How paper is made
Pulp contains three main components (excluding water):Cellulose fibers (desired for papermaking), lignin (a three-dimensional polymer that binds the cellulose fibers together) and hemicelluloses, (shorter branched carbohydrate polymers). The aim of pulping is to break down the bulk structure of the fiber source, into the constituent fibers. There are basically two main methods of pulping.
“Chemical” pulping removes the lignin and hemicellulose away from the cellulose fibersvia a chemical process without weakening them. This process is more expensive as the resulting yield is 40-50% of the original wood but it allows the fibers to retain their strength. This will give you a more expensive “quality” paper.
“Mechanical” pulping physically tears the cellulose fibers one from another. Much of the lignin remains adhering to the fibers resulting in a yield greater than 95% of its original wood. However the strength is impaired because the fibers are cut. This gives you a cheaper lower quality paper such as newspaper.
The paper mill refines the pulp and mixes in water with other additives to make a pulp slurry. This slurry is then filtered out onto a continuous fabric mesh conveyor belt to form a wet web of fiber.
This wet fiber then passes between large rollers loaded under high pressure to squeeze out as much water as possible.
The web of fiber then passes through a section of heated rollers which dries the pressed sheet and removes the water content to around 6%.
This web of dried paper then goes through a final process called “Calendering” which consists of heavy steel rollers that apply pressure and heat to the passing paper. This is used to make the paper surface extra smooth and glossy.