| Biotechnology involving modification of recycled fiber with enzymes offers new, environmentally friendly methods of utilizing wastepaper sources. Specifically, enzymatic deinking and enzymatic drainage improvement with cellulases and xylanases offer new ways of dealing with some of the historical problems associated with recycling wastepaper, e.g., high chemical consumption and paper machine operating problems. The mode of action of the enzymes on recycled fiber, however, is not well understood.;Thus, several studies were performed to characterize the interaction of cellulases and xylanases on high quality, recycled bleached kraft fiber and, hopefully, to help identify new biotechnical approaches for enzymatic modification of recycled fiber. Simulated recycled bleached kraft fiber was studied with respect to enzyme adsorption, hydrolysis, and enzyme activity recovery. Drying dramatically decreased the kraft fiber's capacity to adsorb cellulases compared to never-dried fiber. Xylanases showed little affinity for this type of fiber substrate. High surface area material, i.e., fines, in a papermaking system is preferentially attacked by the enzymes. It was suggested that such material protects the long fiber from the enzymes' action. Depending on the fiber type in use, cellulase and xylanase activity adsorbed on the fiber during the biotechnical procedures has the potential to be recovered, either by recycling the hydrolysate or washing with dilute alkali and a non-ionic surfactant.;An additional application for xylanase was identified; the use of cold alkali extractions in combination with xylanase treatment can purify once-dried bleached kraft hardwood fiber and wastepaper sources high in bleached hardwood kraft fiber content to carbohydrate levels and viscosities similar to chemical cellulose, or dissolving pulps. Xylanase accessibility to xylan, lost during drying in the papermaking process, can be recovered by applying an initial cold alkali extraction to the fiber. |
