Noel L. Owen

Infrared Studies of “Hard” and “Soft” Woods

FT-IR spectra of 24 different woods have been studied with the use of whole wood pieces and a diffuse reflectance accessory. Three absorptions have been identified, the positions or relative intensities of which are characteristic of the holocellulose/lignin ratio or of the type of lignin present in the wood. These spectral features serve as useful indicators to distinguish between “soft” or “hard” woods.

Infrared Studies of Wood Weathering. Part II: Hardwoods

Four different hardwoods—yellow poplar, quaking aspen, white oak, and hard maple—have been subjected to a range of artificial weathering conditions, and their surfaces monitored with the use of diffuse reflectance infrared spectroscopy. The first two species show a weathering pattern rather similar to that of softwoods, whereas the latter two are more resistant to the effects of light and water. The differences in wood density are thought to be significant in the different behavior of the woods towards weathering, in addition to any contributing effects that might be caused by a variation in the overall chemical composition. After 2400 hours of full artificial weathering, all traces of lignin seem to have been removed from the surfaces of all four woods.

INFRARED SPECTROSCOPIC STUDIES OF SOLID WOOD

Wood is probably the oldest structural material utilized by man, and despite the invention and development of new materials over the past century or so, the use of wood in the construction industry...

Weathering and photostability of benzoylated wood

Abstract Chemical modification shows promise as a means of protecting wood from deterioration by fungi, but the systems tested to date have shown limited ability to photostabilise wood. In this study wood was esterified with benzoyl choride and the photostability of the modified wood was assessed. Benzoyl chloride was chosen because it was thought that the introduction of benzoyl groups into wood might act as a UV screen protecting wood from photodegradation. Benzoylation of wood to high weight gains (∼70%) was effective at protecting wood from photodegradation and there was an inverse relationship between weight gains due to benzoylation and mass losses of modified Scots pine wood veneers during weathering. FTIR spectroscopy and SEM of benzoylated wood exposed to natural weathering provided strong evidence for the stabilisation of lignin as a result of benzoylation. Benzoylation to high weight gain, however, caused extensive swelling of the wood cell wall and large losses in the tensile strength of veneers. The UV absorption characteristics of wood were modified by benzoylation and ESR spectroscopy of UV irradiated veneers clearly showed that benzoylation reduced the concentration of free radicals that are involved in the photodegradation of wood.

Weathering of chemically modified wood surfaces - Natural weathering of Scots pine acetylated to different weight gains

Summary Scots pine wood veneers were acetylated to weight gains of 5, 10, 15 or 20% and exposed to natural weathering. Veneers acetylated to low weight gains of 5 and 10% and exposed to the weather showed greater losses in mass and tensile strength due to increased delignification and depolymerisation of cellulose than similarly exposed, untreated controls. Acetylation to 20% weight gain restricted the loss of veneer mass and holocellulose during exposure. Initially it also slightly reduced the depolymerisation of cellulose, and this was reflected in lower losses in veneer zero-span tensile strength after 35 days exposure. However, the photoprotective effects of acetylation, with the exception of veneer mass, were lost with prolonged exposure of veneers to the weather. Acetylation of wood blocks to 20% weight gain caused a bulking of the wood cell wall, particularly the S3 layer of the secondary wall, and reductions in lumen size. Acetylated latewood cells maintained their shape and radial orientation during exterior exposure, but acetylation did not prevent erosion of the middle lamella. Mechanisms to explain how acetylation may affect the weathering resistance of wood are suggested.

The vibrational spectra, rotational isomerism, normal coordinate analysis and mean amplitudes of ethyl formate, ethyl chloroformate and ethyl cyanoform

Abstract The infrared spectra of ethyl formate, chloroformate, and cyanoformate in the liquid phase have been recorded in the region 4000–4020 cm −1 , and in the solid and vapour phase and in solution in the region 4000–4200 cm −1 . Evidence is reported for the existence of two rotameric forms in each case. Normal coordinate calculations are reported for both rotameric forms of the first two esters, and assignments based on potential energy distributions are given. These assignments show considerable mixing of the normal modes and suggest the inadequacy of simple assignments made by comparison with related molecules. Calculated mean amplitudes are also reported for the first two molecules.

FT-IR Studies of Weathering Effects in Western Redcedar and Southern Pine

Diffuse reflectance infrared spectroscopy has been used to monitor the changes in functional groups on the surface of two woods (western redcedar and southern pine) when they are subjected to a range of artificial weathering conditions. The effects of light only, water only, and light plus water have been studied for a variety of exposure times. The changes in the chemical composition of the wood caused by light plus water is considerably greater than that caused by light only, whereas water alone causes no permanent chemical changes. The effects of some of these weathering conditions have been investigated for wood protected by varnish, for earlywood and latewood and for tangentially, radially, and cross-sectionally cut wood samples. The application of two coats of varnish was found to considerably reduce the weathering effects caused by UV radiation; earlywood undergoes light-only degradation faster than late wood; and the effect of weathering was found to be greatest for cross-sectional cut samples and least for radially cut samples. The weathering profile with depth of penetration has been studied in some detail for western redcedar, and our results show that, after 300 h of continual artificial weathering, the chemical changes are confined to the first 200 μm.

Synthesis of 2,3-dihydropyridines, cyclobutanopyrrolines and quinolines from lithiated allenes and isothiocyanates

Abstract The products obtained by S -alkylation of the adducts from lithiated allenes and alkyl or aryl isothiocyanates undergo thermal rearrangements with ultimate formation of derivatives of 2,3-dihydropyridine, cyclobutanopyrroline and quinoline, depending on the structure of the isothiocyanate. In some reactions azatrienes with a fully conjugated system can be isolated.

Infrared and microwave spectra, molecular conformation and electric dipole moment of methyl thiolformate

Abstract The microwave spectrum (41-10 GHz) and the infrared spectrum (4000-50 cm −1 ) of methyl thiolformate have been obtained and analyzed. The spectra are consistent with a single molecular conformation having a planar array of heavy atoms and with the alkyl group cis to the carbonyl group. The measured rotational constants are: A , 11042.22 MHz; B , 5118.27 MHz; C, 3562.03 MHz (κ = −0.5839). No internal rotation doublets were observed in the microwave spectrum for the ground vibrational state, which implies that the barrier hindering internal rotation of the methyl group is either much larger or much smaller than the corresponding value for methyl formate. If the former is true then a lower limit of 10.5 kJ mol −1 may be placed on the barrier height. The dipole moment of methyl thiolformate was measured using the Stark effect to be 1.58 ± 0.05 Debyes ( μ A = 1.52 D; μ B = 0.43 D) for the vapor, and for dilute solutions in benzene at 295 K the value of 1.6 ± 0.1 D was found from capacitance measurements. SCF computations using minimal basis sets of STO 3G atomic orbitals and extended basis sets of STO 4.31G atomic orbitals have been carried out for methyl thiolformate and methyl formate. Energy differences between rotational isomers and estimates of barrier heights are given together with the calculated dipole moments.

Wood used by Stradivari and Guarneri

Whether or not the great Italian violin-makers used wood that had been chemically processed in order to preserve it and enhance the instruments sound quality has long been a contentious issue. Here we use nuclear magnetic resonance and infrared spectroscopy to analyse organic matter in wood taken from antique instruments made by Stradivari and Guarneri del Gesu. Our results indicate that the wood used by the masters could indeed have been chemically treated, a technique that may inspire an approach to violin making that is more chemistry-based.