Abstract: This invention describes a new method to measure kappa number or lignin content of kraft pulps based on the voltammetric measurement of catalytic reactions involving lignin and redox mediators. This method comprises measuring the rate of regeneration of a lignin redox catalyst in the presence of pulp following its oxidation at a voltammetric electrode. The intensity of the catalytic current generated at the electrode surface is shown to be proportional to the amount of lignin present in a pulp. Within pulp types (softwood, hardwood or oxygen delignified) linear relationships can be obtained between the intensities of the generated current and a range of kappa numbers. The redox characteristics and concentration of the mediator, and the voltage sweep rate of the voltammetric procedure, are among parameters that can be tuned to obtained linear relationships with kappa number of various pulps.

Abstract: A process for the bleaching of kraft pulps with non-chlorine chemicals, employing a sequential reaction of oxidative enzymes and hydrogen peroxide. The kraft pulp can be from conventional or extended pulping, or from an oxygen delignification step. The enzyme reaction is monitored by methanol release which results from the demethylation of lignin. The process essentially comprises three steps. The first step is the oxidation of kraft pulp either with manganese peroxidase enzyme in the presence of Mn(II) salts, hydrogen peroxide and chelator, or with laccase enzyme preferably in the presence of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), or a combination of both enzymes in a crude mixture as typically produced by certain fungi. The Mn(II) salts and chelator may already be present in sufficient amount in the pulp. This first step is performed at an acidic pH, and moderate temperatures for a period of time between 30 and 240 minutes.