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Papermaking

[pey-per-mey-ker]

Papermaking is the process of making paper, a material which is used ubiquitously today for writing and packaging.

In papermaking a dilute suspension of fibers in water is drained through a screen, so that a mat of randomly interwoven fibers is laid down. Water is removed from this mat of fibers by pressing and drying to make paper. Most paper is made from wood pulp, but other fiber sources such as cotton and textiles may be used.

The history of papermaking can be traced to China about AD 105, when it was made by Cai Lun. Modern papermaking began in the early 1800s in Europe with the development of the Fourdrinier machine, which produces a continuous roll of paper rather than individual sheets. These machines have become very large, up to 500 feet (~150 m) in length, producing a sheet 400 inches (~10 m) wide, and operating at speeds of over 60 mph (100 km/h).

History

Papyrus

The word paper derives from its mistaken identity by Greek-speaking scholars with the ancient Egyptian writing material called papyrus, which was woven from papyrus plants. The Egyptians invented papyrus around 3000 BC. It is made by crisscrossing thin sections of the papyrus reed, which grows in the delta of the Nile river and is held together by natural glues within the reeds. Papyrus was smoothed on one side by rubbing it against a flat stone surface. The development of the great library of Alexandria resulted in a shortage of papyrus, which pushed Attalus of Pergamum (who was building his own rival library) to search for a substitute for papyrus.

Parchment

Around 200 BC parchment, the split skin of a sheep or goat, was developed. Parchment, or vellum, which is the best quality material, has the great benefit over papyrus of extreme longevity, but was always expensive. The ancient world continued to use papyrus (thus accounting for much of the loss of classical literature, as outside the very dry conditions of Egypt it has a short life) but parchment became increasingly important, and by Late Antiquity had very largely superseded papyrus.

True paper

Papermaking has traditionally been traced to China about 105 AD, when Cai Lun, an official attached to the Imperial court during the Han Dynasty (202 BC-220 AD), created a sheet of paper using mulberry and other bast fibres along with fishnets, old rags, and hemp waste. However a recent archaeological discovery has been reported from near Dunhuang of paper with writing on it dating from 8 BC, while paper had been used in China for wrapping and padding since the 2nd century BC. Paper used as a writing medium became widespread by the 3rd century, and by the 6th century toilet paper was starting to be used in China as well. During the Tang Dynasty (618-907 AD) paper was folded and sewn into square bags to preserve the flavor of tea, while the later Song Dynasty (960-1279 AD) was the first government on Earth to issue paper-printed money (see banknote).

Diffusion of paper

The technology was first transferred to Korea in 600 and then imported to Japan by a Buddhist priest, Dam Jing (曇徴) around 610 from Goguryeo, where bast fibers from the mulberry tree were used. Printing seems to have been invented in Japan, where 1000 prayers were printed for temples in 760 from stone 'blocks'. The idea went back to China, where the widespread use of paper also enhanced two innovations in the field of printing: woodblock printing by at least the 9th century (see the Diamond Sutra) and movable type printing, first invented by Bi Sheng (990-1051 AD) during the Song Dynasty.

Water was the problem for papermakers in the dry western part of China, and the slow westward progress of printing reflects experiments with different raw materials. Western paper was made from old clothes. In 751, the secret of papermaking reached Samarkand, in Central Asia, after papermakers were captured by the Arabs at the Battle of Talas. The method spread through the Arabic empire, and paper was first made in Baghdad during the time of Harun in 793. Soon after, the first paper mills were invented in Baghdad in 794, which transformed papermaking from an art into a major industry.

The secret of paper and silk manufacture had by then diffused to Damascus, and from there to the rest of the Muslim world, reaching India via Persia. It reached Western Europe via Islamic Spain: the earliest Christian book, or document, on paper was the 11th century Mozarab Missal of Silos, no doubt on Muslim-made paper. Production of paper moved to Italy in the 13th century. They used hemp and linen rags as a source of fiber. Rags from old clothing etc. were commonly bought by rag collectors and sold to paper makers. Bones were collected to make glue size to seal the paper.

The use of paper became increasingly common during the 14th century, and is documented as being manufactured in both Italy and Germany by 1400. Paper then spread rapidly, and was used for letters, records, old master prints, popular prints and manuscript books. Prints were initially in woodcut , and from the 1430s in engraving also.

But it was not until printing with movable type was invented that rag paper became more popular. Parchment was not ideal for printing, being expensive and susceptible to humidity. Paper on the other hand was ideal. But as the demand for books rose, the supply of rags became more and more inadequate and other sources of fiber were actively sought.

By the time of the invention of movable type printing in Germany about 1450, paper was readily available, although still expensive. Vellum remained in use as well, and it was on this that the most expensive copies of the Gutenberg Bible were first printed.

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

The Bataks, living in Sumatra, sometimes use as writing material long strips of bamboo, welded by "beating" them together, then folded together, accordion-like, between wooden covers, and bound together with a string of woven rushes. Often long strips of the thin bark of trees -- such books being known as pustakas -- are used. Specimens of writing on bark from India are preserved in the British Museum. The people of the Malabar coast also frequently wrote upon bark with a stylus. Ancient books of the Bataks were written in ink on paper made of bark. The Lampong and Rendjang tribes, also inhabiting Sumatra, scratch their messages and books on bamboo, tree bark, or certain kinds of leaves.

Significance

Some historians speculate that paper was the key element in global cultural advancement. According to this theory, Chinese culture was less developed than the West in early ancient times because bamboo, while abundant, was a clumsier writing material than papyrus (although silk was used as a writing medium, but was often too expensive). Chinese culture advanced during the Han Dynasty and preceding centuries due to the Chinese 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 19th century. However even poor families could often afford a few books 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 in the 19th century of steam-driven paper making machines, which could make paper with fibres from wood pulp. Although it was not the earliest of its kind, 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 in 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 gradually became available to everyone by 1900. Cheap wood based paper also meant that everyone literate could keep a personal diary and write letters. The clerk, or writer, ceased to be a high-status job, and by 1850 had become a mere "office worker" or white-collar worker. This transformation can be considered as a part of the industrial revolution.

The demand for paper has increased steadily. For example, in 1900, the U.S. papermaking industry produced approximately 5,000,000 tons of paper per year. A century later that industry produced over 90,000,000 tons of paper and paperboard per year. Predictions that electronic storage of data would lead to a decline in the demand for paper have not been realized. It has been estimated that by 2020 paper mills will produce almost 500,000,000 tons of paper and paperboard per year

Method

Papermaking, regardless of the scale on which it is done, involves making a dilute suspension of fibers in water and allowing this suspension to drain through a screen so that a mat of randomly interwoven fibers is laid down. Water is removed from this mat of fibers by pressing and drying to make paper.

Manual preparation

Fibers are suspended in water to form a slurry in a large vat. The mold is a wire screen in a wooden frame (somewhat similar to an old window screen), which is used to scoop some of the slurry out of the vat. The slurry in the screen mold is sloshed around the mold until it forms a uniform thin coating. The fibers are allowed to settle and the water to drain. When the fibers have stabilized in place but are still damp, they are turned out onto a felt sheet which was generally made of an animal product such as wool or rabbit fur, and the screen mold immediately reused. Layers of paper and felt build up in a pile (called a 'post') then a weight is placed on top to press out excess water and keep the paper fibers flat and tight. The sheets are then removed from the post and hung or laid out to dry. A step-by-step procedure for making paper with readily available materials can be found online.

When the paper pages are dry, they are frequently run between rollers (calendered) to produce a harder writing surface. Papers may be sized with gelatin or similar to bind the fibres into the sheet. Papers can be made with different surfaces depending on their intended purpose. Paper intended for printing or writing with ink is fairly hard, while paper to be used for water color, for instance, is heavily sized, and can be fairly soft.

The wooden frame is called a "deckle". The deckle leaves the edges of the paper slightly irregular and wavy, called "deckle edges", one of the indications that the paper was made by hand. Deckle-edged paper is occasionally mechanically imitated today to create the impression of old-fashioned luxury. The impressions in paper caused by the wires in the screen that run sideways are called "laid lines" and the impressions made, usually from top to bottom, by the wires holding the sideways wires together are called "chain lines". Watermarks are created by weaving a designe into the wires in the mold. This is essentially true of Oriental molds made of other substances, such as bamboo. Hand-made paper generally folds and tears more evenly along the laid lines.

Laboratory-made paper

Hand-made paper is also prepared in laboratories studying papermaking and in paper mill quality labs. The "handsheets" made according to TAPPI Standard T 205 are circular sheets 15.9 cm (6.25 in) in diameter and are used to measure paper brightness, strength, degree of sizing and so on.

Industrial papermaking

The following section is a simple overview of a complex industrial process. There are variants of the basic equipment and processes which are described in numerous books on papermaking.

A modern paper mill is divided into several sections, roughly corresponding to the processes involved in making hand-made paper. Pulp is refined and mixed in water with other additives to make a pulp slurry, the headbox distributes the slurry onto a moving, continuous screen, water drains from the slurry (by gravity or under vacuum), the wet paper sheet goes through presses and driers and is finally rolled into large rolls, often weighing several tonnes.

Refining

The fibers in the pulp must be separated and made pliable. This process is known as "beating" and is usually accomplished by passing the fibers between a rotating drum and a fixed plate. Ideally the fibers are not shortened or broken during beating. Beating fibrillates or "roughens" the surface of the fibers so that the fiber surface becomes frayed. This helps in bonding the fibers when the paper sheet is formed. One measure of how well a pulp has been beaten is how quickly water drains from a pulp slurry. A well-beaten pulp will retain water longer and remain in suspension to allow good sheet formation.

Wet end chemistry

After the pulp has been beaten, various additives are introduced to the slurry to give the paper desired properties. Internal sizing agents like alkylketene dimer (AKD) or alkylsuccinic anhydride (ASA) are added to control the hydrophobicity of the paper, which determines how much water the paper will absorb. For example toilet paper needs to absorb water quickly, printing paper needs carefully controlled uptake so that water-based inks can be used and paper used for disposable paper cups must be very resistant to water uptake. Fillers such as clay, talc, calcium carbonate and titanium dioxide are added to increase the opacity of the paper. Materials to increase the strength of the paper when it is wet, dyes, and so on are also added to the pulp slurry.

It was common practice to add alum to the pulp slurry to assist in paper sizing with rosin. One side effect of the use of alum was to make the paper slightly acidic. Acidic paper degrades faster, by a process known as slow fires.

Headbox

The pulp slurry prepared in the wet end contains between 0.1% and 1% pulp fibers by weight. The slurry passes through a slit 2-6 mm wide and is spread onto a moving mesh belt called the "wire" which is the full width of the paper machine. The key function of the headbox is to distribute the slurry very uniformly and consistently across its full width.

The wire

The following description is for one type of paper machine called a single wire machine. Other configurations such as twin wire are also used. The wire is a continuous mesh belt, usually made of woven metal wire. The speed of the paper machine, currently up to 60 mph (100 km/h), is governed by the speed at which the wire moves. Water drains from the pulp slurry through the open mesh of the wire, either by gravity or under a slight vacuum leaving a wet mat or web of pulp fibers. At the end of the wire section the wet web of fibers has lost enough water so that it can be transferred from the wire into the next section of the paper machine. This is accomplished by the couch (pronounced "cooch") roll.

Documents written on more expensive rag paper were more stable. Both rag and woodpulp paper will develop tan spots called "foxing" caused by impurities or fungi reacting with humidity. The majority of modern book publishers now use acid-free paper. Modern newspapers are commonly printed on cheaper high-acid paper which turns tan and disintegrates rather rapidly, especially in the presence of strong light and humidity. Wood-free paper is most often made from cellulose fibre extracted from wood in a chemical pulping process that removes the lignin. This results in a more stable paper, similar to rag paper.

Archival paper is lignin-free and acid-free (between pH 6.0 upwards is considered acid-free, between pH 7.1 and 8.0 is called alkaline buffered). This delays the gradual deterioration of the sheet). i

Paper sizes

In the beginning of Western papermaking, paper size was fairly standard. A page of paper is referred to as a "leaf". When a leaf was printed on without being folded, the size was referred to as "folio" (meaning leaf). It was roughly equal to the size of a (small!) newspaper sheet. ("Folio" can also refer to other sizes - see paper sizes.)

When it was folded once, it produced two leaves (or four pages), and the size of these leaves was referred to as "quarto" (4to) (about 230 x 280 mm - see paper sizes).

If the original sheet was folded in half again, the result was eight pages, referred to as "octavo" (8vo), which is roughly the size of an average modern novel.

An "octavo" folding produces four leaves; the first two and the second two will be joined at the top by the first fold. The top edge is usually "trimmed" to make it possible to look freely at each side of the leaf. However, many books are found that have not been trimmed on the top, and these pages are referred to as "unopened". Many people reading "unopened" books will use their finger, a pencil, or some other inadequate instrument to rip open the top of the pages, leaving an irregular tear. A letter opener or a knife carefully used is a more appropriate tool.

An octavo book produces a printing puzzle. The paper is obviosly printed before being folded. To provide for the proper alignment of the pages, pages 8 and 1 are printed right-side-up on the bottom of the sheet, and pages 4 and 5 are printed upside-down on the top of the same side of the paper. On the opposite side, pages 2 and 7 are printed right-side-up on the bottom of the sheet, and pages 6 and 3 are printed upside-down on the top of the sheet. When the paper is folded twice and the folds trimmed, the pages fall into proper order.

Smaller books are produced by folding the leaves again to produce 16 pages, known as a "sixteen-mo" (16mo) (originally sextodecimo). Other folding arrangements produce yet smaller books such as the thirty-two-mo (32mo) (duo et tricensimo).

When a standard-sized octavo book is produced by twice folding a large leaf, two leaves joined at the top will be contained in the resulting fold (which ends up in the gulley between the pages). This group of eight numberable pages is called a "signature" or a "gathering". Traditionally, printed signatures were stacked on top of each other in a "sewing frame" and each signature was sewn through the inner fold to the signature on top of it. The sewing ran around leather bands or fabric tapes along the backs of the signatures to stabilize the growing pile of signatures.

The leather bands originally used in the West to stabilize the backs of sewn books appear as a number of ridges under the leather on the spine of leather books.

The ends of the leather strips or fabric bands were sewn or glued onto the cover boards and reinforced the hinging of the book in its covers.

Vatmen paper

Vatmen Paper was a type of paper made in The Netherlands that was 17 inches (~43 cm) wide and 44 inches (~112 cm)long. 44 inches was (reputedly) chosen because that is how far the papermaker could stretch his arm. The reason for 17 inches is unknown. A single vatman can generally handle a mold and deckle which produce up to a 25" wide sheet.

See also

References

Notes

Sources

  • Needham, Joseph (1986). Science and Civilization in China: Volume 5, Part 1. Taipei: Caves Books, Ltd.

Further reading

  • Cropper, Mark (2004). The Leaves We Write On. London: Ellergreen Press
  • Westerlund, Leslie C "Science and Practice of Handmade Paper" ISBN 1876141-131: 2004; WES
  • Westerlund Leslie C. "How to Make a Papermaking Hydropulper" ISBN 1876141-441: 2007; WES
  • Westerlund Leslie C. "How to Make a Papermaking Press" ISBN 1876141-44X: 2007; WES
  • Westerlund Leslie C. "Dictionary of Papermaking" ISBN 1876141-247: 2005; WES
  • Westerlund Leslie. C."How to Make a Papermaking Mould and Deckle" ISBN 1876141-468; 2007; WES
  • Westerlund Leslie. C. "How to Make a Papermaking Couching L'Transfer Curve" ISBN 1876141-492;2007;WES
  • Westerlund Leslie. C. " How to Make Smooth Papermaking Technology" ISBN 1876141-557;Westerlund Eco Services; Rockingham; W.Australia. 2008.

Westerlund L.C., Ho G., Anda M., Wood D., Koshy K.C., (2008) Case Study of Technology Transfer to a Fiji Rural Village using an Improved ‘Sustainable Turnkey Approach’. Technologies and Strategic Management of Sustainable Biosystems; First International Conference. Murdoch University. W.Australia.6-9 July 2008.

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