History of paper production

Paper is a product of human civilization with a long history of thousands of years. Since ancient times, Egyptians have been able to make paper from the fibers of the papyrus growing on the banks of the Nil River.

At first the paper production method was quite simple: people wet the ingredients from plant fibers (such as wood, bamboo .) into a paste and spread them thinly and dried. Thanks to this process, plant fibers bind together to form a sheet of paper. Centuries passed, until the middle of the 8th century this invention of the Chinese was spread to Muslim countries in Central Asia. After that, the paper production process was introduced to Europe. By the 14th century paper manufacturers had appeared in Spain, Italy, France and Germany. At that time, paper is produced by manual method, raw materials are broken cotton and linen.

In the early 19th century, paper production was more and more mechanized, increasing labor productivity and increasing demand for rags. In fact, the demand for paper and paper-making materials has also been steadily increasing since the invention of the printer in the mid-15th century. Fortunately, at the time of paper making machines appeared, wood was studied for as raw material for paper production instead of rags. In 1840 in Germany, a method of crushing wood into pulp was developed by mechanical grinding equipment. In 1866, American chemist Benjamin Tighman introduced a process of making pulp by chemical methods, using Na2SO3 to cook wood chips into pulp. In 1880 German chemist Carl F.Dahl invented the method of cooking pulp with Na2SO3 and NaOH. Since then, wood has become the main material for paper production.

The main component of paper is cellulose, a straight and long chain polymer that is found in wood, cotton and other plants. In wood, cellulose is surrounded by a lignin network that is also polymer. To separate cellulose from the polymer network, one has to chop wood into crumbs and wet them into a dough. The pulp is poured through the sieve with metal mesh, the water will flow and the cellulose fibers join together into a rough sheet of paper. This rough sheet of paper is put through many rollers for drying, flat pressing and finishing handling to suit the requirements of use. For example, writing paper is impregnated with water repellent to prevent ink from becoming smudged when we write.

The process of producing pulp by mechanical grinding is a highly efficient process of recovering cellulose but consuming a lot of energy and does not remove all lignin, making the quality of paper not high. So this process is mainly used to produce newsprint, tissue paper, wrapping paper or other low quality paper. In today's paper production, Kraft processes are most commonly used. Although cellulose recovery efficiency in chemical process is not as high as that of mechanical grinding process, this chemical process allows removal of lignin quite thoroughly, so paper products have relatively high durability.

Lignin residues in pulp make brown paper, so to produce high quality yellow white paper, all lignin must be removed. It is common to oxidize lignin by chlorine or ClO2, but these methods cause high levels of environmental pollution. So chemists have been actively studying environmental-friendly processes to apply paper bleaching, including processes that use ozone. In the late 1980s, in Finland, paper bleaching processes were used with enzyme catalysts.

Some inorganic catalysts are also being used to bleach paper. Scientists in Atlanta (USA) are studying paper bleaching catalysts SiV2W10O40 - a type of polyoxometalate capable of oxidizing lignin to CO2 and water and preparing to bring this process to apply on a large scale.

In the early 1990s, American scientists developed the process of eliminating ink on paper in order to recycle old newspapers and magazines. This process is based on catalyzed cellulose enzymes and low energy consumption, which is now being used by many companies in the US and other countries.

On the other hand, scientists are also studying biological processes to apply to pulp production, with the aim of reducing energy consumption and increasing paper durability. About 10 years ago, a white-red fungus was discovered that had lignin digestibility. This is a very remarkable method and is considered to be highly feasible on a large scale, so some paper manufacturing companies are studying to complete the application.

Today, hundreds of millions of tons of paper are produced worldwide every year. The amount of wood consumed for paper production is very large, so people need to take measures to plant and manage forests so that they can supply enough materials for paper production (and other wood products) but still preserve forest ecosystems.

Rags are still used to produce very high quality durable paper. For example, US dollar notes are produced with cotton blends recovered from rags and waste in the production of cotton yarns as well as waste yarns. The long cellulose fibers in cotton and flax make this note very durable, even the neglected dollar notes in the pants pocket after washing in the washing machine are not torn.

MEANING (C & EN 8/2000)