Unmodified Lignin Research Articles

Thermal degradation behavior of lignin-modified porous styrene-divinylbenzene and styrene-bisphenol A glycerolate diacrylate copolymer microspheres

This paper describes the thermal properties of polymeric porous microspheres that contain a natural wood-derived polymer, lignin, as one of the components. Polymeric microspheres were obtained by the reaction of divinylbenzene (DVB) or bisphenol A glycerolate diacrylate (BPA.DA) with styrene (St) and a lignin component. The lignin components were unmodified lignin (L), lignin esterified with acrylic acid (LA) or lignin initially reacted with epichlorohydrin and then with acrylic acid (LEA). The copolymers were obtained by emulsion-suspension polymerization at a constant mole ratio of the tetrafunctional monomer DVB or BPA.DA to styrene St (1:1w/w) and different types of lignin components. The thermal stabilities and degradation behavior of the obtained microspheres were studied by a thermogravimetric (TG/DTG/DSC) analysis. The evolved gases were analyzed by FTIR spectrometry. The influence of the lignin component on thermal properties of the obtained polymeric microspheres is evaluated and discussed. Due to the presence of the specific functional groups and well-developed porous structure, the obtained lignin-containing microspheres have a potential application as specific sorbents. Based on the high char content during the pyrolysis, the copolymers containing the lignin additives can be also considered as potential precursors for preparation of carbon materials.

Esterification of Kraft lignin as a method to improve structural and mechanical properties of lignin‐polyethylene blends

ABSTRACTLignin is a promising candidate for blends with thermoplastic polymers. Still, this endeavour is a challenge due to poor compatibility between both components. In this article, the effect of lignin esterification on the improvement of the compatibility between hardwood Kraft lignin and high‐density polyethylene (PE‐HD) is investigated. For this purpose, lignin was esterified with acetic, propionic, and butyric anhydride; its amount in the blends varied from 10 to 40%. Light microscopic images of blends show a reduction in particle size and a more homogeneous distribution with increasing length of the ester carbon chains (C2 to C4). Modification of lignin enhances the moduli and strength characteristics of the blends. Butyrated lignin performs best, as tensile strength of blends can be retained near that of pure PE‐HD with up to 40% lignin content. An additional investigation of unmodified lignin with reduced particle size confirms that modification is the decisive factor to enhance blend properties; a sole reduction of particle size is insufficient. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44582.

Sustainable polymers and polymer science: Dedicated to the life and work of Richard P. Wool

Welcome to this special issue of the Journal of Applied Polymer Science dedicated to the Life and Work of Richard P. Wool on Sustainable Polymers and Polymer Science. Prof. Richard P. Wool examining an eco-leather shoe made from natural fibers and plant oils. Credit: University of Delaware/Photo Services This special issue begins with a review of the sustainable polymers research Richard undertook – from triglyceride-based thermosets, structural composites, adhesives and foams, to using chicken feathers to fabricate electronics, modified lignin additives in polymer resins and lignin-derived monomers for high performance polymers. The second review article is on the subject of green chemistry alternatives to petroleum-sourced epoxy resins and epoxy curing agents (including alternatives to epoxy systems that contain bisphenol A (BPA)) that demonstrate potential for reduced toxicity while maintaining high thermal and mechanical properties. Although Richard focused on alternatives to BPA largely for (meth)acrylate polymer chemistries, his leadership helped influence other researchers, guiding them towards these areas. The last review focuses on the development of carbon fibers from lignin (an interest Richard had during his sabbatical at University College Cork in 2002). Polyacrylonitrile-derived carbon fibers currently dominate the carbon fiber market; however lignin-based carbon fibers potentially enable a major industrial shift to the use of sustainably-sourced and environmentally friendly-manufactured carbon fibers for a wide variety of applications. The primary research articles in the issue begin with the principal focus of Richard's sustainable polymers work: thermosetting polymers. The papers span the latest developments in alternatives to styrene in vinyl esters, the use of CO2 to produce polycarbonate polyols for the development of polyurethane foams, and epoxy resins derived from p-cymene, carvacrol and eugenol. Additional works center on the development of renewable thermoplastic polymers, including polyacetals, polyamides, polyesters and polylactic acid. Next, the articles focus on nanocomposites using renewable binders, such as bio-polyurethane, starch and polylactic acid, and/or renewable fibers, including cellulose nanofibers. Advances in the use of renewables in the field of traditional fiber-reinforced composites are also presented in the issue – introducing chicken feather/glass reinforced epoxy composites and a sandwich structure composed of palm-oil composite foam and flax/epoxy laminates. Lastly, developments in lignin-based carbon fibers are reported for unmodified organosolv lignin and acetylated Kraft pine lignin. As Guest Editors, we would like to thank all of the contributors for joining us in commemorating the life and work of Richard P. Wool by submitting their new research and reviews to the Journal of Applied Polymer Science. Additionally, we would like to thank all of Richard's collaborators over the years, and our fellow sustainable polymers and green chemistry and engineering researchers for their profound influence on him, his career and that of his students. We would also like to extend our thanks to the Journal of Applied Polymer Science Deputy Editor, Hilary Crichton, and the rest of the editorial team for their hard work, dedication and consistent professionalism in handling all the manuscripts of this special issue. The issue would not have been possible without their collective input. Importantly, we would like to thank Richard's family, including his wife Deborah and daughters, Sorcha, Meghan and Breeda, for their graciousness and welcoming spirit to all new students in the Wool group. We very much appreciate their fostering of Richard's creativity, as well as their courage in 1995, embracing a new home when Richard joined the faculty of the University of Delaware. The move catalyzed a seismic change in the Wool research group from polymer physics to the chemistry and materials science and engineering of sustainable polymers, helping spark a new era in renewable polymers across the globe. Lastly, we would like to thank you, the reader, for spending the time to learn a little bit about Richard Wool and for reading about the promising path towards a more sustainable polymers future we, as Wool-inspired scientists and engineers, are representing and highlighting in this special issue. Enjoy! Joseph Stanzione, III Department of Chemical Engineering, Rowan University Glassboro, U.S.A. John La Scala Army Research Laboratory, Weapons and Materials Research Directorate Aberdeen Proving Ground, U.S.A.

The effect of soda bagasse lignin modified by ionic liquids on properties of the urea–formaldehyde resin as a wood adhesive

ABSTRACT The aim of this research was to investigate the influence of lignin modified by ionic liquids on physical and mechanical properties of plywood panels bonded with the urea–formaldehyde (UF) resin. For this purpose, soda bagasse lignin was modified by the 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) ionic liquid and then the various contents of unmodified and modified lignins (10, 15, and 20%) were added at pH=7 instead of second urea during the UF resin synthesis. The physicochemical properties of the prepared resins as well as the water absorption, shear strength, and formaldehyde emission of the plywood panels made with these adhesives were measured according to standard methods. According to Fourier Transform Infrared (FTIR) Spectrometry, by treatment of lignin, the C=O, C–C, and C–H bonds decrease while the content of the C–N bond dramatically increases. Based on the finding of this research, the performance of soda bagasse lignin in UF resins dramatically improves by modification by ILs; as the resins with modified lignin yielded lower formaldehyde emission and water absorption when compared to those made from unmodified lignin and commercial UF adhesives, respectively. The shear strength as well as wood failure percentages are lower for the panels produced with modified lignin than for the panels produced with UF resins alone.

A comparison between lignin modified by ionic liquids and glyoxalated lignin as modifiers of urea-formaldehyde resin

ABSTRACTThe aim of this research was to compare the influence of modified lignin by ionic liquid (IL) on the physical and mechanical properties of wood-based panels bonded with urea-formaldehyde (UF) resin with the effect of glyoxalated lignin (GL) on UF properties. For this purpose, soda bagasse lignin was respectively modified by 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) IL and glyoxal and then the various content of modified lignins (10, 15, and 20%) were added at pH=7 during the UF resin synthesis instead of the second urea . The changes in the structure and thermal properties of lignin, after and before modification with glyoxal and IL, were analyzed by Fourier transform infrared spectrometry (FTIR) and differential scanning calorimetry (DSC). The physicochemical properties of the prepared resins as well as the water absorption, shear strength, and formaldehyde emission of the plywood panels made with these adhesives were measured according to standard methods. According to the FTIR spectra, the content of C=O bond increased in GL while in the IL-treated lignin the content of C–N bond markedly increased. DSC analysis indicated that lignin modified by IL had lower glass transition temperature (Tg) value compared to those modified with glyoxal and unmodified lignin, respectively. The UF resins containing IL-treated lignin exhibit a faster gel time compared to those prepared with GL. Equally, the plywood panels prepared with an IL had lower formaldehyde emission and higher mechanical strength compared to those made from UF resin containing GL. There were no significant differences in dimensional stability of the panels bonded with UFs modified with GL and those with IL-modified lignin.

Influence of lignin source and esterification on properties of lignin-polyethylene blends

Lignins from pulp mills and biorefineries will gain increasing commercial importance in the next years. Their utilisation in polyolefin blends is of growing research interest as it offers a value-added usage of lignin as well as substitution of non-renewable resources. However, the low compatibility of lignin and polyolefins restrains a satisfying blend production and leads to poor mechanical properties. This can be overcome by modifying lignin prior to its incorporation into polymers in order to reduce its polarity. In this study, five lignins from different raw material sources and production processes were esterified with acetic, propionic and butyric anhydride and subsequently mixed with polyethylene with a weight ratio of 1:1. The paper provides a comprehensive and systematic evaluation of the influence of esterification as well as chemical composition of lignins on mechanical properties and, for the first time, water absorption of lignin-polyethylene blends. Properties of blends were found to improve upon lignin esterification. Compared to blends with unmodified lignin, a progressive increase of tensile (+45%) and flexural (+30%) strength could be observed with increasing length of the ester carbon chain. Lignin source and chemical composition affect water absorption of blends, but show no significant effect on mechanical properties as similar values were observed for blends produced with the respective lignin esters.

Fabrication of Green Lignin-based Flame Retardants for Enhancing the Thermal and Fire Retardancy Properties of Polypropylene/Wood Composites

Despite growing extensive applications, until now the poor thermal stability and flame retardancy properties of wood–plastic composites (WPC) remain effectively unsolved. Meanwhile, industrial lignin has emerged as a potential component for polymer composites due to many advantages including abundance, rich reactive functional groups, high carbon content and tailored capability for chemical transformations. Herein, we have fabricated one biobased flame retardant based on industrial lignin chemically grafted with phosphorus, nitrogen and copper elements, as the functional additive for the WPC. Compared with unmodified lignin (O-lignin), functionalized lignin (F-lignin) is more effective to improve the thermal stability and flame retardancy of WPC because of presence of the flame retardancy elements (P and N) and the catalytic effect of Cu2+ on the char-formation. The presence of F-lignin not only reduces the heat release rate, total heat release and slows down the combustion process but also decreases tota...

An approach towards tailoring interfacial structures and properties of multiphase renewable thermoplastics from lignin–nitrile rubber

High-performance multiphase thermoplastics were synthesized by reactive mixing of unmodified industrial lignin and low-cost additives in a matrix of general-purpose acrylonitrile-butadiene rubber (NBR).

Synthesis and photocatalytic activity of mesoporous TiO2 nanoparticle using biological renewable resource of un-modified lignin as a template

Mesoporous TiO2 was synthesized by a hydrolysis precipitation method with the utilization of the biological renewable resource of lignin as template and TiCl4 as reactant. The photocatalytic activity of TiO2 was investigated by the degradation of phenol under UV light irradiation. The microstructure, crystallinity, powder characteristic, and chemical bonding of the catalyst were analyzed. The 500 °C-calcined TiO2 had average crystallite size of about 11.1 nm and a mesoporous structure with specific area of 165.8 m2/g and pore volume of 0.312 cm3/g. The results showed that TiO2 synthesized with lignin template exhibited high photocatalytic activity, which can be attributed to the electronegativity and the network skeleton of lignin to uniformly distribute the TiO2 precursor for forming TiO2 mesoporous particles. The mechanism for the improved photodegradation of the lignin-assisted TiO2 was proposed.

Modified Lignin as an Environmentally Friendly Surfactant

The effect of softwood sulphate lignin modified by its oxidation in alkaline medium on its behaviour at the air-water and oil-water interface, where rapeseed oil and technical fish fat oil served as the oil phase, was investigated. It has been found that, irrespective of the рН values of the water solution, the ability of the modified lignin to be adsorbed at the interfaces exceeds that of unmodified lignin, which is obviously caused by the pronounced differentiation of the hydrophilic and hydrophobic parts of the molecular structure in the oxidised lignin and the decrease in the content of the high-molecular fraction (Mw is greater than 1000) in it. At low concentrations (≤ 0.01 g/dl), the stabilising action of the modified lignin in the rapeseed oil-water emulsion is the same as that of sodium dodecyl sulphate. The enhanced surface activity of the oxidised sulphate lignin enables it not only to substitute the 30% of the mass of the commercial surfactant in the detergent composition for washing stainless steel plates, used during fish smoking, but also to upgrade its properties.

Improved corrosion inhibition of mild steel by chemically modified lignin polymers from Elaeis guineensis agricultural waste

This article describes that the modification of lignin by incorporation of aromatic scavengers (2-naphthol: AHN EOL and 1,8-dihydroxyanthraquinone: AHD EOL) during delignification process has improved the physical properties of the lignin fractions. Smaller fragments of lignin with high phenolic –OH content, increased solubility and antioxidant activity have led to improved inhibitive property of the modified lignin. The inhibition efficiency (84–93%) of both modified lignin (500 ppm) were observed to be better than unmodified organosolv lignin (EOL). It was deduced that the inhibition process was spontaneous and the inhibitors were mainly physically adsorbed onto the mild steel surface.

Wood particleboards produced with unmodified and esterified Kraft lignins

Hardwood Kraft lignins were esterified with succinic anhydride and chemically, thermally and morphologically characterised compared to their unmodified counterparts. Esterification was confirmed by NMR and Fourier transform infrared spectrometer (FT-IR). Esterified lignins were found to be porous, less thermally stable and slightly more hydrophilic than unmodified lignins because esterification with cyclic acid anhydride is accompanied with the simultaneous liberation of carboxylic acid groups. These free carboxylic acid groups are interesting for panel production as they could create new ester groups with wood components. The wood particleboard panels were produced via compression moulding using different concentrations of unmodified and esterified Kraft lignins as sole binders (10, 20 and 30%). All the mechanical properties [impact strength, modulus of elasticity (MOE) and modulus of rupture (MOR)] of the studied wood particleboard panels significantly increased with the addition of the succinated and unmodified Kraft lignins. However, the best mechanical properties were determined for panels containing 20% of unmodified Kraft lignins. Therefore, the condensation reactions of the unmodified Kraft lignins taking place during the compression moulding seem explain why these lignins act as a more efficient binder than the succinated lignins.

Characterization and Optimization of the Glyoxalation of a Methanol-Fractionated Alkali Lignin using Response Surface Methodology

The glyoxalation of a methanol-fractionated alkali lignin was executed at 60 °C for 8 h with different amounts of glyoxal (40% in water) and 30% NaOH. The weights of the lignin and water were fixed at 10.0 and 15.0 g, respectively. The gel permeation chromatography (GPC) results indicated that depolymerization of lignin molecules occurred during the glyoxalation process. However, a higher polydispersity index (Mw/Mn) of all glyoxalated lignins compared to the unmodified lignin (ML) showed that lignin polymers with a variety of chain lengths were generated through the crosslinking and through the repolymerization of lignin molecules via methylene (CH2) bridges and new, strong C-C bonds after the condensation reaction. This was confirmed by thermogravimetry analysis (TGA). Optimum amounts of glyoxal and NaOH to be used in the glyoxalation process were ascertained by quantifying the intensity of relative absorbance for the CH2 bands obtained from FT-IR spectra and by using response surface methodology (RSM) and central composite design (CCD), which facilitated the development of a lignin with appropriate reactivity for wood adhesive formulation. The experimental values were in good agreement with the predicted ones, and the model was highly significant, with a coefficient of determination of 0.9164. The intensity of the relative absorbance for the CH2 band of 0.42 was obtained when the optimum amounts of glyoxal and NaOH, i.e., 0.222 and 0.353, respectively, were used in the glyoxalation process.

Reduction of Formaldehyde Emission from Particleboard by Phenolated Kraft Lignin

The aim of this study was the reduction of formaldehyde emission from particleboard by phenolated Kraft lignin. For this purpose, the lignin was extracted from black liquor and then modified by phenolation. During the urea formaldehyde (UF) resin synthesis different proportions of unmodified and phenolated Kraft lignins (10%, 15%, and 20%) were added at pH = 7 instead of the second urea. Physicochemical properties and structural changes of resins so prepared, as well as the internal bond (IB) strength and formaldehyde emission associated with the panels bonded with them were measured according to standard methods. The Fourier transform infrared (FTIR) analysis of lignin indicated that the content of O–H bonds increased in phenolated lignin while the aliphatic ethers C–O bonds decreased markedly in the modified lignin. Since both synthesis of UF resins and lignin phenolation are carried out under acid conditions, phenolation is an interesting way of modifying lignin for use in wood adhesive. The panels bonded with these resins showed significantly lower formaldehyde emission compared to commercial UF adhesives. The UF resin with 20% phenolated lignin exhibited less formaldehyde release without significant differences in internal bond strength and physicochemical properties compared to an unmodified UF resin. XRD analysis results indicated that addition of phenolated lignin decreased the crystallinity of the hardened UF resins.

Preparation of cationic softwood kraft lignin and its application in dye removal

The cationization of polymers was regarded as an effective method to improve their performance for various applications. In this work, the cationization of kraft lignin was investigated using glycidyl-trimethylammonium chloride (GTMAC) with kraft lignin in an aqueous solution under altered conditions. The conditions investigated were temperature, time, pH, GTMAC to lignin molar ratio, and lignin concentration. The optimized conditions based on charge density and solubility of cationic lignin were found to be 70°C, 1h, 12.5 pH, 2/1 GTMAC/lignin molar ratio, and 1.0wt.% lignin concentration. The solubility of the resulting cationic lignin reached 90% in 1wt.% lignin concentration and the charge density reached 1.10meq/g under the optimized conditions. The cationic lignin was characterized and compared with unmodified kraft lignin using elemental analysis, Fourier Transform Infrared (FTIR) spectrophotometer, proton nuclear magnetic resonance (1H NMR) and thermogravimetry (TGA) analysis in order to confirm the success of the grafting reaction. The cationic lignin was used as a flocculant for dye removal (Remazol Brilliant Violet, Reactive Black, and Direct Yellow) from model wastewater.

Fungus-Modified Lignin and Its Use in Wood Adhesive for Manufacturing Wood Composites*

Abstract Organosolv lignins were modified with different fungal species. The modified lignins were used as raw materials for preparing lignin-phenol-formaldehyde (LPF) resins. Oriented strandboard (OSB) panels were produced with these laboratory-synthesized LPF resins for evaluating the bond performance of the LPF resins in the manufacturing of wood composites. Ultraviolet spectroscopy results show that the phenolic hydroxyl contents in the lignins were changed after the lignins were treated with fungi. The lignin modified with the brown-rot fungi extended the gel time of the LPF resin compared with the corresponding unmodified lignin, while the lignin modified with the white-rot fungi shortened the gel time. The OSB test results show that the internal bond strength and the bending properties of the panels bonded with the LPF resins containing the modified lignin were comparable to or better than those of the panels bonded with the commercial phenolic resin or the LPF resin containing the unmodified lignin. It is worth noting that the fungi-modified lignin reduced the thickness swell and water absorption of the OSB panels, implying the water resistance of the LPF resins was improved with the fungi-modified lignin. It is also suggested that up to 50 percent of phenol can be potentially replaced with fungi-modified lignin in phenolic resins used as wood adhesives.

Utilization of softwood lignin as both crosslinker and reinforcing agent in silicone elastomers

Composite foams result from one-shot integration of unmodified lignin into a silicone pre-elastomer, where it performs as both crosslinker and reinforcing agent.

Recycled Polystyrene Composites Reinforced With Esterified and Non-Esterified Kraft Lignins

Recycled polystyrene and Kraft lignins represent waste materials/by-products, generated in huge quantities worldwide, which remain inadequately valorized. In this study, unmodified and maleated Kraft lignins were used as fillers in recycled polystyrene (RPS) to produce composites at different concentrations (0, 10, 20 and 30%) via melt blending. Also, RPS composites with 20% of maleated Kraft lignins were prepared by applying a previous surface treatment to the maleated Kraft lignins with RPS in solution. A complete mechanical, thermal and morphological characterization was performed on the RPS based composites containing Kraft lignins. The morphological study revealed better compatibility with RPS for unmodified Kraft lignins than maleated Kraft lignins except for the composite where maleated lignins surface treatment was applied. In this case, the RPS was well incorporated in the porous structure of maleated Kraft lignins. The results also showed that addition of unmodified Kraft lignins led to better mechanical and thermal properties of the composites than when maleated Kraft lignins were added. For the composite formulated with 20% maleated Kraft lignins with a previous surface treatment, the properties were improved to become comparable to those of composites with unmodified Kraft lignins. The poor mechanical and thermal properties of RPS composites with maleated Kraft lignins could be related to the porous structure of the maleated Kraft lignins.

Solvent-free catalyst-free microwave-assisted acylation of lignin

Valorization of lignin into biomaterials requires its good compatibility with the polymeric matrix it is incorporated into. Softwood Kraft lignin was esterified with various anhydrides (acetic, propionic, butyric, methacrylic, maleic) using a solvent-free, catalyst-free, microwave-assisted method. The esterification was fast and efficient (degrees of substitution >90% after 10min). The reaction was worked up using water or ethanol as purification agent. Esterified lignins were characterized by FT-IR, GPC, quantitative 31P NMR and TGA/DSC. NMR analyses indicated that non-cyclic anhydrides reacted with both aliphatic and phenolic OH groups, while maleic anhydride reacted exclusively with aliphatic OH groups. All acylated lignins except the maleated one showed higher thermal stability than the unmodified lignin. Lignins acylated with non-cyclic anhydrides can be applied as green fillers in apolar polyolefins while maleated lignin can serve as metal adsorbent or macroreagent for the synthesis of polyesters or polyamides. We showed in this study that lignin can be modified in a fast and easy way.

Improving urea formaldehyde resin properties by glyoxalated soda bagasse lignin

The aim of this research was a reduction of formaldehyde emission and the improvement of the water resistance of urea formaldehyde (UF) resins by incorporating glyoxalated soda bagasse lignin. For this purpose, various contents of unmodified and glyoxalated lignins (10, 15 and 20 %) were added at pH = 7 instead of second urea during the UF resin synthesis. The properties of the resins as well as water absorption, shear strength, and formaldehyde emission of plywood panels made with these adhesives were measured. Among all the resins synthesized, the resin yielding the best results (based on formaldehyde emission and gelation time as well as water absorption, mechanical strength, and formaldehyde content of the associated panels) was selected, and its properties were further analyzed by Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectrometry (FTIR), and X-ray Diffractometry (XRD). The lignin based resins yielded good shear strength of the plywood panels, passing comfortably relevant international standard specifications; the panels also showed lower formaldehyde emission and water absorption when compared to commercial UF adhesives. Based on these findings, it was attempted to improve the performance of soda bagasse lignin in UF resins by glyoxalation. The UF resin containing 15 % glyoxalated lignin (GLUF15) still exhibited less water absorption and formaldehyde release without significant differences in shear strength and physicochemical properties compared to the UF resin control. DSC analysis indicated that in comparison to UF resin the curing process of GLUF resin shifted to lower temperatures. According to the FTIR spectra, by addition of lignin the proportion of C–N bond in methylene linkages decreases when urea is partly replaced by lignin or glyoxalated lignin. XRD analysis indicated that the crystallinity of the UF resins decreased with addition of glyoxalated lignin.