Cardboard is a widely used packaging material that comes in two main forms: corrugated cardboard (fluted layer between two flat sheets) and paperboard (thinner, used for items like cereal boxes). Recycling allows the cellulose fibers to be reused, conserving virgin timber resources and extending the material’s useful lifespan. This process offers a sustainable alternative to landfill disposal and begins with consumer preparation.
Preparing Cardboard for Collection
Cardboard boxes must first be flattened to reduce their volume, which makes transport and initial sorting more efficient. Consumers must remove any non-paper materials, such as packing tape, plastic liners, or metal staples, as they act as contaminants later in the process. Food-soiled cardboard, such as greasy pizza boxes, is often rejected from recycling programs. Grease and oil soak into the paper fibers, making it extremely difficult to separate these contaminants during the pulping stage. This contamination can reduce the quality of the resulting pulp batch, potentially ruining an entire load of otherwise perfectly recyclable material. Therefore, only clean, dry cardboard should be included in collection containers.
Transformation: From Bale to Pulp
When the prepared cardboard arrives at a Material Recovery Facility (MRF), it undergoes initial mechanical sorting, where Old Corrugated Containers (OCC) are separated from mixed paper and other recyclables. The sorted cardboard is then compressed into large, dense blocks known as bales for efficient transport to the paper mill. At the mill, the bales are broken open, and the material is shredded into smaller pieces. The shredded cardboard is then introduced into a large vat called a hydropulper, which mixes the material with hot water and sometimes chemicals. Intense agitation breaks the cardboard down into individual cellulose fibers, creating a slurry, or pulp, where the fibers are suspended in water. While the water separates the fibers, it does not remove contaminants like glue residue or wax coatings. The consistency of the pulp must be carefully monitored to ensure the fibers are adequately separated before the next stage of cleaning.
Refining and Manufacturing New Material
After the cardboard has been reduced to a fibrous slurry, the refining stage begins with a series of cleaning steps. The pulp is first passed through various screens and centrifugal cleaners, which physically filter out larger debris, such as remaining pieces of plastic, tape, or stones. Following this initial screening, the process targets smaller, lighter contaminants, particularly printing inks. De-inking is achieved using a chemical process called flotation, where air is injected into the pulp mixed with chemicals. These chemicals cause ink particles to detach from the fibers and attach to the rising air bubbles, forming a foam that is skimmed away and disposed of. Further washing removes smaller pigment particles and fine contaminants.
The cleaned and refined pulp is then ready for the manufacturing stage. This slurry is spread out onto a moving screen where excess water drains away, beginning the process of forming a cohesive sheet. The wet sheet then passes through a series of heavy press rollers that squeeze out more moisture and compress the fibers together. The partially dried sheet is transported over heated drying cylinders to remove the remaining water content, which solidifies the sheet structure. Finally, the finished recycled paper or cardboard is wound onto large master reels, ready to be converted into new packaging materials. Cellulose fibers shorten slightly each time they are processed, meaning cardboard can typically only be recycled about five to seven times before the fibers become too short to create a strong, usable new product.