How Is Paper Made From Trees?

Raw Materials

Tree wood consists of cellulose fibers that are bonded together by lignin, a natural adhesive; these fibers are separated and reorganized to make paper. Hardwoods, such as oak and maple, have short fibers, producing paper that is weak but very smooth. Softwoods, such as pine and spruce, have long fibers, producing paper that is strong but rough. Most paper is a combination of both types, which allows for various levels of strength and texture.

Wood for paper comes from three sources: tree farms, lumber scrap and recycled paper. Tree farms produce pulpwood logs specifically for paper production, typically from smaller trees that are continuously replanted. Lumber yards cut large logs into various size lumber, which produces a lot of unusable scraps called waste. The pulpwood logs and waste are cleaned and processed into wood chips by an industrial chipper. The size of these wood chips is typically the size of cornflakes.

The purpose of the pulping stage is to separate the cellulose fibers. Wood chips are fed into "pulp digesters," which use steam and chemicals to turn the chips into a gooey mixture of fibers and other wood components. The chemicals, resins and lignin are then removed, and the fibers are uncoiled, flattened and refined through machines called beaters and refiners. At the end of this stage, the pulp appears like a mushy soup, consisting of 99 percent water.

A unit called the head box sprays the liquid pulp onto a long wide screen called the wire, which can range up to 20 feet wide and moves at speeds of up to 60 miles per hour. The water that drains off the wire is reused in the pulping stage. The wire then travels through large felt rollers that press and absorb water from the pulp, causing the fibers to begin bonding, forming a thin mat on the surface of the wire. At the end of the wet stage, the water content of the pulp is around 60 percent.

Following the presses, the wire is fed through a series of large metal cylinders, or rollers, which are heated internally by steam. The rollers slowly dry out the pulp, sealing the fibers closer and closer together. By the time the pulp mat has emerged from the last dryer, it has become paper. This paper is rolled onto enormous spools cut into appropriate sizes and converted into paper products during separate manufacturing processes.