spread to the Middle East. Production was started in Baghdad, where the Arabs invented a method to make a thicker sheet of paper. The manufacture had spread to Damascus by the time of the First Crusade in the 11th century, but the wars interrupted production, and it split into two centers. Cairo continued with the thicker paper. Iran became the center of the thinner papers, where it was adopted in India. The first paper mill in Europe was in Spain, at Xavia (modern Valencia) in 1120. More mills appeared in Fabriano Italy in about the 13th century, as an import from Islamic Spain. They used hemp and linen rags as a source of fiber. The oldest known paper document in the West is the Mozarab Missal of Silos from the 11th century, probably written in the Islamic part of Spain. Paper is recorded as being manufactured in both Italy and Germany by 1400, just about the time when the woodcut printmaking technique was transferred from fabric to paper in the old master print and popular prints.

Some historians speculate that paper was a key element in global cultural advancement. According to this theory, Chinese culture was less developed than the West in ancient times prior to the Han Dynasty because bamboo, while abundant, was a clumsier writing material than papyrus; Chinese culture advanced during the Han Dynasty and preceding centuries due to the invention of paper; and Europe advanced during the Renaissance due to the introduction of paper and the printing press.

In the very small quantities needed for popular prints, paper was affordable by the European urban working class and many peasants even in the 1400s, but books remained expensive until the nineteenth century. However, even poor families could often afford a few by the 1700s in England, if they so chose.

Paper remained relatively expensive, at least in book-sized quantities, through the centuries, until the advent of steam-driven paper making machines in the 19th century, which could make paper with fibres from wood pulp. Although older machines predated it, the Fourdrinier paper making machine became the basis for most modern papermaking. Together with the invention of the practical fountain pen and the mass produced pencil of the same period, and in conjunction with the advent of the steam driven rotary printing press, wood based paper caused a major transformation of the 19th century economy and society in industrialized countries. With the introduction of cheaper paper, schoolbooks, fiction, non-fiction, and newspapers became gradually available to all the members of an industrial society by 1900. Cheap wood based paper also meant that keeping personal diaries or writing letters became universal. The clerk, or writer, ceased to be a high-status job, and by 1850 had nearly become an office worker or white-collar worker , which transformation can be considered as a part of the industrial revolution.

Unfortunately, the original wood-based paper was more acidic and more prone to disintegrate over time, through processes known as slow fires. Documents written on more expensive rag paper were more stable. Mass-market paperback books still use these cheaper mechanical papers (see below), but the more careful book publishers now use acid-free paper for hardback and trade paperback books.

Papermaking

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Fiber processing/pulping

Wood or plant cell walls are composed of fibers bound together. During pulping, these fibers are separated from each other and carbohydrate surfaces, primarily cellulose or hemicellulose, are exposed. Hydrogen bonding between these carbohydrate surfaces gives paper its strength. Fibers can be separated chemically, mechanically, or via a combination of the two.

Chemical 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 fibers and makes pulp. The pulp must be bleached to produce white paper for printing, painting and writing. Chemical pulps tend to cost more than mechanical pulps, largely due to the low yield, 40-50% of the original wood. Since the process preserves fiber length, however, chemical pulps 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.

Papers made from chemical wood-based pulps are also unhelpfully known as woodfree papers.

The Kraft process 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, thermomechanical pulp (TMP) and mechanical pulp. The latter is known in the USA as groundwood pulp. In the TMP process, wood is chipped and then fed into large steam-heated refiners where the chips are squeezed and fiberized between two steel discs. In the groundwood process, debarked logs are fed into grinders where they are pressed against rotating stones and fiberized. 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 fiber lengths and produce weak paper. Although large amounts of electrical energy are required to produce mechanical pulp, it costs less than chemical pulp.

Recycled paper

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 fibers separated again. Most recycled paper contains a proportion of virgin fiber in the interests of quality.

Additives

Besides the fibers, 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.

Drying

After the paper web is produced, the water must be removed from it in order to create a usable product. This is accomplished through pressing and drying. The methods of doing so vary between the different processes used to make paper, but the concepts remain the same.

Pressing the sheet removes the water by force. Once the water is forced from the sheet, another absorbent material must be used to collect this water. On a paper machine this is called a felt (not to be confused with the traditional felt). 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 dryer cans 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 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 matt, semi-matt 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 fibers 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 Fourdrinier-type machines is 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.

Applications

• 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.

• To represent a value:
  • paper money
  • bank note
  • check
  • security
  • voucher
  • ticket
• For entertainment:
  • book
  • magazine
  • newspaper
  • art
  • zine
• For packaging:
  • corrugated box
  • paper bag
  • envelope
  • wrapping tissue
  • wallpaper
• For cleaning
  • toilet paper
  • handkerchiefs
  • paper towels
  • facial tissue
  • cat litter
• For construction
  • papier-mâché
  • origami
  • quilling
  • Paper honeycomb, used as a core material in composite materials
  • paper engineering, see also construction paper
  • clothing
• Other uses
  • emery paper
  • sandpaper
  • blotting paper
  • litmus paper
  • universal indicator paper
  • paper chromatography
  • Capacitor Dielectrics (Permittivity 1.5 - 3)

Types

The future of paper

Some manufacturers, notably AMD, 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.

With increasing environmental concerns about synthetic coatings (such as PFOA) and the currently higher prices of hydrocarbon based petrochemicals, there is a recent focus on zein (corn protein) as a coating for paper in high grease applications such as popcorn bags.

Synthetics such as Tyvek and Teslin have been introduced as printing media as a more durable material than paper.

In 2006, the world's first "Paper Technology Centre" was opened in Heidenheim, Germany, the headquarters of the Voith paper machine company, at the cost of 75 million Euros .

Notes

1. ^ Needham, Volume 4, 122.
2. Needham, Volume 4, 1.
3. ^ Needham, Volume 4, 123.
4. The Construction of the Codex In Classic- and Postclassic-Period Maya Civilization Maya Codex and Paper Making
5. "Document Doubles" in Detecting the Truth: Fakes, Forgeries and Trickery, a virtual museum exhibition at Library and Archives Canada

References

• Needham, Joseph (1986). Science and Civilization in China: Volume 4, Part 1. Taipei: Caves Books, Ltd.
• "Document Doubles" in Detecting the Truth: Fakes, Forgeries and Trickery, a virtual museum exhibition at Library and Archives Canada

See also

• Paper recycling
• Arches paper
• Paper size

External links

• TAPPI Technical Association of the Pulp and Paper Industry
• How is paper made? at The Straight Dope, 22 November 2005
• How Paper Is Made
• United States Government Printing Office: Government Paper Specification Standards
• How is cotton paper made in India?

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• Materials
• Paper
• Stationery
• Art materials
• Paper art
• Recyclable materials