Robert A. Franich

Effect of drying and rewetting of wood on cellulose molecular packing.

Abstract Drying and rewetting of Pinus radiata sapwood latewood was studied by synchrotron wide angle X-ray scattering in transmission mode. Scattering from cellulose was interpreted in terms of chains distributed on a monoclinic lattice. Drying wood material to below the fibre saturation point resulted in decreased spacing between adjacent cellulose polymers within the hydrogen-bonded sheets of chains, and also decreased the monoclinic angle. The changes were partly reversed when the dried wood was rewet, but accumulated through multiple cycles of oven-drying and rewetting. No changes were observed in the fibre repeat distance, thus the distortion of the crystal lattice was not attributed to mechanical stresses associated with drying. Instead, the changes were attributed to formation of intrachain hydrogen bonds at dehydrated crystallite surfaces, causing conformational changes within the cellulose chains and increasing the density of packing. The results help account for the hysteresis observed in moisture desorption-adsorption isotherms during wood material drying and rehydration.

Advances in understanding bioactivity of chitosan and chitosan oligomers against selected wood-inhabiting fungi

Abstract Nitrous acid deaminative depolymerisation was used to prepare three chitosan oligomer (CO) mixtures from high-molecular weight chitosan. These mixtures of chitosan oligosaccharides were analysed by electrospray ionisation mass spectroscopy, potentiometric titration and gel permeation chromatography. A method based on potentiometric titration of the amino groups of the oligomers gave an average degree of polymerisation (DP) for the three preparations of 5 (CODP5), 9 (CODP9) and 14 (CODP14). Chitosan acetate and the chitosan oligomer mixtures were assayed against Leptographium procerum, Sphaeropsis sapinea and Trichoderma harzianum on nutrient media. Leptographium procerum and S. sapinea growth was prevented by chitosan acetate and chitosan oligomers at concentrations of 0.3–0.4% (w/v), whereas T. harzianum was able to overcome the fungistatic action of these compounds. The oligomer preparation CODP14 exhibited superior specific activity to both CODP5 and chitosan acetate, suggesting an optimum molecular weight for bioactivity. All oligomer preparations were more effective at pH 4 than at pH 6. This result, in combination with the inactivity of N-acetylated CODP14, indicated that amino group protonation was an important factor for fungistatic activity. The CODP14 preparation was reduced with sodium borohydride and fractionated by alkali precipitation and ion exchange chromatography. Bioassays of these fractions pointed towards DP and degree of deacetylation (DD) as key factors in chito-oligosaccharide bioactivity. Conversely, the terminal aldehyde groups generated by depolymerisation did not contribute to the activity observed.

The Relationship Between Pit Membrane Ultrastructure and Chemical Impregnability of Wood

Summary The woods of Alder and Eucalypt were examined by light microscopy before and after a chemical treatment by the Indurite process to increase the hardness of the wood. The pattern of wood cell impregnation for Alder differed significantly from Eucalypt in some respects. In Alder wood all cell types eg. vessels, fibres and rays, were impregnated in similar proportions. In comparison, in Eucalypt wood the impregnation material was largely confined to ray cells and the lumina of vessels; other cell types were either not impregnated or impregnated in very small numbers. Transmission electron microscopy of Alder and Eucalypt woods suggests that ultrastructural differences in the texture and porosity of pit membranes may be the main reason for the observed differences between these wood species with regard to their impregnability by the impregnation material used.

A comparative study of dewatering of Pinus radiata sapwood using supercritical CO2 and conventional forced air-drying via in situ magnetic resonance microimaging (MRI)

Abstract A comparison of moisture loss from Pinus radiata sapwood by conventional forced air-drying and a novel supercritical carbon dioxide (scCO2) dewatering process has been examined in situ using magnetic resonance microimaging. Air-drying results in the nonuniform removal of moisture within the wood volume, leading to a dry core and wet perimeter where water evaporated, whereas the scCO2 dewatering process resulted in moisture expulsion more uniformly throughout the volume of the specimen, especially so within the earlywood.

Detection of wood cell wall porosity using small carbohydrate molecules and confocal fluorescence microscopy

A novel approach to nanoscale detection of cell wall porosity using confocal fluorescence microscopy is described. Infiltration of cell walls with a range of nitrophenyl‐substituted carbohydrates of different molecular weights was assessed by measuring changes in the intensity of lignin fluorescence, in response to the quenching effect of the 4‐nitrophenyl group. The following carbohydrates were used in order of increasing molecular weight; 4‐nitrophenyl β‐D‐glucopyrano‐side (monosaccharide), 4‐nitrophenyl β‐D‐lactopyranoside (disaccharide), 2‐chloro‐4‐nitrophenyl β‐D‐maltotrioside (trisaccharide), and 4‐nitrophenyl α‐D‐maltopentaoside (pentasaccharide). This technique was used to compare cell wall porosity in wood which had been dewatered to 40% moisture content using supercritical CO2, where cell walls remain fully hydrated, with kiln dried wood equilibrated to 12% moisture content. Infiltration of cell walls as measured by fluorescence quenching, was found to decrease with increasing molecular weight, with the pentasaccharide being significantly excluded compared to the monosaccharide. Porosity experiments were performed on blocks and sections to assess differences in cell wall accessibility. Dewatered and kiln dried wood infiltrated as blocks showed similar results, but greater infiltration was achieved by using sections, indicating that not all pores were easily accessible by infiltration from the lumen surface. In wood blocks infiltrated with 4‐nitrophenyl α‐D‐maltopentaoside, quenching of the secondary wall was quite variable, especially in kiln dried wood, indicating limited connectivity of pores accessible from the lumen surface.

Quantitative analysis of 2,6-di-tert-butyl-4-methylphenol (butylated-hydroxytoluene) antioxidant in a solvent-formulated liquid polychloroprene adhesive and in cured polychloroprene adhesive films

Two simple methods using internal standards are described for the quantitative analysis of 2,6-di-tert-butyl-4-methylphenol (butylated-hydroxytoluene, BHT) antioxidant in samples of solvent-formulated liquid adhesive and in cured polychloroprene adhesive films. Because only very small samples of cured adhesive could be taken from articles or components without substantially detracting from the product, the methods were developed to use minimal quantities of cured adhesive. The pyrolysis gas chromatography (PyGC) method required less than 1 mg of adhesive for analysis. The extraction method required less than 100 mg. A satisfactory correlation (r= 0.8) was obtained between the two methods. Recovery of BHT by extraction from cured Neoprene adhesive was better than 90%. Using 2,6-di-tert-butylphenol as internal standard, the error for the PyGC analysis method was 10%, while that of the extraction method was 1%.

COMMENT ON THE STRUCTURE OF OSMIUM TETROXIDE-CHITOSAN COMPLEX

Reaction of an aqueous solution of osmium tetroxide with the chitosan polymer model, the oligomer tetradeca(β(1→4)2-amino-2-deoxyglucopyranose)-β(2→5)mannitol, afforded a brown solid, the structure of which was proposed to contain osmium imido groups, −N˭Os. The product showed a new, distinct absorption band at 850 cm−1 in the FTIR spectrum, while the 13C CP-MAS NMR spectrum showed a lower signal relative intensity ratio for C2:C3/5 compared with that in the NMR spectrum of the starting oligosaccharide due to a downfield shift of C2 where allylic to the -N˭Os bond. Results from quantum chemical calculations were used to compare computed properties of the previously described “osmium tetroxide-chitosan complex” in which osmium tetroxide was coordinated to chitosan amino ligands with single dative N→Os bonds, and the product prepared in this study, proposed to have covalently-bonded imido bonds between osmium and nitrogen. The consequences of multiple bonding of two chitosan N to the Os atom in the 5d 3 6s hybrid tetrahedral configuration and with the C-N˭Os bond angle greater than 150° required one of the carbohydrate pyranose rings attached to Os to adopt a boat conformation.

Formation of 7-Ketodehydroabietic Acid at the Radiata Pine Wood Surface. and its Effect on Wood Yellowing

ABSTRACT Dehydroabietic acid (1), an extractive of radiata pine wood has been shown to undergo light-catalysed oxidation at the wood surface to 7-ketodehydroabietic acid (3), identified by mass spectrometry as the methyl ester (4). and compared with authentic compound. 7-Ketodehydroabietic acid (3) was not generally further oxidised, except in two samples examined which contained a trace amount of 7-ketoabieta-6.8,ll,13-tetraen-18-oic acid (7). Consequently, 7-ketodehydroabietic acid (3) accumulated as a major oxidised resin acid product at the radiata pine wood surface when the surface was exposed to air and light. After one year, the compound (3) comprised approximately half of the extractable aromatic ring-C resin acids. Application of synthetic 7-ketodehydroabietic acid (3) to exhaustively methyiene chloride extracted radiata pine wood blocks, and exposure of treated and untreated blocks to sunlight did not result in alteration of the yellowing rate of the wood surface.

The trans-continental distributions of pentachlorophenol and pentachloroanisole in pine needles indicate separate origins

The production and use of pentachlorophenol (PCP) was recently prohibited/restricted by the Stockholm Convention on persistent organic pollutants (POPs), but environmental data are few and of varying quality. We here present the first extensive dataset of the continent-wide (Eurasia and Canada) occurrence of PCP and its methylation product pentachloroanisole (PCA) in the environment, specifically in pine needles. The highest concentrations of PCP were found close to expected point sources, while PCA chiefly shows a northern and/or coastal distribution not correlating with PCP distribution. Although long-range transport and environmental methylation of PCP or formation from other precursors cannot be excluded, the distribution patterns suggest that such processes may not be the only source of PCA to remote regions and unknown sources should be sought. We suggest that natural sources, e.g., chlorination of organic matter in Boreal forest soils enhanced by chloride deposition from marine sources, should be investigated as a possible partial explanation of the observed distributions. The results show that neither PCA nor total PCP (ΣPCPxa0=xa0PCPxa0+xa0PCA) should be used to approximate the concentrations of PCP; PCP and PCA must be determined and quantified separately to understand their occurrence and fate in the environment. The background work shows that the accumulation of airborne POPs in plants is a complex process. The variations in life cycles and physiological adaptations have to be taken into account when using plants to evaluate the concentrations of POPs in remote areas.

Investigations of wood veneer during furfuryl alcohol modification using DMTA

Dynamic mechanical thermal analysis has been used to monitor the change in wood veneer stiffness due to furfuryl alcohol impregnation and plasticization of wood components and subsequent polymerization of furfuryl alcohol within wood material. This explains the improvement in the moulding ability of wood veneer where furfuryl alcohol aids in wood plasticization, and the increase in moulded shape stability achieved when furfuryl alcohol is polymerised within wood cell walls.