In the packaging industry, paper is known as matted sheet usually composed of plant fiber. Historically, paper has been made from linen, sugar cane, cotton, and straw fibers. Modern paper is made almost exclusively from wood fibers.
Paper is made from two types of wood fibers: short and long. Short fibers come from hardwoods with broad leaves, and long fibers come from softwoods with needles. The longer the fibers used in papermaking, the better the fibers entangle and hold together. Long fibers make for a stronger paper product that is better able to withstand folds, tears, and punctures. However, paper made from long fibers is rougher than paper made from short fibers. Longer fibers can also clump together during the papermaking process and produce a product with uneven density, causing issues with printing and bonding adhesives. Fibers are collected from wood by pulping, and pulping can be done in a variety of ways. There are three different methods of pulping.
The first method is mechanical pulping. The mechanical pulp making method is a cutting or grinding process that breaks fibers into smaller pieces, resulting in weaker pulp. This process is the least expensive of the three as it does not require the use of chemicals, and it uses all parts of the wood. It is primarily used for newspaper or to blend with stronger pulps to reduce the cost or improve density formation.
The second method is chemical pulping. In chemical pulping, a dissolving process that leaves fibers undamaged and produces stronger pulp is used. However, it is more expensive to make. This method is primarily used for corrugated boxes, shopping bags, and board for food products.
The third method is semi-chemical. This pulping dissolves the wood with chemicals and then the wood is mechanically pulped resulting in intermediate cost and strength for your paper product. Wood pulp is not fine enough to produce small fibers for papermaking. The pulp must be further processed through refining. Refining involves beating the pulp between rotating metal bars or swirling between the surfaces of metal disks. A small amount of refining keeps longer fibers intact and results in stronger paper. Longer refining results in weaker but more dense paper. Grease-resistant paper is one example of long refined fibers.
Learn more about Paperboard and the best processes and practices at https://www.packagingschool.com/courses/paperboard-cartons-101