Definitions

pulp-wood

Wood-pulp paper

Wood-pulp paper is paper made from wood pulp, which is produced from trees by a variety of mechanical and chemical processes. Paper made from wood pulp ranges from toilet paper (obviously a single-use product) to newsprint (meant to be used once then recycled), to high quality paper for books and legal documents (100-1000 years). Pulpwood accounts for about 90% of all pulp, with the balance coming from fiber crops like bamboo, kenaf and hemp. Paper production uses about 43% of all harvested wood, and represents 0.6% of the world's total economic output .

History

Development

Using wood to make paper is a fairly recent innovation. In the early 1800s, cotton rag and fiber crops such as linen were the primary source for fibers to make paper. An increased demand for books and writing material meant that the supply of discarded linen rags for making paper could not keep up with the increased demand for paper. Manufacturers had to find an alternate resource or raw material, for paper production, and shifted from linen to wood pulp. Paper was relatively expensive, at least in book-sized quantities until the advent of steam-driven paper making machines in the 19th century. Although older machines predated it, the Fourdrinier paper making machine, first built in London in 1804 became the basis for most modern papermaking. The use of wood to make pulp for paper began with the development of mechanical pulping in Germany by F.G. Keller in the 1840s. Chemical processes quickly followed and by 1900 sulfite pulping had become the dominant means of producing wood pulp, surpassing mechanical pulping methods. Since the 1940s pulp make by the kraft process is the most common type of wood pulp.

Significance

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. This increase in paper resources can be credited with the birth of ephemera, and consequently the birth of modern paper preservation.

Paper stability

Much of the early paper made from wood pulp contained significant amounts of alum, a variety of aluminium sulfate salts that are significantly acidic. Alum was added to paper to assist in sizing the paper, making it somewhat water resistant so that inks did not "run" or spread uncontrollably. The early papermakers did not realize that the alum they added liberally to cure almost every problem encountered in making their product would eventually be detrimental. The cellulose fibers which make up paper are hydrolyzed by acid, and the presence of alum would eventually degrade the fibers until the paper disintegrated in a process which has come to be known as "slow fire". Documents written on rag paper were 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, 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.

It is important to note that just because a paper is made of wood-pulp, does not necessarily mean it is any less durable than a rag paper. The factor that determines the ageing behavior of a paper is how it was manufactured, not the original source of the fibers. 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.

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), which is about twice as much as chemical pulping. Consequently, paper made with mechanical pulps is often cheaper than that made with bleached chemical pulps. Mass-market paperback books and newspapers use these mechanical papers. Book publishers tend to use acid-free paper, made from fully bleached chemical pulps for hardback and trade paperback books.

Recycling

Paper is one of the main targets for recycling. A concern about recyclig wood-pulp paper is that the fibers are degraded with each and after being recycled 4-6 times the fibers become too short and weak to be useful in making paper.

See also

References

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