Pedro Fardim

Ionic liquids--promising but challenging solvents for homogeneous derivatization of cellulose.

In the past decade, ionic liquids (ILs) have received enormous interest as solvents for cellulose. They have been studied intensively for fractionation and biorefining of lignocellulosic biomass, for dissolution of the polysaccharide, for preparation of cellulosic fibers, and in particular as reaction media for the homogeneous preparation of highly engineered polysaccharide derivatives. ILs show great potential for application on a commercial scale regarding recyclability, high dissolution power, and their broad structural diversity. However, a critical analysis reveals that these promising features are combined with serious drawbacks that need to be addressed in order to utilize ILs for the efficient synthesis of cellulose derivatives. This review presents a comprehensive overview about chemical modification of cellulose in ILs. Difficulties encountered thereby are discussed critically and current as well as future developments in this field of polysaccharide research are outlined.

Modification of fibre surfaces during pulping and refining as analysed by SEM, XPS and ToF-SIMS

Abstract The effects of laboratory pulping and refining on the surface properties of eucalyptus kraft pulp fibres were investigated using Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS or ESCA) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Refining affected fibre structure, surface morphology, lignin (φlig), carbohydrate (φcarb) and extractive (φext) surface coverage. The φlig and φcarb, estimated with XPS, decreased and increased with refining, respectively. The φext changed according to the pulping conditions. Cellulose, xylan, lignin, sterols, fatty acids and their salts were identified by ToF-SIMS. Significant changes in the normalized ToF-SIMS peak intensities were observed after refining. The release of xylan and fatty acid salt aggregates formed in pulping and entrapped in the cell wall pores with subsequent adhesion to the fibre external surfaces was suggested as a source of surface chemical modification by refining.

Topochemical pretreatment of wood biomass to enhance enzymatic hydrolysis of polysaccharides to sugars

The surface chemistry of milled birch and pine wood pretreated by ionic liquid, hydrothermal and hydrotropic methods, followed by enzymatic hydrolysis was studied in this work. Surface coverage by lignin was measured by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to describe the surface chemical composition after pretreatment in detail, and the morphology after pretreatment was investigated by FE-SEM. Ionic liquid (1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride) pretreatment at room temperature made the samples swell but did not dissolve the wood. Comparing the surface coverage by lignin, both in the case of birch and pine wood, hydrotropic worked best to remove the lignin hampering enzymatic hydrolysis. ToF-SIMS supported this finding, and showed that in birch, the carbohydrates were degraded more than in pine after hydrotropic pretreatment. The glucose yield of birch was improved by hydrotropic pretreatment from 5.1% to 83.9%, more significantly than in case of pine.

Topochemistry of alkaline, alkaline-peroxide and hydrotropic pretreatments of common reed to enhance enzymatic hydrolysis efficiency.

Common reed was studied as raw material for sugar bioconversion. The low temperature alkaline, alkaline-peroxide and hydrotropic pretreatments were employed to overcome the recalcitrance of reed before enzymatic hydrolysis. After pretreatments, lignin was efficiently decreased from the fiber cell wall. Xylan was significantly reduced by hydrotropic pretreatment as well. The surface chemical compositions of reed before and after pretreatments were investigated by X-ray spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). Reed had a high surface coverage by lignin. Hydrotropic pretreatment was outstanding to decrease the surface coverage by lignin and expose the polysaccharides to fiber surface. The surface lignin reduction was also supported by attenuated total reflectance (ATR)-FTIR results. Furthermore, the topochemical modification of the fiber wall by hydrotropic pretreatment could improve the fiber digestibility, and thus the maximum glucan and xylan yields with the cellulase dosage of 20 FPU/g raised to 93.1% and 25.5%, respectively.

MULTIVARIATE CALIBRATION FOR QUANTITATIVE ANALYSIS OF EUCALYPT KRAFT PULP BY NIR SPECTROMETRY

ABSTRACT Near infrared spectrometry and multivariate data analysis were applied to predict the chemical composition and physico–chemical characteristics of eucalypt unbleached kraft pulps obtained at different laboratory pulping conditions. Viscosity, degree of polymerization (DP), kappa, brightness and contents of glucan, xylan, uronic acids, and lignin were the modeled variables using diffuse reflectance near infrared spectra obtained on pulp handsheets and the partial least squares (PLS) method. Models with two to four PLS components and good predictive ability were established after first derivative spectra pre-processing and application of cross-validation methodology. The predictive models can reduce the time consuming traditional analyses in the pulping industry laboratories, and also lead to a better process monitoring for suitable applications.

Measuring the concentration of carboxylic acid groups in torrefied spruce wood

Torrefaction is moderate thermal treatment (∼200-300°C) to improve the energy density, handling and storage properties of biomass fuels. In biomass, carboxylic sites are partially responsible for its hygroscopic. These sites are degraded to varying extents during torrefaction. In this paper, we apply methylene blue sorption and potentiometric titration to measure the concentration of carboxylic acid groups in spruce wood torrefied for 30min at temperatures between 180 and 300°C. The results from both methods were applicable and the values agreed well. A decrease in the equilibrium moisture content at different humidity was also measured for the torrefied wood samples, which is in good agreement with the decrease in carboxylic acid sites. Thus both methods offer a means of directly measuring the decomposition of carboxylic groups in biomass during torrefaction as a valuable parameter in evaluating the extent of torrefaction which provides new information to the chemical changes occurring during torrefaction.

Oligolignans in Norway spruce and Scots pine knots and Norway spruce stemwood

Abstract Oligolignans present in substantial amounts in Norway spruce and Scots pine knots were characterised. The hydrophilic knotwood substances were extracted and different chromatographic methods were applied to obtain fractions for analysis by GC, GC-MS, HR-EI-MS, LC-ESI-MS, NMR, and FTIR. β-O-4-Linked guaiacylglyceryl ethers of hydroxymatairesinol (Ia, Ib, Ic), secoisolariciresinol (II), lariciresinol (III), isolariciresinol (IV), lignan A (V), liovil (VI), conidendrin (VII), and pinoresinol (VIII) were identified in the spruce knotwood extract and β-O-4-linked guaiacylglyceryl ethers of nortrachelogenin (IX) and secoisolariciresinol (II) in the pine knotwood extract. The structures of allo-hydroxymatairesinol-4′-guaiacylglyceryl ether (Ia), hydroxymatairesinol-4-guaiacylglyceryl ether (Ib), hydroxymatairesinol-4′-guaiacylglyceryl ether (Ic), secoisolariciresisinol-4-guaiacylglyceryl ether (II), and lariciresinol-4′-guaiacylglyceryl ether (III) were determined via GC-MS, HR-MS, and 1H and 13C NMR analyses. The structures of (Ia), (Ic), (IV), (V), (VI), (VII), and (IX) have not been reported earlier. Spruce stemwood, both heartwood and sapwood, also contained oligolignans in small amounts. In addition, some dilignans with four phenylpropanoid units were tentatively identified in the hydrophilic knotwood substances.

Studies on the tosylation of cellulose in mixtures of ionic liquids and a co-solvent.

The tosylation of cellulose in ionic liquids (ILs) was studied. Due to the beneficial effect of different co-solvents, the reaction could be performed at 25°C without the need of heating (in order to reduce viscosity) or cooling (in order to prevent side reactions). The effects of reaction parameters, such as time, molar ratio, and type of base, on the degree of substitution (DS) with tosyl- and chloro-deoxy groups as well as on the molecular weight were evaluated. Products with a DStosyl≤1.14 and DSCl≤0.16 were obtained and characterized by means of NMR- and FT-IR spectroscopy in order to evaluate their purity and distribution of functional groups within the modified anhydroglucose unit (AGU). Tosylation of cellulose in mixtures of IL and a co-solvent was found to result in predominant substitution at the primary hydroxyl group. Size exclusion chromatography (SEC) revealed only a moderate degradation of the polymer backbone at a reaction time of 4-8h. Finally, the nucleophilic displacement (SN) of tosyl- and chloro-deoxy groups by azide as well as recycling of the ILs was studied.

Sorption of spruce O-acetylated galactoglucomannans onto different pulp fibres

Sorption of spruce acetylated galactoglucomannans (GGM) onto different pulps, among which unbleached and peroxide-bleached mechanical pulps, and unbleached and bleached kraft (BK) pulps, was studied as a means of understanding the retention of acetylated GGMs in mechanical pulping and papermaking. The fibre surface coverage of lignin and carbohydrates was estimated by X-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA). GGM sorption was clearly favoured on kraft pulps. Hardly any differences in sorption were, however, observed between unbleached and BK pulps, even if the surface coverage of lignin was lower on the bleached pulp. Neither thermomechanical pulp (TMP) nor chemithermomechanical pulp (CTMP) manufactured from spruce sorbed any acetylated GGMs. Peroxide bleaching of the pulp did not increase sorption. Only CTMP produced from aspen sorbed some GGMs. The anionic charge of neither chemical nor mechanical pulps influenced GGM sorption.

Characterization of Lignin Extracted from Birch Wood by a Modified Hydrotropic Process

In this work an environmentally friendly hydrotropic process was used to extract lignin from industrial birch wood chips. Two hydrotropic treatments were performed, a conventional and a modified process. The lignins were characterized using FTIR, pyrolysis-gas chromatography-mass spectrometry (pyrolysis-GC-MS), (31)P and (1)H-(13)C HSQC NMR, and size exclusion chromatography (SEC). The chemical (carbohydrates, extractives, etc.) and elemental compositions of the lignins were also determined. The yields of both lignins were 16.1% (dry wood basis), and the obtained lignins had very low contents of non-lignin compounds. The treatments resulted in significant changes of the structure of the lignins, a decrease in aliphatic hydroxyls and an increase in phenolic ones. The lignin isolated by the modified treatment underwent more substantial change than the reference one. It is believed that the data presented will facilitate utilization of hydrotropic lignin and promote the adoption of the hydrotropic process in the pulp and biorefinery industry.