Anderson Guerra

Structural Characterization of Lignin during Pinus taeda Wood Treatment with Ceriporiopsis subvermispora

ABSTRACT Pinus taeda wood chips were biotreated with Ceriporiopsis subvermispora under solid-state fermentation for periods varying from 15 to 90 days. Milled wood lignins extracted from sound and biotreated wood samples were characterized by wet-chemical and spectroscopic techniques. Treatment of the lignins by derivatization followed by reductive cleavage (DFRC) made it possible to detect DFRC monomers and dimers that are diagnostic of the occurrence of arylglycerol-β-O-aryl and β-β, β-5, β-1, and 4-O-5 units in the lignin structure. Quantification of these DFRC products indicated that β-O-aryl cleavage was a significant route for lignin biodegradation but that β-β, β-5, β-1, and 4-O-5 linkages were more resistant to the biological attack. The amount of aromatic hydroxyls did not increase with the split of β-O-4 linkages, suggesting that the β-O-4 cleavage products remain as quinone-type structures as detected by UV and visible spectroscopy. Nuclear magnetic resonance techniques also indicated the formation of new substructures containing nonoxygenated, saturated aliphatic carbons (CH2 and CH3) in the side chains of lignins extracted from biotreated wood samples.

Molecular weight distribution of wood components extracted from Pinus taeda biotreated by Ceriporiopsis subvermispora

Significant contributions have been made to understand the ligninolytic system of the biopulping fungus, Ceriporiopsis subvermispora; however, the reason why this fungus selectively degrades lignin is still unclear. This study evaluates the depolymerization of wood components induced by C. subvermispora during wood decay under solid-state fermentation. Pinus taeda wood chips were biotreated for periods from 15 to 90 days. The fungus degraded lignin and extractives extensively without removing large amounts of glucan. Alpha-cellulose samples were prepared from decayed and undecayed wood chips for evaluation of cellulose depolymerization. The yields of alpha-cellulose decreased from 47.8% for undecayed wood to 42.6 and 34.2% for the wood samples biotreated for 30 and 90 days, respectively. High performance size exclusion chromatography of tricarbanyl derivatives of these alpha-cellulose preparations indicated a progressive decrease in the polymerization degree values from the 30th day of biotreatment. Lignin depolymerization, evaluated by gel permeation chromatography (GPC) of residual MWLs, was rapid in the first 30 days of biodegradation. After this period an extensive mineralization occurred. Some relevant hydrolytic and oxidative enzymes present in the culture extracts were studied. Xylanase was the main hydrolytic enzyme produced, while laccase was not detected in any biodegradation period evaluated. A correlation between the levels of wood-degrading enzymes produced and the pattern of wood constituents degradation was tentatively established.

Propensity of Lignin to Associate: Light Scattering Photometry Study with Native Lignins

Many studies of lignins in solution invoke association and aggregation phenomena to explain their solution behavior (e.g., reprecipitation onto pulp fibers, condensation, etc.). Following their colloidal (apparent) molecular weights in solution as a function of time allows us to explore observable dissociation phenomena. These measurements were carried out using multiple angle laser light scattering (MALLS) photometry in the static mode. The challenges and opportunities of measuring the specific refractive index increment (dn/dC) of lignin solutions and determining the kinetics of the dissociation process were thus investigated. Hardwood and softwood representative lignins were isolated, and method for their full dissolution in THF was further developed, which then lead to accurate dn/dC values being obtained as a function of time. When coupled to additional work using light scattering static measurements and Zimm plots for the same solutions, this effort offers insight into the aggregation and ensuing dissociative events that operate within the lignin macromolecules.

Characterization of the Residual Lignins in Pinus taeda Biodegraded by Ceriporiopsis subvermispora by Using in situ CuO Oxidation and DFRC Methods

Biopulping, defined as the fungal pretreatment of wood chips and designed as a solid-state fermentation process for production of mechanical or chemical pulps, is a promising technology developed in the last two decades (Akhtar et al. 1998; Scott et al. 1998). Although this technology has been evaluated on mill scale (Breen and Singleton 1999; Scott et al. 1998), the chemical and biochemical bases of biopulping are not well understood. Usually, the beneficial effects of biopulping are obtained at the early stages of biodegradation, weight losses being lower than 5 % (Akhtar et al. 1998). A lack of correlation between the biopulping benefits and the extent of wood weight or component losses has been reported (Setliff et al. 1990; Akhtar et al. 1998; Ferraz et al. 1998, 2000 a). This indicates that several wood modifications caused by fungal pretreatment, including ultrastructural changes, extractives removal and lignin degradation reactions, could be responsible for the behavior of biotreated samples submitted to chemical or mechanical pulping (Ferraz et al. 1998, 2000 a). An evaluation of the chemical changes occurring at the initial stages of biodegradation could help to elucidate the chemical basis of biopulping. However, only few of the methods available are suitable for this purpose. The derivatization followed by reductive cleavage (DFRC) method, which is suitable for in situ lignin characterization, is specific for releasing quantifiable monomers from aryl-glycerol beta-aryl ether linkages (Lu and Ralph 1997 a, b; 1998 a, b). This short communication reports the applications of this characterization method, and provides some current attempts to understand the structural alterations that occur during the biodegradation of Loblolly Pine (Pinus taeda) by Ceriporiopsis subvermispora. CuO oxidation was also used for in situ characterization of the main lignin moieties in decayed wood samples. Materials and Methods

Isolation and characterization of lignins from Eucalyptus grandis Hill ex Maiden and Eucalyptus globulus Labill. by enzymatic mild acidolysis (EMAL)

Abstract Despite the growing importance of Eucalyptus wood as raw material for pulp and paper, there is a lack of knowledge on the chemistry of their macromolecular components. The present paper addresses this issue by applying the recently developed protocol for isolating enzymatic mild acidolysis lignins (EMAL) from Eucalyptus grandis, Eucalyptus globulus and the softwood species Douglas fir and white fir, which were used for comparative purposes. The structures of EMALs were investigated by quantitative 31P NMR, DFRC/31P NMR (derivatization followed by reductive cleavage followed by quantitative 31P NMR) and size exclusion chromatography (SEC). Overall, the yields of EMALs isolated from Eucalyptus were higher than those from the softwoods examined. Lignin from E. globulus was found to contain higher contents of arylglycerol-β-aryl ether structures, free phenolic hydroxyl groups and syringyl-type units than lignin from E. grandis. New insights provided by the DFRC/31P NMR revealed that up to 62.2% of arylglycerol-β-aryl ether structures in E. globulus are uncondensed, while in E. grandis the amount of such uncondensed structures was found to be lower than 48%. SEC analyses showed that lignins from E. grandis and softwoods associate in greater extension than lignin from E. globulus.

Determination of Arylglycerol−β-Aryl Ether Linkages in Enzymatic Mild Acidolysis Lignins (EMAL): Comparison of DFRC/31P NMR with Thioacidolysis⊥

Enzymatic mild acidolysis lignins (EMAL) isolated from different species of softwood and Eucalyptus globulus were submitted to comparative analysis that included thioacidolysis, derivatization followed by reductive cleavage (DFRC), and DFRC followed by quantitative (31)P NMR (DFRC/(31)P NMR). While gas chromatography (GC) was used to determine the monomer yields from both thioacidolysis and DFRC, (31)P NMR studies quantified the various phenolic hydroxy groups released by DFRC. The monomer yields from thioacidolysis and DFRC were substantially different, with thioacidolysis resulting in higher yields. In contrast, an excellent agreement was obtained in the total number of beta-aryl ether structures determined by thioacidolysis and DFRC/(31)P NMR, indicating that the combination of DFRC with quantitative (31)P NMR overcomes, at least in part, the limitations presented by the DFRC method. Both thioacidolysis and DFRC/(31)P NMR were further used to better understand the lignin isolation process from wood. The results show that mild rotary ball milling minimizes, but does not prevent, the degradation of beta-O-4 structures during the early stages of wood pulverization. The extent of such degradation was found to be higher for E. globulus than for a variety of softwoods examined. Furthermore, the structures of the EMALs isolated at yields ranging from 20% to 62% were very similar, indicating structural homogeneity in the lignin biopolymer within the secondary wall.

Bio-chemimechanical pulps from Eucalyptus grandis : Strength properties, bleaching, and brightness stability

Abstract Eucalyptus grandis wood chips were treated with the white‐rot fungus Ceriporiopsis subvermispora in a 100‐L bioreactor for 15 days. The treatment was characteristic of a selective biodelignification (7.6±0.2% and 0.3±0.2% of lignin and glucan losses, respectively) with concomitant extractive removal (17.7±0.2%). Biotreated samples and non‐inoculated controls were pre‐cooked in alkaline sulfite and post‐refined in a Jokro mill. The biotreated pulps fibrillated more rapidly and contained lower amounts of rejects than the control. To achieve a freeness of 400 mL, the control pulp required 125 min of beating, whereas the biopulp required only 95 min, a reduction of 24%. Unbleached biopulps had better strength properties than control pulps because higher tensile indexes were obtained for the entire range of tear indexes. Bleaching with 8% hydrogen peroxide increased the brightness of these pulps by 17 points. At low peroxide loads, the brightness increase for biopulps was lower than for the control pulps. Still, the bleachability of sboth pulps was similar for peroxide loads higher than 2%. After a two‐stage H2O2‐bleaching sequence, final brightnesses for the control and biopulps were 59.7±0.8% and 60.5±0.4%, respectively. Brightness stability of the bleached control and bio‐CMP pulps to photo and thermal aging were very similar.

Near‐Infrared Spectra and Chemical Characteristics of Pinus taeda (Loblolly Pine) Wood Chips Biotreated by the White‐Rot Fungus Ceriporiopsis subvermispora

Abstract Near‐infrared (NIR) spectroscopy was evaluated as an analytical tool for monitoring changes in Pinus taeda (loblolly pine) induced by the white‐rot fungus Ceriporiopsis subvermispora. Intensities of several NIR bands increased with biodegradation time, but a direct correlation between band intensities and biodegradation periods or weight losses due to the biotreatment were not observed. On the other hand, the intensities of NIR bands correlated with properties reflecting the macromolecular characteristics of the components of the biotreated wood samples. Bio‐kraft pulps were also characterized by wet chemical analysis and NIR spectroscopy. In this case, appropriate prediction models related NIR spectral information with the chemical composition of the pulps, r 2 values ranged from 0.96 to 0.99.