Volume 55, Issue 6

The localisation of lignin and phenolic extractives in woody tissue was determined using scanning UV microspectrophotometry. This improved cellular analytical technique enabled direct imaging of the topochemical lignin distribution within individual cell wall layers with a resolution of 0.25 μm 2 . Selected softwood ( Picea abies ), hardwood ( Fagus sylvatica , Entandrophragma cylindricum, Prunus serotina ) and monocotyledon ( Phyllostachys edulis ) sections of 1 μm thickness were scanned at a fixed wavelength and evaluated with the “APAMOS” software. This approach allowed the distribution pattern of lignins and aromatic extractives within the cell wall to be visualised simultaneously. The method was found to be ideally suited to the study of their subcellular distribution in plant cell walls.

Twenty 3′-substituted-3-stilbenols were synthesized and tested for fungicidal activity (agar plate IC 50 values) against two brown-rot fungi rot Gloeophyllum trabeum and Postia placenta and one white-rot fungus Trametes versicolor . Compounds synthesized were eight trans -3-X-3′-stilbenols (X = OMe, Me, Cl, OH, OPr, OBu, OOct, and O- p -Tol), three cis -3-X-3′-stilbenols (X = OMe, Me, Cl), three 3-hydroxy-α-(3-X-phenyl)cinnamic acids (X = OMe, Me, Cl), and six multisubstituted-3′-substituted-3-stilbenols (3′,4-diOMe, 3′-Me-4-OMe, 3′-Cl-4-OMe, 3′-OH-4-OMe, 3′-Cl-4-OMe-4′-OH, and 3′-Cl-4′-OH). The three cinnamic acids and 3′-OOct showed low to no activity against all three fungi. Most of these 3′-substituted-3-stilbenols (15 of 20) had fungicidal activity against the white-rot fungus T. versicolor , in contrast to earlier studies on 3′-substituted-4-stilbenols which were inactive against T. versicolor . These 3′-substituted-3-stilbenols also had fungicidal activity against G. trabeum and P. placenta , with the latter fungus having a parabolic lipophilic Quantitative Structure Activity Relationship (QSAR). 3′-O- p -Tol-3-stilbenol was the most active against T. versicolor and fifth most active against P. placenta of the twenty 3′-substituted-3-stilbenols examined here.

The decay patterns of brown and soft rot fungi in Sapelli wood ( Entandrophragma cylindricum Sprague), with respect to natural durability, were examined by light and transmission electron microscopy as well as UV spectroscopy. Analyses revealed that the typical brown rot fungus Coniophora puteana can cause a soft rot-like decay in the sapwood of Sapelli at high moisture contents of approx. 100%. In accordance with the decay pattern of the typical soft rot fungus Chaetomium globosum , the hyphae of C. puteana penetrated the S 2 wall of fibres and formed characteristic rhomboidal cavities orientated parallel to the microfibrillar angle. However, these cavities were larger in diameter (3.9 μm ± 0.9) than those formed by C. globosum (2.1 μm ± 0.5) and with a distinct interspace between the hyphae and surrounding walls. Hyphae of C. globosum were directly attached to the undecayed secondary wall. No lignin degradation for both fungi in close vicinity to the cavities was observed, as evidenced by UV spectroscopy. The inclusion of microscopy for definitive decay type identification is recommended.

The effects of pentachlorophenol (PCP) and 2-chlorophenol (2CP) on white rot fungi, Abortiporus biennis, Cerrena unicolor, Gloeophyllum odoratum , and Trametes versicolor were investigated. With the exception of C. unicolor and A. biennis , concentrations of PCP higher than 50 ppm inhibited fungal growth completely. However, extreme concentrations of PCP (500 ppm) caused a 61% increase in growth of C. unicolor compared to the control culture within 14 days. When initial PCP concentrations were 50 ppm A. biennis and C. unicolor achieved, respectively, 87% and 78% of chlorophenol transformation within 3 days. However, when 2,5-dimethylaniline (0.2mM) was added to the C. unicolor culture, 98% of PCP transformation was achieved after one hour. Under the same conditions, A. biennis transformed 44% of PCP. Both chlorophenols are completely removed, when laccase activity reaches its maximum. In conclusion, among the four fungi investigated, C. unicolor and A. Biennis were very effective in transforming PCP and 2-CP. This biotransformation was greatly intensified by 2,5-dimethylaniline and accompanied by an increase in laccase activity.

The fixation reaction of copper-ethanolamine preservatives in wood was studied using the reaction between vanillin, a lignin model compound, and ethanolamine-copper sulphate solution. The green compound precipitated after the reaction has been characterized spectroscopically as di(ethanolamine)-bis (vanillinato)dicopper(II); [Cu(vanillin) (ethanolamine)] 2 . Single crystal X-ray crystallographic studies showed that the crystals of [Cu(vanillin)(ethanolamine)]2 are triclinic with the space group P1 with a = 9.1271(7), b = 10.8723(9), c = 6.360(1) Å, α = 97.08(1), β = 100.63(1), and γ = 110.024(7)°. Z = 1. The binuclear molecule has crystallographic inversion symmetry. The ligand arrangement around the Cu(II) is a distorted square based pyramid, with a base plane made up of two oxygen atoms from the ethanolamine ligands, one oxygen atom from a hydroxyl group in vanillin and one nitrogen atom from ethanolamine. Two Cu-O [1.916(2) and 1.950(5) Å], one Cu-O (hydroxyl) [1.926(4) Å] and one Cu-N [1.999(3) Å] bonds form a plane with Cu-O (methoxyl) [2.303(2) Å] bond in an axial direction at an angle 77 ° to the plane. The result suggests that after treatment with copper-ethanolamine wood preservatives, stable copper-nitrogen-lignin complexes can be formed through reaction with guaiacyl units in lignin.

Samples of mahogany wood ( Swietenia macrophylla King) from Peru were used for moisture sorption tests associated with swelling tests at 25°C. Seven adsorption and five desorption moisture conditions were investigated to study the differences in swelling between adsorption and desorption curves at a given equilibrium moisture content. The results demonstrated that dimensional changes in the tangential direction and in volume were greater for desorption than for adsorption. The presence of these second order effects of moisture sorption in mahogany wood were not detected in the radial direction. Finally, the tangential/radial swelling ratio of this wood was lower in both states of sorption, and was lower in adsorption than in the desorption state.

The overall silica content in 10 rattan species was analyzed. Its distribution within the stem of Calamus merrillii Becc. was also tested. Anatomical observations were performed to explain the silica content variation. Ash and silica content varied among species. Regardless of diameter class, silica accounts for 44% to 48% of the overall ash content of the stem. Silica in the medium and small diameter stem was twice as much as in the large diameter stem. Within Calamus merrillii Becc., silica was abundant in the epidermal layer. It was responsible for 74% to 85% of the total silica content of the stem, which explains the variation in silica content between diameter classes. The proportion of epidermal layer contained in the sample deviated among the species causing a variation in silica content. Epidermal silica did not vary along the length of the stem while silica in the stem itself varied significantly from base to top. Differences in silica body frequency per vascular bundle caused such deviation.

The effect of heat treatment on changing the color of light-irradiated wood was investigated. The change in the lightness, ∆L*, of light-irradiated wood with heat treatment was much greater than that of unirradiated wood. The chroma coordinates, ∆a*, of irradiated wood increased with treatment temperature and time. ∆b* decreased after showing a sharp increase with a short period of heat treatment. It is thought that the changes are related to a change in the chemical composition which was accelerated by heat. With low temperature treatment, the color of irradiated wood changed remarkably with high relative humidity. Little change in color was observed with low relative humidity. Therefore, heat and the presence of water accelerated the change in the color of irradiated wood. This treatment is available as a new coloring method.

Static bending tests were conducted on seasoned plantation-grown Pinus radiata D. Don specimens. After the tests, core specimens of two different sizes (ø 10 × 30 mm and ø 10 × 20 mm) and small clear specimens of 20 × 20 × 60 mm were taken from intact zones of the post-test specimens. Ultrasonic measurements were made on the core specimens and the apparent longitudinal dynamic modulus of elasticity (E LD ) calculated. The small clear specimens were subjected to parallel-to-grain compression tests. The coefficient of determination was 0.85 between the static bending modulus of elasticity and E LD , 0.62 between the modulus of rupture and E LD , and 0.56 between the maximum crushing strength and E LD .

A phenolic β- O -4 type lignin model compound, guaiacylglycerol- β -guaiacyl ether ( 1 ) was treated with 70 wt% aq 1,3-butanediol solution at 160–200°C to investigate the delignification mechanism under HBS (high-boiling solvent) pulping conditions. The following compounds were identified from the reaction products by use of GC-MS: guaiacol ( 2 ), coniferyl alcohol ( 3 ), γ-etherified coniferyl alcohols ( 4 ) and α-etherified guaiacylglycerol- β -guaiacyl ethers ( 5 ), but acidolysis products, such as Hibbert's ketones were not detected. These results strongly suggest that the phenolic β-O -4 linkage was cleaved homolytically under HBS pulping conditions. The cleavage of β -ether exhibited a pseudo first-order rate behavior. The pseudo first-order rate constants were as follows: k = 0.94 × 10 −2 min −1 at 160 °C; k = 1.97 × 10 −2 min −1 at 170°C; k = 3.22 × 10 −2 min −1 at 180 °C; k = 9.76 x 10 −2 min −1 at 200 °C. The activation energy was 98.3 kJmol −1 . The formation of higher molecular weight compounds was confirmed by GPC. It is highly probable that the oligomeric products were derived from the recombination of phenoxy radicals formed by homolysis of the β -aryl ether.

Guaiacylglycerol-β-guaiacyl ether (GG) was used as a lignin model compound to study the liquefaction reaction mechanism of lignin in the presence of phenol under the catalysis of several typical acids such as sulfuric, phosphoric and oxalic acids. The reaction products were isolated by silicagel column chromatography and high performance liquid chromatography (HPLC). The structures of the obtained compounds were identified by means of GC-MS, 1 H-NMR, 13 C-NMR, 1 H- 1 H COSY, HMBC and HMQC. As a result, about 30 compounds were obtained as the main reaction products. It was found that their structural characteristics were significantly different from those yielded at the non-catalyzed liquefaction (Lin et al. 1997a), and independent on the acid species. The dominant products were guaiacylglycerol-α-phenyl-β-guaiacyl ethers, followed by guaiacol, triphenylethanes, diphenylmethanes, benzocyclobutanes and phenylcoumarans. The structural characteristics and yields of these main reaction products indicated that condensation between phenol and GG in its C-α and further cleavages in both the β-O-4 linkage and C β –C γ bonding could be the dominant reaction pathways.

By means of high performance liquid chromatography (HPLC) and gel permeation chromatography (GPC), the yields of the main reaction products and the polymeric portion formed in the reaction of guaiacylglycerol-β-guaiacyl ether (GG) under various acid-catalyzed conditions were quantified as a function of reaction time. Based on their forming sequence and reaction behavior, as well as their structural characteristics, an acid-catalyzed reaction mechanism of GG with phenol was proposed.

A major problem in the development of new bleaching technologies for pulp is the difficulty of analysing the changes induced by bleaching chemicals in the structures of residual lignin. Separation and isolation of the residual lignin before the analysis may modify the constituents of interest, whereas if the pulp is analysed directly, the responses from cellulose and hemicelluloses will overlap the signal from the residual lignin. In this study, UV resonance Raman spectroscopy, a powerful technique for detecting trace components in complex mixtures, was applied to detect the changes in the residual lignin content after bleaching stages. The resonance Raman technique was found to be highly sensitive and selective for lignin structures allowing the detection of trace amounts of lignin after the final bleaching stages. Furthermore, it enabled rapid and easy determination of hexenuronic acid content. UV resonance Raman spectroscopy would appear to be a technique of great potential for pulping and bleaching research.

In this work the role of xylan in spruce kraft pulp fibres was investigated by selectively removing the pulp fibre xylan and also by sorbing xylan onto the pulp fibres. The effects of xylan removal and sorption on fibre properties were measured and the chemical composition of the fibres and also that of the selectively removed xylans was analyzed. According to the results the xylanase could act on both sorbed and native xylan located on accessible fibre surfaces. Xylan was found to affect the strength properties of handsheets. The location and the charge of xylan had a considerable impact on the formation of interfibre bonds. Scott Bond-values correlated with the amount of surface xylan on fibre surfaces, whereas tensile strength was affected by the total amount of xylan and particularly by the total charge of the fibres. The fracture energy was determined by the combined effect of interfibre bonding ability and effective fibre length.

Residual lignins were isolated from unbleached and oxygen-bleached Eucalyptus kraft pulps by acid hydrolysis. The structural changes and degradation of residual lignin occurring during kraft pulping and oxygen bleaching were followed and identified by elemental analysis, residual carbohydrate analysis, molecular mass distribution, as well as qualitative and quantitative solution 13 C NMR. The dissolved lignins in the kraft cooked and oxygen bleached liquors were also studied and compared with the corresponding residual lignins. Milled wood lignin treated under acid hydrolysis conditions served as a reference for the structural comparison. The results show that etherified syringyl structures were quite resistant towards degradation in the oxygen bleaching, causing little depolymerisation in residual lignin and a small increase in carboxylic acid content, but producing appreciable amounts of saturated aliphatic methylene groups.

The patterns of acoustic emissions generated during tension test of finger-joints from three tropical African hardwoods, Obeche ( Triplochiton scleroxylon ), Makore ( Tieghemella heckelii ) and Moabi ( Baillonella toxisperma ) were evaluated to assess their potential usefulness for non-destructively predicting ultimate tensile strength. The acoustic emission patterns generated were observed to differ depending on the type of finger profile and the wood species. Regression coefficients from cumulative acoustic emission count versus applied stress squared functions also varied with the profile and species type. When ultimate tensile strength was correlated with these regression coefficients, for stresses applied up to 50% of mean ultimate strength, the logarithmic regression model developed could predict finger-joint strength accurate to ±12%, ±13% and ±18% for Obeche, Makore and Moabi, respectively. The model was also sensitive to the type of finger profile used for all three tropical African hardwoods. The results indicate that this acoustic emission monitoring procedure could be useful for non-destructively predicting ultimate tensile strength of finger-joints from the three tropical African hardwoods.

Refluxing of cellulose samples in N,N -dimethylacetamide (DMAc, 1 ), or in DMAc containing low concentrations of LiCl, is a common protocol to facilitate dissolution of the cellulose for GPC measurements. The formation of chromophoric condensation products, whose structures have been elucidated for the first time, and of secondary chromophores by reaction with carbohydrate structures has been demonstrated. DMAc containing traces of water is slowly hydrolyzed to dimethylammonium acetate ( 2 ) under reflux conditions. The reaction is accelerated in the presence of lithium chloride. In contrast, absolute DMAc produces five different condensation products upon thermal treatment, which were isolated by non-traditional column chromatography approach. The primary condensation product N,N -dimethylacetoacetamide ( 3 ) is formed as the major component and acts as the precursor to the other chromophore products, namely dehydroacetic acid and isodehydroacetic acid derivatives. Compound 3 is able to form furan derivatives by reaction with reducing end groups or carbonyls in carbohydrate structures as demonstrated by reactions with model compounds. As a consequence, it must be concluded that heating/refluxing in DMAc or DMAc/LiCl generates a number of potent chromophores from the solvent and, furthermore, can chemically alter pulp samples by introducing reactive structures.

A new resin system, in which liquefied wood was reacted with various epoxy compounds, was previously developed. This paper reports the syntheses of two types of liquefied wood/epoxy resins with the ratio of liquefied wood to epoxy compounds (L/E ratio) of either 1/0.5 or 1/1. Furthermore, the viscoelastic properties obtained from the dynamic mechanical measurements of the cured resins and their adhesive bond properties measured as tensile shear strength are reported. The results from dynamic mechanical measurements indicated that the resins with a L/E ratio of 1/0.5 could be cured at 90°C, while the resins with L/E ratio of 1/1 were cured at 150°C. The resins cured with triethylene tetramine (TETA) at 150°C or 90°C had almost the same level of the normal adhesive shear strength as that of the commercial epoxy resin. The high level of adhesive shear strength of the resin cured at 150°C was maintained after the glued specimens were soaked in water at 60°C, while the share strength of the resins cured at 90°C was reduced by either the water soaking at 60°C or the cyclic boiling test.