Solution properties of lignin. Thermodynamic properties and molecular weight determinations

Number-average molecular weights and the thermodynamic parameters ΔF?₁, ΔH?₁, and ΔS?₁ have been obtained for lignin in the solvents dimethylsulfoxide, dimethyl-formamide, and dioxane. Widely different molecular weights were found in the different solvents and at the different temperatures as a consequences of molecular association. Analysis of the thermodynamic parameters revealed that these quantities are dominated by the change in solvent structure accompanying the solution process. A correlation between the “goodness” of a lignin solvent and the Hildebrand solubility parameter is consequently misleading in such systems.     

Degradation of lignin with monomethylamine

Wood chips were treated with gaseous mixtures of monomethylamine and water vapour at temperatures between 160 and 120°C and pressurs ranging between 1.5 and 7.0 MPa. The degradation products were subsequently extracted with different solvents at ambient pressure. First, The degradation products of lignin were extracted with highly selective organic solvents such as diethyl ether or 2-butanone. Then, the remaining decomposition products were extracted with water or an aqueous solution of monomethylamine. The latter extract contains the degradation products of the hemicelluloses in a relatively high concentration. After a three hour digestion, the residue obtained from spruce had a lignin content of 3.1 wt-% (pine: 3.7 wt-%; birch 0.3 wt-%). The total yield of unbleached cellulose was approximately 60 wt-%.     

Graft copolymers of lignin with electron poor alkenes

The synthesis of copolymers between lignin and electron poor alkenes is described. Lignin from steam‐exploded pine, from steam‐exploded straw, and organosolv were used as starting materials. Beforehand, lignins were fully characterized by using elemental analysis, ultraviolet spectroscopy, gel permeation chromatography (GPC), Fourier transform infrared (FTIR), and both¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy. The synthesis of copolymers was performed using a previously described procedure utilizing calcium chloride and hydrogen peroxide as reagents. FTIR of copolymers showed absorptions due to the presence of both lignin and the electron withdrawing group on the alkene. GPC analysis showed the presence of fractions with high molecular weights: the M_z of lignin from pine was 3729 while the copolymer with methyl acrylate showed M_z = 383790. Differential calorimetry showed the presence of glass transitions in the range of ?9 to 4.5°C due to the presence of grafted polyalkene chains. When acrylonitrile was used as starting material DSC analysis of the product showed a glass transition at 119°C, which can be attributed to grafted polyacrylonitrile chain. Lignin from steam explosion could be a good raw material in the preparation of graft copolymers. Furthermore, lignin from pine gave better results than that from straw. Finally, lignin from steam explosion gave better results than organosolv lignin. These results can be explained on the basis of the structural properties of used lignins. Both UV and ¹³C NMR spectra showed that lignin from pine contained a consistent amount of double bonds. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1163–1171, 2003     

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.     

Polyurethanes and polyesters from lignin

Lignin, obtained through steam explosion from straw, was completely characterized via elemental analysis, gel permeation chromatography, ultraviolet and infrared spectroscopy, and ¹³C and ¹H nuclear magnetic resonance spectrometry. Polyurethanes were obtained by treating steam‐exploded lignin from straw with 4,4′‐methylenebis(phenylisocyanate), 4,4′‐methylenebis(phenylisocyanate) –ethandiol, and poly(1,4‐butandiol)tolylene‐2,4‐diisocyanate terminated. The obtained materials were characterized by using gel permeation chromatography, infrared spectroscopy, and scanning electron microscopy. Differential scanning calorimetry analysis showed a T_g at ?6°C, assigned to the glass transition of the poly(1,4‐butandiol) chains. The presence of ethylene glycol reduced the yields of the polyurethanes. The use of the prepolymer gave the best results in polyurethane formation. Steam‐exploded lignin was used as the starting material in the synthesis of polyesters. Lignin was treated with dodecanoyl dichloride. The products were characterized by using gel permeation chromatography, infrared spectroscopy, ¹³C and ¹H nuclear magnetic resonance spectrometry, and scanning electron microscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1451–1456, 2005     

Determination of the interaction parameter χ of poly(ethylene oxide) by gas-liquid chromatography below the melting temperature

The interaction parameter χ of poly(ethylene oxide) in different solvents at temperatures below the melting point (T_m) of the polymer has been determined by means of the solubility parameters of the polymer and solvents at this temperature, chromatographically obtained from their values at higher temperatures (70°–140°C). The value of the interaction parameter so obtained is not only in good agreement with those calculated by other techniques but also independent of the temperature range employed in the chromatographic measurements. Moreover, using the equation-of-state theory formulation, we have determined values of the interaction parameter χ1 for different poly(ethylene oxide)/probe systems and from it the contact interaction energy X₁₂, in the temperature range between 70° and 140°C.     

Polyols production by chemical modification of autocatalyzed ethanol‐water lignin from Betula alnoides

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     

Preparation and characterization of graft copolymer from dealkaline lignin and styrene

Graft copolymerization of styrene onto dealkaline lignin by ferrous chloride and hydrogen peroxide coinitiator has been achieved successfully. The influence of temperature and reaction time as well as the amount of the styrene monomer, initiator, and catalyst on the grafting copolymerization was investigated. The optimum reaction conditions were determined as follows: c (styrene) = 20.00 mmol, c (H₂O₂) = 5.00 mmol, c (FeCl₂) = 0.10 mmol, T = 30°C and t = 48 h. The optimum yield (Y), total conversion (TC), grafting efficiency (GE), and degree grafted (DG) values were 96.6, 96.3, 59.5, and 53.7%, respectively. The copolymer of lignin grafted PS was separated and characterized by elemental analysis, differential scanning calorimetry, Fourier transform infrared, thermogravimetry analysis, field emission‐scanning electron microscopy, gel permeation chromatography, and nuclear magnetic resonance. It was demonstrated that the solubility what the copolymer exhibited turned out to be the very reverse of the original lignin. The surface properties and structure of lignin were completely changed after grafting copolymerization. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41900.     

Synthesis and characterization of nonlinear optical side-chain polyimides containing the thiadiazole chromophores

Thermally stable second-order nonlinear optical (NLO) polyimides were synthesized using a standard condensation polymerization technique. The polyimides were prepared from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and pyromellitic dianhydride (PMDA) with two aromatic azo- and diazo-diamine derivatives as the NLO chromophores. The resulting polyimides were characterized by FTIR, ¹H-NMR, UV-vis spectroscopies, differential scanning calorimetry, thermogravimetric analysis, and gel permeation chromatography. The weight-average molecular weights of polyimides determined by gel permeation chromatography (GPC) were in the range of 32,100 to 39,300 (M_w/M_n = 1.58–1.74). All the polyimides exhibited an excellent solubility in many of the aprotic polar organic solvents, manifesting that these polyimides offer good processability. The glass transition temperature for the resulting polyimides was in the range of 152 to 194°C and most of them showed high thermal stability. Particularly, the polyimides containing diazo group and PMDA backbone showed an enhanced thermal stability and glass transition temperature. The second harmonic generation (SHG) coefficients (d₃₃) of the poled polyimide films range from 43.71 to 80.49 pm/V at 532 nm. Further, it is noticed that there was no SHG decay below 180°C because of the partial main-chain character of the polyimide structure, which is acceptable for nonlinear optical device applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Physicochemical characterization of lignin fractions sequentially isolated from bamboo (Dendrocalamus brandisii) with hot water and alkaline ethanol solution

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     

Low molecular weight water‐soluble chitosans: Preparation with the aid of cellulase,characterization, and solubility

Preparation of water‐soluble chitosan (WSC) was made by treating partially N‐deacetylated chitosan with acetic anhydride in aqueous acetic acid. The optimal conditions of preparing WSC were determined on the basis of orthogonal tests. Low molecular weight WSC with broad molecular weight (600–1.5 kDa) were obtained by the depolymerization of WSC using cellulase at optimum condition of pH 4.5 and 60°C. The solubility of WSC in water and aqueous organic solvents was investigated in detail. Weight–average molecular weight (M_w) and molecular weight distribution (M_w/M_n) of samples were measured by gel permeation chromatography. The structure of WSC and its degraded products were characterized by XRD, FTIR, and MALDI‐TOF MS. The decrease of molecular weight led to transformation of crystal structure and the increase of solubility, but the chemical structures of residues were not modified compared to WSC, which was not hydrolyzed. The solubility of the WSC in water and aqueous organic solvents increased with the decrease of molecular weight. The solubility of the WSC with low molecular weight was rather high even in aqueous dimethylacetamide and dimethylsulfoxide. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1098–1105, 2006     

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.     

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.     

Polyether-segmented nylon hemodialysis membranes. III. Preparation and properties of new polyether-segmented nylon

In order to apply a blood-compatible polymer to hemodialysis membrane, a new polyether-segmented nylon which dissolved in common organic solvents was designed. The basic polyether-segmented nylon was synthesized by melt polycondensation from sebacic acid, m-xylenediamine, and α,ω-bisaminopropyl-poly(ethylene oxide). To improve the solubility, azelaic acid and hexamethylenediamine were copolycondensed with the basic copolymer. The solubility was correlated with the heat of fusion (ΔH_m) of the copolymer. When ΔH_m is < 30 mJ/mg, the polymer is soluble in dimethylsulfoxide and makes a stable solution. The nonthrombogenicity was investigated in the viewpoint of adhesion of platelet onto the copolymer surface. It is made clear that the surface of the block copolymer, having > 10 wt % of poly(ethylene oxide), suppresses the adhesion of platelet, and the composition of the nylon block has no effect on the adhesion of platelet. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1723–1729, 1997     

Polyesters from lignin. 1. The reaction of kraft lignin with dicarboxylic acid chlorides

Kraft lignin was treated with dicarboxylic aliphatic (sebacoyl) or aromatic (terephthaloyl) acid chlorides in N,N-dimethylacetamide or N-methyl-2-pyrrolidone as solvents in the presence of triethylamine or pyridine as catalysts. The polyester gels obtained were characterized by IR after specific extractions and the chemical incorporation of lignin was proved unambiguously. Their thermal behaviour was determined by DSC and TGA; they are amorphous and stable up to 200°C in a nitrogen atmosphere. The reactivities of the two types of hydroxyl group (aliphatic and phenolic) were assessed from model reactions carried out in the same conditions.     

Grafting of poly(ethylene oxide) onto C60 fullerene using macroazo initiators

In order to improve the solubility of C₆₀ fullerene in conventional solvents, grafting of hydrophilic poly(ethylene oxide) (PEO) by utilizing the radical-trapping nature of C₆₀ fullerene was investigated. Macroazo initiators containing a poly(ethylene oxide) unit, known as Azo-PEO, were prepared at various molecular weights by the reaction of 4,4′-azobis(4-cyanopentanoyl chloride) with poly(ethylene glycol) methyl ether. PEO radicals formed by thermal decomposition of Azo-PEO were successfully trapped by C₆₀ fullerene to give PEO-grafted C₆₀ fullerene. Their structures were confirmed by FT-IR spectroscopy, size exclusion chromatography, UV-vis spectroscopy, and differential scanning calorimetry. When Azo-PEO with low-molecular weight was reacted with C₆₀ fullerene, a bis-adduct, C₆₀-(PEO)₂, and a tetrakis-adduct, C₆₀-(PEO)₄, were formed. In contrast, in reactions with Azo-PEO of higher molecular weight, only the bis-adduct was formed, and no formation of the tetrakis-adduct was observed. The structure of bis-adduct was found to be 1,4-type. The solubility of C₆₀ fullerene in water, THF, methanol, and other conventional organic solvents was remarkably improved by grafting of PEO. In addition, the thermal stability of PEO was dramatically increased by grafting onto C₆₀ fullerene.     

Comparative studies of oil compositions produced from sawdust,rice husk,lignin and cellulose by hydrothermal treatment

The objective of this study is to investigate the distribution of products, i.e. liquid, gas and solid from wood (sawdust) and non-wood biomass (rice husk), and major biomass components, i.e. lignin, cellulose produced by hydrothermal treatment (280 °C for 15 min) and analysis of liquid hydrocarbons (oils) for the differences in the hydrocarbon composition with respect to feed material. Cellulose showed the highest conversion among the four samples investigated in the present study. Sawdust and rice husk has almost similar conversions. Liquid products were recovered with various solvents (ether, acetone, and ethyl acetate) and analyzed by GC–MS. The oil (ether extract) from the hydrothermal treatment of cellulose consisted of furan derivatives whereas lignin-derived oil contained phenolic compounds. The compositions of oils (ether extract) from sawdust and rice husk contained both phenolic compounds and furans, however phenolic compounds were dominant. Rice husk derived oil consists of more benzenediols than sawdust derived oil. The volatility distribution of oxygenated hydrocarbons were carried out by C-NP gram and it showed that the majority of oxygenated hydrocarbons from sawdust, rice husk and lignin were distributed at n-C₁₁, whereas they were distributed at n-C₈ and n-C₁₀ in cellulose-derived oil. The gaseous products were carbon dioxide, carbon monoxide, methane in sawdust, rice husk, lignin and cellulose. In addition to this, ethylene, ethane and propane were observed for sawdust, rice husk and lignin. The major gas product was carbon dioxide for all samples.     

Thermolysis of glycol lignin in the presence of tetralin

An organosolv (ethylene glycol) hardwood lignin has been thermally treated in the presence of tetralin, a hydrogen donor solvent. The effects of reaction temperature and time on product distribution were studied as a function of a seventy index, X_c = ?n (R_ω with R_ω = Δt t × exp [(T_r - T_b)/ω] where Δt = time, T_r = reaction temperature, T_b = base temperature, and ω = characteristic parameter. Under the conditions used, up to 60% of the lignin can be converted to liquid and gaseous products. Syringols, guaiacols, aromatic aldehydes and ketones predominate at low treatment severities whilst phenol, catechol and their methyl and ethyl derivatives are the main monomers at high severities. Comparison of our data with parallel works is shown to be effectively done through the severity index, X_c.     

Effect of molar size and solubility parameter of solvent molecules on swelling of a gel: a fluorescence study

Gels were swollen in various solvents with different molar volume V and solubility parameter δ. In situ steady state fluorescence (SSF) measurements were performed for swelling experiments in gels formed by free radical crosslinking copolymerization (FCC) of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM). Gels were prepared at 75 °C with pyrene (Py) as a fluorescence probe. After drying these gels, swelling and slow release experiments were performed in various solvents with different V and δ at room temperature by time monitoring of the Py fluorescence intensity. The Li–Tanaka equation was used to produce time constant τ₁ values. Cooperative diffusion coefficients (D_c) were measured and found to be strongly correlated to the molar volume of the solvents used. Solvent uptake and degree of swelling were found to be dependent on the solubility parameter of the solvent. © 2000 Society of Chemical Industry     

Thermal properties of epoxy resins crosslinked by an aminated lignin

Aminated lignin possessing significant amount of reactive amino groups was studied as a curing agent of epoxy resin. Fourier transform infrared spectroscopy results proved the reactivity of the aminated lignin with the epoxy resin. Both appearance features and scanning electron microscopy images indicated that the transparent and homogeneous epoxy resin films could be formed with the aminated lignin less than 40% in the hardener mixture. In addition, thermogravimetric analysis and dynamic thermomechanical analysis results revealed that the epoxy resin cured by aminated lignin had better thermal stability compared with ones cured by a common hardener. The mass loss of the epoxy resin cured by the aminated lignin before 300°C was small around only 2.5%. The T_g (the glass transition temperature) of epoxy resin sample after cured by mixed hardener increased from 79°C to 93°C. The obvious difference (70–84°C) of T_d (the thermal deformation temperature) was also observed from the samples with and without the aminated lignin after cured at a high temperature. POLYM. ENG. SCI., 55:924–932, 2015. © 2014 Society of Plastics Engineers