Reactions of Conventional Kraft and Superbatch Pulp Residual Lignins with Peroxyformic Acid

Abstract

The residual lignins KRL and SRL, isolated from a conventional kraft pulp and a SuperBatch pulp respectively, were reacted with peroxyformic acid (PFA). The reagent consumptions were determined and the products fractionated according to their solubility. Both lignins consumed a roughly equal amount of PFA, which was nearly 50% higher than that consumed by kraft lignin. The undissolved fractions of PFA-treated residual lignins (yield >80%) contained less aromatic units, phenolic hydroxyl and methoxyl groups, and considerably more carboxyl groups (including those of formate esters) than the untreated lignins. The extent of these modifications was approximately equal for KRL and SRL, which together with the similar PFA consumptions and product yields of KRL and SRL indicates that the two residual lignins showed no essential difference in reactivity toward PFA. The effect of fiber wall morphology on delignification efficiency during PFA delignification is suggested to be small because of the cleavage of lignin-carbohydrate linkages occurring under acid conditions. The part of KRL remaining insoluble after PFA-treatment had a 40% higher molar mass than KRL while in the case of SRL there was hardly any such difference in molar mass. The lignins solubilized during the PFA treatments represented the most highly degraded part of the lignins, having very low molar masses and being richer in carboxyl groups and lower in aromatic units, phenolic hydroxyl, and methoxyl groups than the undissolved lignins.     

Controlling stabilization of oil-in-water emulsions with lignins through fractionation,functionalization, and formulation

Lignins, heterogeneous assemblies of polyphenolic oligomers present in lignocellulosic plant biomass, are valorized mainly by combustion because of their low solubility in commonly used solvents. However, in addition to antioxidant, anti-UV and antimicrobial properties, and marked interfacial properties are part of lignins physicochemical properties, thus making them good candidates for sustainable colloids. It is hypothesized that lignins solubility and emulsifying performances could be modulated by fractionation, functionalization, and formulation strategies. The importance of the solvent, and of the pH on lignins solubilization in aqueous phase was investigated. Accordingly, simple O/W emulsions stabilized by different lignins were designed and characterized. The whole results demonstrated that lignins solubility in water can be optimized using appropriate co-solvent and pH readjustment resulting in a homogeneous dispersion with only 7.2 ± 1.8% wt/wt of insoluble lignins. Both fractionation and biocatalytic modification of lignins allowed increasing stabilization of the oil–water interface by limiting coalescence (23%–24% of relative increase of the D90) compared with non-fractionated lignins (32%), thus advocating their potential use as multifunctional emulsion stabilizers. As a result, a direct link between the molar mass profile of lignins and their ability to stabilize the oil–water interface as well as to reduce emulsion's sedimentation could be established.     

造纸黑液木质素作为EPDM橡胶偶联剂的研究

采用硝酸和硫酸由碱法造纸黑液中酸析得到2种木质素,对其进行了粒径分布分析。研究了分别添加这2种木质素和硅烷偶联剂对三元乙丙橡胶（EPDM）性能的影响。结果表明,2种木质素具有较小的中位径和较大的比表面积,加入EPDM橡胶中,比硅烷偶联剂更能改善其力学性能;当加入1.5 %（基于100 g橡胶）硝酸盐木质素时,EPDM橡胶的拉伸强度、断裂伸长率和肖A硬度分别提高了21.42 %、 22.55 % 和8;傅里叶红外光谱分析（FTIR）和扫描电子显微镜（SEM）结果证实木质素对橡胶有补强作用;而热失重（TG）结果说明木质素和硅烷偶联剂一样均能提高EPDM橡胶的热稳定性;木质素替代硅烷偶联剂用于EPDM橡胶,可改善其性能,降低生产成本,有较好的应用前景。     

Comparison of inhibition effects of various isolated lignins on enzymatic hydrolysis of cellulose

Various isolated soluble and insoluble lignins isolated from ammonia recycle percolation (ARP), dilute sulfuric acid, and hot-water pretreatments and two commercially available lignins (alkali and organo-solv lignin) were tested to evaluate their inhibitory effects on the enzymatic hydrolysis of cellulose. The purpose of this study was to compare the effects by adding various isolated lignins in the enzyme hydrolysis. The results showed that enzyme reaction was generally inhibited by addition of lignins. The order of lignins from most to least inhibitory effects were alkali, ARP-soluble, water-soluble, acid-soluble, ARP-insoluble, and organo-solv lignins. With 0.344 g ARP-soluble or alkali lignin/g-glucan lignin loadings, 72-h digestibilities were decreased by 16% and 20%, respectively. It was also observed that the digestibilities were decreased, as the lignin loadings increased. The hindering effect by ARP-insoluble or organosolv lignin was not significant.     

Acetosolv Lignins from Bagasse: Characterization by TG and DTA

Thermal characteristics are described for acetosolv lignins, isolated after pulping bagasse with 90% and 70% acetic acid solution in presence or absence of 0.5% sulfuric acid as a catalyst. Tested lignins exhibited three well-developed TG waves and DTA peaks; their amplitude depends on the pulping conditions. Activity of the lignins was correlated with weight loss, DTA peaks, and activation energy. This followed the sequence: 90% acetosolv lignin > acetosolv lignins with sulfuric acid > 70% acetosolv lignin.     

蒜头果木质素提取及成分分析

采用一般碱法、超声波辅助和微波辅助从蒜头果壳和枝中提取木质素,分别测定了蒜头果壳和枝中木质素含量及木质素的提取率,并对所提取木质素进行红外和紫外光谱分析。克拉森木素定量法测得蒜头果壳和枝中木质素质量分数分别为44.41%±0.65%和34.57%±0.52%,在碱浓度0.5 mol/L、碱液量30 mL/g、超声波处理时间1 h、水浴温度40℃的提取工艺条件下,蒜头果壳和枝的木质素提取率分别为45.21%±0.59%和63.78%±0.73%。紫外和红外光谱显示超声波辅助方法提取的木质素保持了木质素原有结构,存在明显的愈疮木基和紫丁香基苯环结构;并通过黏度法比较了3种不同提取方法所得木质素的相对分子质量。     

Structural Changes in Lignin During Kraft Cooking Part 3. On the Structure of Dissolved Lignins

Two series of pine kraft lignins were prepared by a) normal kraft cooks to different pulp yield levels and precipitation of the lignins from the black liquors by acidification and b) by successive acidification of the black liquor obtained from a flow-through cook. All the lignins were extensively purified, subjected to elemental and methoxyl analysis and subsequently acetylated.

Quantitative ¹³C-NMR analysis was carried out on acetylated samples and the results were combined with the results of phenolic group determination by means of aminolysis and with elemental analysis data. The various acetylated lignins were also subjected to analysis by size exclusion chromatography.

All results are discussed with reference to known features of kraft cooking and of kraft lignins.     

Some physical properties of acetosolv lignins from bagasse

Acetosolv-solubilized lignins were characterized by their solubility in different organic solvents, Fourier transform infrared, ¹³C-NMR, UV, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. Solvents having a solubility parameter in the range of 10–12.7 and a hydrogen-bonding parameter in the range of 3.6–5 were considered good solvents for acetosolv lignins. Fourier transform infrared spectra of the lignins were typical for lignins containing p-hydroxy phenylpropane (H), guaiacyl (G), and syringyl (S) units. The lignins contained more conjugated and fewer nonconjugated CO groups, and the guaiacyl groups were etherified and condensed. ¹³C-NMR confirmed partial acetylation of the lignins and the presence of β-O-4 and β-5 linkages. Acetosolv lignins also showed the typical UV spectrum of annual plants. The effects of the acetic acid concentration and pulping time on the molecular weights of the lignins were explained with the presieving and condensation concepts. The thermal behavior of the acetosolv lignins was also studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Characterization of Lignins from Organosolv Pulping According to the Organocell Process,Part 2. Residual Lignins

Abstract

Residual lignins were isolated from cooking residues obtained from 20 1 batch cookings of spruce chips by either ball-milling or enzymatic treatment. The lignins were characterized in terms of yield, elemental composition, polysaccharide moieties and functional groups and compared with the corresponding dissolved lignins.

The residual lignins generally proved to be less changed than the dissolved lignins. They show considerable adherence to cellulose and xylose portions. Aliphatic OH groups were found to decrease remarkably towards the end of the cook, which was explained by the formation of new lignin-lignin and lignin-polysaccharide bonds as well as by side chain degradation.

Lignin methylation by methanolic liquor was almost negligible.     

Influence of Lignin Type on the Mechanical Properties of Lignin Based Compounds

Several types of sulfur‐free lignins were melt compounded in a Werner & Pfleiderer twin screw extruder (ZSK 25) together with polyamide 11 (PA11), a biodegradable polyester (Ecoflex®) and a biodegradable polyesteramide (BAK®). Sulfur‐free lignins, precipitated from black liquors of alkaline pulping of annual plants, like sisal and abaca, were compared to a sulfur‐free lignin (Alcell™) obtained by organosolv wood pulping. Lignin content and lignin type were varied systematically in order to examine stress/strain characteristics and impact behavior. Compounds with lignins from annual plants showed similar or better mechanical properties in comparison to compounds with Alcell™ lignin. A polyamid 11 compound containing 30 wt.‐% abaca lignin gave a Young's modulus of 1 890 MPa, compared to 1 420 MPa for PA11 and a 28% increase of yield stress. The morphology of the lignin compounds was investigated by means of environmental scanning electron microscopy (ESEM) and transmission electron microscopy (TEM).     

The thermal behaviour of lignins modified by chlorophosphazenes

The thermal behaviour in air of lignins modified by chlorophosphazenes as well as that of the raw materials of lignins has been investigated using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA). The thermogravimetry and derivative thermogravimetry studies of lignins modified by chlorophosphazenes have shown their thermal resistance to be relatively higher than that of the intital raw materials of lignins in concrete kraft lignin and sodium ligninosulfonate. The differential thermal studies have demonstrated that the thermal degradation of products investigated takes place via exothermic processes. The lignins modified by chlorophosphazenes have been shown to be thermal and flame-resistant materials.     

兴安落叶松木素化学结构特性的研究

从兴安落叶松的边材、心材和经0．1mol／NaOH抽提过的心材中分离出二氧六环木素，用化学分析和光谱分析研究了分离木素的化学结构特性．结果表明兴安落叶松的边材和心材术素都是典型的针叶材木素，三种分离木素的元素组成、官能团含量和光谱性质没有显著差异，心材多酚类化合你又少与木素存在化学连接，只是心材木素的缩合程度略高，分子量低于边材术素．兴安落叶松边材、心材和经0．lmol／NaOH抽提的心材的二氧六环木素C9单元式分别为C9H8.80O3.06（OCH3）0.96C9H8.80O3.14（OCH3）0.93和C9H8.55O3.03（OCH3）0.96，与马尾松二氧六环木素十分相似。     

Lignin and Other Aromatic Substances Released from Spruce Wood During Pressurized Hot-Water Extraction,Part 1: Extraction,Fractionation and Physico-Chemical Characterization

Ground spruce wood was extracted with pressurized hot water in an accelerated solvent extractor (ASE) at 170°C during 20, 60, and 100 min. Released aromatic substances (from 2.2 to 2.5% on wood basis) were isolated on XAD-7 resin and fractionated into lignin, oligomeric aromatic substances (OAS), and compounds insoluble in methanol (IMC). The separated aromatic fractions, and the ground wood before and after extraction, were characterized by physico-chemical methods (GC, GC-MS, HPLC-SEC, TG, DSC). The major part of the aromatic substances was oligomeric aromatic substances (OAS). This fraction increased significantly with the extraction time, while the yield of dissolved lignin increased only slightly with extraction time. Isolated lignins had a lower molar mass and differed considerably from spruce milled wood lignin (MWL). The isolated lignins were more stable against oxidative thermodegradation than spruce MWL. The UV-extinction coefficients at 280 nm were lower for the isolated lignins than for MWL.     

The Lignin of the Diffuse Porous Angiosperm Tree Triplochyton scleroxylon K. Schum with Low Syringyl Content

“Milled wood lignin” was isolated from Triplochyton scleroxylon tree (wawa MWL) and subjected to elemental analysis before and after acid treatment, and to analytical pyrolysis. Both FT-IR and ¹H NMR spectra were recorded. For comparison, lignins from spruce and beech isolated by the MWL, dioxane/HCl (DIL), and Cuene (CUL) techniques were also characterized. The residual carbohydrate content of the lignins was estimated. Wawa MWL is a GS lignin with 88% G and 12% S content. The utility of analytical pyrolysis and FT-IR for lignin classification is discussed. FT-IR spectroscopy, calibrated with data of 50 MWLs (PLS approach), gives reliable results with a minimum of experimental work. The yields of S phenols obtained by pyrolysis has to be multiplied with a factor around 0.5 for correction if the S content of a lignin is low. The cross-linking indices and OH_phen/OH_aliph ratios of lignins increase in the order MWL < DIL < CUL. ¹H NMR spectroscopy is also helpful to recognize the S/G ratio of a lignin.     

Quantitative Phosphorus-31 NMR Analysis of Six Soluble Lignins

By using a set of lignin samples, which have been subjected to thorough analyses by the international wood chemistry community, the recently developed quantitative method of ³¹P NMR spectroscopy was comprehensively examined. The values of total phenolic hydroxyl groups and those of total hydroxyl groups were found to favourably compare with those obtained by other laboratories, applying independent methods of analysis. Furthermore, the application of quantitative ³¹P NMR spectroscopy offered additional detailed structural information for the examined lignins which was in accord with literature accounts for similar wood species and lignin preparations. More specifically, the steam explosion lignins from aspen and yellow poplar woods and that produced by ball milling/enzyme hydrolysis of cottonwood were found to contain relatively high amounts of β-O-4 structures. In contrast, the kraft, organosolv, and the acid hydrolysis processes were found to induce significant chain scission on the resulting lignins. Ball milled cottonwood lignin contained the highest frequency of β-O-4 bonds and the lowest amount of free phenolic hydroxyls. The erythro form of β-O-4 structures were invariably predominant in the lignins from aspen, yellow poplar and cottonwood, in accord with the conclusions of previous reports on hardwood lignins. Thus, the application of quantitative ³¹P NMR spectroscopy offered the detailed chemical composition of the examined lignins.     

Electrochemistry of Biomass-Derived Materials I. Characterization,Practionation, and Reductive Electrolysis of Ethanol-Extracted Explosively-Depressurized Aspen Lignin

The chemical characterization (functional group distribution) and spectroscopic properties (¹³C, ¹H, IR, UV-Vis) of a number of lignins obtained from ethanol extraction of explosively-decompressed aspen (Populus tremuloides) lignin (EEEDAL) are described. In this process mod is heated to ～240°C by direct steam and fiberized by sudden decompression. Both mechanical and chemical degradation occur which lead to a decrease of the molecular weight of all of the natural polymers. The lignin fraction is soluble in alcohols; it has a low number average molecular weight (925) and is very reactive. EEEDAL was subjected to fractionation by differential solubility prior to and after electrolyses on mercury cathodes at ?2.6 V vs. Ag/AgCl in methanol/tetraethyl-ammonium perchlorate. After recovery of 85–90% of the original weight of material used by precipitation with acid, followed by a series of extractions, the chemical and spectroscopic properties of each fraction were determined. The acid-insoluble fractions are more condensed than the acid-soluble fractions and have lower phenolic OH and lower aliphatic OH contents than the acid-soluble fractions. The acid-soluble fractions phenolic OH content approaches one per phenylpropane (5) unit of the Lignin. Electrolyses increase the amount of lower molecular weight, high phenolic content, acid-soluble lignins and changes the molecular weight distribution by decreasing the polydispersity of the resulting lignins. These low-molecular-weight lignins are chemically reactive (for instance, with formaldehyde) and can be used in the partial replacement of phenol in phenol-formaldehyde thermosetting resins.     

Comparison of different methods for lignin determination as a basis for calibration of near-infrared reflectance spectroscopy and implications of lignoproteins

Three commonly employed methods for lignin determination, i.e., the thioglycolic acid (TGA), the acetylbromide (AB), and the acid detergent fiber (ADF) method, were compared using leaves and xylem tissue from five species (Nicotiana tabacum, Populus x canescens, Fagus sylvatica. Quercus robur, and Picea abies). In each case, cell walls were isolated before lignin determination. Each of the three methods estimated a different lignin concentration in a given tissue, except for spruce wood. The lignin concentration determined with the AB method was strongly dependent on whether or not the cell walls were subjected to alkaline hydrolysis to remove covalently bound aromatic nonligneous components before lignin determination. Lignin concentrations determined in hydrolyzed cell walls of different tissues and species by the AB method showed a good correlation with those obtained by the TGA method and, thus, were convertible. In contrast, gravimetrically estimated ADF lignins did not or only moderately correlate with lignins measured with methods based on the UV absorbance of the solubilized lignin degradation products. Leaves of a given species generally contained higher ADF-lignin concentrations than the corresponding stem tissue. Both ADF and TGA lignin data of beech were used to calibrate near-infrared reflectance spectra (NIRS) for lignin prediction. Both NIRS calibration procedures gave good statistical fits with correlation coefficients close to 1, indicating that TGA and ADF lignin concentrations of beech can be estimated by NIRS with high accuracy. However, the two calibrations were based on different empirical terms, showing that TGA and ADF lignins did not share the same physical basis for calibration. C/N analysis revealed the presence of 3.1 and 1.4% nitrogen in ADF lignins of beech leaves and wood, respectively. The major fraction of this nitrogen was recovered in amino acids, which corresponded to 14% and 3% protein in ADF lignins of leaves and wood, respectively. These results show that ADF lignins contain significant concentrations of lignin-bound proteins, which renders this method unsuitable to determine genuine lignin.     

Thermoplastic behavior of lignin with various synthetic plasticizers

The thermoplasticization of thiolignin (TL) and dioxane lignin (DL) with various synthetic plasticizers has been investigated. The thermal softening temperatures T_s of the lignin–plasticizer systems were measured applying the flow tester technique which is useful for investigating the thermal properties of polymers. It was found that the T_s of the lignins were lowered considerably as the solubility parameters (after Hildebrand) of the plasticizers approach close to that of lignin, namely, around 11. The lowering in the T_s of the lignins with the plasticizers was described by a linear equation with respect to the plasticizer concentration which ranged up to 20 wt-%. The sorption of the limited amounts (< 5%) of water to the lignins also considerably decreased the T_s, however, the extent of lowering in the T_s by water sorption is less than that by the plasticizer addition at their contents over about 15%. The relationship of T_s to water content (up to about 30%) was curved, not linear. It was clearly shown that a combined use of the plasticizer and water brought about the most effective plasticizing for the lignins compared with the use of either of those alone.     

Characterization of Residual Lignins Isolated from Unbleached and Semibleached Softwood Kraft Pulps

Abstract

Residual lignins in an unbleached and a semibleached softwood (Pinus taeda L.) kraft pulp were isolated by enzymatic hydrolysis of polysaccharides in the pulps. After purification, the residual lignins were characterized. A dissolved lignin was also isolated from the alkaline extraction spent liquor by acidification and characterized.

Results of the characterization indicate that extensive degradation of residual lignin in kraft pulp occurred during the first two stages of bleaching. The results also strongly support the previous finding that stable covalent linkages between residual lignins and carbohydrates in pulp any be the most probable cause for the residual lignins to resist delignification during kraft pulping and prebleaching.     

Effect of different organosolv treatments on the structure and properties of olive tree pruning lignin

Different organosolv processes (acetosolv, formosolv and acetosolv/formosolv) were applied to extract lignin from olive tree pruning. Obtained lignins were characterized by several methods to determine their composition, structure and functional groups with the aim of evaluating their potential to be used for obtaining added value compounds. All lignins had very high purity and low sugar and inorganic contamination, especially in the case of lignin obtained from formosolv treatment. Hydroxyl groups were the main functional groups in all lignin samples while the carbonyl groups were the lowest. Finally, the main difference between the lignins was the average molecular weight.