Fiber Fractionation of recycled office waste for production of value-added products

A new technology has been developed to fractionate a given fiber stream into two streams of value greater than the feed stream. This effect is achieved with the sequential use of centrifugal screens and hydrocyclones. For recycled ledger pulps, one stream is produced with improved properties for tissue making, an improved relationship between softness and strength, and a decreased need for deinking. Another stream is produced with improved strength potential and higher freeness relative to the feed stream. This study investigated the effect of operating variables (reject nozzle tip diameter, feed pressure, and pressure drop) on the fractionating characteristics of the hydrocyclone. Fiber length and coarseness values tended to be slightly higher in the reject stream compared to the accept stream. The relative fiber length increase was generally higher at a higher ratio of pressure drop to feed pressure. In general, coarseness values in both the accept and reject streams increased as the fiber length increased. With respect to normalized coarseness values, optimum fractionation was generally obtained at a ratio of pressure drop to feed pressure of 0.5, which corresponded to a reject ratio of about 0.5.