write the process of paper making in 200 words
Answers
Most paper pulp is made from trees (mainly fast-growing, evergreen conifers), though it can also be made from bamboo, cotton, hemp, jute, and a wide range of other plant materials. Smooth papers used for magazines or packaging often have materials such as china clay added so they print with a more colorful, glossy finish.
1. Paper making by hand
The raw plant material is placed in a large vessel filled with water and literally beaten to a pulp to make a thick suspension of fibers called half-stuff. This is formed into sheets of paper using a very basic frame made of two parts: a metal mesh called a mold that sits inside a wooden frame known as a deckle (a bit like a picture frame). The mold and deckle are dipped into the half stuff and gently agitated so an even coating forms on top, with most of the water (and some of the pulp) draining through. The deckle is then removed from the mold and the soggy mat of paper is placed on a sheet of felt. This process is repeated to make a number of interleaved sheets of paper and felt, which are then placed inside a screw-operated press and squeezed under immense pressure to squash out virtually all the remaining water. After that, the sheets of paper are taken out and hung up to dry.
2. Paper making by machine
Although some expensive papers are still crafted by hand, most are churned out quickly, efficiently, and automatically by gigantic machines. Pulp is prepared for papermaking machines either mechanically or chemically. The mechanical method (generally used to make lower-grades of paper) is called the groundwood process, because the pulp was originally made by using huge stones to grind up logs. Nowadays, pulp is prepared by giant machines that cut, wash, chop, beat, and blend wood, rags, or other raw materials into a soggy mass of fibers. In the chemical method, known as the Kraft process (from the German word for "strength," because it produces strong paper), plant materials are boiled up in strong alkalis such as sodium sulfide or sodium hydroxide to produce fibers. At this point, loading materials (surface coatings such as clays), dyes (to make colored paper), and sizes (to strengthen and waterproof and prevent inks from spreading) can be added to the mixture to change the properties of the finished paper (sometimes they're added later).
Once the pulp has been prepared, it's turned into paper by an enormous roller machine. The best known type of paper making machine is called a Fourdrinier machine (named for the two English brothers who invented it at the start of the 19th century), though there are alternatives (including the cylinder machine developed a few years afterward by John Dickinson). Wet pulp enters the machine from a trough called a head box at one end and is spread over a moving, wire-mesh conveyor belt. The belt is shaken, sucked, and blown to remove water from the mat of fibers, before a watermark, texture, or other finish is pressed into it by a patterned roller called the dandy roll. The paper is then pressed further and fully dried, looping again and again around a series of rollers, before getting its final, very smooth pressing by large, heavy, steel rollers called calenders. The finished paper emerges as webs (very large sheets) or rolls (for printing things like newspapers and magazines). The biggest Fourdrinier machines produce paper at an astonishing rate of over 60 km/h (40 mph)!