Potential of producing carbon fiber from biorefinery corn stover lignin with high ash content

The possibility of producing carbon fiber from an industrial corn stover lignin was investigated in the present study. As‐received, high‐ash containing lignin was subjected to methanol fractionation, acetylation, and thermal treatment prior to melt spinning and the changes in physiochemical and thermal properties were evaluated. Methanol fractionation removed most of the impurities in the raw lignin and also selectively removed the molecules with high melting points. However, neither methanol fractionation nor thermal treatment rendered melt‐spinnable precursors. The precursors were highly viscous and decomposed easily at low temperatures, attributed to the presence of H, G phenolic units, and abundant hydroxycinnamate groups in herbaceous lignin. A two‐step acetylation of methanol fractionated lignin greatly improved the mobility of lignin, while enhancing the thermal stability of the precursor during melt‐spinning. Fourier Transform Infrared and 2D‐NMR analysis showed that the contents of phenolic and aliphatic hydroxyls, as well as the hydroxycinnamates, decreased in the acetylated precursors. The optimum precursor was a partially acetylated lignin with a glass transition temperature of 85 °C. Upon oxidative stabilization and carbonization, the carbon fibers with an average tensile strength of 454 MPa and modulus of 62 GPa were obtained. The Raman spectroscopy showed the I_D/I_G ratio of the carbon fiber was 2.53. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45736.     

Synthesis and polymerization of lignin macromonomers. II. Effects of lignin fragments on methyl methacrylate radical polymerization

In the course of a study on the synthesis and polymerization of lignin macromonomers, the effect of lignin fragments and acetylated lignin ones on the radical polymerization of methyl methacrylate has been investigated. Kinetics show that lignin moieties act first as inhibitors of the MMA polymerization. The inhibition process has been attributed to the phenolic groups, which primarily react through hydrogen transfer with free radicals issued from benzoyl peroxide dissociation, thus leading to a series of lignin free radicals inactive towards ethylenic groups. The derivatization of lignin hydroxyl groups into ester groups totally suppresses the inhibition process. Besides, it was also shown that both lignin and acetylated lignin units act as chain limiting agents towards MMA polymerization. As indicated both by the chemical composition of the polymers produced and the kinetic data, the latter process might involve the formation of a new type of lignin free radicals, able to initiate MMA polymerization. A reaction scheme is proposed.     

Miscible raw lignin/nylon 6 blends: Thermal and mechanical performances

Environmentally friendly bio‐filled composites of various proportions of polyamide 6 (PA6) and technical lignin have been prepared using a twin‐screw extruder. Transmission electron microscopy has been used to investigate the morphology of the composites. It reveals homogeneous single phase system, indicating the miscibility of PA6 and lignin. The glass transition temperature of the blends, determined by DMA, was shifted systematically to higher temperature with increasing concentration of lignin which highlights the miscibility of both components. In addition, Fourier Transform Infrared analyses have shown that new specific hydrogen‐bonding interactions are formed between hydroxyl groups of lignin and amine groups of the PA6. The presence of these intermolecular interactions between PA6 and lignin strongly influenced the thermal stability of the blends by lowering the onset of the blend's degradation process. However, the blends exhibit good mechanical properties whatever the lignin content. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42963.     

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.     

Succinylation of three different lignins by reactive extrusion

Succinate esters of three lignin materials were prepared by reactive extrusion. Reactive extrusion was developed as a facile route to chemically modify lignin with the benefits of being a scalable, solvent‐free, and economic process. Kraft lignin and crude and purified enzyme saccharification lignins were reactively extruded with varying amounts of succinic anhydride. The resulting products were characterized chemically and thermally. Succinylation occurred preferentially at the aliphatic hydroxyl groups of kraft lignin, with phenolic substitution occurring at higher amounts of succinic anhydride addition. The degree of substitution was dependent on the relative amounts of succinic anhydride and lignin substrate. Thermal stability of the products decreased with increasing levels of substitution, primarily due to the loss of succinate groups on heating. The degree of substitution influenced the glass transition temperature, which reflected the melt flow and solubility of the products. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

竹子木素在GIF仿酶漂白中的降解机理

研究了竹子木素在GIF仿酶漂白中的降解机理,结果表明,GIF仿酶处理后,竹子木素酚羟基、醇羟基和对羟苯基增加,甲氧基、羰基、愈创木基和紫丁香基减少,β-O-4、β-1、β-5联接发生断裂,芳环开裂。此外,GIF仿酶处理后,竹子木素分子量下降,多分散性提高。     

Light-Induced Yellowing of Mechanical and Ultrahigh Yield Pulps. Part 2. Radical-Induced Cleavage of Etherified Guaiacylglycerol-β-Arylether Groups is the Main Degradative Pathway

Bleached softwood mechanical pulp was treated with sodium borohydride to reduce carbonyl groups and dimethyl sulphate to block phenolic hydroxyl groups. Upon irradiation with near ultra-violet light, new phenolic hydroxyl groups and aromatic carbonyl groups formed. Existing mechanisms for photoyellowing require that either aromatic ketones or phenolic hydroxyls be initially present in the pulp, and cannot explain these observations. We interpret our results in terms of light-induced breakdown of etherified arylglycerol-β-arylether structures in lignin. Degradation occurs via the corresponding ketyl radicals, which cleave rapidly at the β-O-4 bond to give a phenoxy radical and an acetophenone enol. The enol tautomerizes to a ketone, while the phenoxy radical is oxidized to coloured groups. We believe that the ketyl route is the main lignin degradative pathway, and estimate that up to 70% of the colour formed during light-induced yellowing is attributable to this reaction.     

Preparation of a Polyhydric Aminated Lignin and Its Use in the Preparation of Polyurethane Film

In this paper, a polyhydric aminated lignin containing both amino and hydroxyl groups was prepared by hydroxylation and amination. The temperature, the reaction time, and the composition of the reaction mixture were found to have a significant influence on the extent and rate of the hydroxylation and amination reactions. Under the optimum reaction conditions, the content of aliphatic hydroxyls in lignin increased from 1.74 to 4.73%. The amine groups, mainly primary amine groups, were also introduced into the product, which lead to the nitrogen content increased from 0.64% to 4.58%. The performances of polyurethane film containing polyhydric aminated lignin (ALPU) were significantly improved compared with those of polyurethane film using soda lignin (LPU). The polyhydric aminated lignin replaced more polyol components in polyurethane (PU) film production. The maximum tensile strength of ALPU film was about 1.7 and 4.6 times of LPU film and PU film, respectively. The thermal stability of PU was also improved because of the addition of polyhydric aminated lignin, while the thermal stabilities of ALPU film and LPU film had similar performance.     

Lignins as macromonomers for polyurethane synthesis: A comparative study on hydroxyl group determination

The hydroxyl group contents of four technical lignins [Indulin AT (Meadwestvaco), Alcell (Repap), Curan 27‐11P (Borregaard LignoTech), and Sarkanda (Granit SA)] were investigated in view of their valorization as polyols in polyurethane synthesis. The different hydroxyl group contents were determined by the following methods: titration and ¹H‐NMR, ¹³C‐NMR, and ³¹P‐NMR spectroscopy. The titration method chosen was on the basis of a standard method commonly used to characterize commercial polyols for polyurethanes synthesis. The values of the total and phenolic hydroxyl contents determined by the different techniques were found to be in good agreement. For the total hydroxyl contents, coefficients of variation of 5.6% (Alcell), 3.2% (Indulin AT), 2.3% (Sarkanda), and 6.2% (Curan 27‐11P) were established. For the phenolic hydroxyl contents, a good correlation was observed between data obtained from ³¹P‐NMR and ¹³C‐NMR for all lignin samples, except for the Sarkanda lignin, for which a relatively high coefficient of variation (12.6%) was found. For softwood lignins (Indulin AT and Curan 27‐11P), the phenolic hydroxyl content determined by ¹H‐NMR was always lower than that deduced from ³¹P‐NMR and ¹³C‐NMR spectroscopy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enhanced oil resistance and mechanical properties of nitrile butadiene rubber/lignin composites modified by epoxy resin

This is probably the first report on developing nitrile butadiene rubber (NBR) composites with enhanced performance s via lignin bridged epoxy resin in the rubber matrix. NBR/lignin masterbatch has been prepared through latex‐compounding method, and then epoxy resin (F51) was added in the NBR/lignin compounds by the melt compounding method. Lignin‐epoxy resin networks were synthesized in situ during the curing process of rubber compounds through epoxide?hydroxyl reactions. Compared with lignin filler, lignin‐F51 networks showed an improved oil resistance ability and led to increased mechanical properties, crosslinking density, and thermal stability of the rubber composites. This method provides a new insight into the fabrication of novel interpenetrating polymer networks in rubber composites and enlarges the potential applications of lignin in high performance rubber composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42922.     

Structural modification and characterization of lignosulfonate by a reaction in an alkaline medium for its incorporation into phenolic resins

We studied the enhancement of lignin reactivity in an alkaline medium, using sodium hydroxide in a microreactor set. The chemical composition and structural characterization of the reacted lignosulfonate in terms of the phenolic hydroxyl groups, aromatic protons, weight‐average molecular weight, number‐average molecular weight, and lignosulfonate content of all reacted lignins were determined. The techniques that we used were ultraviolet spectroscopy, proton nuclear magnetic resonance spectroscopy, and aqueous gel permeation chromatography. Using response surface methodology, we studied how the temperature and reaction time affected the lignin properties. The reaction conditions were temperatures between 116 and 180°C and reaction times between 18 and 103 min. Modeled response surfaces showed that the two factors affected the lignin properties within the studied ranges. The phenolic hydroxyl groups, aro matic protons, and lignosulfonate content increased when the severity of the treatment increased. The weight‐average molecular weight, number‐average molecular weight, and solid yield (%) decreased when the severity of the treatment increased. The reactivity of the modified lignins was studied with a formaldehyde reactivity test: more severe conditions produced greater improvements in the formaldehyde reactivity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3286–3292, 2006     

新型聚氨酯助剂——酶解木质素的研制

研究了采用无机碱性水溶液和有机溶剂从玉米秸秆发酵制备乙醇的残渣中分离得到酶解木质素的方法.结果表明,用有机溶剂提取后的残渣继续用无机碱水溶液再次提取,酶解木质素的产率为25%～35%,其红外光谱与磨木木质素红外光谱相似.酶解木质素的分子中含有丰富的苯环、酚羟基和醚键等官能团,具有较高的反应活性,能直接用于聚氨酯的改性.     

Methanol synthesis in a three‐phase catalytic bed under nonwetted condition

To overcome the heat removal problem encountered in methanol synthesis at high syngas concentrations in the gas phase, a three‐phase nonwetted catalytic system was established by introducing an inert liquid medium into a fixed‐bed reactor. To form a repellent interface between the liquid and the catalyst, the catalyst was modified into hydrophobic, while the liquid medium was chosen as a room temperature ionic liquid with hydroxyl groups. The liquid‐solid contact angle was measured to be 115°, and only 20% of the catalyst external surface was wetted by the liquid. Under three‐phase condition, the reaction rate was measured to be 60%–70% of gas‐phase reaction, while it was merely 10%–20% for the fully wetted catalyst. From the resistance analysis on the mass transfer and reaction steps, the overall reaction rate is expected to increase further if the surface could be more wet proofed. © 2016 American Institute of Chemical Engineers AIChE J, 63: 226–237, 2017     

Chemical Groups and Structural Characterization of Lignin via Thiol-Mediated Demethylation

A new approach to increase the reactivity of lignin by thiol-mediated demethylation was investigated in this study. Demethylated lignin was characterized by the changes in its hydroxyl and methoxyl groups, molecular weight, and other properties using titration and spectroscopy methods including FT-IR, ¹H NMR, UV, and GPC. The total, phenolic, and aliphatic hydroxyl contents in lignin increased while the methoxyl content decreased after demethylation reaction, which indicated the occurrence of demethylation reaction. The results from FT-IR and UV analysis also indicated that the kraft lignin in this study contains mainly guaiacyl moiety and demethylated lignin has a higher guaiacyl content than original lignin. The average molecular weight of lignin decreased after demethylation reaction due to the cleavage of ether linkages in lignin macromolecules. No severe degradation of lignin was observed during the demethylation reaction.     

Effects of NCO:OH ratio on the mechanical properties and chemical structure of Kraft lignin–based polyurethane adhesive

ABSTRACT

This work aimed to evaluate the influence of the aliphatic and aromatic hydroxyl level on the polyurethane adhesive property and chemical structure. This adhesive was obtained through the reaction of technical Kraft lignin (TKL) as polyol with diphenylmethane diisocyanate (MDI). Thus, lignopolyurethane adhesives were obtained with NCO:OH ratios of 0.8:1.0, 0.9:1.0, 1.0:1.0, 1.1:1.0, and 1.2:1.0. Initially only the TKL aliphatic hydroxyl level was taken into consideration in the stoichiometry in order to define the mass ratio between MDI and polyol. Subsequently, lignopolyurethane adhesive was obtained using the same NCO:OH ratios considering TKL total hydroxyls’ level, and aromatic and aliphatic hydroxyls. The chemical structures of the synthesized adhesives were analyzed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹³C NMR). The mechanical property of the adhesively bonded joints, comprising wood substrates and synthesized adhesives, was measured using single lap shear tests. Results illustrated that by increasing the NCO:OH ratio, there is an increase in the free isocyanate content leading to higher shear strength values. Higher free isocyanate content leads to MDI dimer formation in the lignopolyurethane structure.     

Depolymerization of renewable resources—lignin by sodium hydroxide as a catalyst and its applications to epoxy resin

Alkali lignin was successfully depolymerized into polyols with high hydroxyl number via direct hydrolysis using sodium hydroxide (NaOH) as a catalyst, without any organic solvent agent. Hydrolysis of lignin can produce a multitude of high‐value products via alkali‐catalyzed cleavage. This process usually gives good results with respect to the yield of phenols. Through this method, the numbers of the hydroxymethyl and phenolic hydroxyl groups of lignin had been dramatically increased, reaching 2.11%, nearly four times higher than that in the original one. Meanwhile, we added the same amounts (20 wt %) of different depolymerization of lignin (DL) into epoxy resin (EP), and the results showed that DL could not only increase the decomposition temperature of EP, but also remarkably improve its mechanical properties. The optimum reaction time was 1.5 h, the reaction temperature was 250°C, and the optimum sodium hydroxide concentration was 15 wt % for depolymerizing lignin. The mechanical and thermal properties of cured lignin‐based epoxy resin (LEP) were compared with cured neat EP. The cured DL‐based epoxy resin (DLEP) showed the highest adhesive shear strength up to 2.66 MPa, which displayed 122% of the adhesive shear strength of EP. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42176.     

Engineering biomass into formaldehyde‐free phenolic resin for composite materials

The use of formaldehyde to prepare phenol‐formaldehyde (PF) resins is one of the primary challenges for the world‐wide PF industry with respect to both sustainability and human health. This study reports a novel one‐pot synthesis process for phenol‐5‐hydroxymethylfurfural (PHMF) resin as a formaldehyde‐free phenolic resin using phenol and glucose, and the curing of the phenolic resin with a green curing agent organosolv lignin (OL) or Kraft lignin (KL). Evidenced by ¹³C NMR, the curing mechanism involves alkylation reaction between the hydoxyalkyl groups of lignin and the ortho‐ and para‐carbon of PHMF phenolic hydroxyl group. The curing kinetics was studied using differential scanning calorimetry and the kinetic parameters were obtained. The OL/KL cured PHMF resins were tested in terms of thermal stability, and mechanical properties for their applications in fiberglass reinforced composite materials. The results obtained demonstrated that OL/KL can be promising curing agents for the PHMF resins. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1275–1283, 2015     

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.     

木质素系水处理剂的研究近况及进展

提出了我国碱木质素利用关键是增加碱木质素醇羟基和酚羟基含量,降低甲氧基含量,提高反应活性.分析了采用化学和物理等方法增加碱木质素自身的反应活性的原理和可能性.介绍了木质素系水处理剂的研究近况,对于我国木质素水处理剂应用研究存在的产品功能单一等问题,认为应根据我国工业木质素来源特点,先采用多种手段提高碱木质素的反应活性,然后研制多功能水处理剂,可充分发挥木质素自身优势,具有较大发展前景.     

Studies of the effects of O-methylation on the pyrolysis behaviour of four coals

O-methylation of coal was found to exhibit a noticeable effect on the pyrolysis behaviour of the original coal. Significant increases in tar yields and a low-temperature fraction, 150–300 °C, were found for the low-rank O-methylated coals. It is proposed that methylation prevents formation of new ether cross linkages through water elimination reactions of hydroxyl functional groups thus allowing for the release of a low-temperature fraction as well as a higher temperature tar. KBr studies of CD₃ labelled O-methylated coals using CD₃I as the methylating agent have resulted in the identification of three distinct i.r. absorptions in the C-D stretching region which have been assigned to methylated phenolic, methylated carboxylic and methylated aliphatic hydroxyl groups. Pyrolysis studies of the O-methylated coals have resulted in better insight into the decomposition mechanisms of different methylated hydroxyl functional groups. Methanol or formaldehyde are seen to be the principle products from the pyrolysis of methylated carboxylic and aliphatic hydroxyls. Decomposition of methylated phenolic groups occurs at a slightly higher temperature and produces principally methane and carbon monoxide.