The basic raw material for the papermaking process is wood. To begin the process, pulpwood logs must be reduced to chip form. Within the drum, logs collide with one another and rub together removing the bark. The bark falls through slots in the cylinder walls and is collected and burned as fuel in the power boilers. Softwood and hardwood chips are kept separate until the pulp is blended at the paper machine since each has its own physical properties.
Wood is made up of small cellulose fibers, bound together by a glue-like substance called lignin.
In the pulping process, these fibers are separated by cooking the wood with chemicals to dissolve the lignin. To accomplish this, the chips are loaded into large vessels called digesters on either a batch or continuous basis. Digesters are designed on the same principle as a kitchen pressure cooker. The chips and chemicals are steamed under pressure for 1.5 to 4 hours until the mixture is reduced to a wet, oatmeal-like mass. The cooking frees the fibers so they can be suspended in water.