Milled Wood Research Articles

Correction: Spruce milled wood lignin: linear, branched or cross-linked?

Correction for ‘Spruce milled wood lignin: linear, branched or cross-linked?’ by Mikhail Balakshin et al., Green Chem., 2020, 22, 3985–4001, DOI: 10.1039/D0GC00926A.

Structural Characterization and Antioxidant Activity of Milled Wood Lignin from Xylose Residue and Corncob.

Xylose residue (XR), after diluted acid treatment of corncob, consists of cellulose and lignin. However, structural changes of XR lignin have not been investigated comprehensively, and this has seriously hindered the efficient utilization of lignin. In this study, corncob milled wood lignin (CC MWL), and xylose residue milled wood lignin (XR MWL) were isolated according to the modified milled wood lignin (MWL) method. The structural features of two lignin fractions were thoroughly investigated via fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and two dimensional nuclear magnetic resonance (2D NMR) spectroscopy techniques. XR MWL with higher yield and lower bound carbohydrate contents presented more phenolic OH contents than CC MWL due to partial cleavage of β-O-4. Furthermore, the molecular weights of XR MWL were increased, possibly because of condensation of the lignin during the xylose production. A study on antioxidant activity showed that XR lignin had better radical scavenging ability than that of 2,6-Di-tert-butyl-4-methyl-phenol (BHT) and CC MWL. The results suggested that the lignin in xylose residue, showing great antioxidant properties, has potential applications in food additives.

Anti-osteoporotic effects of syringic acid and vanilic acid in the extracts of waste beds after mushroom cultivation

In recent years, the number of patients with osteoporosis has increased as population grows older. Therefore, the chemoprevention of osteoporosis by better nutrition is important. White-rot fungi degrades milled wood lignin for growth and development. This degradation results in the formation of phenolic compounds such as syringic acid (SA) and vanillic acid (VA). In the artificial culture of edible mushrooms using a mushroom bed, the disposal of waste beds after mushroom cultivation is an important issue. The present study investigated the presence and amount of both SA and VA in the discarded waste beds after mushroom cultivation. The extracts from waste beds after cultivation of shiitake mushrooms, Lentinula edodes; buna shimeji, Hypsizygus marmoreus; maitake, Grifola frondosa; king trumpet mushrooms, Pleurotus eryngii; and butterscotch mushrooms, Pholiota microspora were analyzed using high performance liquid chromatography. Although the content of SA and VA was considerably different among the mushrooms, SA and VA were present in extracts obtained from all the waste beds. We also demonstrated that SA and VA exert their anti-osteoporotic effect independently of the estrogen receptor-mediated pathway using murine monocytic RAW264.7cells, ovariectomized mice, and human breast cancer MCF-7cells. Thus, these results suggest that the extracts are effective sources of SA and VA, which are effective in preventing osteoporosis.

Comparison of pyrolyzed lignin before and after milled wood lignin purification of Norway spruce with increasing steam explosion

Increasing energy and chemical needs have to be covered by renewable resources, such as biomass, in the near future. Steam explosion is a green pretreatment for utilizing biomass, but it produces a by-product, pseudo-lignin. By comparing milled wood lignin purified and unpurified samples after steam explosion with pyrolysis–GC–MS, the components of pseudo-lignin should be evident. 2D NMR HSQC was also conducted on the purified samples, in addition to compositional analysis after steam explosion. After steam explosion, there is about 6 wt% of pseudo-lignin, and the pyrolysis shows an increase in diol benzenes and furan components in the unpurified samples, which is associated with pseudo-lignin.

Cleavage of lignin model compounds and ligninox using aqueous oxalic acid.

Aqueous oxalic acid cleaves oxidised β-O-4 lignin model compounds by two distinct mechanisms that are dependent on the presence of the hydroxymethyl substituent. Various β-O-4 phenoxyacetophenones that do not contain the hydroxymethyl substituent undergo oxidative cleavage upon exposure to aqueous oxalic acid in the presence of air, likely through concerted ring opening of a dioxetane intermediate to give the corresponding benzoic acid and phenyl formate. Importantly, detrimental side reactions arising from singlet oxygen and hydroperoxy radicals (from both O2 and oxalic acid) are minimal when the cleavage is run under air compared to neat oxygen. When oxidised β-O-4 lignin model compounds bearing the hydroxymethyl group are cleaved by aqueous oxalic acid, the resulting diketone and phenol products arise from a redox neutral cleavage that is analogous to the formic acid-sodium formate mediated lignin cleavage process reported by Stahl. Aqueous oxalic acid also cleaves lignin itself, with oxidised milled wood lignin (MWLox) from Pinus radiata giving a 14% yield of ethyl acetate soluble aromatics with good selectivity for vanillin. Aqueous oxalic acid appears to be a promising lignin cleavage system given the benign, bio-based reagents, absence of metals and organic solvents and a simple extraction procedure that enables oxalic acid recycling.

Thermal stability of lignin in ground pulp (GP) and the effect of lignin modification on GP’s thermal stability: TGA experiments with dimeric lignin model compounds and milled wood lignins

Abstract For ground pulp (GP) utilization in wood fiber composites as reinforced material, its thermal behavior is relevant. The contribution of lignin to thermal performance of GP from Pinus densiflora was the focus of the present study. Dimeric lignin model compounds and isolated milled wood lignins (MWLs) from three sources were submitted for thermogravimetric analysis (TGA). The temperatures leading to 1% weight loss (T per 1% WL) for the material were determined. The thermal stability of β-O-4 models was the lowest. Among the MWLs, the abaca MWL with its high β-O-4 content was the least thermostable. An acetylated nonphenolic β-O-4 lignin model compound showed that acetylation improves the thermal stability of this type of dimeric models. The acetylation of benzylic OH groups in β-O-4 linkages is especially relevant for the thermal resistance, which was also shown based on pre-acetylated benzylic OH groups in the GP before the total acetylation.

Influence of wood component on physical and chemical transformations during high temperature heating of composite fuel based on bituminous coal

Experimental studies of ignition delay time for mixtures of dispersed hard coal of two types and milled wood over a wide temperature range have been performed. Time of total completion of organic part pyrolysis of both components at different concentrations have been established in order to assess the prospects for such fuels application in large- and small-scale power engineering (combustion in boiler furnaces of different capacities). It has been established that simultaneous thermal decomposition of mixture of coal and wood particles leads to a significant change of pyrolysis temperature range and release of anthropogenic gases (sulfur and nitrogen oxides) in case of high-temperature heating of the mixture based on lean coal. The same effect, but in much smaller scale, has been recorded for a mixture based on long-flame coal. A hypothesis has been formulated on the mechanism of sulfur and nitrogen oxides precipitation during thermal decomposition of the mixture of lean coal and wood particles as a result of interaction between transitory gaseous and solid pyrolysis products of coal and wood in the temperature range up to 1000°C. Prospects of applying the milled coal and wood mixtures as fuel for steam and hot water boilers have been substantiated. With a small decrease of energy characteristics of such fuels, compared to homogeneous coals, significant improvement of ecological and economic characteristics of the fuel combustion processes can be achieved. It has been shown that vital synergistic effect of co-combustion of coal and wood particles is achieved only with certain coals.

Ball Milling's Effect on Pine Milled Wood Lignin's Structure and Molar Mass.

The effect of ball milling expressed as the yield of milled wood lignin (MWL) on the structure and molar mass of crude milled wood lignin (MWLc) preparation is studied to better understand the process’ fundamentals and find optimal conditions for MWL isolation (i.e., to obtain the most representative sample with minimal degradation). Softwood (loblolly pine) MWLc preparations with yields of 20–75% have been isolated and characterized based on their molar mass distribution (by Size Exclusion Chromatography (SEC)), hydroxyl groups of different types (31P NMR), methoxyl groups (HS-ID GC-MS), and sugar composition (based on methanolysis). Classical MWL purification is not used to access the whole extracted lignin. The results indicate that lignin degradation during ball milling occurs predominantly in the high molar mass fraction and is less pronounced in the low molar mass fraction. This results in a significant decrease in the Mz and Mw of the extracted MWLc with an increase in the yield of MWLc, but has only a very subtle effect on the lignin structure if the yield of MWLc is kept below about 55%. Therefore, no tedious optimization of process variables is necessary to achieve the required MWLc yield in this range for structural studies of softwood MWL. The sugar composition shows higher amounts of pectin components in MWLs of low yields and higher amounts of glucan and mannan in high-yield MWLs, confirming that lignin extraction starts from the middle lamella in the earlier stages of MWL isolation, followed by lignin extraction from the secondary wall region.

Robust Surface Plasmon Resonance Chips for Repetitive and Accurate Analysis of Lignin-Peptide Interactions.

We have developed novel surface plasmon resonance (SPR) sensor chips whose surfaces bear newly synthesized functional self-assembled monolayer (SAM) anchoring lignin through covalent chemical bonds. The SPR sensor chips are remarkably robust and suitable for repetitive and accurate measurement of noncovalent lignin–peptide interactions, which is of significant interest in the chemical or biochemical conversion of renewable woody biomass to valuable chemical feedstocks. The lignin-anchored SAMs were prepared for the first time by click chemistry based on an azide–alkyne Huisgen cycloaddition: mixed SAMs are fabricated on gold thin film using a mixture of alkynyl and methyl thioalkyloligo(ethylene oxide) disulfides and then reacted with azidated milled wood lignins to furnish the functional SAMs anchoring lignins covalently. The resulting SAMs were characterized using infrared reflection–absorption, Raman, and X-ray photoelectron spectroscopies to confirm covalent immobilization of the lignins to the SAMs via triazole linkages and also to reveal that the SAM formation induces a helical conformation of the ethylene oxide chains. Further, SPR measurements of the noncovalent lignin–peptide interactions using lignin-binding peptides have demonstrated high reproducibility and durability of the prepared lignin-anchored sensor chips.

Improvement of enzymatic digestibility of wood by a sequence of optimized milling procedures with final vibratory tube mills for the amorphization of cellulose

AbstractA three-stage wood milling process was investigated leading to coarse, fine and amorphization of milled wood (MW) as a pretreatment for enzymatic wood hydrolysis. An eccentric vibratory tube mill (EVTM) and a spring suspended vibratory tube mill (SSVTM) were found to be suitable for wood cellulose amorphization. Both methods gave rise to highly digestible and amorphous wood powders amenable to enzymatic hydrolysis. The SSVTM had superior energy efficiency. The resulting MW afforded a 70% sugar yield via enzymatic hydrolysis and the total energy consumption was around 1.5 kWh kg−1oven-dried wood (odW) for all three milling stages. In contrast, EVTM consumed 17 kWh kg−1odW energy. Accordingly, SSVTM has a high potential for preparing wood for enzymatic hydrolysis.

Зменшення вмісту формальдегіду у фанері, склеєній карбамідоформальдегідними клеями з використанням деревинного волокнистого шламу

Щоб зменшити вміст формальдегіду у фанері, карбамідоформальдегідні клеї наповнювали деревинним волокнистим шламом. Під час досліджень використано: сухий подрібнений деревинний волокнистий шлам з розміром частинок менше 0,2 мм і вологістю 10%; карбамідоформальдегідну смолу КФ-МТ; амоній хлорид; березовий лущений шпон товщиною 1,5 мм і вологістю 6%. За допомогою багатофакторного планування експерименту досліджено вплив параметрів режиму склеювання шпону (кількості волокнистого шламу в клеї, витрати клею, тривалості та температури пресування) на вміст формальдегіду у фанері та міцність фанери на зріз. Вміст формальдегіду у фанері визначено методом WKI; міцність фанери на зріз – згідно з ДСТУ EN 314-1:2003 і ДСТУ ЕN 314-2:2006 (клас з’єднання 1). На вміст формальдегіду у фанері найбільше впливають витрата клею, у разі зменшення якої від 130 до 100 г/м2 вміст формальдегіду зменшується на 30-42 %, та температура пресування, в разі підвищення якої від 100 до 150˚С вміст формальдегіду зменшується на 34-41 %. У разі додавання до клею до 4 мас. ч. волокнистого шламу вміст формальдегіду у фанері зменшується на 16-30 %. На міцність фанери на зріз впливають кількість волокнистого шламу, в разі збільшення якого міцність частково знижується на 11-12 %, залишаючись більшою у 2,3-2,5 рази, порівняно з вимогами чинного стандарту, та температура пресування, в разі підвищення якої міцність зростає на 14-17 %. Отримані адекватні та відтворювані регресійні залежності властивостей фанери від досліджуваних факторів дають змогу спрогнозувати вміст формальдегіду у фанері та міцність фанери на зріз від параметрів режиму склеювання шпону.

Isolation of Lignin from Masson Pine by Liquid-Liquid Extraction Based on Complete Dissolution in NaOH Aqueous Solution

A method for lignin isolation from softwood based on complete dissolution in NaOH aqueous solution and liquid-liquid extraction was introduced. The structural features of milled alkali-soluble lignin (MAL) were comparatively analyzed with those of classical milled wood lignin (MWL) by means of alkaline nitrobenzene oxidation (NBO) and molecular weight, as well as Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectra analyses. The results showed that the yield of crude MAL (34.2%) was about twice as much as that of MWL (16.4%). The NBO product yields of MWL and MAL were quite similar. The weight-average molecular weight of MAL (10,400 g mol-1) was much higher than for MWL (6,970 g mol-1). Both MWL and MAL displayed similar FTIR, UV, 1H NMR, and 1H-13C HSQC NMR spectra. The total OH content of MAL (4.48 mmol g-1) was higher than that of MWL (3.89 mmol g-1). Compared with MWL, MAL showed similar structural characteristics but better isolation yield and higher molecular weight.

Fractionation of lignin macromolecules by sequential organic solvents systems and their characterization for further valuable applications

Lignin solvent fractionation is one of the promising methods for homogenizing and utilizing lignin commercially. In this work, fractionation characteristics of two lignin fractions were compared to investigate the potential of utilization of fractionated lignin. Two lignins [milled wood lignin(MWL) and organosolv lignin(OL) from yellow poplar] were sequentially fractionated with ethyl acetate(F1), 2-butanone(F2), methanol(F3), acetone(F4), and dioxane/water(F5). Yields of five MWL fractions F1 to F5 were 11.7%, 11.7%, 15.3%, 11.8%, and 49.6%, respectively, and yields of OL fractions were 26.2%, 26.1%, 18.7%, 3.7% and 25.4%. Average molecular weight of F1 (lowest molecular weight fraction) ranged from 1000 to 2400Da, whereas that of F5 (highest molecular weight fraction) was above 10000Da. According to functional group analysis, contents of phenolic hydroxyl groups and methoxyl groups decreased gradually with increasing molecular weight. DFRC analysis was performed to investigate the frequency of β-O-4 linkages and it revealed that the higher molecular weight fractions yielded larger amounts of DFRC monomers, indicating that those fractions more frequently contain aryl ether linkages. TG/DTG showed that the low molecular weight fractions generally have lower initial thermal stability. Tg of the fractions ranged from 126°C to 156°C, increasing as the molecular weight of the lignin fraction increased.

Efficient Method of Lignin Isolation Using Microwave-Assisted Acidolysis and Characterization of the Residual Lignin

Microwave heating is characterized by high efficiency and selectivity in biomass treatment. Due to the high thermal stability and low polarity of lignin, isolation of lignin by high-temperature microwave treatment is a promising subject for investigation. In this paper, microwave treatment is applied to polysaccharide liquefaction and lignin isolation from softwood at 160–210 °C for 10 min with dilute sulfuric acid. Mass balance/element analysis/FTIR/TG/solid-state 13C NMR/Py-GC/MS are applied to investigate the processed residues (residual lignin). At 190 °C processing temperature, the residual lignin is a material rich in aromatics. High lignin purity (93 wt %) and yield (82 wt %) could be achieved by a simple protocol, which usually takes days or even weeks using conventional milled wood lignin protocols. The Py-GC/MS is applied to check the structure of lignin by a newly developed approach. The liquid phase after isolation is analyzed by GC-MS and liquid carbon NMR. Most chemicals in processed liquid ...

Use of tube flow fractionation in wood powder characterisation

The size and shape of powdered wood particles are important properties when considering their use in wood burning or the production of biofuels, biocomposites and biochemicals. Different measurement techniques can be used to measure particle size, but unfortunately these do not provide information about the shape of the wood particles. In this study, a fast and reliable tube flow fractionation method (analysing time 3min; particle size range 1 μm-2000 μm; analysed particles per sample 30,000–200,000) is used to separate water-diluted wood powders which varies by size and shape. 30 different milled wood powder samples are analysed (average particle size from 20 μm to 300 μm and average aspect ratio from 3 to 10). The major benefit in tube flow fractionation method is that the concealment of the finest particles in CCD imaging is avoided by applying the imaging unit after the fractionation of wood particles. Wood powder can easily be separated into different fractions by leading the water-diluted sample flow into different beakers for certain time periods. The transmittance signal after tube flow fractionating yields information about the particle size, and optical imaging provides information about the morphology of the particles. It was found in this study that rotor impact milling to a finer size range produces small but elongated particles. Additionally there were only small differences in the particle size distributions between jet milled and oscillatory ball milled samples, but it was noticed that oscillatory ball milled powders have a significantly lower aspect ratio than jet milled samples.

Effects of Solvation and Ionization on 13C NMR Spectra of Lignin Model Compounds, Spruce Milled Wood Lignin and Kraft Lignin

The effects of alkali and polar aprotic solvent on the aromatic carbons signals in 13C NMR (Carbon-13 nuclear magnetic resonance) spectra of lignin model compounds and spruce milled wood lignin (MWL) were studied. It was found that in 1 M aqueous NaOH signal shifts of C-1 and C-4 carbon atoms in the aromatic ring were the most noticeable in lignin models with free phenolic hydroxyl groups, which are ionized under the conditions. A similar effect in the spectra of the studied model compounds was observed in 0.5 M aqueous NaOD-deuterated dimethyl sulfoxide (DMSO) mixture (DMSO: water ratio 3:7 v/v). The model data help explaining changes in the 13C NMR spectra of MWL and lignin in situ dissolved in spruce kraft black liquor caused by ionization. In the 13C NMR spectra of spruce black liquor the signals of phenolic and non-phenolic lignin units are clearly separated and do not overlap with the signals of the carbon atoms of carbohydrates and other aliphatic products of wood degradation. The data obtained are useful in understanding the important role of solvation and ionization processes leading to lignin solubilization.

Effect of Ethanol Organosolv Lignin from Bamboo on Enzymatic Hydrolysis of Avicel

The interactions between lignin and cellulase play a key role in the effective enzyme saccharification of lignocellulose. This work investigated the enhancing effect of ethanol organosolv lignins (EOL) from bamboo on enzyme hydrolysis of the pure cellulose. The addition of EOL-P. amarus and EOL-D. sinicus (8 g/L) remarkably increased the 72 h glucose yields of Avicel, from 51.3% to 61.1%, and from 51.3% to 59.4%, respectively, and made much more cellulase available for cellulose. Langmuir adsorption isotherms showed that ethanol organosolv lignins from bamboo had a lower binding ability to the cellulase enzymes than milled wood lignin (MWL), which resulted in less nonproductive binding. Also, FTIR and 13C and 2D HSQC NMR spectra showed that lignin degradation occurred by cleavaging β-O-4 linkages in the ethanol organosolv process; EOL-D. sinicus showed a less condensed structure of isolated lignins at the Cβ position than MWL-D. sinicus. In addition, carboxylic groups, ferulic acid, and p-coumarate acid u...

Yield of Stirred Cold Maceration and Extraction of Milled European Black Alder Wood and Bark using Different Solvents

Wood extractives, especially polyphenols, have great influence on the xylem colour of many wood species, which affects the success of hydrothermal wood processing, such as wood drying. One such wood species is European black alder (Alnus glutinosa (L.) Gaertn.), which is prone to forming intense and uneven reddish-orange or reddish-brown discolourations immediately upon harvesting and processing. However, there is lack of published scientific data on the wood and bark extractives of black alder, as well as the most suitable solvents to extract them. In this work, total soluble extractives, phenols, and flavonoids have been quantified in the wood and bark of black alder. Furthermore, the influence of four different polar organic solvents and deionized water on extractives removal yields has been measured. It was found that the bark has much higher levels of extractives as compared to the wood. Furthermore, it has been found that the highest extractive yields were obtained by using methanol as the extraction solvent for all observed compound group classifications.

Composition and structure of an antioxidant acetic acid lignin isolated from shoot shell of bamboo (Dendrocalamus Latiforus)

Bamboo shoot shell (BSS), which contains a large amount of insoluble fibre and lignin, is the main agricultural waste from the production of bamboo shoots. To utilize this waste in a value-added manner, the acetic acid lignin (AL) fraction from BSS was extracted via a combination of hot water pre-treatment and acetic acid post-treatment in the present study. The chemical composition, structural characteristics, and antioxidant activity of AL were investigated and compared to the corresponding milled wood lignin (MWL). The results showed that AL had a higher yield (74%) and lower content of associated carbohydrates (2.96%) than MWL (5.16%). GPC analysis revealed that AL possessed a moderate molecular weight (Mw=2789Da) and narrow polydispersity index (Mw/Mn=1.54). Structural characterization via FT-IR, 1H NMR, 2D-HSQC, and 31P NMR indicated that AL from BSS was a typical HSG-type lignin and was partially acylated at the γ-carbon of the side chain by p-coumarate. Moreover, the bonds between lignin units were predominately β-O-4⿲ linkages. Compared to MWL, AL possessed a characteristically higher phenolic hydroxyl group content and S/G ratio. In terms of the DPPH radical scavenging activity, ABTS radical cation scavenging activity and ferric reducing antioxidant power, AL showed stronger antioxidant activity than MWL and was superior to the commercial synthetic antioxidant BHT. In summary, by applying a modified two-step procedure, which included hot water pre-treatment and acetic acid extraction, AL from BSS was effectively extracted, and the antioxidant potential of AL was characterized.

Eco-Friendly Constituents for Making Wood-Polymer Composites

The aim of this work was to obtain eco-friendly constituents for making wood-polymer composites (WPCs) by rational utilisation of hardwood residue with its mechanical processing and purposeful chemical modification. To reduce the energy input for residue milling for obtaining a lignocellulosic filler as well as to activate its surface for the further modification, the optimal parameters of low temperature acid hydrolysis of the hardwood residue under mild conditions were found. To enhance the wetting of the lignocellulosic filler with respect to recycled polypropylene, the milled hydrolysed wood particles were modified by ammoxidation. For obtaining a lignin-containing surface tension regulator (compatibiliser) that is able to reinforce the interaction between the constituents at the interface, soda lignin was obtained via delignification of the hydrolysed hardwood residue under laboratory conditions. The developed compatibiliser represented nanoparticles of a non-stoichiometric polyelectrolyte complex, incorporating soda lignin and synthetic polyamine - polyethylenimine. By using appropriate laboratory equipment and the determined technological regime, aspen wood-recycled polypropylene composites were made and tested.