Pulp Mills (Virgin)Pulp Mills make pulp, a mixture of cellulose fibers and water used as the basis of all paper products. Pulp is made in several ways, depending on the type of paper being produced. Wood chips, which come from logs or from residues from sawmills, furniture manufacturers and other sources, can be chemically or mechanically separated into individual wood fibers in a process called pulping.In chemical pulping, the most common pulping process in the United States, wood chips are “cooked??? in a digester at an elevated pressure with an appropriate solution of chemicals to dissolve the lignin (the “glue??? that binds the fibers in the wood) and allow the cellulose fiber bundles in the wood to separate into individual cellulose fibers. Since chemical processing is gentle on the cellulose fiber, chemical pulps tend to have longer fibers and make strong paper such as printing and writing papers and paperboard.In mechanical pulping, chemicals are not used to remove the lignin in the wood chips. Instead,wood chips are pressed against a grinder that physically separates the fibers. Mechanical pulps have shorter fiber lengths and produce papers which do not require as much strength, such as newsprint. After the fibers have been separated, the mill washes and decontaminates the pulp. To produce a white paper product, the mill must bleach the pulp to remove color associated with remaining residual lignin. Typically, the bleaching chemicals (such as chlorine dioxide, oxygen, or hydrogen peroxide) are injected into the pulp and the resulting mixture is washed with water.The bleached or unbleached wood pulp, which at this point is very dilute slurry, is pumped out of a headbox onto a wire screen felt that allows water to drain out of the pulp and help the fibers interlock into a sheet. By varying the amount of pulp pumped onto the wire, the speed of the wire different qualities and properties of paper can be achieved. The continuous sheet then pass through a long series of rollers that press out any remaining moisture, followed by steam-heated drums that dry the paper. Finally, a process called calendaring polishes the sheets and smoothes out wrinkles. The continuous sheet of paper is wound onto jumbo rolls and then cut to a variety of paper widths.Recycled Paper Processing MillsRecycled paper processing mills use paper as their feedstock. The recovered paper is combined with water in a large vessel called a pulper that acts like a blender to separate fibers in the paper sheets from each other. The resultant slurry then passes through screens and other separation processes to remove contaminants such as ink, clays, dirt, plastic and metals. The amount of contaminants that are acceptable in the pulp depend upon the type of paper being produced. Mechanical separation equipment includes coarse and fine screens, centrifugal cleaners, and dispersion or kneading units that break apart ink particles. De-inking processes use special systems aided by soaps or surfactants to wash or float ink and other particles away from the fiber.Recovered fiber can be used to produce new paper products made entirely of recovered fiber (i.e. 100 percent recycled content) or from a blend of recovered and virgin fiber. Fiber cannot, however, be recycled endlessly. It is generally accepted that a fiber can be used five to seven times before it becomes too short (as a result of repulping and other handling) to be useable in new paper products. Recovered paper with long cellulose fibers (such as office paper) has the greatest flexibility for recycling as it can be used to produce new paper products that use either long or short fibers. Recovered paper with short cellulose fibers (such as newspaper) can only be recycled into other products that use short cellulose fibers. For this reason, recovered paper with long fibers is generally of higher value than recovered paper with short fiber.