Published by De Gruyter

Volume 74 Issue 6 - Special issue: The 20th International Symposium on Wood, Fiber and Pulping Chemistry (Tokyo, Japan, September 9–11, 2019); Issue editor: Thomas Rosenau

Issue of Holzforschung

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Contents
Journal Overview

Publicly Available June 16, 2020

Review

February 28, 2020

Wood-based resins and other bio-based binders for the production of mineral wool

Arianna Lucia, Hendrikus W.G. van Herwijnen, Thomas Rosenau

Page range: 539-550

Abstract

The traditional binder used in mineral wool is phenolic resin that makes mineral wool insulations reliable and efficient. The toxicity and health hazards of phenol and formaldehyde are becoming more and more pressing, and the industrial production needs to focus on safer precursors. Several formulations of bio-based binders for mineral wool have been developed, meeting the challenge of performing equally well as conventional binders. Technical lignins, due to their intrinsic structure and their abundance, are good candidates for future industrial adhesives. Carbohydrates are other class of biomaterials widely used in both research and patent formulations toward mineral wool binders. Proteins and cardanol are still largely unknown precursors, although they have hidden potentials for reliable binder systems. Even if conventional binders are not replaced completely with bio-based alternatives today, a partial use is already a step forward in the right direction – toward future biorefinery-based industries and knowledge-based bioeconomies in general.

Original articles

Publicly Available April 1, 2020

A branched structure provides kraft lignins a denser morphology and a high molar mass for a given hydrodynamic radius

Linping Wang, Kengo Shigetomi, Keiichi Koda, Aori Gele, Yasumitsu Uraki

Page range: 551-558

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Abstract

Size exclusion chromatography with multi-angle laser light-scattering detectors was applied for acetylated softwood and hardwood kraft lignins (Ac-SKL and Ac-HKL) and 8- O -4′ type of linear polymeric lignin model (Ac-M-8O4′) to compare their swelling behaviors. The plot of molar mass (MM) vs. retention time for Ac-M-8O4′ was similar to that of polystyrene, which revealed that Ac-M-8O4′ exhibited swelling behavior that was similar to that of polystyrene. However, the MM values of both Ac-KLs were larger than those of polystyrene standards at any retention time. This difference indicated that both Ac-KLs had a more compact structure than those of polystyrene and Ac-M-8O4′. One hypothesis is that the larger MM of both Ac-KLs stems from their branched structures. To verify this hypothesis, the frequency of 5-5′ interunit linkage in lignin samples was determined by 1 H NMR after nitrobenzene oxidation. A linear relationship between MM and 5-5′ abundance was observed in the high MM region.

February 28, 2020

Effects of lignin structure and solvent on the formation rate of quinone methide under alkaline conditions

Fuyu Yamauchi, Toko Ito, Osamu Kawamoto, Toshihiro Komatsu, Takuya Akiyama, Tomoya Yokoyama, Yuji Matsumoto

Page range: 559-566

Abstract

The purpose of this study was to examine how differences in the type of aromatic nucleus, side-chain structure and type of solvent affect the formation rate of quinone methide (QM) in the alkaline reaction of lignin. The reaction was done at a NaOH concentration of 1.0 mol l −1 and temperature of 75–140°C under an anaerobic condition. The formation rates of QM were in the order: syringyl > guaiacyl > p -hydroxyphenyl, when model compounds with lignin-type aromatic nuclei were compared. This and other results on various phenolic compounds suggested that the formation of QM is rapid from compounds having a high electron density in the aromatic π -electron system. The formation of QM was faster from a C 6 -C 2 -type than from a C 6 -C 1 -type lignin model compound, which was attributed to the fact that QM is an alkene and hence more stable when an unsaturated carbon in QM has an alkyl substituent, like the C 6 -C 2 -type compound. When aqueous 1,4-dioxane solutions with different 1,4-dioxane contents were used, the formation of QM became slower with increasing 1,4-dioxane content. This can be explained by the variation in the negative charge density in the rate-determining step, where the density is larger at the transition than at the initial state and consequently the activation energy is lower in a solvent with higher polarity.

June 2, 2020

Effect of different catalysts on the oxyalkylation of eucalyptus Lignoboost® kraft lignin

Fernanda R. Vieira, Ana Barros-Timmons, Dmitry V. Evtuguin, Paula C. R. Pinto

Page range: 567-576

Abstract

Lignin obtained by Lignoboost® procedure from black liquor after kraft pulping of Eucalyptus globulus wood was characterized and converted into liquid polyols via an innovative and safe procedure using base catalyzed oxyalkylation with propylene carbonate (PC). The effect of four catalysts, Potassium carbonate (K 2 CO 3 ), 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU), dicyanodiamide (DICY), and 1,4-diazabicyclo [2.2.2] octane (DABCO) was evaluated in terms of lignin polyol yield and weight gain. The ensuing polyols were also characterized by fourier transform infrared (FTIR), 1 H NMR, 13 C NMR, and size exclusion chromatography (SEC) to determine the degree of the substitution (DS), degree of polymerization (DP), and the molecular weight, respectively. Only a minor proportion of PC ( ca. 3–15%) was converted to propylene glycol/homooligomers as revealed by high performance liquid chromatography (HPLC). All catalysts promoted preferential derivatization of lignin phenolic OH groups by oxypropyl moieties. The maximum average DP of propylene oxide chains in oxyalkylated Lignoboost® kraft lignin (oKL) was 1.85 per one phenylpropane unit (PPU) using DBU. Conversely, the DP of oKL using DICY was very low (0.27/PPU). DICY’s catalytic activity seems to be jeopardized due to the formation of unreactive adducts with lignin. The oKL obtained using DBU, DABCO, and K 2 CO 3 have potential to be used as polyols in the production of polyurethanes as the corresponding hydroxyl number (I OH ) is in the range of 198–410 mg KOH g −1 .

May 29, 2020

Preparation of kraft lignin-based activated carbon fiber electrodes for electric double layer capacitors using an ionic liquid electrolyte

Nutthira Pakkang, Manish Kumar, Shogo Taira, Keiichi Koda, Kengo Shigetomi, Yasumitsu Uraki

Page range: 577-588

Abstract

This article demonstrates the development of activated carbon fiber electrodes produced from hardwood kraft lignin (HKL) to fabricate electric double layer capacitors (EDLCs) with high energy and power densities using an ionic liquid (IL) electrolyte. A mixture solution of HKL, polyethylene glycol as a sacrificial polymer, and hexamethylenetetramine as a crosslinker in dimethylformamide/acetic acid (6/4) was electrospun, and the obtained fibers were easily thermostabilized, followed by carbonization and steam activation to yield activated carbon fibers (ACFs). The electrochemical performance of EDLCs assembled with the ACFs, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF 4 ) as an IL electrolyte and a cellulosic separator was insufficient due to the low conductivity of the electrode. The conductivity of the electrode was improved successfully by spraying conductive carbon black (CB) onto the fibers mat during electrospinning. The CB containing electrodes with improved conductivity gave the resulting EDLCs a higher electrochemical performance, with an energy density of 91.5 Wh kg −1 and a power density of 76.2 kW kg −1 .

February 11, 2020

Laccase-catalyzed oxidative modification of lignosulfonates from acidic sulfite pulping of eucalyptus wood

Sandra Magina, Ana Barros-Timmons, Dmitry V. Evtuguin

Page range: 589-596

Abstract

Lignosulfonates (LS) from acidic magnesium-based sulfite cooking of Eucalyptus globulus wood were modified via laccase-catalyzed oxidative treatment with the aim to improve their performance as plasticizing additives in concrete formulations. The target parameters were the increment of molecular weight (M w ) and the amount of oxidized groups. The laccase-assisted oxidation under optimized conditions (40°C, pH 4.5, enzyme loads of 83–500 U g −1 for 90 min) allowed M w increment up to 11-fold and almost doubled the amount of carbonyl and carboxyl groups without using any mediators. Modified LS maintained their solubility in water and possessed a zeta- potential close to that of initial LS. The characterization of modified LS has been carried out by ultraviolet-visible (UV-Vis), Fourier transform infrared-attenuated total reflectance (FTIR-ATR) and quantitative 13 C nuclear magnetic resonance (NMR) spectroscopy, and the sulfonic and phenolic groups were assessed by conductometric titration. It was concluded that LS polymerization occurred mostly via the formation of new aryl ether bonds (two thirds of the modification) and biphenyl bonds (the remaining third). However, part of the newly formed bonds of unknown origin are temperature labile and cleaved during the concentration of LS at pH 4 and 80°C under vacuum, which led to the reduction of the M w of the modified lignin to almost one third.

Open Access May 5, 2020

Reduction of adsorbable organically bound halogens (AOX) formation at near-neutral pH chlorine dioxide bleaching of softwood kraft pulp

Sara Starrsjö, Olena Sevastyanova, Peter Sandström, Juha Fiskari, Maria Boman, Mikael E. Lindström

Page range: 597-604

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Abstract

Recently, a new type of bleaching sequence, Elemental Chlorine Free (ECF) light with one D stage, has been developed. It combines the efficiency and high selectivity of chlorine dioxide (ClO 2 ) bleaching with more environmental friendly oxygen based bleaching chemicals. This work examines the effect of pH on the formation of adsorbable organically bound halogens (AOX) in an intermediate D stage – a single ClO 2 stage at the middle of an ECF light bleaching sequence. Carbon dioxide (CO 2 ) is used to generate a bicarbonate buffer in situ , stabilizing the pH during the bleaching. Near-neutral pH is hypothesized to decrease the formation of strongly chlorinating species, so that the AOX formation is reduced. The results indicate that a near-neutral pH D stage can reduce the AOX content in the effluents with up to 30%. The ISO brightness was unchanged to a lower ClO 2 consumption. The pulp viscosity was slightly higher after near-neutral pH D stage, but to its disadvantage a lesser delignification and removal of HexA was obtained. The degradation of HexA correlated well with the AOX, affirming earlier theories that HexA has a major impact on the AOX formation. The higher amounts of residual HexA and lignin resulted in more thermal yellowing of the pulps bleached with a near-neutral pH D stage.

May 13, 2020

Use of UV resonance Raman spectroscopy for assessing the brightness stability of ozone TCF bleached pulp

Etienne Montet, Estefania Isaza Ferro, Jordan Perrin, Dominique Lachenal, Christine Chirat

Page range: 605-613

Abstract

This study intends to explain the difference in brightness stability between hardwood ECF and TCFz kraft pulps bleached by DEpDD and A(ZEo)(ZEo)(ZP) sequences respectively, using UV Resonance Raman (UVRR) spectroscopy. The brightness stability of the pulps was tested via dry aging experiments where the Post-Color Number (PCN) of the ECF pulp was twice that of the TCF pulp. The aged and non-aged bleached pulps were analyzed with UVRR spectroscopy to identify the cause of the large difference in PCN. The spectra of ECF and TCF bleached pulps presented clear differences in the intensities of the Raman shifts associated to lignin, lignin-like compounds, and degradation products such as muconic acids. To identify more specifically the compounds affecting the PCN, several post-bleaching treatments were applied on the ECF pulp including single stages (E, B, P, Z) or combinations (ZE, ZB, ZP), and their UVRR spectra analyzed. It was found that alkaline-soluble compounds were the main culprits for the difference in PCN values between ECF and TCFz pulps. ZP combination was the most efficient in eliminating residual lignin and other unsaturated components and for the development of brightness and brightness stability.

June 2, 2020

Multi-step purification method of water-soluble oligosaccharides produced from hardwood and softwood

Juliette Francillon, Christine Chirat, Claire Boisset, Laurine Buon

Page range: 615-623

Abstract

Pressurized hot water pretreatment was performed on softwood (SW) and hardwood (HW) chips following the same conditions (1 h at 170 °C) in order to partly hydrolyse hemicelluloses. The complete characterization of these sugar enriched autohydrolysates (AH) being rather complex, two different purification methods were conducted. Nanofiltration (NF) 1kDa membrane and ultrafiltration (UF) 3 and 5kDa membranes were used to separate oligosaccharides (OS) from undesired compounds and for their molar mass fractionation. Granulated activated charcoal (GAC) adsorption was also used for hydrolysates detoxification. The chemical nature of OS and side charge groups vary significantly depending of the fractions obtained, e. g. xylans' chain length is positively correlated with the degree of acetylation. UF at 5kDa allows for the total separation of galactoglucomannans (GGMs) from xylans, in SW AH, however, this result was not achieved with HW. From the acid soluble lignin (ASL) removal point of view, membrane filtration from 1kDa is more efficient than activated carbon treatment concerning HW AH, on the contrary to SW AH. Regarding the lignin to OS ratio, for both species, GAC leads to a better sugar purity.

February 28, 2020

Structural features of macromolecular components of cork from Quercus suber L.

Diana G. Branco, Joana R. Campos, Luís Cabrita, Dmitry V. Evtuguin

Page range: 625-633

Abstract

The structural features of macromolecular components of cork (suberin, lignin, cellulose and hemicelluloses) from Quercus suber L. used for the production of stoppers were assessed after their isolation and purification. Suberin is the major component of cork (ca. 44%) and is constituted mainly by hydroxy fatty acids (C 14 –C 26 ). Cork lignin was found to be highly condensed (16.2%) and revealed a syringyl:guaiacyl:p-hydroxyphenyl (S:G:H) ratio of 26:71:3 with predominant β- O -4′ (0.38%), β-5′, β-β and tetrahydrofuran (THF) type (totally ca. 27%) structures. Cork lignin also has a remarkable amount of ferulic acid structures, which are considered the binding point between lignin and suberin. The cellulose of cork cells (17.2%) is a typical cellulose I polymorph with a degree of crystallinity (DC) of 70.3% and an average crystallite width of 3.5 nm. The major hemicellulose of cork is glucuronoxylan (near 6.0%) possessing a molar Xyl p :MeGlc p A ratio of 14:1.

About this journal

Objective
Holzforschung (HF) is an international scholarly journal that publishes cutting-edge research on the biology, chemistry, physics and technology of wood and wood components. High quality papers about biotechnology and tree genetics are also welcome. Rated year after year as one of the top scientific journals in the category of Pulp and Paper (ISI Journal Citation Index), Holzforschung represents innovative, high quality basic and applied research. The German title reflects the journal's origins in a long scientific tradition, but all articles are published in English to stimulate and promote cooperation between experts all over the world. Ahead-of-print publishing ensures fastest possible knowledge transfer.

Topics

Biology, chemistry, physics and technology of wood and wood components
Biotechnology and tree genetics

Article formats
Original articles, Reviews, Short notes

> Information on submission process

Volume 74 Issue 6 - Special issue: The 20th International Symposium on Wood, Fiber and Pulping Chemistry (Tokyo, Japan, September 9–11, 2019); Issue editor: Thomas Rosenau

Issue of Holzforschung

Frontmatter

Wood-based resins and other bio-based binders for the production of mineral wool

Abstract

A branched structure provides kraft lignins a denser morphology and a high molar mass for a given hydrodynamic radius

Abstract

Effects of lignin structure and solvent on the formation rate of quinone methide under alkaline conditions

Abstract

Effect of different catalysts on the oxyalkylation of eucalyptus Lignoboost® kraft lignin

Abstract

Preparation of kraft lignin-based activated carbon fiber electrodes for electric double layer capacitors using an ionic liquid electrolyte

Abstract

Laccase-catalyzed oxidative modification of lignosulfonates from acidic sulfite pulping of eucalyptus wood

Abstract

Reduction of adsorbable organically bound halogens (AOX) formation at near-neutral pH chlorine dioxide bleaching of softwood kraft pulp

Abstract

Use of UV resonance Raman spectroscopy for assessing the brightness stability of ozone TCF bleached pulp

Abstract

Multi-step purification method of water-soluble oligosaccharides produced from hardwood and softwood

Abstract

Structural features of macromolecular components of cork from Quercus suber L.

Abstract