Beneficiation of sawdust waste in the context of an integrated forest bio-refinery mill: Kraft and pre-hydrolysis Kraft pulping properties

Abstract

As part of a broader objective to extract cellulose from sawdust waste material for the production of nano-crystalline cellulose, conventional industrially available processes such as the Kraft and pre-hydrolysis Kraft (PHK) processes were investigated for delignification of sawdust produced from Eucalyptus grandis wood. In the context of the integrated forest biorefinery, it was felt that it may be useful to provide South African papermakers with preliminary data on the Kraft and PHK pulping properties of sawdust as none appeared to be available in the country. The results showed that E. grandis sawdust Kraft pulps with acceptable yields (48 %) and fibre morphologies comparable to conventional Kraft pulps, produced from wood chips, could be produced in the laboratory using typical Kraft pulping conditions. As expected, the exception was pulp strength properties such as burst, tear and tensile strengths which were 50-70 % lower than conventional pulps. During the pre-hydrolysis stage of the PHK process, up to 24 g.l-1 xylose could be removed from sawdust with minimal removal of lignin (0.1 g.l-1) and cellulose (2.5 g.l-1). Pulping of the pre-hydrolysed sawdust resulted in a pulp yield of ca. 35 %. Preliminary characteristics measured on the unbleached PHK sawdust pulp such as pentosan content (3-4 %), brightness (41 %) and viscosity (760 – 850 ml.g-1) alluded to its potential for the production of dissolving pulp.