Wood is a renewable resource that consists mainly of cellulous and lignin—a resinous material that binds the cellulose fibers together. So how do we get from wood chips to paper? Here’s a simplified overview of the paper-making process.
A mixture of wood chips and cooking liquor is heated in a large pressure vessel called a digester. As the chips are expelled from the digester, the mechanical force breaks up the wood chips into individual fibers, producing wood pulp.
Oxygen delignification of pulp removes 40-50% of the lignin left after cooking. Pulp washing and bleaching removes more of the raw brown pulp color.
Before the refined pulp enters the paper machine, water is added to it to form a slurry of less than 1% fibers and more than 99% water. The slurry flows evenly onto moving wire forming a uniform sheet. As the wet sheet travels on the wire, water drains through the fine wire mesh.
The wet sheet is picked up on a moving belt made of felt. The felt carries the sheet through the press section, which squeezes out more water and compacts the fibers.
As the sheet leaves the press, it is transferred onto dryer felts that carry the paper up and over a series of heated rollers. At the end of the dryer, 95% of the water is removed, leaving a small percentage of moisture to prevent cracking.
The paper is wound onto large reels. When a reel is full, it is cut into smaller rolls for shipment to customers or conversion into sheets or packaging.
Want to know more about the beginning of the process? See what one landowner and wood chip mill representative have to say about responsible forestry management.