Step 1: Collection
Recycling begins with individual users (homes, businesses, universities, industrial manufacturers) that collect and store paper waste in bins. Recyclers and paper merchants collect this paper and combine it together in a large recycling container.
Step 2: Sorting and transportation
After collection, the paper is measured and graded for quality. Waste paper with similar qualities are combined since they have similar amounts of fiber which can be extracted from the pulp. The paper is then hauled to paper mill recycling facilities .
Upon arrival at the recycling facility, the quantity and quality (cleanliness and type) of the paper is measured and a purchase contract is issued to the recycler. These measurements of paper quality are also used to determine whether the type of waste paper is accepted or rejected; some recyclers accept mixed grades of recovered paper, while others only accept preferred quality of waste paper grades .
Once accepted by the recycling facility, the recovered paper is then further sorted based on its surface treatment and structure. For instance, very thin lightweight paper such as newspapers are sorted separately from thick paper materials such as paper folders. This sorting is important because different grades of paper material are produced based on the materials being recovered .
Step 3: Shredding and pulping
After sorting, the paper is then shredded to break down the material into small bits. After the material in finely shredded, a large amount of water is added along with other chemicals such as hydrogen peroxide, sodium hydroxide, and sodium silicate to break down and separate the fibers of the paper.
The resultant slurry solution, known as pulp, has an oatmeal consistency and is the raw material used to make paper. This process of transforming the recovered paper materials to pulp is known as pulping.
The pulp is then passed through a series of screens, and a centrifuge-like process to remove larger contaminants such as paper clips, staples, tape, and plastic films that were included in the recovered paper.
Step 4: Floatation tank / de-inking
After removing larger contaminants, pulp is added to a flotation tank where chemicals and air bubbles remove dyes and inks to enhance the purity and whiteness of the product.
Hydrogen peroxide, and other whitening agents may be added to further enhance the whiteness if a white color is desired as the product. This step continually bleaches the pulp until it is ready for the final processing stage.
Dyes are sometimes added to create colored products, and in some cases a small amount of blue and black dye are added to create a bright white printing paper . Brown paper pulp, such as paper pulp used to make paper towels, is not bleached.
The pulp, which is now 99 percent water and one percent fiber at this stage, may be combined with pulp made from new materials to enhance its properties, and is then pumped over onto a paper machine .
Step 5: Drying / finishing for reuse
The pulp is then passed over rollers that press out excess water, or a vibrating machine to create a product made of 50 percent water and 50 percent fiber. The pulp can be used alone or additional virgin wood fiber can be added to the pulp to give the paper extra strength or smoothness.
If coated paper is desired for smooth printing, a coating mixture may be applied to the paper near the end of the paper-making process or after the process is completed.
Next, the sheets pass through steam heated rollers, at temperatures as high as 130 degrees Fahrenheit to form long rolls of continuous sheets of flattened paper. A single roll of this paper can be as wide as 30 feet and weigh up to 27 metric tons .
At this stage, coatings such as potato starch are sometimes added to the paper to keep ink from spreading like it does when writing on tissue paper. The ends of the roll are then trimmed and recycled to make new pulp .
The resulting paper roll is then shortened into smaller sections and sent to various manufacturers that use paper to make their product, such as newspaper printing, wrapping paper, printing paper, and blown-in cellulose insulation.