Differential calometric analysis of wood and wood components

Summary The prolysis of cellulose, hemicelluloses, lignin preparations, and wood was studied by differential calorimetric analysis (DCA) for the range of 25° to 800° C. The test samples included powdered and filter paper celluloses; hardwood xylan; softwood galactoglucomannans, compression wood galactan, and arabinogalactan; a synthetic (DHP), sulfuric acid, Björkman, Brownell, and cellulase lignins; and unextracted and extracted hardwoods and softwoods. Heats of reaction were determined from the DCA thermal transition areas. Distinct differences were found between the thermograms of each hemicellulose and lignin sample. Although wood species could not be separated thermally, hardwood and softwood thermograms differed because of the hemicellulose degradation pattern.Trade names and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment of the product by the U.S. Department of Agriculture.Formerly Research Technologist, Forest Products Laboratory, Forest Service, U.S. Department of Agriculture. The Laboratory is maintained at Madison, Wis. 53705, in cooperation with the University of Wisconsin. Present address: The Pennsylvania State University, University Park, Pennsylvania 16802.     

Preparation of activated carbon moldings from the mixture of waste newspaper and isolated lignins: mechanical strength of thin sheet and adsorption property

To expand the utilization of waste newspapers and lignin, activated carbon (AC) sheets, as an example of AC moldings, were prepared from those mixtures. The isolated lignins used were softwood and hardwood acetic acid lignins (SAL and HAL), softwood kraft lignin (KL), and wheat-straw lignin (WSL). The mixtures were molded into precursory sheets by thermal compression and then converted to AC sheets by carbonization and steam activation. The flexural strength of the precursory sheets was dramatically improved by additing the lignins compared to that of sheets without lignin. The strength of several sheets was more than 25 MPa. This suggested that lignins act as adhesives. SAL and HAL sheets with 40% newspaper were strengthened by the carbonization, whereas the strength of other lignin sheets was depressed. Finally, the AL-based AC sheets showed higher flexural strength (>6MPa) than others. Most of the AC sheets had adsorption ability comparable to that of commercially available AC powder and granules. The capacities were almost independent of paper content. Among the AC moldings tested, the AL-based AC sheets showed the fastest adsorption top-chlorophenol. Thus, viable AC moldings can be prepared from lignin-wastepaper mixtures, particularly SAL and HAL.     

Lignin characteristics of bast fiber and core in kenaf, bark and wood of paper mulberry and mulberry

The structural features of bast fiber and core lignins in kenaf (Hibiscus cannabinus), bark and wood lignin of paper mulberry (Broussonetia papyrifera (L.) Vent × Broussonetia kazinoki Sieb.) and mulberry (Morus bombycis) were characterized by alkaline nitrobenzene oxidation, ozonation and methoxyl group determination. Bj?rkman lignins were isolated from bast fiber and core, and bark and wood fractions of the plant samples, and structural characteristics were investigated by ¹H NMR and ¹³C NMR spectroscopies. Kenaf bast fiber gave very high molar ratio of syringaldehyde to vanillin (S/V) of alkaline nitrobenzene oxidation products, while methoxyl content was about the same as that of the core fraction. Results of ¹H NMR and ¹³C NMR of Bj?rkman lignin suggested the presence of aliphatic fragments in lignins isolated from paper mulberry and mulberry bark, but not in kenaf bast fiber. The lower yield of alkaline nitrobenzene oxidation products from bast fiber and bark might be due to the higher content of condensed structure of lignin compared to core fraction. Total yield of erythronic (E) and threonic (T) acids of ozonation products and the molar ratio of erythronic acid to threonic acid (E/T) of the bast fibers and bark were lower than the corresponding core and wood fractions, suggesting that the contents of arylglycerol-β-aryl ether intermonomer linkages in the bast fiber and bark lignin were lower than those of the core and wood fractions. Methoxyl content of bark lignin was lower than the corresponding wood lignin. The methoxyl content of the extract-free kenaf bast fiber was similar to that of the core fraction, while the values of paper mulberry and mulberry bark were about one-half of the corresponding wood fractions, respectively. In bark lignins, the methoxyl contents of Klason lignin and Bj?rkman lignin from bark were lower than those of the extract-free barks. This result suggests that the purity of Klason lignin and Bj?rkman lignins of bark may be rather low.     

Studies on milled wood lignins from spruce part 1. Composition and molecular properties

Summary Isolation of six milled wood lignins (MWL) from spruce under different conditions resulted in variable yields between 2.2% and 11.8% related to wood lignin. The composition of crude and purified lignins was evaluated with regard to non-hydrolyzable residue, acid-soluble lignin and polysaccharide content, which varied from 0.9 to 2.5%, depending on isolation conditions. The polysaccharide moiety of the crude and purified lignins contained a high percentage of glucose, probably derived from cellulose. The molecular size distributions determined by gel chromatography on different gels showed a broad distribution for all isolated lignins. A probable maximum of 40,000 for the molecular weight of milled wood lignins was determined by ultracentrifugation. Some of the lignin fractions were examined in the electron microscope.The authors are indepted to Prof. E. Killmann and Mrs. M. Bäumle (Institute for Technical Chemistry, Technical University of Munich) for assistance with the ultracentrifuge measurements and Dr. M. Stoll for precious suggestions and discussions. Submitted by Deutsche Forschungsgemeinschaft (DFG).     

Phenyl nucleus-exchange method for the degradation of lignin

Summary The phenyl nucleus-exchange method (NE-method) is a procedure for the degradation of lignin which allows the C–C linkages between the side chains and the phenyl nuclei to be cleaved selectively, and the phenyl nuclei to be liberated finally as polyhydric phenols. The important characteristic of this method is to take advantage of the dealkylation in diphenylmethane type structures in the presence of boron trifluoride and excess phenol, for the degradation of lignin. The lignin building units which give phenol monomers (guaiacol and/or catechol in softwood lignin) almost quantitatively by this method are noncondensed types and diphenylmethane types, and each of these units has any of the benzyl alcohol, the benzyl ether, the conjugated double bond, the -carbonyl group and the C-aryl bond, in the side chain. The yields of phenyl nuclei are about 25–30% in softwood protolignins and about 8–13% in technical lignins. In this paper, the reaction theory and the degradation mechanism of lignins in the NE-method are outlined.     

Characterization of lignin-carbohydrate linkages in the residual lignins isolated from chemical pulps of spruce (<Emphasis Type="Italic">Picea abies</Emphasis>) and beech wood (<Emphasis Type="Italic">Fagus sylvatica</Emphasis>)

To investigate the linkage types between carbohydrates and lignin, residual lignins were isolated from three different unbleached pulps [kraft, alkaline sulfite anthraquinone methanol (ASAM), and soda with anthraquinone (AQ) and methanol] of spruce and beech wood and then characterized by oxidation with 2,3-Dichloro-5,6-dicyanobenzoquinone and followed by Prehm’s methylation. In residual lignins, sugar moieties were bound to lignins via benzyl ether bonds. In particular, galactose and mannose are predominantly linked to lignin fragments in residual lignins of spruce wood, while xylose and galactose are favored in the formation of LC bonds in the residual lignins of beech wood. In the case of hexoses, primary hydroxyl groups (C6 position) preferentially take part in benzyl ether linkages. Hydroxyl groups in the C2 and C3 positions of xylose participate in LC bonds and a small portion of arabinose was notably connected to lignin via the C5 position. Approximately seven or eight sugars were connected in soda/AQ/methanol residual lignin per 100 C9 lignin units, while the frequencies of LC bonds in kraft and ASAM residual lignins were distinctively less at one to three sugars per 100 C9 lignin units. The publication of this article was made possible by an Emachu Research Fund. The authors are grateful for the fund.     

A structural model of softwood lignin

Summary Various degradation products from soft-and hardwood lignins by hydrolysis with dioxanewater and catalytic hydrogenolysis are discussed. And a structural model for softwood lignin is proposed mainly based on these degradation products. The model has 28 units and indicates good agreement with the various analytical data obtained so far in the lignin chemistry.     

The mechanism of the Mäule colour reaction introduction of methylated syringyl nuclei into softwood lignin

Summary Ezo spruce (Picea jezoensis) wood meal and milled wood lignin were successively reduced with sodium borohydride, methylated with methanol-HCl, oxidized with Fremy's salt, reduced with sodium dithionite, and methylated with diazomethane. Permanganate oxidation of the treated milled wood lignin showed that 0.08–0.1/C9 units of 3,4,5-trimethoxyphenyl groups were introduced into the softwood lignin. Although hardwood meal (beech, Fagus crenata) methylated with diazomethane gave a purple-red colour with the Mäule test, the treated softwood meal gave only a dark brown colour. The aromatic nuclei of lignin were broken down by the Mäule treatment. The consumption of permanganate by treated softwood lignin was higher than by hardwood lignin, which suggests that the guaiacyl nuclei were broken down severely. It is proposed that the purple-red colour obtained from methylated hardwood lignin with the Mäule colour test is generated by reaction of syringyl groups which were liberated by -ether cleavage under the permanganate oxidation conditions.     

Composition and structure of organosolv lignins from four eucalypt species

Lignins were extracted from different species using organosolv process (ethanol/water). Obtained organosolv lignins were characterised by various methods to determine their composition, structure and functional groups with the purpose of evaluating their potential use for obtaining value-added compounds. The purity of organosolv lignins was determined. The total phenols content and the antioxidant power were analysed in order to know the reactivity of lignins. The ratio S/G was determined by nitrobenzene oxidation. In addition, molecular weight distribution, infrared spectroscopy and thermo gravimetrical analysis were carried out in order to determine the physical and chemical properties of organosolv lignins. Obtained organosolv lignins have very high purity and low sugar and inorganic contamination. All organosolv lignins samples have high polydispersity, and lignin from grey ironbark wood had the highest molecular weight average. Among the organosolv lignins, lemon-scented gum showed the highest average value of S/G ratio and the lowest average value of total phenols.     

Chemical characteristics of surfaces of hardwood and softwood deteriorated by weathering

The factors that cause weather-induced deterioration of wood surfaces were determined by chemical and spectroscopic analyses. Albizzia (Paraserianthes falcata Becker.) and sugi (Cryptomeria japonica D. Don) were exposed to two temperate conditions of natural weathering with and without rainfall and to accelerated conditions of artificial weathering coupled with ultraviolet (UV) light irradiation and water flashing. Infrared spectroscopic analysis showed that the oxidative reaction of lignin was observed under all conditions of weathering for both wood species. However, a marked decrease in lignin and hemicellulose content were recognized when albizzia woods were exposed to weathering with water. Lignin content in the softwood sugi did not decrease as much as in albizzia even in the presence of water, but the modification of lignin macromolecules was assumed to be accelerated by water, as seen by electron spin resonance spectroscopy. These results showed that the presence of water promotes the weathering deterioration of wood under UV irradiation.     

Anatomy and lignin distribution of reaction wood in two Magnolia species

Summary Anatomical features of reaction wood formed in two Magnolia species, M. obovata Thunb. and M. kobus DC. which are considered to be among the primitive angiosperms, were observed. In addition, the distribution of guaiacyl and syringyl units of lignins in the cell walls of normal and reaction wood was examined using ultraviolet (UV)- and visible light (VL)- microspectrophotometry coupled with the Wiesner and M?ule reactions. The two Magnolia species formed a tension-like reaction wood without possessing the typical gelatinous layer (G-layer) on the upper side of the inclined stem or branch, in which a radial growth promotion occurred. Compared with the normal wood, the reaction wood had the following anatomical features: (1) the secondary walls of fiber tracheids lacked the S₃ layer, (2) the innermost layer of fiber-tracheid walls showed a small microfibril angle, a fact being similar to the orientation of the microfibril angle of the G-layer in tension wood, and (3) the amounts of lignin decreased in the cell walls of fiber tracheids, especially with great decrease in proportion of guaiacyl units in lignins. In addition, VL-microspectrophotometry coupled with the Wiesner and M?ule reactions adopted in the present study showed potential to estimate the lignin contents in the cell walls and the proportion of guaiacyl and syringyl units in lignins. Received: 15 July 1998     

FTIR spectroscopy, chemical and histochemical characterisation of wood and lignin of five tropical timber wood species of the family of Dipterocarpaceae

The goal of this study was to characterise chemical and histochemical properties of five dipterocarp timber wood species (Dipterocarpus kerrii, Hopea plagata, Parashorea malaanoman, Shorea almon, and Shorea contorta) differing in wood service life and utilisation. Wood of H. plagata, the most durable species, contained the lowest concentrations of nitrogen and ligno-protein, the highest C/N ratio and the lowest lignin concentration per dry mass but the highest lignin and extractive concentrations per wood density. FTIR spectroscopic studies of wood and isolated lignins of D. kerrii and H. plagata revealed differences compared to P. malaanoman and Shorea sp., which are species with short service life. Lignins of the Shorea/Parashorea species had a higher G/S ratio than those of H. plagata and D. kerrii. This was also evident from histochemical staining. Principle component analysis of FTIR spectra identified differences in both lignin composition and ligno-protein content as major source of variation.     

Characteristics of lignin obtained from steam-exploded softwood with soda/anthraquinone pulping

Lignins were obtained from a mixture of softwood sawdust using a hydrolytic pretreatment and a subsequent soda-anthraquinone delignification/pulping stage. Their potential uses and the effect of the pretreatment conditions on the yield (% of recovered lignin from black liquors) and chemical composition of isolated lignins were evaluated. The severity factor used combined the temperature and time of the hydrolytic process in a single ordinate (R_o). The severity range was modified from log R_o = 2.6 to log R_o = 4.6 and the pulping conditions were constant throughout the experiments. The effect of the cooking time on the chemical composition of precipitated lignins was also studied between 135–170 min for original (non-pretreated) material. Yield, elemental analysis, molecular weight distribution, Fourier transform infrared spectra (FTIR), structure, and the methoxyl and aliphatic/aromatic alcohol content of the various lignins, were compared.     

Lignin-carbohydrate bonds in a residual soda spruce pulp lignin

Summary The behaviour of lignin-polysaccharide complex of spruce wood in soda pulping was studied by the characterization of lignin-saccharide fractions isolated from a series of soda pulps. The dioxane pulp lignins contain 8–14% of carbohydrates in which glucose was the predominant component. Its content increased with increasing degree of delignification indicating the formation of secondary lignin-carbohydrate linkage. Both glycosidic and ether type of bond between residual lignin and cellulose in pulp was proved by methylation analysis of the pulp dioxane lignin.The work was supported by the Slovak Academy of Sciences grant number 2/999389/92.     

Enthalpy relaxation behavior of dry wood detected by temperature-modulated differential scanning calorimetry

Enthalpy relaxation of dry wood has been investigated by temperature-modulated differential scanning calorimetry. The reversing and non-reversing heat flow changes revealed that enthalpy relaxation occurred in dry wood, which did not exhibit any clear glass transitions. This enthalpy relaxation behavior seemed to differ significantly from those of previously reported isolated lignins, which implies that the microstructure of dry wood possesses a rigid amorphous state derived from interactions among wood components. The observed enthalpy relaxation is considered to be related to other components besides lignin, and the time-dependent physical properties due to unstable states or physical aging of wood originate not only from lignin but also from other components, such as cellulose and hemicellulose and the interactions between them.     

Attempts to understand the nature of phenolic and etherified components of wood lignin

Summary 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.Financial support from the Empire State Paper Research Associate (ESPRA) and by the NRICGP of USDA (No. 93-37103-9318) is greatly appreciated     

Development of acid soil conditioning agent from lignin by ozone treatment I

A purified softwood kraft lignin was modified by ozone treatment and its activity as an acid soil conditioning agent, mainly focusing on elimination of aluminum toxicity, was assayed by planting experiments. The growth of radish root was examined in nutrient solution containing CaCl₂ and AlCl₃ at pH 4.8 with and without modified kraft lignins. The modified kraft lignins that absorbed 1.8 and 3.9 moles of ozone per C6-C3 unit (M _w 180) showed two effects: the elimination of aluminum toxicity and the acceleration of root growth. The effect on the elimination of aluminum toxicity was observed even with modified kraft lignin that absorbed 1.0 mole of ozone per C6-C3 unit. The high molecular weight part of the modified kraft lignin that absorbed 3.9 moles of ozone per C6-C3 unit also proved to be effective not only in elimination of aluminum toxicity but also in acceleration of root growth. The acceleration effect of ozone-treated lignins on root growth was also observed under the absence of aluminum in planting experiments. This report was presented in part at the 56th Annual Meeting of the Japan Wood Research Society, Akita, Japan, August 2006     

Effect of severe thermal treatment on spruce and beech wood lignins

? The structure, proportion and mode of assembly of lignin, celluloses and hemicelluloses have marked effects on the reaction mechanisms during thermal treatment and therefore have a strong influence on the quality of the final product. The effect of treatment conditions, including severe conditions (up to 553 K) and treatment duration (up to 8 h) on the structure of native spruce and beech lignins was studied.

? Lignin content was determined by the Klason method and lignin structure was evaluated by thioacidolysis.

? The results highlighted the strong reactivity of the native spruce and beech lignins towards severe heat treatments. The distinct susceptibility of syringyl (S) and guaiacyl (G) units towards thermal treatment is confirmed by comparing the data for beech and spruce samples. The most severe treatment of spruce wood (280 °C) induced a dramatic enrichment in lignin content together with the almost complete disappearance of G lignin units, whereas a more moderate treatment substantially changed lignin structure by degradation reactions that affect the p-hydroxyphenyl (H) and G lignin units similarly.

? Thioacidolysis revealed that the thermal treatment induces the appearance of vinyl ether structures in spruce lignins. The decreased yield of the G and S thioacidolysis monomers reflects the progressive disappearance of G and S lignin units only involved in β-O-4 bonds and the formation of condensed linkages in proportions related to treatment severity. In severe conditions, β-O-4 linked S units are more degraded than their G homologues.

     

Delignification of cell walls of <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis> during alkaline nitrobenzene oxidation

To clarify the behavior of whole lignins in wood cell walls during alkaline nitrobenzene oxidation, the delignification process from cell walls in normal and compression woods of Chamaecyparis obtusa Endl. (Cupressaceae) was observed using ultraviolet and transmission electron microscopies. The lignin content conspicuously decreased to around 10% after 35min in normal wood. The lignin content in compression wood finally leveled off at aroumd 10% after 50min. In gel filtration of oxidation products in ethyl acetate, a high molecular weight fraction was prominent in extracts from the early stage of the reaction. As the oxidation progressed, the high molecular weight fraction became less prominent in both normal and compression wood. Changes in the weights of cell wall residues during reaction indicated that approximately half of the components other than lignin were also removed from the cell walls. This shows that the majority of lignin with relatively high molecular weight is removed from the cell walls together with polysaccharides in the early stage of the reaction and that further oxidative degradation occurs in solution in later stages. Only a small amount of the lignin with low molecular weight could be analyzed by gas chromatography.Parts of this report were presented at the 47th (Kochi, April 1997) and 48th (Shizuoka, April 1998) Annual Meetings of the Japan Wood Research Society, and at the Lignin Symposium, Sapporo, October 1997     

Structural changes of residual lignin in softwood kraft pulp treated with manganese peroxidase

Structural changes of residual lignin in unbleached softwood kraft pulp (SWKP) during manganese peroxidase (MnP) treatment were investigated to obtain some understanding of the biobleaching action of SWKP with MnP treatment. Alkaline-extracted lignin from darkened SWKP by MnP showed more intense color and contained moreo-quinone than that from control SWKP. However, no difference in the conjugated-carbonyl was observed between the lignins from MnP-treated and control SWKP. The nitrobenzene oxidation analysis revealed that oxidative condensation of non-condensed lignin in SWKP occurs during an early stage of MnP treatment. These observations were supported by the model experiment in which the lignin prepared from control SWKP was subjected to MnP treatments three times, and the changes of color and functional groups in the lignin were determined after each treatment. These results suggested that an increase ino-quinone and the condensation reaction of non-condensed lignin in SWKP are responsible for the characteristic darkening of SWKP during MnP treatment. It was also ascertained that darkened lignin was degraded and brightened by repeated MnP treatments.