Effects of wet-pressing-induced fiber hornification on enzymatic saccharification of lignocelluloses
This article reports the effect of wet-pressing-induced fiber hornification on enzymatic saccharification of lignocelluloses. A wet cellulosic substrate of bleached kraft eucalyptus pulp and two wet sulfite-pretreated lignocellulosic substrates of aspen and lodgepole pine were pressed to various moisture (solids) contents by variation of pressing pressure and pressing duration. Wet pressing reduced substrate moisture content and produced irreversible reduction in fiber pore volume—fiber hornification—as reflected in reduced water retention values (WRVs), an easily measurable parameter, of the pressed substrates. Wet pressing resulted in a reduction in substrate enzymatic digestibility (SED) by approximately 20% for the two sulfite-pretreated substrates when moisture content was reduced from approximately 75% to 35%. The reduction in SED for the cellulosic substrate was less than 10% when its moisture content was reduced from approximately 65% to 35%. The results indicated that reduction in SED is negligible when samples were pressed to solids content of 40% but observable when pressed to solids content of 50%. It was also found that WRV can correlate to SED of hornified substrates resulting from the same never-dried or pressed sample independent of the hornification process (e.g., pressing or drying). This correlation can be fitted using a Boltzmann function. Cellulase adsorption measurements indicated that wet-pressing-induced fiber hornification reduced cellulose accessibility to cellulase. The results obtained in this study provide guidelines to high-solids enzymatic saccharification of pretreated biomass.
KeywordsHigh-solids enzymatic hydrolysis/saccharification Fiber hornification Wet pressing Cellulose accessibility Water retention value (WRV)
This work was sponsored by the USDA Forest Service through the Program of Woody Biomass, Bioenergy, and Bioproducts (WBBB, 2009) that provided financial support to Luo for his visiting appointment at the University of Wisconsin–Madison and USDA Forest Service, Forest Products Laboratory (FPL).
- Carlsson G, Lindstrom T (1984) Hornification of cellulosic fibers during wet pressing. Svensk Papperstidning 87(15):R119–R125Google Scholar
- Jayme G (1944) Milkro-quellungsmessungen an Zellstoffenn. Papier-Fabr/Wochbl Papierfabr 6:187–194Google Scholar
- Laivins GV, Scallan AM (1993) The mechanism of hornification of wood pulps. In: Baker CF (ed) Products of papermaking. Pulp and Paper Fundamental Research Society, Oxford, pp 1235–1260Google Scholar
- Maloney TC, Li TG, Weise U, Paulapuro H (1997) Intra- and inter-fibre pore closure in wet pressing. Appita J 50:301–306Google Scholar
- Robertson AA (1964) Some observations on the effects of drying papermaking fibers. Pulp Paper Mag Can 65:T161–T168Google Scholar
- Scallan AM (1974) The structure of the cell wall of wood—A consequence of anisotropic inter-microfibrillar bonding? Wood Sci 6:266–271Google Scholar
- SCAN (2000) SCAN-C 62:00 water retention value of chemical pulps. Nordic Standardization ProgramGoogle Scholar
- Stone JE, Scallan AM (1967) The effect of component removal upon the porous structure of the cell wall of wood. II. Swelling in water and the fiber saturation point. TAPPI J 50(10):496–501Google Scholar