How Is Paper Made from Trees?
Most paper is produced from wood fibers. To make paper, such as the type used in newspaper, wood from trees is cut into chips. Wood can be turned to pulp in a couple of different ways. Mechanical pulping involves using machines to grind wood chips into pulp. The more commonly used method is chemical pulping, also known as “kraft.”
Chemicals are used to separate lignin from the cellulose fibers, leaving a pulp mixture that can make stronger papers. The wood chips are cooked in a chemical solution to form a watery mixture called pulp slurry. A watery “soup” of cellulose wood fibers, lignin, water and the chemicals used during the pulping process.
Once the pulp is ready, it is then used to make paper in a process that is quite similar (in the basics) to the process first used by the ancient Chinese more than 1,900 years ago. Because the pulp mixture is so watery (sometimes as much as 99 percent water!), the cellulose fibers need to be separated from the watery mixture.
The pulp is washed and bleached, and then sprayed onto a moving screen in the paper-making machine. Most of the water in the pulp drains through the screen, leaving an even mat of fibers. This mat passes through a series of rollers that remove the rest of the water, and press the fibers tightly together. The result is paper!
When the paper has the desired thickness, it may be colored or coated with special chemicals to give it a special texture, extra strength or water resistance. As a last step, the paper rolls are cut to size and packaged for shipping to other facilities for additional processing to turn it into all sorts of specialized papers.