How’d They Do That? Recycling Paper
The first step involves sorting the paper to be recycled. Recycled paper should be kept free of contaminates such as food, plastic, metal, and other trash as these can make paper difficult to recycle. Contaminated paper which cannot be recycled is composted, burned for energy, or sent to a landfill.
Paper mill workers store the recovered paper in warehouses where it is kept until needed. Different paper grades such as newspapers and corrugated boxes are kept separately, as different grades are used to make different types of recycled paper products.
Re-pulping and Screening
The paper is moved by conveyor to a large vat called a pulper , which chops the recovered paper into small pieces and mixes it with water and chemicals. Heating the mixture breaks the paper into tiny strands of cellulose fibers, and the paper becomes a pulp.
The pulp is then forced through screens containing holes of various shapes and sizes to remove small contaminants such as plastic and globs of glue in a process called screening. Mills also clean the pulp by spinning it in cone shaped cylinders to remove other contaminants.
Sometimes pulp also undergoes a process called deinking to remove ink, and sticky materials such as glue and adhesives. Small particles are rinsed from the pulp with water, and larger particles and sticky materials are removed with air bubbles in a process called flotation.
Refining, Bleaching, and Color Stripping
During the refining process, the pulp is beaten to make the fibers swell, making it ideal for paper making. Then, if white paper is being made, the pulp may need to be bleached with hydrogen peroxide, chlorine dioxide, or oxygen to make it whiter and brighter. If brown recycled paper is being made, such as that for brown paper bags, the pulp does not need to be bleached.
The clean pulp is now ready to be made into paper! The recycled fibers can be used alone or blended with new wood fibers.
The pulp is mixed with water and chemicals and the watery mixture is sprayed onto a huge flat wire screen. On the screen the water drains from the pulp and the recycled fibers bond together. The sheet moves rapidly through a series of felt-covered press rollers to squeeze out more water.
The sheet, which now resembles paper, passes through a series of heated metal rollers which dry the paper. If coated paper is being made, a coating texture can be applied near the end of this process.
Finally the finished paper is wound into a giant roll which can be as wide as 30 feet and weigh as much as 20 tons! The roll of paper is cut into smaller rolls or sheets, before being shipped to a converting plant where it will be printed or made into products such as paper, envelopes, boxes, etc. [via TAPPI Technical Association for the Worldwide Pulp, Paper, and Converting Industry]
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