Wood and Pulp
Paper could be said to grow on trees, since it's made from wood pulp. However, manufacturers don't use all types of trees to make paper. The choice of trees and the types of wood fiber dictate the finished texture and strength of the paper. Trees used for paper-making include hardwood, softwood and a blend of these trees. Hardwood trees with short fibers yield weak, but finely textured paper. Fibers from softwood trees make paper that's tough and durable, but ill-suited for writing. According to Tappi's Paper University website, combining hardwood and softwood trees enables paper manufacturers to find a compromise between durability and a fine writing surface on their product.
To begin the pulp-making process, the trees have their bark stripped by rolling in a drum. Mechanical pulping uses large wood grinders to crush the de-barked trees between two rotating plates, a process described by the How Products Are Made website. Some paper makers opt to produce pulp using a chemical process. The wood goes into a chipper after its bark comes off. The resulting wood chips pour into vats known as digestives along with sodium hydroxide and sodium sulfide. The mixture boils under high pressure to break down the wood chips.
As part of both pulp-making processes, the pulp passes through large sieves to filter out foreign matter. Adding bleach or coloring to the pulp creates white or colored paper, according to How Products Are Made.
Wood pulp contains roughly 99 percent water. Ridding the paper of water is known as the "wet end" of paper manufacturing. Nozzles spray the wood pulp onto very fine screens, which allow the water to flow through but not the wood fibers. The fibers collect together on top of the screen to form a wet paper. To remove even more water from the paper, rollers covered in felt move over the top and bottom of the paper. According to Paper University, the end result still contains 60 percent water as it moves on to the "dry end" of the process.
In the dry end of paper manufacturing, steam fills large metal rollers to heat them. The wet paper gets pressed between these cylinders. The cylinders act as large, round irons to dry and heat the paper, sealing the bonds between the wood fibers, reports Paper University.
Before completion, the paper moves between rollers of a calendar. This machine ensures uniform paper thickness. Optional coatings, color or cutting could be added to the paper before completion. How Products Are Made states that the finished paper then feeds onto large rolls for storage.