Making paper
- Mechanical Pulper
When making paper from wood, the logs are trimmed and their bark removed. The wood is then ground by rotating grindstones in the presece of water to form wood pulp. Fiber quantity can be controlled by varying the water supply. For example, if the water supply is reduced so that more heat is generated, longer fibers are obtained. Mechanical pulping is typically used to produce pulp for newsprint.
- Chemical Pulper
In a chemical pulper logs of wood are sliced and chipped. Chips of the appropriate size are pressure cooked in the presence if either an acid or a base. The size of the chips, the strength of the acid or base and pressure applied, determines the fineness of the pulp.
- Pulp preparation
The pulp is washed to remove impurities, by rotating rapidly in cleaner so that rubbish collects at the bottom. Pure pulp comes out through an outlet at the top. Bleaching agents are added to make the paper extra white. Now the pulp can be pored out into flat sieves and dried. This crude paper can be shipped to different mills.
- At the paper mill
Pulp arrives to a paper mill in the form of sheets. These are disintegrated in water. Loading materials, usually china clay or chalk, are added to the paper to make it less transparent. Sizing agents, like resin, make the paper resident to soaking, so that one can write on it with water-based ink. Dyes and pigments are added to lend colors. The mixer thoroughly mixes everything. A beating machine now takes over. The beating affects the fibers of the pulp. This stage determines the sort of paper that will be produced. The end produce is called stock. The stock comes onto a continuous belt made of wire. Sideways shaking of the belt improves the way the fibers bond. Water is drained out from below the wire mesh. A huge roll rides on the upper surface of this web. By improving s design on this roll, a watermark can be impressed on the web. The web is further squeezed of its water as it goes through a pair of rollers. It then passes over steam-heated iron cylinders where most of the water is removed. If the cylinders are polished, the end product gets a glazed finish. Finally the paper is wound onto reels.
Pulp facts
A sieve was then dipped into the pulp and removed horizontally with a layer of pulp on it. Excess water drained away through the mesh of the sieve. The layer of pulp was then pressed and dried to obtain paper. In principle, the same process is used today . The word paper comes from the Egyptian papyrus a water reed. It was used as writing material more than 5000 years ago by the Egyptians. Papyrus is different from paper: it is made of players of reed placed across each other (like a mat), pressed and then rags or plants are completely realigned (like mattress) Paper-making spread to the west when Chinese paper makers were captured by the Arabs in the 18th century. It reached Europe in the twelfth century when Jean Montgolfier escaped from the Saracens (in Syria) and returned to France to set up paper mill.
He learned this art while working as a slave in a paper mill. While the basic process, making pulp and drying of that pulp to make paper remains the same, paper-making had seen technological advances. So much so that these new advances were exported back to china from the west- the technology has truly made a complete circuit of the globe! Paper- making, which started as a small scale industry confined to homes, is now almost completely mechanized. The most common type of paper-making machine is the Fourdrinier, named after two brothers who built the machine in 1803. Paper became so popular for writing that there was soon a shortage of rags! Newspapers had already started way back around the year 1600, but now they became widespread.
K. V. Subrahamanyam Max Planck Institute, Saarbrucken
You must be logged in to post a comment.