In this study, four biorefinery technical lignins were used to synthesize lignin–phenol–formaldehyde (LPF) resin adhesives with a proposed formulation that was designed based on accurate analysis of the active sites in lignin with ³¹P nuclear magnetic resonance (NMR). The properties of the LPF resin adhesives and the plywoods prepared with them were tested. The structural features and curing behavior of the LPF resin adhesives were thoroughly investigated by solution- and solid-state ¹³C NMR. Results indicated that the proposed formulation exhibited favorable adaptability for all four of these technical lignins for synthesis of LPF resin adhesives. High-performance plywood with low emissions of formaldehyde could be successfully prepared with the synthesized LPF resin adhesives. All the LPF resin adhesives exhibited similar structure and curing behavior with the commercial phenol–formaldehyde (CPF) resin adhesive. However, the LPF resin adhesives showed relatively higher curing temperatures as compared with the CPF resin adhesive. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42493.

Hydrogels based on acrylamide (AM) and ethanol organosolv lignin (EOL) with high swelling and good mechanically elastic properties were synthesized in an alkaline solution. EOL was used as a reactive filler for the preparation of AM-based hydrogels. The impact of EOL addition on the physicochemical properties of AM-based hydrogels was investigated using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy, and their mechanical properties were examined. The water swelling ratio of the prepared hydrogels increased with the increase of EOL content, and their maximum swelling ratio could reach up to 180. Mechanical measurements indicated that their tensile strength was highly dependent on the amount of EOL, and their elongation at break reached up to 1400%. The formation mechanism of EOL composite hydrogels was probably that most of AM was synthesized into the crosslinked poly(acrylic amide) network, and small quantities of AM was hydrolyzed to acrylic acid ions under alkaline condition. The chain transfer of free radicals from AM and/or AA to EOL molecules occurred in the polymerization process. With increasing EOL content in the hydrogels, an interpenetrating polymer network might be mainly formed by the hydrogen bonding between EOL and AA and/or AM molecules. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42638.

Triploid poplar was fractionated using mild organosolv process, and detailed characteristic elucidation of the lignin obtained was performed to determine the effects of various chemicals (sodium hydroxide, triethylamine, and formic acid) and solvents (methanol, ethanol, n-propanol, and n-butanol). Both nondestructive techniques (e.g., NMR technology) and degradation methods (e.g., alkaline nitrobenzene oxidation) were performed to comparatively evaluate the structural degradation of lignin molecules. The addition of acidic and basic catalysts improved the purity of lignin by acid hydrolysis and the cleavage of the ester groups and other types of lignin–carbohydrate interactions formed by polyoses and lignin under the basic conditions. A certain amount of aryl alkyl ether linkages (β-O-4) was cleaved during the fractionation process, whereas other carbon–carbon linkages were resistant to degradation. The formation of new carbon–carbon bonds led to the lignin fraction with obviously higher molecular weight and thermal stability, resulting from the induced carbon cation under the acidic condition. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39673.

Lignin, a major component of the cell wall of vascular plants, has long been recognized for its negative impact and treated as a by-product in a biorefinery. This highly abundant by-product of the biorefinery is undervalued and underdeveloped due to its complex nature. The development of value-added products from lignin would greatly improve the economics of the biorefinery. The inherent properties of lignin significantly affect the productivity of the biorefinery processes and its potential applications. Although the structure and biosynthetic pathway of lignin have been studied for more than a century, they have not yet been completely elucidated. In this mini-review, the primary obstacles to elucidating the structure of native lignin, including separation and characterization, are highlighted. Several classical methods for separation and various NMR techniques, especially 2D HSQC NMR, for characterization of lignin are reviewed. Some potential applications of lignin are introduced. It is believed that a knowledge of the method to separate lignin from the cell wall and structural features of the lignin polymer from lignocellulosic materials will help to maximize the exploitation of lignocelluloses for the biorefinery as well as the utilization of lignin for novel materials and chemicals. © 2012 Society of Chemical Industry

Betula alnoides lignin, recovered as a byproduct in autocatalyzed ethanol-water pulping process, was converted into viscous polyether polyols through oxypropylation and liquefaction methods, with the aim of adding value to this byproduct. The oxypropylation reaction was performed by reacting autocatalyzed ethanol-water lignin (AEL) with propylene oxide under the acidic and alkaline conditions at room temperature, respectively. In contrast, the liquefaction reaction was carried out using the mixed solvents of polyethylene glycol and glycerol at 160°C with sulfuric acid as a catalyst. The resulting polyether polyols from each method was characterized by Fourier transform-infrared (FTIR), ¹H and ³¹P nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), and thermogravimetric analysis. Quantitative ³¹P NMR indicated that all the aliphatic hydroxyl group values of polyols increased significantly by the above two methods. More secondary hydroxyl groups (2.016 mmol/g) were obtained in the alkaline oxypropylation reaction, whereas more primary hydroxyl groups (4.296 mmol/g) were found in the liquefied product. GPC analysis showed that the alkaline oxypropylated product (M_w 3130 g/mol, M_n 2080 g/mol) and liquefied product (M_w 4990 g/mol, M_n 4630 g/mol) have higher molecular weights than AEL (M_w 2560 g/mol, M_n 1530 g/mol). Thermal stability analysis suggested that the polyether polyols have a lower degradation temperature than AEL. These polyols used as precursors in polyurethane synthesis give promising properties, which open new avenues of exploitation of AEL. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Nine lignin fractions from bamboo (Dendrocalamus brandisii) were sequentially isolated with hot water at 80, 100, and 120°C for 3 h and 60% aqueous ethanol containing 0.25, 0.5, 1.0, 2.0, 3.0, and 5.0% NaOH at 80°C for 3 h. Molecular weight and purity analysis revealed that the lignin fractions isolated by hot water (L₁, L₂, and L₃) had lower weight-average molecular weights (between 1350 and 1490 g mol⁻¹) and contained much higher amounts of associated hemicelluloses (between 9.26 and 22.29%), while the lignin fractions isolated by alkaline aqueous ethanol (L₄, L₅, L₆, L₇, L₈, and L₉) had higher weight-average molecular weights (between 2830 and 3170 g mol⁻¹) and contained lower amounts of associated hemicelluloses (between 0.63 and 1.66%). Spectroscopy (UV, FTIR, ¹³C-NMR, and HSQC) analysis showed that the bamboo (Dendrocalamus brandisii) lignin was typical grass lignin, consisting of p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units. The major interunit linkages presented in the alkaline aqueous ethanol extractable bamboo lignin were β-O-4′ aryl ether linkages (about 74.3%), followed by β-β′ resinol-type linkages and β-1′ spirodienone-type linkages (both for 7.8%), together with small amounts of β-5′ phenylcoumaran (6.8%) and p-hydroxycinnamyl alcohols end groups (3.1%). In addition, a small percentage (1.0%) of the lignin side-chain was found to be acetylated at the γ-carbon, predominantly over syringyl units. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A novel cellulose-click-chitosan polymer was prepared successfully in three steps: (1) propargyl cellulose with degrees of substitution (DS) from 0.25 to 1.24 was synthesized by etherification of bamboo Phyllostachys bambusoide cellulose with propargyl chloride in DMA/LiCl in the presence of NaH. The regioselectivity of propargylation on anhydrous glucose unit determined by GC-MS was in the order of 2 >> 6 > 3; (2) the functional azide groups were introduced onto the chitosan chains by reacting chitosan with 4-azidobenzoic acid in [Amim]Cl/DMF and the DS ranged from 0.02 to 0.46; (3) thus, the cellulose-click-chitosan polymer was obtained via click reaction, that is, the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction, between the terminal alkyne groups of cellulose and the azide groups on the chitosan backbone at room temperature. The successful binding of cellulose and chitosan was confirmed and characterized by FTIR and CP/MAS ¹³C NMR spectroscopy. TGA analyses indicated that the cellulose-click-chitosan polymer had a higher thermal stability than that of cellulose and chitosan as well as cellulose–chitosan complex. More interestingly, some hollow tubes with near millimeter length were also observed by SEM. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Polysaccharide fractions were extracted from partially delignified bamboo (Neosinocalamus affinis) culms pretreated with ultrasonic irradiation for varied times and cold sodium hydroxide/urea solution, and their structure and thermal stability were comparatively characterized. In this case, ball-milled bamboo culms were treated with ultrasonic irradiation for varied times (0, 5, 15, and 25 min), dissolved with 7% sodium hydroxide/12% urea solution at −12°C, and then extracted with ethanol and dioxane to obtain partially delignified solid fractions. Subsequently, the solid fractions were subjected to be extracted with dimethyl sulfoxide followed by precipitation in ethanol and yielded the polysaccharide fractions. Sugar analysis indicated that the total sugar content increased from 60.63% in the polysaccharide fraction prepared without ultrasonic irradiation to 81.26% in the polysaccharide fraction prepared with an ultrasonic irradiation time of 25 min. Glucose (∼ 50–55%) was the major sugar component, and xylose (∼ 41–44%) was the second major sugar in polysaccharide fractions in all cases. Spectroscopy (FTIR, ¹H-NMR, ¹³C-NMR, and HSQC) analysis suggested that the polysaccharide fractions were mainly composed of (14)-linked α-D-glucan from amylose and (14)-linked β-D-xylan attached with minor amounts of branched sugars from hemicelluloses. In addition, thermal analysis showed that the main degradation stage of the polysaccharide fractions occurred between 210 and 320°C. Compared to the polysaccharide fraction prepared without ultrasonic irradiation, the polysaccharide fraction prepared with ultrasonic irradiation had a slightly lower thermal stability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Lignin fractions obtained by steam explosion pretreatment and subsequent alkaline ethanol solution post-treatment from Lespedeza cyrtobotrya stalks were studied in terms of chemical characteristics, to reflect the influence of elevating steam pressure from 15 to 25 kg/m². Because of the remarkable selectivity with respect to lignin, the post-treatment with 60% ethanol solution containing 1% NaOH yielded 8.3, 13.0, 16.0, 16.4, and 17.8% lignin fractions from the samples steam-exploded at 15, 17.5, 20, 22.5, and 25 kg/m² for 4 min, respectively, comparing to 7.7% lignin removal from the raw material. Steam explosion pretreatment, not only obviously cleaved the linkage between carbohydrates and lignin resulting in the significantly decrease of the associated hemicelluloses in lignin fractions, but also broke the β-O-4 bond between lignins to some degrees. In particular, slightly more guaiacyl moieties than syringyl units were affected. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010