Effects of wet-pressing-induced fiber hornification on enzymatic saccharification of lignocelluloses

Abstract

This article reports the effect of wetpressing-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 hornificationas 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.

Effect of Hot-Pressing Temperature on the Subsequent Enzymatic Saccharification and Fermentation Performance of SPORL Pretreated Forest Biomass

“…Recent studies [6][7][8] have demonstrated that this practice can also be used prior to transporting feedstock to biochemical conversion facilities without negatively impacting bioconversion efficiencies. These studies confirm a general understanding from wood fiber science that densification of untreated lignocelluloses does not influence the recalcitrance of biomass or produce fiber hornification, i.e., the irreversible collapse of fiber pores due to hydrogen bonding observed in chemically produced fibers upon pressing or drying [9][10][11].…”

“…One recent study suggested that pelletizing ammonia fiber expansion (AFEX)-treated corn stover at 70°C did not substantially reduce enzymatic saccharification efficiency [13]. This result seems to contradict the current understanding of the deleterious effects of drying and pressing on subsequent enzymatic saccharification [9,10]. Pelletizing utilizes both heat and pressure to increase the energy density of the lignocellulosic biomass.…”

Proposed Nano-Scale Coalescence of Cellulose in Chemical Pulp Fibers During Technical Treatments

“…Wet pressing causes similar reduction in fiber swelling as drying (Carlsson and Lindström 1984;Luo et al 2011). However, wet pressing is much less homogenous compared to drying, as the stresses are concentrated at certain parts of the fiber matrix (Carlsson and Lindström 1984).…”

“…"Microfibrillar aggregation: Review," BioResources 7(4), 6077-6108 The accessibility of the hydroxyl groups is important for new innovative products from wood that require chemical or enzymatic treatments. For instance, cellulose microfibril coalescence is seen to hinder both the functionality of enzyme complexes (Samejima et al 1998) as well as the actual enzymatic processes (Luo et al 2011). In addition, the reactivity of dissolving pulp in acetylation is said to be dependent on the lateral fibril aggregate dimension (Chunilall et al 2010).…”

“…The reduction in fiber swelling is more pronounced in pulps with a high initial swelling capacity (Carlsson and Lindström 1984). Hornification due to wet-pressing is also seen to reduce the accessibility of cellulose in its further processing with cellulase enzyme (Luo et al 2011).…”