Mechanical Pulping Process
Mechanical pulp yields over 90% of the wood as fiber is produced by forcing
debarked logs, about two meters long, and hot water between enormous rotating
steel discs with teeth that literally tear the wood apart. Alternatively, logs
can be pressed against grindstones which is why this process is also known as
ground wood pulp.
Trees contain up to 30% lignin, a material which is sensitive to light and
degrades, and turns brown in sunlight, which explains why papers made from
mechanical pulp will discolor. An example of this is newsprint. Newsprint is
designed to have a short life span, and if left for a long period of time will
lose its whiteness and strength. The special advantages of mechanical pulp are
that it makes the paper opaque and bulky.