From fiber to pulp to paper

The amount of fiber in a cubic foot of wood varies greatly from species to species. Hardwoods (broad-leafed species) tend to have greater wood densities than softwoods (conifers), meaning they have more fiber per cubic foot of wood.

When trees are harvested for papermaking, the limbs are removed and the trunk is transported to a pulp mill. At the mill, the bark is removed and burned for fuel or processed to use as garden mulch. The wood is often chipped into small pieces about the size of a quarter, and then broken down further into individual fibers in a process call pulping. The pulping method influences the amount of fiber the wood yields.

Sometimes pulping is done mechanically by pressing and grinding the wood to separate the fibers. This mechanical pulping process is very efficient. Up to 95% of the dry weight of the wood is converted into pulp. Most newsprint is made from mechanical pulp, recycled fiber, or a combination of the two. Paper made from mechanical pulp is opaque and has good printing properties, but it is weak and discolors easily when exposed to light due to the residual lignin in the pulp. (Lignin is a natural wood chemical that holds fibers together.)

A second pulping method is chemical pulping, in which a chemical/water solution dissolves the lignin to help separate the fibers. The absence of lignin means that paper made from chemical pulp is stronger and less prone to discoloration. The pulp yield from chemical pulping is much lower, though, since the lignin has been removed. Chemical pulps are used to make shipping containers, paper bags, printing and writing papers, and other products requiring strength.

The type of paper being produced determines what pulping method is used. Remember the paper you used when learning to write in kindergarten - the paper with the very wide rule lines? This paper was grayish in color, and you could actually see bits of wood in the paper. Kindergarten writing paper and newsprint do not require high strength, brightness or purity, so mechanical pulps are probably the best choice for making these types of papers.

Papermakers combine mechanical, chemical, and recycled pulp in varying amounts to produce the highest quality paper required by the customer from the least possible amount of fiber.

Some people say that it takes "17 trees to make a ton of paper." This might make you believe that if a ton less paper were used every year, then at the end of the year, 17 more trees would remain standing.

This is really an oversimplified conclusion. Many of the trees used for papermaking would be harvested or die anyway, even if not one piece of paper were produced. Many are already dying, and must be removed to improve the health of the forest. It makes good sense for papermakers to use these trees for wood pulp.