Delving into the Fundamental LMS Delignification of High-kappa Kraft Pulps

摘要

The bleaching of high-kappa kraft pulps with a laccase mediator system (LMS) was found to provide 43-61% delignification following an (E+P) stage when violuric acid was used as the mediator. Pulp yields after the LMS(E+P) treatment were +99.9%. Molecular modeling of violuric acid (VA), N-hydroxybenzotriazole (HBT), and N-acetyl-N-phenylhydroxylamine (NHA) indicates an elevated unpaired electron density for violuric acid over the other mediators, which may account for VA's improved performance. Structural analysis of the residual lignin after LMS_(VA) treatments indicated that the LMS stage oxidizes primarily the phenolic structures of lignin. Full sequence ECF bleaching of high and low-kappa SW kraft pulps after a LMS_(VA)(E+P+O) or (LMS_(VA))(LMS_(VA))(E+P+O) indicated the pulps could be readily bleached to +85 TAPPI brightness. The physical strength properties of the fully bleached LMS-treated pulps exhibited tensile, tear, and burst indexes comparable to control ECF-bleached pulps.