Volume 69, Issue 6 - Special Issue: This issue contains selected papers from the 13th European Workshop on Lignocellulosics and Pulp (EWLP) Seville, Spain, June 24–27, 2014

Pulp and black liquor produced by alkaline sulfite anthraquinone (ASA) process were comprehensively characterized to evaluate the effects of ion concentration on the delignification and polysaccharide preservation. Scots pine wood meal was pulped at 160°C with a sulfite-to-hydroxide ion ratio of 0.75 and liquor-to-wood ratio of 200:1. Two concentration levels were studied in presence and absence of anthraquinone (AQ). Contrary to the expectations, already the lower concentration level (L-ASA) revealed rapid delignification in presence of AQ, while only moderate acceleration was obtained at the high concentration level (H-ASA). However, H-ASA liquor resulted in a slightly higher pulp yield of 1–2% (based on wood) but only in case of pulps with kappa numbers (KN) above 60. With progressing delignification, the yield advantage was gradually lost. The higher pulp yield at H-ASA conditions was mainly due to improved galactoglucomannan retention, which was around 2% on KN 60 pulp and around 0.5% after prolonged delignification. The xylan content, on the other hand, was found to be 1% (based on wood) lower under H-ASA conditions compared to L-ASA conditions, which may be attributed to an increased solubility of short-chain polysaccharides at high alkali concentration.

A mathematical model is presented, in which the yield loss (YL) and the decline in polymerization of carbohydrates is comprehended. The model is applicable to the treatment of cellulose and hemicelluloses in alkaline media, and it features the actions of peeling, stopping, and alkaline hydrolysis of the polymer chains. The peeling reaction is further subdivided into primary and secondary peeling depending on whether it originates from an initial reducing end-group (REG) or from an REG created by alkaline hydrolysis. Fitting the model to experimental data provides estimates of the various reaction rate constants. When available, simultaneous observations of the YL and the decrease in chain length contribute to the evaluation of the parameters. Alternatively, if the data are limited to the YL, the obtained parameter estimates allow for a projection of the time development of chain length. The model has been applied on data from two types of experiments: soda-anthraquinone treatment of cotton linters and kraft treatment of Scots pine. It was possible to evaluate the impact of the different processes on degradation as well as the portions of polymer chains possessing active or stabilized REGs.

Recovered fibers are reused for manufacturing bright paper after deinking and fiber decolorization. This second process generally starts with an alkaline hydrogen peroxide (H 2 O 2 ) stage, referred to as P. However, the color-stripping effect of P is often limited due to the low reactivity of H 2 O 2 on the azo groups of dyes. The purpose of this study was to improve the removal of these azo dyes by H 2 O 2 . A bleached kraft pulp was dyed with a model azo dye and submitted to activated H 2 O 2 bleaching. Phenanthroline and copper(II)-phenanthroline (Cu-Phen) served as activating compounds. The color-stripping trials were carried out at weak or conventional alkaline pH. The results were mainly evaluated in terms of dye removal index and degree of polymerization of cellulose. The theoretical composition of Cu-Phen in the bleaching conditions was calculated by means of the geochemical software PHREEQC. The results show that Cu-Phen was able to activate H 2 O 2 color stripping, although it was accompanied by additional cellulose degradation. Moreover, the color stripping was more effective under alkaline conditions, in which case CuPhen(OH) 2 would be present. Two hypotheses are proposed to explain this activated decolorization: a free radical mechanism and the influence of CuPhen(OH) 2 as an activating species.

2,5-Dihydroxy-[1,4]-benzoquinone (DHBQ) is one of the key chromophores in cellulosics. Due to its special resonance stabilization, it is a prime survivor of bleaching treatments and its degradation is essential in pulp bleaching. The clarification of the degradation mechanism of this compound is indispensable for targeting improvements of pulp bleaching processes. Previous studies revealed that DHBQ degradation by hydrogen peroxide (H 2 O 2 ) is influenced by salts. This study addresses the effects of alkaline metal salts, alkaline earth metal salts, and Al 2 (SO 4 ) 3 on the degradation of DHBQ under simulated conditions of pulp bleaching in a peroxide stage. The degradation by excess H 2 O 2 followed first-order kinetics in the presence of alkaline metal salts and alkaline earth metal salts, which enhanced and retarded the reaction, respectively. Kinetic studies and theoretical computations provided detailed mechanistic insights: Li + , Na + , and K + stabilize several reaction intermediates by complex formation, causing the enhancement of the degradation, whereas Mg 2+ and Ca 2+ coordinate and stabilize the reactant, resulting in the observed retardation. Al 2 (SO 4 ) 3 exhibited a strong enhancing effect, but the degradation followed second-order kinetics with regard to DHBQ, suggesting a fundamentally different degradation mechanism.

An analytical method for the determination and quantification of the main organic degradation products of viscose spinning baths was outlined herein and successfully applied. Samples were ethoximated and silylated for GC-MS analysis. The main challenge in the analysis was the quantification of the degradation products because standard compounds are often not commercially available. Analyte recovery was optimized with regard to pH and lyophilization conditions. Given that the spinning bath analytes showed a very broad range of volatility, internal standardization by the degradation product of uniformly 13 C-labeled glucose in alkaline media was used. This approach allowed for the first time for the accounting of a major part of the organic components in the viscose spinning baths. On average, 57% of total organic carbon was characterized by quantifying 21 individual substances. The methodology opens new perspectives of keeping track of the formation and origin of organic degradation products. It is a prerequisite to all further efforts to avoid contamination of the spinning bath and achieve a higher product quality and a better closure of process cycles. Furthermore, it can be easily applied to other highly complex industrial process streams involving polysaccharide degradation products as they are emerging, for instance, in biorefineries.

Pulp was treated with cellulase, and the chemical, physical, and optical properties of the refined pulps in paper sheets were measured in terms of the degree of polymerization of cellulose, tensile strength, elongation, burst strength, light scattering, and brightness. The sheets were thermally treated for 20 and 60 min at 225°C in the presence of 1% and 75% (v/v) water vapor. The cellulase treatment intensified the fibrillation of fibers and reduced the specific energy consumption during refining. It was demonstrated based on the water retention value that the refining modified the water-bonding ability of the pulp fibers, which was further enhanced in the case of cellulase-treated pulps. However, the enzymatic pretreatment impaired the physical properties, such as the tensile strength, elongation, and burst strength of the high-density paper. These changes further reduced the thermal strength stability of the paper. In addition, considerable brightness loss of the cellulase-treated high-density paper was observed compared to the reference paper, indicating more severe thermal degradation reactions as a consequence of enzyme-assisted refining.

The purpose of this study was to design new biomaterials based on functionalized xylan derivatives. In one approach, 4- O -methylglucuronoxylan (MGX) of beechwood was oxidized by sodium periodate (NaIO 4 ). A ratio of 0.2 NaIO 4 /xylose leads to a degree of oxidation of 0.15 with 75% yield. Then, the oxidized MGX aldehyde was submitted to reductive amination reaction with benzylamine, and as a result, the xylan backbone was effectively grafted with benzyl groups with a degree of substitution of 0.11. In another approach, controlled sulfuric acidic hydrolysis of MGX was performed to get well-defined xylooligosaccharides (XOS). Then, the reductive amination reaction of the XOS aldehyde functions was performed with allylamine or 2-aminoethylazide to graft the chain ends with an allyl or an azide function, respectively. The proposed methods can open a route to the design of new functional biomaterials.

Suberin is a natural hydrophobic material that could be used to improve the water repellency of cellulose surfaces. It is also abundant in the outer bark of birch ( Betula verrucosa ); birch bark is a side-stream product in Scandinavia from the forest industry, which is generally burned for energy production. A suberin monomer, cis-9,10-epoxy-18-hydroxyoctadecanoic acid, was isolated from birch outer bark and polymerized via lipase (immobilized Candida antarctica lipase B). The resulting epoxy-activated polyester was characterized by nuclear magnetic resonance (NMR) imaging, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, and size exclusion chromatography. Then the polyester was cured with tartaric or oxalic acid, and the crosslinked polyesters were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry. Hydrophobic materials were prepared by compression molding of polyester-impregnated cellulose sheets, and the final products were characterized by FTIR, cross-polarization magic angle spinning 13 C NMR, and field-emission scanning electron microscopy. The water contact angle was significantly increased from 0° for the original cellulose sheets to over 100° for the produced hydrophobic materials.

A cold holocellulose treatment (cHolT) was studied on a bleached kraft pulp (BKP) of Eucalyptus to observe the degradation of polysaccharides in pulp by chlorite at room temperature under conditions of slightly acidic pH and high chlorine charge (313% of active chlorine on BKP). Based on literature data, cellulose depolymerization is expectable by chlorite treatments at 70°C and reinforced chlorite charge, while the addition of dissolved lignin could protect cellulose. In the present study, polysaccharide degradation was followed by TAPPI viscosity, size-exclusion chromatography coupled to multidetectors, pulp yield, kappa number, elemental sugar analysis of pulps, and total organic carbon detection in filtrates. cHolTs were repeated several times without significant polysaccharide degradation, but the insertion of a caustic extraction stage at 70°C induced little degradation. This study opens the way to the setup of inert delignification procedures to be applied on raw or processed lignocellulosic samples from biorefinery studies.

The solubility of electrospun poly(vinyl alcohol) nanofiber mats (PVA ES-NFM ) is strongly influenced by loading with nanocellulose (NC). The NC was derived from hemp shives obtained by steam explosion autohydrolysis followed by water and alkaline extraction, ball milling, and ultrasonication treatments. It was demonstrated for the first time that PVA ES-NFM does not disintegrate in aqueous medium after simple adding of NC without any additional chemical or physical modification (PVA ES-NFM NC). The structural and thermal studies on PVA ES-NFM NC indicated that enhanced stability in aqueous medium can be explained by interactions between surface groups of NC and PVA macromolecules as well as by reinforcing the effect of NCs. The experimental findings could be important for filtration applications in environments with high relative humidity.

The effect of coatings on paper sheets has been studied. For this purpose gels were prepared from unextracted and extracted bark. The gels represented dispersions of micro- and nanoparticles. The coatings were also prepared from mixtures of gels with chitosan solutions in 1% acetic acid and aqueous Na-carboxymethylcellulose (Na-CMC) solutions. The properties – Gurley air resistance, water vapour sorption, and mechanical properties of paper sheets – were tested. For obtaining the gels, the bark was destructed by a thermocatalytic method and then dispersed in water in a ball mill. The gels contained mainly nanoparticles with an average size of about 300 nm. Paper sheets produced by the Ligatne Paper Mill (Latvia) were coated on both sides. Gurley air resistance increases with increasing thickness of the coatings and with increasing gel concentration. At a gel concentration of 10% and a coating thickness of 35 μm, air resistance increases by 57% (gel from unextracted bark) and 72% (gel from extracted bark) compared to uncoated paper sheets. The coatings from bark gels in combination with Na-CMC and chitosan solutions increase further the air resistance. The coatings at gel concentrations up to 6% elevate the burst strength and tensile strength in a dry state. The coatings from mixtures of bark gel and chitosan and Na-CMC heighten further the mechanical properties and elevate the water vapour sorption of paper sheets.

Supercritical water gasification of weak sulfur-free black liquor (BL) was performed in a batch autoclave at temperatures between 430°C and 470°C, pressure between 24 and 27 MPa and residence time between 2 and 63 min. Results show that the gas produced was a mixture of mainly hydrogen, methane, and carbon dioxide. Maximum conversion was achieved at 470°C and 60 min. Energy recovery (ER, ratio between the energy in the gas and in the initial BL) was 46%. Thirty-four percent of the carbon and 53% of the hydrogen initially present in BL were converted into gases. Nearly 15% of initial organic carbon remains in the liquid phase and consists mainly of phenolic compounds, which are stable under those conditions. A higher temperature is needed to convert all the organic carbon. Thermodynamic equilibrium should be reached at 700°C leading to a complete conversion and a better efficiency. Sodium recovery is close to typical kraft recovery value and compatible with causticizing.

Technical hydrolysis lignin (THL) was micronized by grinding in a rotary-jet mill to obtain a fraction of approximately 5 mm. Both initial and milled THLs were liquefied by thermal alkaline treatment at 220°C for 2 h. Upgraded THLs that were nonmilled (L1) and milled (L2) were desalted by treatment with cation-exchanged resin and were dried. Micronization affected the course of hydrothermal alkaline treatment and the structure and composition of the obtained lignin. Thus, L2 contained much less concomitant polysaccharides and extractives than L1 and was more condensed. The molecular weights of L1 and L2 were 1100 and 1000 Da, respectively, as determined by size-exclusion chromatography. Structural characterization carried out by employing tandem electrospray ionization-mass spectrometry and 1D and 2D nuclear magnetic resonance spectroscopy revealed that small amounts of β-O-4 (∼6 mol.%), β-5, and β-β structures still remained in L1 and L2. Overall, upgraded lignins are oligomers (trimers-pentamers) with highly degraded propane chains and possess polyconjugated condensed aromatic structures. Upgraded THL seems to be a promising raw material for polymeric formulations.

A novel method for synthesizing microspheres from lignin or lignin acrylate derivatives through copolymerization with styrene (St) and divinylbenzene (DVB) has been developed. The copolymers were obtained by the emulsion-suspension polymerization with a constant molar ratio of DVB to St of 1:1 (w/w) and different amounts of lignin or its derivatives. The morphologies of the obtained materials were examined by scanning electron microscopy. Two types of lignin modifications were performed to introduce vinyl groups into the lignin molecules: modification with acrylic acid and modification with epichlorohydrin plus acrylic acid. The course of modification was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy. The thermal stability and degradation behavior of the obtained microspheres were investigated by thermogravimetric analysis, and the pore structure was characterized via nitrogen sorption experiments. Owing to the presence of specific functional groups and the well-developed pore structure, the obtained Lignin-St-DVB microspheres may have potential application as specific sorbents for the removal of phenolic pollutants from water, as demonstrated by the solid-phase extraction technique.

The thermocatalytical synthesis conditions required for the activation of wood charcoal with NaOH in terms of the formation of pores in its structure were investigated. The present study was conducted to explore the potential application of activated carbons as electrodes in supercapacitors with organic electrolyte. The total pore volume and micro- and mesopore ratio were controlled by the activation temperature and alkali addition rate. The working characteristics of carbon electrodes (e.g., specific capacity and ohmic losses) in supercapacitors are strongly influenced by the properties of the pores in their structures. Herein, the optimal ratio of raw material to activator and activation temperature are established: an increase in the ratio of NaOH to carbonizate rate by a factor of 2 and setting the synthesis temperature at 700°C positively influence the electrochemical characteristics of supercapacitors and provide them with specific capacities of up to 160 F g -1 .

The new organosolv process of wheat straw fractionation elaborated by Compagnie Industrielle de la matiere Vegetale (France) corresponds to the biorefinery approach, which allows separating cellulose, hemicelluloses, and lignin. The straw lignin (Biolignin ™ ) is an attractive product, for which new applications are sought. In the present work, straw lignin (L) was converted into liquid lignopolyols via a batch reaction with propylene oxide (PO). The effects of the lignin content (L%) in the initial reaction mixture (L/(L+PO) on the oxypropylation process and the properties of whole lignopolyols and L/PO copolymers were studied. Almost complete disappearance of L-OH phen and L-COOH groups in copolymers was accompanied by an increase in the L-OH aliph groups’ content therein. The polydispersity ( M w /M n ) of all copolymers obtained decreased essentially compared to the reference. The extent of PO grafting onto OH groups increased with decreasing lignin content in the initial reaction mixture. At a lignin content of 15–30% in the initial reaction mixture, the lignopolyols fulfil the requirements of polyol polyethers for rigid polyurethane foam production. The further increase in the lignin content leads to the appearance of the non-liquefied fraction and the undesirable increase in the viscosity of the liquefied part.

The antioxidant activities (AoAs) of 50 different technical lignins have been determined. The lignins of various botanical origins (annual plants, coniferous trees, and deciduous trees) were isolated and fractionated by different techniques (delignification by alkali, kraft process, fast pyrolysis, and hydrolysis). The structure and the functionality of lignins were characterized by functional group analyses (phenolic OH, carboxyl, and methoxyl groups), analytical pyrolysis pyrolysis/gas chromatography/mass spectrometry/flame ionization detector (Py-GC/MS/FID), electron paramagnetic resonance, size exclusion chromatography, and titrimetric methods, and the AoAs were evaluated as the capacity to scavenge the DPPH · and ABTS ·+ free radicals. The relationship between the lignin structure and the AoA was characterized by pair correlation, partial correlation, and multivariate regression analyses, including correlated components regression. The results were compared with those of lignin model compounds and low molecular weight phenylpropanoids. It has been shown that molecular weight does not influence essentially the AoA of lignins. There is a relationship between the activities of low and high molecular weight polyphenols; their mechanisms of action are also similar. The structure-related AoA of lignins has been quantified for the first time.

31 P nuclear magnetic resonance (NMR) based on the derivatization reagent 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane is a common approach for the hydroxyl group determination of lignins, but the results are sometimes less reproducible compared to other methods. In the present work, common pitfalls in 31 P NMR analysis of kraft lignin (KL) and lignosulfonates (LS) are addressed and the results are compared to those obtained by 1 H NMR spectroscopy. Several experimental parameters are revisited in terms of the reliability of the obtained data, such as the choice of relaxation delay, internal standards, and the best solution technique for the 31 P NMR analysis of LS. For the first time, 31 P NMR data of LS are presented based on a new dissolution protocol. The analytical data of a set of lignins consisting of three KLs, one LS, and one milled wood lignin are presented based on the optimized 31 P NMR approach.

Trees with natural resistance to decay by pests contain extractives, which are candidates for wood preservatives. In this study, the bark of Psorospermum febrifugum Spach and Milicia excelsa Welw. was extracted with hexane, acetone, methanol, and dichloromethane by pressurized liquid extraction. The chemical analysis of the extracts was performed by gas chromatography-mass spectrometry and the identified compounds were reviewed for known bioactivity. The results show that these species contain compounds with known antimicrobial activity and as such could serve for the development of antifungal wood preservatives, especially for local usage.