Hank W. Kroese

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.

Effect of specimen dimension and pre-heating temperature on supercritical CO2 dewatering of radiata pine sapwood

Abstract Removing water from wood is a critical requirement for applications in building and construction and for chemical modifications. Normally, green radiata pine (Pinus radiata D. Don) timber, with a moisture content (MC) range at harvest between 150% and 200%, is kiln dried to below fiber saturation point (FSP) to 10–14% MC. In the present work, a physical-chemical-mechanical dewatering process is presented, which involves pressure cycling with supercritical CO2 to remove water to near the FSP. When the CO2 was cycled from ∼4 MPa into the supercritical state, at pressures up to 20 MPa, specimens of cross-sectional dimensions of up to 52 mm were successfully dewatered from a MC of 174%, typical of the green state, to approximately 39% in seven cycles. The specimens with the smallest cross-sectional dimensions dewatered more slowly than the larger specimens. Preheating the green wood before loading it into the dewatering vessel increased the rate of dewatering. The final MCs were similar in all experiments and were independent of specimen dimension (15–52 mm) or preheating temperature between 40°C and 60°C. Pressure-temperature phase diagrams show that it is necessary to compress the CO2 to the supercritical state for efficient dewatering. Diffusion rates and solubility of CO2 in sap were important, but channel opening within specimens was proposed to be a critical factor in the dewatering process. The reason why pressure-based experiments remove water from wood to an MC greater than the established FSP of 30% is not yet clear.

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.

Primer blocking and pre-service adhesion of acrylic coating systems applied to light organic solvent preservative (LOSP) treated radiata pine sapwood boards

2) for the relationship between residual solvent level and time was 0.98. Rate of solvent loss was dependent on the magnitude of the solvent uptake level. For an uptake level of 34 L/m3, the rate of loss was 2.3 L/m3/day after three days; 1.8 L/m3/day after 28 days; and 0.1 L/m3/day after 51 days. Within 3 to 14 days of preservative treatment, primed 20 mm thick boards can be expected to retain 35–83% of the absorbed solution. For 34 mm boards, retention levels will be higher (42–87%).P. radiata) wurden mit Holzschutzmitteln in leichten organischen Lösemmitteln behandelt und grundiert. Ein Teil der grundierten Bretter wurde danach mit einer von vier Acrylfarbtypen bestrichen. Die Lösemittelaufnahme wurde über einen Zeitraum von 51 Tagen gemessen. Ebenso wurde die Haftfestigkeit der Anstriche und der Einfluß der Grundierung auf das Verkleben der Bretter abgeschätzt. Letzteres wurde bei Grundierungen auf Acryl- jedoch nicht auf Öl-Basis festgestellt. Die Farb- haftfestigkeit unterschied sich in den vier Systemen und war beeinflußt von der Restmenge an Lösemitteln in den Brettern. Keine Haftungsfehler ergaben sich bei einem System mit Hybrid-Grundierung (mit einer Charakteristik sowohl von wasserlöslichen als auch von Lösemittellöslichen Anstrichen). Zwei andere Acryl-Systeme zeigten sich Fehler in einer oder zwei Farbschichten, jedoch war dies in einem Fall auf die ersten 14 Tage beschränkt. Bei anderen Acrylfarben konnten Haftungsfehler auf eine fehlerhafte Auftragmethode zurückgeführt werden. Ein System auf Alkydbasis zeigte die größten Haftungsfehler über die Dauer von 51 Tagen. Eine exponentielle Gleichung wurde entwickelt, die die Abgabe der Lösemittel aus den behandelten Brettern beschreibt. Der Korrelationskoeffizient für die Beziehung zwischen Restmenge und Zeitdauer betrug: R2=0,98. Die Abgaberate war abhängig von der Höhe der Lösemittelaufnahme. Bei einer Aufnahmemenge von 34 L/m3 betrug die Rate der Lösemittelabgabe 2,3 L/m3 nach drei Tagen, 1,8 L/m3 nach 28 Tagen und 0,1 L/m3 nach 51 Tagen. Innerhalb von 3 bis 14 Tagen nach Schutzmittelbehandlung kann für 20 mm dicke Bretter eine absorbierte Lösemittel-Menge von 35–83% der absorbierten Lösung erwartet werden. Bei 34 mm starken Brettern liegt die Menge höher (42–87%).