Paper is a product of human civilization with a history spanning thousands of years. Since ancient times, the Egyptians have known how to make paper from the fibers of the papyrus plant that grows along the banks of the Nile River.
Initially, the method of producing paper was quite simple: raw materials from plant fibers (such as wood, bamboo, and rattan) were soaked and ground into a pulp, then spread into thin layers and dried. Through this process, the plant fibers would bond together to form sheets of paper. Many centuries passed until the 8th century when this invention by the Chinese was introduced to Islamic countries in Central Asia. Subsequently, the paper production process was brought to Europe. By the 14th century, paper mills had appeared in Spain, Italy, France, and Germany. At that time, paper was produced by hand using cotton and linen rags as raw materials.
In the early 19th century, paper production became increasingly mechanized, leading to higher labor productivity and a growing demand for raw textile materials. In fact, the demand for paper and its raw materials had continuously increased since the invention of the printing press in the mid-15th century. Fortunately, when paper-making machines emerged, researchers had already been exploring the use of wood as a raw material for producing paper instead of rags. In 1840, Germany developed a method for grinding wood into pulp using mechanical milling equipment. In 1866, American chemist Benjamin Tighman introduced a chemical process for producing pulp using sodium sulfite (Na2SO3) to cook wood chips into pulp. In 1880, German chemist Carl F. Dahl invented a method for cooking pulp with sodium sulfite and sodium hydroxide (NaOH). From that point on, wood became the primary raw material for paper production.
The main component of paper is cellulose, a type of long, linear polymer found in wood, cotton, and other plants. In wood, cellulose is surrounded by a lignin network, which is also a polymer. To separate cellulose from this polymer network, wood must be chopped into small pieces and then ground into a slurry. The pulp is poured through a metal mesh screen, allowing water to flow away while the cellulose fibers bond together to form a rough sheet of paper. This rough sheet is then passed through multiple rollers to dry, flatten, and finish it to meet usage requirements. For example, writing paper is treated with water-repellent chemicals to prevent ink from smudging when writing.
The mechanical pulping process is effective at recovering high cellulose yields but consumes a lot of energy and does not completely remove lignin, resulting in lower paper quality. Therefore, this process is mainly used to produce newsprint, tissues, wrapping paper, or other lower-quality papers. In modern paper production, the Kraft process is widely applied. Although the cellulose recovery efficiency in the chemical process is not as high as in mechanical pulping, this chemical process allows for the almost complete removal of lignin, resulting in relatively durable paper products.
Residual lignin in the pulp causes paper to have a brown color; thus, to produce high-quality white paper, it is necessary to eliminate all lignin. Typically, lignin is oxidized using chlorine or chlorine dioxide (ClO2), but these methods can cause significant environmental pollution. As a result, chemists have been actively researching environmentally friendly processes for bleaching paper, including processes that use ozone. In the late 1980s, Finland adopted paper bleaching processes using enzyme catalysts.
Some inorganic catalysts are also being used for paper bleaching. Scientists in Atlanta, USA, are researching a paper bleaching catalyst called SiV2W10O40—a type of polyoxometalate capable of oxidizing lignin into carbon dioxide (CO2) and water, and they are preparing to scale this process for large-scale application.
In the early 1990s, American scientists developed a method for removing ink from paper aimed at recycling old newspapers and magazines. This process is based on the enzymatic catalysis of cellulose and consumes little energy; it has now been adopted by many companies in the USA and other countries.
On the other hand, scientists are also researching biological processes for pulp production aimed at reducing energy consumption and increasing paper strength. About ten years ago, a type of white-red fungus that can digest lignin was discovered. This method is considered very promising and feasible for large-scale application, so several paper companies are researching to refine it for practical use.
Today, hundreds of millions of tons of paper are produced worldwide each year. The amount of wood consumed for paper production is enormous, so measures must be taken to plant and manage forests to provide sufficient raw materials for paper production (and other wood products) while preserving forest ecosystems.
Rags are still used to produce high-quality durable paper. For instance, U.S. dollar bills are made from a mixture of reclaimed cotton from rags, waste from cotton production, and flax fiber waste. The long cellulose fibers in cotton and flax make these dollar bills very durable; even dollar bills left in pockets and washed in the washing machine remain intact.
THẾ NGHĨA (According to C & EN 8/2000)
