Multiphase materials with lignin. IV. Blends of hydroxypropyl cellulose with lignin

Polymer blends of hydroxypropyl cellulose (HPC) and organosolv lignin (OSL) were prepared by mixing in solutions of both pyridine and dioxane, and casting as films, and by mixing in the melt followed by extrusion. All preparations exhibited partial miscibility as evidenced by a single T_g up to a composition of 40 wt % lignin above which phase separation was detected. Dioxane-cast and injection-molded blends were distinguished from the pyridine-cast materials by a positive T_g deviation from additivity, an approximation which adequately described the latter. This positive deviation in T_g is attributed to the formation of a liquid-crystal mesophase with a resultant reduction of amorphous HPC available for interaction with the lignin component. This explanation is supported by a rapid rise in modulus (～150%) and tensile strength with very low lignin content, and by an associated sharp decline in ultimate elongation. The development of morphological features, as observed by scanning electron microscopy provide further substantiation of this hypothesis.     

Application of optical microscopy as a screening technique for cellulose and lignin solvent systems

Rapid and facile screening techniques to determine the effectiveness of solvents for cellulose or biomass dissolution can advance biomass processing research. Here, we report the use of a simple optical microscopy method to screen potential cellulose and lignin solvents. The described methodology was used to screen the dissolution of cellulose and lignin in two imidazolium‐based ionic liquids (ILs), two phosphonium‐based ILs, as well as a N,N‐dimethylacetamide/lithium chloride (DMAc/LiCl) solution in less time than other techniques. The imidazolium‐based ILs and the DMAc/LiCl were found to dissolve both cellulose and lignin. Also, it was observed that one of the phosphonium‐based ILs dissolved lignin and not cellulose, demonstrating a potential for biomass fractionation applications. © 2011 Canadian Society for Chemical Engineering     

Engineering plastics from lignin II. Characterization of hydroxyalkyl lignin derivatives

Several types of hydroxyalkyl lignin derivatives were synthesized from milled wood, organosolv, steam explosion, acid (H₂SO₄) hydrolysis, and kraft lignin with ethylene oxide, propylene oxide, and butylene oxide by either batch reaction in toluene at 180°C using KOH as catalyst, or in aqueous alkali at room temperature. The isolated derivatives were characterized in terms of their chemical structures by H-NMR and FT-IR spectroscopy. Thermal properties were determined by differential scanning calorimetry. Molecular weights were measured by gel permeation chromatography on polystyrene/lignin model compound calibrated high pressure μ-spherogel columns. Solubilities in various organic solvents spanning a solubility parameter (δ) range from 9.3 to 14.5 and a hydrogen bonding index (γ) range from 1.5 to 18.7 were tested using UV₂₈₀ absorption of solutions of up to with degrees of substitution of between 1 and 2.6 (except for ethylene oxide derivatives which were higher) and with lignin contents of around 60%. The drastic reduction of glass transition temperature of between 50° and 100° is explained with increased free volume of the copolymer and with disruption of hydrogen bonds involving especially phenolic hydroxy groups. The greatly enhanced solubility in organic solvents indicates absence of the gel structure typical of network polymers. No molecular breakdown was observed as a consequence of oxyalkylation. The derivatives had molecular weights (M_w) of between 2000 and 50,000 at dispersity factors of between 2.5 and 25. The derivatives seem to constitute useful prepolymers for thermosetting engineering plastics.     

Engineering plastics from lignin. XV. Polyurethane films from chain-extended hydroxypropyl lignin

A series of polyurethane (PU) films was prepared from chain-extended hydroxypropyl lignins (CEHPL). In appearance, these films ranged from brittle and dark brown to rubbery and bronze. The thermal, mechanical, and network properties of these PUs were investigated by DMTA and DSC analysis. All films exhibited single T_g's which varied between ?53° and 101°C, depending on lignin content. From swelling experiments, molecular weight between crosslinks (M _c) was determined and found to vary over 2.5 orders of magnitude. The M _c's were related to the change in T_g that accompanied network formation. Stress–strain experiments showed a variation in Young's modulus between 7 and 1300 MPa. Most of the variation in material properties was related to lignin content and to a lesser extent to diisocyanate type, hexamethylene diisocyanate, or toluene diisocyanate. The source of the CEHPL had no effect on the observed properties. From these results it was concluded that the properties of PUs can be controlled and engineered for a wide variety of practical uses.     

Engineering plastics from lignin. I. Synthesis of hydroxypropyl lignin

Hydroxypropylation of lignin in a batch reactor under alkaline conditions at 180°C was studied using propylene oxide (PO) by itself, and PO in combination with several ligninlike model compounds and with kraft lignin. While the PO homopolymerization rate increased rapidly at temperatures above 85°C, and was too fast to be determined accurately at 180°C, the addition of model compounds and lignin was found to delay homopolymerization in relation to the presence of ionizable functional groups. The observations are consistent with a reaction mechanism involving first order kinetics with regard to each alkoxide and PO concentrations. Where the reaction rates toward PO increase with increasing pK_a values, the reaction sequence proceeds in the order of declining basicity. Thus lignins with high acidity were found to be subject to greater degrees of modification than those with more neutral character. This explains the earlier observed beneficial effect of lignin carboxylation on the properties of lignin–PO reaction mixtures.     

The isolation and characterization of lignin of kenaf fiber

In this article, milled wood lignin (MWL) was isolated and purified from retted kenaf fiber, the lignin obtained was characterized by elemental analysis, FTIR, ¹H‐NMR, and ¹³C‐NMR spectroscopy. The C₉ formula is calculated for kenaf fiber MWL as C₉H_9.32O_3.69(OCH₃)_1.30. The spectra of FTIR, ¹H‐NMR, and ¹³C‐NMR show the kenaf fiber lignin to be of the G/S type with high proportion of syringyl (S) unit. The numbers of phenolic and aliphatic hydroxyl groups in the kenaf fiber MWL are estimated to be 0.14 and 1.31, respectively, per C₉ unit. The OH_aliph is 90.3% in total numbers of hydroxyl groups of kenaf fiber MWL, and the OH_ph is 9.7%. It is evident that the β‐O‐4 structures are mainly linkage in the MWL of kenaf fiber, which contain more erythro stereochemistry type in β‐O‐4 units than thero stereochemistry type. In general, the characteristics of lignin of kenaf fiber are similar to that of hardwood. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fiber formation and properties of polyester/lignin blends

Thermotropic liquid crystalline polyesters with varied chemical structure are synthesized by melt transesterification polycondensation. They are employed as matrix for blends with lignin materials to obtain melt-spinnable precursors for carbon fibers. The lignin samples are carefully purified by fractionation, enzymatic removal of reducing sugars, and subsequent modification of the terminal OH groups. Effective melt blending is achieved with liquid-crystalline aromatic–aliphatic polyesters having melting ranges that match the softening temperature of the lignin fractions, which is necessary to prevent thermal decomposition of the lignin. Polyester/lignin blends are partially compatibilized, phase-separated materials. The polyester/lignin materials are melt-spun successfully. The fiber properties depend on the lignin purification process. X-ray scattering reveals that orientation in lignin-containing fibers is maintained. First experiments show that the fibers can be converted successfully to carbon fibers by thermal annealing procedures. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48257.     

Molecular composite of lignin: Miscibility and complex formation of organosolv lignin and its acetates with synthetic polymers containing vinyl pyrrolidone and/or vinyl acetate units

Binary blends and pseudo-complexes of organosolv lignin (OSL) or its acetate (OSL-Ac) with synthetic polymers including poly(vinyl acetate) (PVAc), poly(N-vinyl pyrrolidone) (PVP), and poly(N-vinyl pyrrolidone-co-vinyl acetate) (P(VP-co-VAc)) were prepared by casting from mixed polymer solutions in N,N-dimethylformamide as good solvent and by spontaneous coprecipitation from solutions in tetrahydrofuran (THF) as comparatively poor solvent. Thermal analysis by differential scanning calorimetry showed that OSL was not miscible with PVAc; however, OSL(-Ac) was miscible with PVP to form homogeneous blends irrespective of the degree of acetylation of OSL. OSL formed homogeneous blends with P(VP-co-VAc) with ≥30 mol % of VP contents. Fourier transform infrared spectra measurements for the miscible blends of OSL/PVP revealed the presence of hydrogen bonding interactions between hydroxyls of OSL and carbonyls of VP units. However, there was no evidence for the development of the hydrogen bonding in miscible blends of fully acetylated OSL with PVP. For complexes via THF solutions, its formation was found to be primarily due to a higher frequency of hydrogen bonding interactions. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Catalytic pyrolysis-GC/MS of lignin from several sources

Lignin from four different sources, extracted by various methods, were pyrolyzed at 650 °C using analytical pyrolysis methods (Py-GC/MS). Pyrolysis was carried out in the absence and presence of two heterogeneous catalysts, an acidic zeolite (HZSM-5) catalyst and a mixed metal oxide catalyst (CoO/MoO₃). Non-catalytic Py-GC/MS was used to identify the lignin as characterized by their H-, G- or S-lignin makeup and also served as the control basis to evaluate the effect of the said catalysts on the production of aromatic hydrocarbons from these lignin sources. Experiments show that the selectivity to particular aromatic hydrocarbons varies with the composition of the lignin for both catalysts. The major pathway for hydrocarbon production over HZSM-5 is likely increased depolymerization efficiency that releases and converts the aliphatic linkers of lignin to olefins followed by aromatization. Simple phenols produced from the deconstruction of the lignin polymer are likely to be a source of zeolite deactivation. The CoO/MoO₃ is likely to produce aromatic hydrocarbons through a direct deoxygenation of methoxyphenol units.     

Tailoring the molecular and thermo–mechanical properties of kraft lignin by ultrafiltration

This study has shown that ultrafiltration allows the selective extraction from industrial black liquors of lignin fraction with specific thermo‐mechanical properties, which can be matched to the intended end uses. Ultrafiltration resulted in the efficient fractionation of kraft lignin according to its molecular weight, with an accumulation of sulfur‐containing compounds in the low‐molecular weight fractions. The obtained lignin samples had a varying quantities of functional groups, which correlated with their molecular weight with decreased molecular size, the lignin fractions had a higher amount of phenolic hydroxyl groups and fewer aliphatic hydroxyl groups. Depending on the molecular weight, glass‐transition temperatures (T_g) between 70 and 170°C were obtained for lignin samples isolated from the same batch of black liquor, a tendency confirmed by two independent methods, DSC, and dynamic rheology (DMA). The Fox–Flory equation adequately described the relationship between the number average molecular masses (M_n) and T_g's‐irrespective of the method applied. DMA showed that low‐molecular‐weight lignin exhibits a good flow behavior as well as high‐temperature crosslinking capability. Unfractionated and high molecular weight lignin (M_w >5 kDa), on the other hand, do not soften sufficiently and may require additional modifications for use in thermal processings where melt‐flow is required as the first step. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40799.     

Efficient solid‐phase synthesis of acetylated lignin and a comparison of the properties of different modified lignins

The chemical modification of lignin can greatly enhance its functionality and exploit its application areas. To avoid the difficulties of separation and environmental pollution in the traditional liquid‐phase method, we prepared acetylated lignin by a mechanical‐activation‐assisted solid‐phase synthesis (MASPS) technology with a customized stirring ball mill as a reactor and studied its structure and properties. Ultraviolet–visible analysis showed that the degree of esterification (DE) of the acetylated lignin produced by the MASPS technique was 77.59%, whereas the DEs of those produced by traditional liquid‐phase synthesis (LPS) and thermal solid‐phase synthesis (TSPS) were only 42.29 and 27.54%, respectively. Fourier transform infrared spectroscopy and NMR analyses indicated that both phenolic hydroxyls and aliphatic hydroxyls participated in the reaction, and the reactivity of the phenolic hydroxyls was higher than that of the aliphatic hydroxyl groups. The acetylation of aliphatic hydroxyl mainly happened at the γ of arylglycerol‐β‐aryl ether (β‐O‐4). Scanning electron microscopy analysis showed that the acetylated lignins prepared by MASPS and TSPS were irregular blocks with coarse surfaces and loose structures, whereas the lignin prepared by LPS consisted mostly of regular balls with a smooth surface and a compact structure. Differential scanning calorimetry and thermogravimetric analyses indicated that the glass‐transition temperatures and thermal stability of the acetylated lignin increased by orders with the processing techniques of MASPS, TSPS, and LPS. MASPS integrated the activation and reaction in the same equipment without the use of a solvent and showed advantages of a high efficiency, environmental protection, and easy operation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44276.     

Multiphase materials with lignin. XV. Blends of cellulose acetate butyrate with lignin esters

Commercially available cellulose acetate butyrate (CAB, unplasticized) was blended in melt and solution with lignin esters having different ester substituents—acetate (LA), butyrate (LB), hexanoate (LH), and laurate (LL). All lignin esters formed phase‐separated blends with CAB with domain size depending on processing conditions and the interaction between phases depending on blend components. CAB/LA and CAB/LB revealed the strongest interactions with domain sizes on the 15–30 nm scale as probed by dynamic mechanical thermal analysis and differential scanning calorimetry. The glass transitions (T_g) followed the Fox equation. Broader transitions corresponding to the T_gs of the two parent components were observed for CAB blends with LH and LL. Transmission electron micrographs revealed differences in the phase dimensions of the blends in accordance with chemical and processing (i.e., melt vs solvent) differences. Modest gains in modulus were observed for low contents (<20 wt %) of LA and LB. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 448–457, 1999     

Polyurethane from kraft lignin

The condensation of lignin with hexamethylene diisocyanate (HDI) or of a mixture of lignin-poly(ethylene oxide) (PEO) with HDI was investigated. The lignin used in this study was a kraft lignin from Pinus maritima, and was obtained from black liquor by acidification, filtration and vacuum drying. Thermogravimetric analysis was carried out to compare the weight loss against temperature of polyurethanes based on kraft lignin and hexamethylene diisocyanate, or of mixed polyurethanes lignin-PEO-HDI, with that of kraft lignin alone. It was shown that lignin can react with isocyanates in rather mild conditions to give polyurethanes, confirming previous results performed with model molecules. Some mechanical properties (Young's modulus and rupture strength) and glass transition temperature were also measured on the various above materials. In all cases it was concluded that lignin participates to the polycondensation reaction. As to rigid foams, it was found that polyurethanes prepared with oxypropylated glycerol, ethylene glycol and kraft lignin, in the weight proportions of 100/30/15, and HDI had good dimensional stability, and thermal and mechanical properties comparable to those of equivalent industrial materials.     

Carbon fibers derived from wet‐spinning of equi‐component lignin/polyacrylonitrile blends

Equi‐component blends of polyacrylonitrile (PAN) and lignin, i.e., with a lignin content as large as 50 wt %, were successfully used as precursors to produce carbon fibers. Rheological measurements demonstrated that increasing lignin content in spinning solution reduced shear viscosity and normal stress, indicating a decrease of viscoelastic behavior. This was confirmed by Fourier transform infrared results that show no discernable chemical reaction or crosslinking between PAN and lignin in the solution. However, the resulting carbon fibers display a large I_D/I_G ratio (by Raman spectroscopy) indicating a larger disordered as compared to that from pure PAN. The macro‐voids in the lignin/PAN blend fibers typically generated during wet‐spinning were eliminated by adding lignin in the coagulant bath to counter‐balance the out‐diffusion of lignin. Carbon fibers resulting from lignin/PAN blends with 50 wt % lignin content displayed a tensile strength and modulus of 1.2 ± 0.1 and 130 ± 3 GPa, respectively, establishing that the equi‐component wet‐spun L/P‐based carbon fibers possessed tensile strength and modulus higher than 1 and 100 GPa. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45903.     

Engineering plastics from lignin. VII. Structure property relationships of poly(butadiene glycol)-containing polyurethane networks

Hydroxypropyl lignin-based thermosetting polyurethanes containing polybutadiene (PBD) glycol soft segments (M_n of 2800 g M^?1) were synthesized with excess hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI) by solution casting. Miscibility of the glycol with the lignin derivative was found to be poor as expected, and phase separation between the two polyol components in polyurethanes was detected by thermal and mechanical analysis, and by electron microscopy. This study examines the effect of concentration of polybutadiene glycol on the thermal and mechanical properties of the polyurethanes. The two-phase network system displayed significantly different properties than either the poly(ethylene glycol)-containing polyurethanes or their soft segment-free counterparts described previously. Macrophase separation was observed at nearly all degrees of mixing and was found to affect thermal and mechanical properties. The glass transition temperature (T_g) of the lignin phase in the TDI-based networks increased with poly(butadiene glycol) content rising from 3.6 to 71.4% of polyurethane, and this was attributed to the employment of a constant diisocyanate weight fraction which gave rise to a variable NCO/OH ratio and crosslink density. Distinct phase separation was evidenced by scanning electron microscopy (SEM) at above 3.6 and 7.1% glycol content for HDI- and TDI-based films, respectively. The polyurethane films behaved like rubber-toughened lignin networks when PBD was the discrete phase, and like lignin-reinforced rubber when the lignin derivative was discrete. This behavior was evidenced by the Young's modulus decreasing from 2000 to 50 MPa and ultimate strain rising from 6 to greater than 150%, with soft segment content increasing from 0 to 71.4%.     

Removal of lignin in a liquid system by an isolated fungus

The screening of a strain which could perform lignin removal was carried out. Based on taxonomic study the isolated strain (LM‐2) was identified as Penicillium sp. LM‐2 could decolorize 0.6 g dm^?3 lignin within 4 days in a shaking culture at 25 °C. The efficiency of decolorization of the lignin was over 80% in the pH range of 4.0–6.0, but was low above pH 6.2. The rise of temperature had a slight adverse effect on the lignin decolorization in the range of 25–35 °C. Lignolytic enzymes such as lignin peroxidase, manganese peroxidase and laccase were not detected in the culture broth or within the fungal cells. The lignin was removed from the high molecular weight fraction mainly by adsorption and accumulation inside the cells. © 2001 Society of Chemical Industry     

Enhanced dispersion of lignin in epoxy composites through hydration and mannich functionalization

Lignin was used as a biobased fill material to create epoxy composites. Lignin was incorporated into diglycidyl ether of bisphenol A–based epoxy using hydration and Mannich functionalization. The effects of chemical functionalization on the interfacial chemistry of lignin are examined, and the corresponding changes in materials properties are examined. Several types of lignin–epoxy composites were formed through dissolution of lignin in aliphatic amine. Lignin–amine solutions were modified through hydration and the Mannich reaction and were used to cure the epoxy. The resulting composites exhibited two‐phase microstructures containing lignin‐rich agglomerates. Thermomechanical properties were examined using dynamic mechanical analysis, differential scanning calorimetry, and fracture testing. Morphological and chemical changes were examined using scanning electron microscopy and Fourier transform infrared spectroscopy. The hydrated lignin samples showed similar glass transitions and mechanical properties to the neat epoxy samples. Interactions between water and the Mannich functionalized lignin decreased the glass transition temperature and mechanical properties of the highly hydrated Mannich reacted lignin samples because of a plasticization effect. Fracture testing was conducted on the samples and showed that the yield strength and elastic modulus were similar to the neat epoxy, but the fracture toughness decreased in the lignin‐containing specimen. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41263.     

Light scattering of acetylated lignin

Organosolv lignin was fractionated on a Sephadex G 75 column with 0.1M aqueous NaOH resulting in 14 fractions. These fractions were acetylated and a high-molecular-weight fraction (F3) was investigated by means of combined static and dynamic light scattering (LS) in solvents acetone, tetrahydrofuran (THF), and trifluoroethanol (TFE). The measurements were found to be reproducible, and recycling of lignin by freeze drying caused slight but unessential changes in solution properties. Depending on the solvent used, weight average molecular weights M_w between two and ten million were found. By contrast, M_n of the fractions, measured by vapor pressure osmometry (VPO), was in the range of a few thousands only. Analysis of the angular dependence in static LS by means of a Casassa–Holtzer plot and the fractal dimensions showed the presence of chain stiffness, most distinct in TFE. Also, the dynamic light scattering results in TFE are typical for semiflexible chains, while in THF, and to some extent in acetone, the dynamic measurements including viscosity suggest the presence of spherical structures. These findings are being explained by large lignin clusters that consist of stiff subunits.     

Characterization and comparison of Acetosolv and Milox lignin isolated from crofton weed stem

Crofton weed (Eupatorium adenophorum Spreng) is an invasive species in China, which has damaged native ecosystems and caused great economic losses. To use the weed instead of simple control and management of it, the weed stem of was delignified by Acetosolv and Milox processes to obtain lignin. The lignins (Acetosolv lignin, AL; and Milox lignin, ML) were characterized and compared through several analysis methods. It was found that both of AL and ML were syringyl‐guaiacyl type (GS) lignin, but that the chemical composition and structure of the two lignins were somewhat different. The obtained C₉ expanded formulas for AL and ML were C₉H_9.16O_3.50N_0.13(OCH₃)_0.97(Ph? OH)_0.34Ac_0.22 and C₉H_7.96O_3.13N_0.13(OCH₃)_1.23(Ph? OH)_0.51Ac_0.14, respectively. According to an elementary analysis, the two lignins had similar higher heat value of 20.0–21.0 MJ kg^?1, which were similar to that of raw coal. Gel permeation chromatography analysis indicated the two lignins had similar molecular weights. Notwithstanding that the Ultraviolet, Fourier transform infrared, and ¹H‐NMR spectra illustrated that the two lignins had similar chemical functional groups, the AL showed more acetyl groups signals. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Engineering plastics from lignin. III. Structure property relationships in solution cast polyurethane films

Lignin-based polyurethane films were synthesized by solution casting from hydroxypropyl lignin derivatives and either an aliphatic or an aromatic isocyanate. Two lignins, kraft and steam explosion lignin, and two diisocyanates, hexamethylene diisocyanate (HDI) and tolylene diisocyanate (TDI), were chosen for the study. It was found necessary to use stoichiometric excess diisocyanate in the synthesis of the thermosetting polyurethanes. This part of the series addresses the effect of synthesis variables on film properties. The study examines the effect of lignin type, of diisocyanate type, and of composition in terms of NCO to OH stoichiometry on thermal and mechanical properties. Stoichiometric NCO-excess was found to cause a more significant increase in the glass transition temperature of TDI-based films than of films made with HDI. The films swelled less with increasing NCO/OH ratio. Use of aliphatic diisocyanate (HDI) resulted in films with lower moduli as compared to aromatic diisocyanate (TDI). Kraft-lignin-based polyurethanes had slightly inferior strength characteristics (Young's modulus and tensile strength) in comparison with those derived from steam explosion lignin. Variation in the NCO/OH stoichiometry had no noticeable effect on modulus or tensile strength, but did significantly influence glass transition temperature, swelling, and strain at break. It is observed that the properties of these thermosetting polyurethanes are very sensitive to their composition. The study illustrates that materials of satisfactory performance characteristics can be engineered by proper selection of synthesis variables and modification of network architecture.