Effects of Enzyme Treatment on Surface Properties of Mg(OH)2-based Peroxide Bleached Deinked Pulp

Enzyme (laccase/mediator or lipase) treatment, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) surface analysis techniques were combined to explore the surface properties of Mg(OH)2-based peroxide bleached DIP (deinked pulp). The XPS survey spectra and SEM images showed that some trace elements, such as calcium, silicon, and aluminum, were present on the sample surface, in addition to the main elements, carbon and oxygen. The surface of enzyme-treated pulp was covered by the precipitated lignin or extractives. However, when the enzyme-treated pulps were bleached, the amount of precipitated lignin or extractives was considerably reduced. Lipase-treated, bleached pulp had better physical properties and lower effective residual ink concentration (ERIC) values than laccase/mediator-treated bleached pulp, which further indicated that lipase not only removed surface lignin and extractives, but it also was able to remove more residual ink contaminants.