Manufacturing of Cellulose Fibers
One of the most useful natural materials put to use by humans, cellulose fibers are the basis for pulp, which has countless uses in contemporary society. Different grades are used for different applications; Weyerhaeuser is a premium supplier of bleached kraft pulp in three general categories:
- Northern softwood kraft fibers
- Southern softwood kraft fibers
- Specialty chemical cellulose fibers
From Chipping to Shipping
Weyerhaeuser has invested in technological advancements to refine and improve our process. We're constantly monitoring our systems to deliver even more uniformity, purity, and functionality in our products. The result? Exceptional pulp that benefits people needing paper, construction materials, money, hospital supplies, and so much more.
Cellulose fiber comes from trees that are uniquely suited to produce a quality, uniform pulp product. We carefully tend the vast forests that closely surround our mills to ensure their health and renewal.
Raw materials enter the mill as logs. The logs are run through a debarker to remove all of the bark, which is collected and burned as fuel. The debarked logs are then chipped into uniform pieces to facilitate the cooking process. The chips are screened to remove any large or small pieces and then sent to the pulping area.
Pulping is the process of cooking wood chips at a certain temperature and pressure with specialized chemicals. The objective of this process is to remove the natural glue (lignin) from the chip to reveal the individual fibers. This process takes place under highly monitored conditions to ensure our products are uncontaminated.
Cooking transforms the chips into pulp, a watery slurry of limp fibers that resembles a large batch of oatmeal. This process is carefully designed to maximize the strength and viscosity of the pulp. After cooking, the pulp is washed to remove chemicals and any remaining lignin and then sent to the bleach plant. To minimize environmental impacts and increase the efficiency of our operations, 98 percent of the cooking chemicals are diverted to a recovery cycle, where they are reconstituted to be used again.
Today's products would not be as usable as they are without the bleaching process, which turns muddy brown fiber into white fibers with 90 to 95 percent brightness. Weyerhaeuser uses a multi-stage process free of elemental chlorine that is carefully monitored for time, temperature, acidity, alkalinity, and chemical concentration.
After being transported by pipes and pumps, the pulp is exposed to a bleaching agent, then neutralized, then bleached again. This process occurs over and over to achieve the desired whiteness without degrading the fibers. Once ready, the bleached pulp is pumped to a headbox to continue its journey into a pulp sheet.
Creating the Sheet
Glance into the headbox and you'll see 99 percent water with a small amount of pulp. At this point in the process, the water is drawn out so that the pulp can be formed into a sheet. The headbox sprays the mixture onto a moving screen, which begins to draw the moisture out of the slurry. At the end of this conveyer screen (called a wire), the wet, flimsy sheet goes through a series of rollers to extract still more water. Then it proceeds to drying (either on heated rolls or in an innovative system that involves floating through heated air) and a jumbo roll of formed sheet comes out the other end.
Each of our customers has unique requirements for size, wrapping, and marking. For producers of absorbent products, the jumbo rolls are moved to a rewinder, where smaller, customer-specific rolls are created. For paper producers, a layboy creates stacks (bales) of uniform rectangular sheets.
On Its Way to You
Once the roll or bale has been cut, wrapped, and marked according to the customer's specifications, the product is stored for future shipment or shipped directly to the customer.