可燃性气体逸出百分率在树种抗火性评价中的应用

以陕西９３种树种的枝为试样，在不同温度条件下对可燃性气体逸出百分率及其变化的测定表明，可燃性气体逸出百分率和温度之间的关系符合ｖ＝ａｂｘ模型，并且在２４０℃条件下可燃性气体逸出百分率变化幅度大，可燃性气体逸出相对于１５０℃、１９０℃明显，用此指标选择抗火树种效果明显。     

The influence of rate of growth on the density and heartwood extractives content of eucalypt species

Summary Basic density and extractives content, of the sapwood and outer heartwood respectively, were compared for a fast-and a slow-grown tree in five, 40 year old, coppice clumps of each of six eucalypt species. Rate of growth did not appreciably influence extracted wood density, although outer heartwood extractives levels were significantly (P<0.05) higher in the larger stems. The juvenile core, as defined by radial variation in basic density, occupied a similar proportion of the tree diameter in the fast-and slow-grown trees, suggesting that sampling was effected in tissues of similar maturity in both tree groups.Helpful discussions with Dr. W. A. Heather, a co-worker, and Dr. W. E. Hillis, Visiting Fellow of this Department, are gratefully acknowledged     

The hydrophobic properties of bark extractives

Summary The hydrophobic properties of benzene-soluble extractives from the bark of Pinus radiata were studied by determining the water-solid-air contact angle and the resistance to water penetration.The material contained in the bark extract possessed wax-like and film-forming properties. It was highly hydrophobic with a contact angle with water of about 98°. Wood samples were impregnated with bark extract in order to study the ability of the hydrophobic bark extractives to prevent preferential wetting with water and the displacement of the impregnant from the hydrophilic wood surface. The wax-like material deposited from the bark extracts showed a remarkable affinity for wood as revealed by the high degree of resistance to water penetration and wetting of the treated wood even after several wetting-drying cycles which otherwise tend to break down the bonds and adhesion between a hydrophilic solid and a hydrophobic coating.Hydrophobic or film-forming additives did not improve the ability of bark extractives to protect a hydrophilic solid from water. The properties of the bark extractives as a water repellent and a water barrier could therefore be assumed to be as near perfect as possible.Nature seems to have solved the problem of producing one single, although complex, material with two properties which are extremely difficult, maybe impossible, to combine in a single synthetic material: one of high affinity for a hydrophilic solid and another of extreme water repellency and resistance to water.The in situ conditions prevailing in the bark tissue, combining bark extractives and cell walls of various anatomical structures, must therefore represent a rather unique and for this specific purpose highly efficient two-phase hydrophobic-hydrophilic solid system.The authors would like to express their appreciation to Kalley Timber Development Corporation for the close co-operation and support for our research on bark products and would also like to thank Lewis and Everitt, Poly-Resin Products Ltd., Taeuber and Corssen, Farbenfabriken Bayer AG, Scado-Archer-Daniels, Triton Chemicals and Rohm and Haas for supplying samples and information.     

Collapse,volumetric shrinkage,specific gravity and extractives in Eucalyptus and other species

Summary The influence of extractive content on the shrinkage behaviour in eucalypts was shown by mathematical extraction after making certain assumptions with respect to available data. The slope of the volumetric shrinkage/specific gravity (S/) ratio changed from negative to positive after the theoretical removal of alcohol/benzene/water soluble or NaOH soluble extractives. Statistical analysis of available data suggested that collapse was positively related to the encrusting and extraneous materials and negatively related to the polysaccharide cell wall component. Conversely, normal volumetric shrinkage was positively related to the polysaccharides and negatively related to lignin and extractive content. Mechanisms by which extractive content might influence collapse development were discussed. R-values (change in external volume during shrinkage or swelling per change in weight of equivalent volume of water) appeared to be negatively correlated with extractive content in eucalypts and calculations for other species showed that R progressively increased with cold and hot water extraction. Further analysis suggested that the apparent change in lumen dimensions suggested by particular R-values was mitigated by the bulking effect of extractives in the cell wall. A possible role for R as an indicator of dimensional stability was postulated.     

Collapse,volumetric shrinkage,specific gravity and extractives in Eucalyptus and other species

Summary An examination of shrinkage behaviour in a range of tree species has demonstrated clear differences between eucalypts and other species with respect to the volumetric shrinkage (S)/specific gravity () ratio. The equation S=f proposed by Stamm (1935a, 1952) to relate this ratio to the fibre saturation point (f) was inapplicable in eucalypts, both before reconditioning, where a highly negatively significant linear correlation was observed between S and , and after reconditioning where the correlation was not significant and the regression line indicated S to be nearly constant. Collapse was found to be highly negatively correlated with specific gravity in the eucalypt species and evidently was primarily responsible for the negative S/ relationship before reconditioning.In non-eucalypts S and were highly positively correlated, but the regression line did not pass through the origin and the slope was 10 to 14% less than the value of 28% suggested by Stamm for f. Only when the regression line was artificially forced through zero did the slope approach postulated fibre saturation point values. A power function was proposed as representing a more reasonable fit of the data.In line with these analyses, unit shrinkage (S_u) was shown not to be equivalent to . This lack of equivalence was expressed as S_u divided by basic density () which was termed the R-ratio and which was shown to be equal to the change in volume during shrinkage (or swelling) divided by the associated change in the weight of an equivalent volume of water. R was seldom equal to one, as required by the Stamm formula, and was negatively correlated with specific gravity in both eucalypts and non-eucalypts. A comparison of regression equations showed R values for eucalypts to be significantly different from those of non-eucalypts. Possible uses for the R-ratio were considered.     

Limitation of XPS for analysis of wood species containing high amounts of lipophilic extractives

Chemical composition of Norway spruce and pine, two softwood species, has been investigated by X-ray Photoelectron Spectroscopy (XPS). Contrary to results previously obtained with beech wood, which allow to obtain information on bulk chemical composition from surface composition analysis, XPS analysis appears to be unsuitable for the characterisation of Norway spruce and pine wood chemical composition. Indeed, chemical compositions calculated from XPS data differ strongly from those obtained from microanalyses which are in good agreement with theoretical composition described in the literature. XPS analysis of both the softwood surfaces indicated high carbon contents explained by migration of lipophilic extractives to the surface under the influence of the vacuum necessary for XPS analysis. Nonvolatile extractives contained in wood were extracted and deposited on glass plates and analysed. Survey and detailed C1s spectra indicated similar signals to those recorded on wood surfaces. This phenomenon was not observed when samples had been previously extracted before analysis. These results strongly evidenced that extractives present in both species are able to migrate through resin canals from the bulk of the sample to the surface when put into ultra high vacuum. XPS presents, therefore, some limits in the case of the analysis of softwood species containing extractives able to migrate to the surface during analysis. This behaviour, difficult to control, could lead to erroneous interpretations due to extractives enrichment of the surface under the effect of vacuum.     

Lipophilic extractives of the inner and outer barks from six different Pinus species grown in Indonesia

The chemical compositions of the dichloromethane extracts of inner and outer barks from six Pinus species(P.elliotii,P.oocarpa,P.caribeae,P.merkusii,P.montezumae,and P.insularis) grown in Indonesia were investigated by GC and GC–MS.Generally,the amounts of extractive contents were higher in the inner bark than in the outer bark except for P.merksuii.Fatty acids,monoterpenes,sesquiterpenes,resin acids,triterpenoids,and steroids were detected and quantified.Inner and outer barks differed not only in content of these compounds but also in their composition.Fatty acids and alcohols were the major classes of lipophilic compounds in the outer bark of P.caribeae, P.insularis,and P.montezumae.Steroids and triterpenoids were the dominant compounds identified in the inner bark of P.elliotii,P.insularis,and P.merkusii.Resin acids were the most abundant group in the inner bark of P.oocarpa whereas monoterpenes and sesquiterpenes were recorded in minor quantities in both bark layers of all species.     

Stomatal and non-stomatal limitations to photosynthesis in four tree species in a temperate rainforest dominated by Dacrydium cupressinum in New Zealand

We assessed the relative limitations to photosynthesis imposed by stomatal and non-stomatal processes in Dacrydium cupressinum Lamb. (Podocarpaceae), which is the dominant species in a native, mixed conifer-broad-leaved rainforest in New Zealand. For comparison, we included three co-occurring broad-leaved tree species (Meterosideros umbellata Cav. (Myrtaceae), Weinmannia racemosa L.f. (Cunoniaceae) and Quintinia acutifolia Kirk (Escalloniaceae)) that differ in phylogeny and in leaf morphology from D. cupressinum. We found that low foliage phosphorus content on an area basis (P(a)) limited light-saturated photosynthesis on an area basis (A(sat)) in Q. acutifolia. Depth in the canopy did not generally affect A(sat) or the relative limitations to A(sat) because of stomatal and non-stomatal constraints, despite reductions in the ratio of foliage mass to area, foliar nitrogen on an area basis (N(a)) and P(a) with depth in the canopy. In the canopy-dominant conifer D. cupressinum, A(sat) was low, consistent with low values of the maximum rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation (V(cmax)). In comparison, the A(sat) response of the three broad-leaved tree species was quite variable. Although A(sat) was high in the canopy-dominant M. umbellata, it was low in the sub-canopy trees W. racemosa and Q. acutifolia. Relative stomatal limitation to photosynthesis was more pronounced in W. racemosa (40%) than in the other three species (28-33%). Despite differences in degree, non-stomatal limitation to A(sat) predominated in all tree species.     

The hydrophobic and water-repellent properties of wattle bark extractives

Summary Based on the fact that bark is an almost perfect water barrier and assuming that bark is impregnated with materials which aid in rendering it impermeable to water, the hydrophobic and water-repellent properties of several bark extractives were investigated. Products obtained after extraction with polar and non-polar solvents showed widely different properties. Some were extremely hydrophobic and water-repellent with a water-solid-air contact angle higher than 100°. These were the products obtained from extraction with benzene and mineral turpentine. Alcohol and acetone extractives had contact angles as low as 23° but coatings from some of these materials nevertheless had a high efficiency as water barriers. The efficiency of the various extractives as water repellents or water barriers was determined by coating wood with 10 per cent solutions of the extractives in different solvents and determining the extent to which water could be prevented from being absorbed and causing swelling of the wood and thereby reduce the dimensional changes of the wood. The extractives obtained with nonpolar solvents were extremely efficient as true water repellents while the polar aleohol extracts were far better than could be expected from their almost hydrophilic properties. Nature has therefore provided for hydrophilic film-formers combined with hydrophobic materials which act as a double line of defence against water absorption. The hydrophilic extractives, in addition, act as a bridging agent between the strongly hydrophobic extractives and the hydrophilic cell wall material.Since some of the extractives from wattle bark have excellent hydrophobic properties, and since this bark is available in large quantities as a waste product after tannins have been extracted, the utilization of certain wattle bark extractives as water repellents could be economically attractive.     

The effect of extractives on water-vapor sorption by wood

Summary The woods of different species vary widely in the nature and amount of their extractive content with a resultant variation in their sorption characteristics. This is particularly evident in the case of tropical woods, many of which are characterized by high extractive content. The nine species included in this study ranged from 3... 17 percent in extractive content. As determined from their desorption isotherms these species ranged from 20.5... 32.8 percent in fiber saturation point prior to extraction, and from 30.4... 38.0 percent after the removal of extractives with a series of neutral solvents. An analysis of variance showed that the variation in fiber saturation point among these species was reduced by about one-half following extraction in desorption and by approximately 7/8 in adsorption.The results of this study lead to several conclusions.The principal effect of extractives is to depress the sigmoid isotherm in the upper range of relative humidity, typically above 60 ... 70 percent. Isotherms of extracted and unextracted wood coincide very closely at relative humidities below about 60 percent.Based on these nine species, the increase in fiber saturation point resulting from the removal of extractives is greatest for a species with a low initial fiber saturation point and least for a species with a high initial fiber saturation point. Model equations accounted for 68 percent of the increase in desorption and 78 percent of the increase in adsorption. The remaining variance is presumed to be due to differences in chemical composition and physical organization of the skeletal cell wall.By employing the Hailwood-Horrobin model equation in analyzing the data, it was possible to partition the sorbed moisture as monomolecular and polymolecular sorption. The presence of extractives has very little effect on the amount of moisture sorbed as a monolayer on the internal surfaces of the cell wall (Langmuir sorption). In contrast, the sorption of moisture in polymolecular layers is reduced in greatly varying degree consistent with the theory of bulking action whereby the extractive substance within the cell wall precludes moisture from occuping the same space.By means of a regression analysis of monomolecular moisture vs. the constant M (a measure of the availability of bonding sites for sorption) in the Hailwood-Horrobin equation, it is evident that monolayer sorption increases with increased availability of bonding sites in both unextracted and extracted wood. By similar analysis polymolecular sorption also increases with increased surface activity in the case of extracted wood, but this effect is completely masked in the analysis of unextracted wood by the predominant bulking action. Total sorption, dominated by polymolecular sorption, shows similar relationships. Only in the case of essentially extractive-free wood can total sorption be expected to reflect the availability of molecular sorption sites and hence reveal variations in degree of crystallinity, cell wall compactness, or chemical composition to a significant degree.

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Zusammenfassung Die verschiedenen Holzarten schwanken hinsichtlich der Art und der Menge ihrer Extraktstoffe in weiten Bereichen, was sich in gleicher Weise in einer Schwankung ihres sorptions verhaltens ausdrückt. Diese Erscheinung tritt bei tropischen Hölzern besonders deutlich hervor, von denen eine ganze Reihe durch hohe Extraktstoffgehalte gekennzeichnet sind. Die in der vorliegenden Arbeit untersuchten neun Holzarten besaßen zwischen 3 und 17 Prozent Extraktstoffgehalt. Anhand der Desorptionsisothermen könnten bei diesen Holzarten die Fasersättigungspunkte vor der Extraktion zwischen 20,5 und 32,8 Prozent und nach der Extraktion mit einer Reihe von neutralen Lösungsmitteln, zwischen 30,4 und 38,0 Prozent liegend festgestellt werden. Eine Varianzanalyse zeigte, daß die Streuung der Fasersättigungspunkte der genannten Holzarten im Anschluß an die Extraktion für die Desorption auf etwa 1/2 und für die Adsorption auf rund 7/8 zurückging. Die Ergebnisse der vorliegenden Untersuchungen lassen folgende Schlüsse zu.Die Wirkung der Extraktstoffe zeigt sich allgemein in einer Abflachung der Isothermenkurve im oberen Bereich der relativen Luftfeuchtigkeit, besonders oberhalb 60 ... 70 Prozent. Die Isothermen der extrahierten und nichtextrahierten Hölzer liegen bei relativen Luftfeuchtigkeiten unterhalb von 60 Prozent verhältnismäßig nahe beieinander. Die mit den gewählten 9 Holzarten erzielten Ergebnisse zeigen, daßdie aufgrund der Extraktion eingetretene Erhöhung des Fasersättigungspunktes für die Holzarten mit ursprünglich niedrigem Fasersättigungspunkt am größten und für die Holzarten mit ursprünglich hohem Fasersättigungspunkt am geringsten war. Mit Hilfe entsprechender Gleichungen wurde für die Desorption ein Anstieg von 68 Prozent und für die Adsorption ein solcher von 78 Prozent errechnet. Die verbleibende Restvarianz wird auf Unterschiede im chemischen Aufbau und in der physikalischen Anordnung der Zellwände des Stützgewebes zurückgeführt.Die Anwendung der Hailwood-Horrobin-Modellgleichung zur Analyse der gefundenen Werte ermöglicht eine Unterscheidung der sorbierten Feuchtigkeit in eine monomolekulare und eine polymolekulare Sorption. Danach zeigt sich, daß das Vorhandensein von Extraktstoffen einen nur geringen Einfluß auf jene Feuchtigkeitsmenge ausübt, die als Monoschicht an die inneren Oberflächen der Zellwand sorbiert wird (Langmuir-Sorption). Im Gegensatz hierzu wird die Feuchtigkeitssorption in polymolekularen Schichten in allerdings sehr unterschiedlich hohem Grade vermindert. Dies steht in Übereinstimmung mit der Bulking-Action-Theorie, die besagt, daß die Extraktstoffe in der Zellwand die Feuchtigkeit daran hindern den gleichen Raum einzunehmen.Mit Hilfe einer Regression von der monomolekular adsorbierten Feuchtigkeit auf die Konstante M der Hailwood-Horrobin-Gleichung (=Maß für das Vorhandensein von freien Bindungsstellen für die Sorption) kann deutlich gemacht werden, daß die monomolekulare Sorption mit dem zunehmenden Vorhandensein von freien Bindungen sowchl im nichtextrahierten als auch im extrahierten Holz ansteigt. Mit Hilfe eines ähnlichen Analysenganges läßt sich zeigen, daß die polymolekulare Sorption bei extrahiertem Holz mit seiner gesteigerten Oberflächenaktivität ebenfalls zunimmt. Dieser Einfluß ist aber bei nichtextrahiertem Holz durch das Überwiegen der Bulking-Action vollständig überdeckt und daher nicht erkennbar. Die Gesamtsorption, die durch die polymolekulare Sorption wesentlich bestimmt wird, zeigt ähnliche Beziehungen. Allein im Falle vollständig extraktstoffreien Holzes kann man annehmen, daß die Gesamtsorption ein adäquates Bild von der Zugänglichkeit freier Bindungen für die molekulare Sorption wiedergibt, so daß hierdurch Schwankungen des Kristallinitätsgrades, der Zellwanddichte oder der chemischen Zusammensetzung in signifikanter Weise zu erkennen sind.

     

Dendrochronological investigation of wood extractives

X-ray microdensitometry was applied to a set of Scots pinewood (i.e. low extractive content). Earlywood and latewood properties were determined as minimum and maximum densities of each tree ring and the potential influence of acetone-soluble extractives (i.e. non-structural and secondary constituents of wood) was estimated using tree-ring statistics. The occurrence of extractives in different portions of wood was determined using dendrochronological methods, by comparing the densities of unextracted and extracted wood. It was not only found that unextracted samples exhibited inflated earlywood and latewood density values, but the growth trends were also altered. Extractives flattened the inter-annual growth variability, both in earlywood and latewood, and influenced the estimation of intra-annual radial growth variations. Characterizing the varying amount of extractives is of inter-disciplinary importance. The results in this study describe their occurrence and show that the radial variations in extractives could be highly detailed by simply using densitometry-based dendrochronology.     

The influence of extractives on the radiation stability of wood

Summary The critical dose above which a decrease in toughness of Western Red Cedar and Peroba wood, extracted with benzene-alcohol is noted, was determined to be approximately 0.5×10⁶ rad lower than that for the same non-extracted species. Investigations have shown that the presence of benzene-alcohol extractives in wood raises its radiation stability. This conclusion is supported by the fact that the toughness curve which generally falls with increasing doses of absorbed irradiation shows a steeper decrease for extracted than for nonextracted wood.     

Antifungal activity of Agapanthus africanus extractives

The ethanolic extract of the rhizomes of Agapanthus africanus showed antifungal activity. In bioassay guided fractionation, n-butanol fraction exhibited significant activity against human pathogens. A saponin, (25R)-spirost-7-en-2alpha,3beta,5alpha-triol-3-O-[alpha-L-rhamnopyranosyl(1-->2)-[beta-D-galactopyranosyl (1-->3)] beta-D-glucopyranoside (1), responsible for the antifungal activity and having MIC value of 15.6 microg/ml against Trychophyton mentagrophytes and Sporothrix schenekii, was isolated and identified as active constituent of the plant.     

Antimicrobial activity of extractives of Sarcocephalus coadunatus

The methanolic extracts and the fractions (petrol, dichloromethane, ethyl acetate, butanol) obtained from the leaves, seeds, stem and root barks of Sarcocephalus coadunatus exhibited a high level of broad spectrum antibacterial activity. The activity was more pronounced in the dichloromethane, ethyl acetate and butanol fractions of the leaves; ethyl acetate and butanol fractions of the seeds; dichloromethane fractions of the stem bark and the ethyl acetate fractions of the root bark. None of the fractions showed any antifungal activity.     

Antimicrobial activity of extractives of Solidago microglossa

The antimicrobial activity of the methanol extract from Solidago microglossa roots, essential oil from its aerial part and some isolated compounds was investigated. The oil exhibited concentration-dependent activity against all the tested bacteria and yeasts.     

Genetic variation of extractives in the wood of trembling aspen

Summary Thirteen clones of Populus tremuloides (Michx.) from central Alberta, Canada, were sampled to determine variation patterns within and among clones for benzene-alcoholwater extractives. Significant differences among clones were present; however, the broadsense heritability for extractive content was low (0.13). Extractive content was highest near the pith and decreased outward. Genetic and phenotypic correlations between rate of growth (ring widths) and extractive content indicated that faster growing clones or trees tend to exhibit less benzene-alcohol-water extractives.The authors would like to thank the Forest Development Research Trust of the Alberta Department of Energy and Natural Resources, and Natural Science and Engineering Research Council of Canada (NSERC A 1281, NSERC-SPF 00291) for financial support     

Chemistry and ecotoxicity of heat-treated pine wood extractives

Pine (Pinus pinaster) wood was heat-treated in an autoclave for 2?C12?h at 190?C210°C. Hemicelluloses were the first compounds affected by the treatment. In general, the sugar decrease was higher for arabinose and galactose followed by xylose and mannose. Lignin started to degrade for small mass losses but at a slower rate than hemicelluloses, and cellulose only degraded significantly for severe treatments. Almost all of the original extractives disappeared, and new compounds arose such as anhydrosugars and phenolic compounds. The compounds that might leach from heat-treated wood were mainly those identified in the water and ethanol extracts, all of which were not harmful at the existing concentrations, thereby reinforcing the wood heat treatment as an environmental benign process.     

Fate and influence of western red cedar extractives in mechanical pulping

The methanol extractives from western red cedar mechanical pulps were found to be radically different in composition to the extractives obtained from the heartwood. The major heartwood extractive components, the tropolones and lignans, were not present in the extractives from the pulps. However, the proportion of a brown polymer doubled. The low and high molecular weight methanol extractives components from the pulps were separated using methyl tert-butyl ether. The low molecular fraction contained mostly guaiacyl-based compounds with dihydroquercetin, thujic acid, 3-hydroxy-1-(4′-hydroxy-3′-methoxyphenyl)-2-oxopropane and 4-ethyl-2-methoxy-6-hydroxyphenol being positively identified. The brown polymeric portion had molecular weights ranging from 1,000 to 10,000. Infrared analysis indicated that the polymers were formed from lignans. Examination of the changes in diffuse reflectance UV-visible and infra red spectra of the pulps on extraction with methanol, suggested that the colour resides in insoluble polymers formed from plicatic acid/plicatin during refining. Received 18 December 1998     

The effect of methylbenzene/ethanol ratios on chemical composition of extractives from Eucalyptus grandis

Chemical components of methylbenzene/ethanol extractives of Eucalyptus grandis were identified by GC/MS and different methylbenzene/ethanol solutions (9/1,4/1,2/1,1/1,1/2) were used to describe their distinctions.The distributions of micro particles in each extractive were studied simultaneously.The results show that there were significant differences between the various extractives,although the extractives were essentially the same,i.e.,alcohols,alkanes,esters and acids.With the increase of ethanol composition in the solutions,the total amount of extractives increased;in solvent with higher amounts of ethanol,some acidic structures or acids,such as glutaric acid,could be seen.An investigation of micro particles indicated that the distribution of particle size of each sample did not change greatly between the solutions.A slight decrease in size was seen with the reduction in the amount of methylbenzene.