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Pycnoporus sanguineus (Ps) and Candida tropicalis (Ct) can selectively degrade the lignin and hemicellulose in lignocellulosic cells respectively; Ps-Ct mixed fermentation may improve the multiphase reaction performance of lignin in the cell walls. Alkaline nitrobenzene oxidation, ozonation and infrared spectroscopy, which are the in-situ analytical techniques of lignin in the cells, were used to characterize the delignification kinetics, the reactions of the non-condensed, β-O-4 structures and their stereochemistry of lignin in wheat straw in Ps and Ps-Ct fermentations. Results indicated that the biodelignification processes in Ps and Ps-Ct fermentations of wheat straw, being divided into a fast phase and a following slow phase, had the characteristics of a pseudo-first-order reaction in both the phases. The lignin reaction pathways in Ps and Ps-Ct mainly included the cleavage of ring, Cα-Cβ, β-O-4, and the cleavage and polymerization of 5-5⿲. Compared with Ps fermentation, Ps-Ct fermentation enhanced the biodegradation of condensed, β-O-4 structures and threo β -O-4 structures in the lignin in the fast phase. A proposal scheme of biodelignification by Ps and Ps-Ct is outlined for the first time. These results will be helpful for the understanding and application of lignocellulosic biomass by mixed fermentations.

Various soybean straw (stem and pod) samples were dissolved in 8% lithium chloride/dimethyl sulfoxide (LiCl/DMSO) following 4 h of planetary ball-milling. The solubility, extractable lignin yield, and crystal structure of the ball-milled soybean straw were greatly affected by the ball-milling pretreatment. The dissolved soybean straw could be regenerated by being poured into excess distilled water under rapid stirring. The total regenerated fraction yield decreased with the increase in the duration of ball-milling. Approximately 10% to 25% of the straw mass was lost in the dissolution-regeneration procedure. For comparison, ethylenediamine (EDA)-pretreated soybean straw was also completely dissolved in 8% LiCl/DMSO to form a homogeneous solution containing 1% straw after 24 h of continuous stirring. The dissolution-regeneration performance of soybean straw submitted to the EDA pretreatment was quite different due to the lack of vigorous ball-milling.

To improve basic knowledge of the properties of soybean straw, its fiber properties, anatomical structure, and components were investigated in detail. Soybean straw contains less ash and silica than some non-woody biomass. Its stem and root have more lignin and holocellulose, but less nitrogen and protein contents than the pod. Additionally, it has much shorter and wider fibers, and the length-width ratio is also lower than other crop straws. Morphologically, there are three main tissues---the ground tissue, the vascular tissue, and the dermal tissue systems in the stem, and two different morphology portions – the intimal layer and the leathery layer – in the longitudinal-section of the pod. A variety of inorganic and metal elements are distributed across the whole stem or pod in different amounts. Lastly, the planetary ball-milled stem and pod are completely dissolved in 8% lithium chloride/dimethyl sulfoxide (LiCl/DMSO) solution. After regeneration, the lignin has the highest retention, followed by silica and sugars, but most of the ash can be removed in this process.

Wood along with the outer portion of tree trunk (bark) [1] (Fig. 28.1) represents the bulk of forestry biomass materials and has been utilized by humans since antiquity. Trees provided a source of many products required by early humans such as food, medicine, fuel, and tools. For example, the bark of the willow tree, when chewed, was used as a painkiller in early Greece and was the precursor of the present-day aspirin. The leaf extracts and nuts from Gingo trees have been used in traditional Chinese medicines for thousands of years. Wood served as the primary fuel in the United States until about the turn of the nineteenth century, and even today over one-half of the wood now harvested in the world is used for heating fuel.

Wood lignin contains significant amounts of acid-labile aryl ether units, which play a significant role in lignin modification or delignification processes. We have evaluated the rate and reaction kinetics on the acid-catalyzed cleavages of aryl ether structures for wood lignin in situ based on the formation of phenolic hydroxyl groups. The content of acid-labile aryl ether units was quite uniform for a variety of softwood wood lignins (∼4% per C9 unit) and it varied appreciably among hardwood species, ranging from 4% for aspen to 9% for beech wood lignin. These variations, however, appear to be related to the content of syringyl units in wood lignin. The reactivity of these reactive aryl ether structures was noticeably higher for the spruce than for the aspen wood lignin. This difference in reactivity, based on the behavior of lignin model compound reactions, can be attributed to the influence of syringyl moieties in aspen wood lignin. It appears that most of the acid-labile aryl ether units in hardwood ...

We explored the feasibility of fractionating wood polymers in situ by carboxymethylation to yield the carboxymethyl derivatives of cellulose (CMC), hemicelluloses, and lignin for potential industrial applications. The initial water-soluble materials formed were a mixture of hemicelluloses and cellulose derivatives, and also contained some lignin (3%–5%). Interestingly, the water-insoluble residue after another carboxymethylation treatment gave essentially a CMC product containing less than 1% of residual lignin. Thus, the bulk of wood lignin is less reactive than the polysaccharide components under typical carboxymethylation conditions. Also, a hot water pre-extraction or dilute acid pre-treatment of wood samples was found to significantly enhance the reactivity of the cellulose component. A preextraction approach would facilitate CMC preparation and also provide the flexibility to convert the extracted hemicelluloses to other bio-based fuels or materials.

The O2 delignification of kraft pulps from Norway spruce was shown having a significant impact on the reactivity of the residual pulp lignin as revealed from their responses to sulfite treatments at pH 7.5. A substantial higher ratio of lignin sulfonation to the phenolic hydroxyl group content of residual pulp lignin was observed for the O2 -delignified kraft pulps (∼ 0.8) as compared to a value of ∼ 0.3 for the unbleached samples and ∼ 1 for the spruce wood lignin. Under the prevailing sulfite treatment conditions, the sulfonation would be largely attributed to the phenolic lignin component and the etherified structures containing an α -carbonyl or -unsaturated group. The contribution from the latter units, evaluated by a borohydride pretreatment of pulps prior to the sulfite treatment, can only account for approximately 15% of the sulfonation observed for the O2 -delignified sample. Thus, the nature of phenolic structures in the O2 -delignified pulps was more similar to that of the wood lignin ...

We investigated the impact of residual extractives on lignin determination by lignin content difference between unextracted and extracted pulps, residual extractives analysis, and lignin content contribution from model extractive compounds. There were two different kinds of extractives in aspen kraft pulp. The extractives impacting on kappa number determination were well removed in oxygen delignification; these were mainly unsaturated fatty acids. However, the extractives impacting on Klason lignin determination were largely resistant to oxygen delignification; these were mainly saturated fatty acids, sterols, and hydrocarbons. Oxidation of unsaturated fatty acids was the main reaction in oxygen delignification. These trends were confirmed by simulation of lignin content determination with three model extractive compounds (β-sitosterol, linoleic acid, and palmitic acid).

The kinetics of end-wise degradation of amylose has been studied varying base concentration and temperature. At 100°C, the rate of peeling increases with hydroxyl ion concentration up to 0.1 N base concentration, remaining constant thereafter, whereas the rate of termination continues to increase beyond this point levelling off finally to a constant value at approximately 1.5 N base concentration. As a consequence, the ratio of peeling to termination is sufficiently high in 0.01–0.1 N sodium hydroxide solutions to effect total degradation of amylose. The kinetic pattern is interpreted in terms of mono- and di-ions of the reducing end-groups acting as reactive intermediates. The potential application of the peeling reaction to structural studies of polysaccharides is discussed.

We observed that the O2 delignification pattern of aspen kraft pulps was distinctly different from that of pine pulps based on a reduction in the apparent pulp kappa number. Much of this phenomenon can be attributed to the variation of the residual extractives and hexeneuronic acid (HexA) unit content in the unbleached and O2‐delignified pulps, as they interfered with the conventional lignin determination methods. However, after a correction for contributions from these non‐lignin components, the hardwood kraft pulps still displayed a lower response to O2 delignification than the pine pulps. It appears that the relative reactivity of residual lignin in the hardwood and softwood pulps differs appreciably with the extent of kraft delignification, and is a significant factor affecting the overall O2 delignification reaction.

The amount of residual extractives in kraft pulps and oxygen‐delignified pulps and their impact on the usual methods of lignin determinations were investigated. The lignin analyses investigated were kappa number and Klason lignin in conjunction with acid‐soluble lignin. The species investigated were loblolly pine, white birch, and aspen. In the hardwoods, significant amounts of extractives remained after kraft pulping and oxygen delignification. These residual extractives in the hardwood pulps had an impact on the lignin determination, more so on the acid lignin method than kappa number. For an accurate lignin determination, solvent extraction of hardwood kraft and oxygen‐delignified pulp is needed, but not for softwood pulps.

The determination of lignin structures by ozonation is rather unique and unlike other analytical techniques is based largely on the formation of side-chain oxidation products. Also, it can readily reveal the proportion of the two stereoisomers of β-aryl ether structures from the yields of erythronic (E) and threonic (T) acids. We have observed that the relative yields of these two acids vary significantly depending on how they are determined. For example, the E/T ratio of these two tetronic acids from the ozonation of spruce wood lignin in situ varies from 1.10 to 1.57 based on their analysis as the free acid and lactone derivatives, respectively. Thus, the work-up procedure of the reaction products is very important to the ozonation technique.

The cleavage of aryl ether linkages has been shown having a direct impact on the alkaline delignification of Norway Spruce up to approximately 90–95% level, and has little influence on further delignification reactions. Interestingly, such impacts were very comparable for both soda and kraft cooks, and were substantially reduced by lowering pulping temperatures. Thus, the lignin degradation and dissolution process were also affected by other chemical factors than aryl ether cleavages. The results also suggest that aryl ether units present in wood lignin vary significantly in reactivity.

The reactivity of a series of phenolic lignin diphenylmethane (DPM) model dimers has been examined in soda and kraft cooks, in an attempt to understand the role of lignin condensation in the alkaline delignification process. These condensed dimers were shown to be rather stable in alkali in the absence of O2 even at elevated temperatures. In contrast, they were sensitive to traces of O2 present in air, and the degradation mechanism involved was shown to be different from that occurring under mild alkali-O2 conditions.

Major products obtained from the permanganate oxidation of unsubstituted guaiacyl α-diphenylmethane-model dimers were the diguaiacylketone compounds (39-45% and veratric acid (3-14%). Also. small amounts of isohemipinic (4%) and metahemipinic (1%) acids were produced from the ct-5 and α-6 dimers, respectively. The results indicate that the α-methylene groups were rather reactive under permanganate oxidation conditions.

A series of unsubstituted phenolic lignin diphenylmethane (DPM)-model dimers of the guaiacyl type has been shown to be quite reactive under alkaline nitrobenzene oxidation conditions resulting in the formation of monomeric products. The yield of vanillin varied considerably with the linkage type (4-32%), and decreases in the order of α-1, α-5, α-6 and 5,5'-DPM dimers. The reactions also included an oxidation of the α-methylene groups, leading to the formation of diphenylketone derivatives, which were obtained in 5-28% yield. In contrast. the etherified DPM-model dimers were relatively stable under nitrobenzene oxidation conditions.

The structural features of depithed bagasse lignin and its changes in soda cooking have been characterized in situ by the nitrobenzene oxidation, phenyl nucleus exchange and periodate oxidation methods. The bulk of bagasse lignin (∼ 75%) can be readily delignified in alkali below 100°C, and does not appear to be resulted from the cleavage of β-aryl ether structures. Concerning the reactivity of uncondensed structures, the p-hydroxyphenyl units were most labile to alkaline treatments, whereas the guaiacyl and syringyl units were removed nearly at the same rate. The residual lignin appears to be rather condensed and to contain an appreciable amount of guaiacyl diphenylmethane-like structures.

Periodate oxidation, because of its high selectivity in degrading phenolic nuclei, has been combined with nitrobenzene oxidation and phenyl nucleus exchange techniques to investigate the nature of wood lignin in situ. For both softwood and hardwood, the phenolic and etherified components of wood lignin have been shown to differ significantly in chemical composition, and the etherified lignin structure appears to be substantially more condensed.

The influence of sulfidity in kraft pulping of Norway spruce chips on the characteristics of residual lignin has been examined at two levels 25 and 40%. Comparing with the reference kraft cook at similar kappa number, the high sulfidity pulp lignin displayed a significantly lower phenolic hydroxyl group content, and a lower response to O2 delignification, but it gave a slightly higher yield of nitrobenzene oxidation products, and was more responsive to a neutral sulfite treatment.

A series of phenolic lignin-model dimers of the guaiacyl diphenylmethane (DPM) type has been shown to be quite reactive under mild alkali-O2 conditions (0.5 N NaOH, 55°C) giving significant amounts of monomeric products. The reactivity of these dimers varies significantly and decreases in the order of α-5, 5,5′, α-6, and α-1 types. Interestingly, the oxidative cleavages of these DPM units, except the α-6 type, all gave the benzyl alcohol products e.g. vanillyl alcohol.

The content of phenolic hydroxyl groups in the unbleached kraft pulp residual lignin was determined in situ by periodate oxidation method. This functional group has been shown to increase steadily with the extent of kraft delignification throughout the entire pulping process.

Periodate oxidation, because of its high selectivity in the degradation of free-phenolic units, has been used along with the combined phenyl nucleus exchange and nitrobenzene oxidation techniques to estimate the distribution of phenolic hydroxyl groups in hardwood lignins. Analyses of the aspen and white birch wood lignin in situ indicate that the percentage of uncon-densed structures having a phenolic hydroxyl group was considerably higher for guaiacyl (∼20%) than for syringyl (−5%) units. Thus, the total phenolic hydroxyl groups of hardwood lignins are largely associated with the guaiacyl propane units.

The chemical properties and performance of aspen percarbonate (P) and sulfite (S) chemimechanical pulp (CMP) fibers are very comparable. The PCMP, when compared with SCMP of the same yield, has a slightly higher tear index, same beatability and light scattering coefficient, but a lower tensile index and brightness. The strength properties of these fibers are closely related to the total acidic group content resulting from lignin oxidation (carboxyls) and sulfonation (sulfonate).

The extent of neutral sulfonation for a variety of softwood and hardwood species was shown to be directly proportional to the phenolic hydroxyl group content of the wood lignin. Sulfonation of hardwoods, in contrast to softwoods, displayed a significant variation among different species.

The pH of sulfite treatments has a profound influence on the efficiency of fiber sulfonation of Norway spruce. Compared at the same pulp yield, the extent of sulfonation decreases in the order of pH value 7·5 > 9·5 > 4·5; the sulfonation reaction is improved significantly by using a two-stage treatment at pH 4·5 and 7·5. The degree of fiber sulfonation plays a dominant role in the tensile and tear strength improvement of these high-yield pulps.

One of the most formidable challenges in kraft pulping to produce bleached chemical pulps is how to effectively remove the last 5-10% of lignin while maintaining the fiber quality. To avoid a severe fiber degradation, kraft pulping is usually terminated in the 25-30 kappa number range and then followed by an elementally chlorine free (ECF) or a totally chlorine free (TCF) bleaching sequence to reduce the environmental impacts.

Specially designed wood blocks from Norway spruce were used to study the nature of the fracture surfaces developed in shear using a tensile tester. In the case of the control (water-soaked blocks), the fracture in the latewood takes place mainly in the S1 layer while in the earlywood the fracture occurs across the double cell wall. After dilute alkali treatment, some earlywood cells also fracture in the S1 layer. For sulfite-treated samples, on the other hand, both earlywood and latewood fracture in the middle lamella.

The phenolic hydroxyl group is one of the most important functionalities affecting the physical and chemical properties of lignin polymers (Adler 1977). It plays a prominent role in commercial pulping and bleaching processes by virtue of its ability to promote the base-catalyzed cleavage of interunitary ether linkages and the oxidative degradation of lignin (Gierer 1985, 1986). The chemical reactivity of lignin in various modification processes is also profoundly influenced by its phenolic hydroxyl content (e.g., in the reaction with formaldehyde for the production of lignin adhesives) (Olivares et al. 1988). On the other hand, the phenolic hydroxyl group significantly contributes to the poor brightness stability of lignin-containing pulps, which seriously limits their more widespread utilization (Gellerstedt and Pettersson 1977, Tschirner and Dence 1988). Quantitative measurement of phenolic hydroxyl groups thus provides pertinent information relating to the structure and reactivity of lignin and to the mechanism and extent of lignin degradation.

The phenolic hydroxyl group content of wood lignin has been determined in situ by a periodate oxidation method for four softwood and six hardwood species. Hardwood lignins, in contrast to softwood lignins, showed a significant variation among different species in this functional group content which decreased with an increase in the proportion of syringyl units in the wood lignin.