Wood which underwent a relatively mild thermal treatment according to a one-step process leading to improved dimensional stability and improved timber performance was extracted with organic solvents to determine the presence of potentially toxic compounds produced by the thermal treatment. The extractives were examined by GC-Mass spectrometry as well as by 13 C NMR to determine which type of loose chemical compounds were produced by the thermal treatment. The formation of some toxic polynuclear aromatic hydrocarbons derivatives of phenantrene as well as other classes of polyaromatics compounds was detected. It is most likely that the presence of all such compounds contributes, perhaps to a relatively substantial extent, to the reported resistance of heat treated timber to fungal and other biological attack. Other allegedly nontoxic compounds due to wood constituents degradation were also found, mainly the by-products of lignin pyrolysis. The extent of toxic and non-toxic compounds in the heat treated wood were not quanti®ed, but it can be stated that their proportion appears to be quite small. The lack of quanti®cation of the concentration of these products does not allow to ascertain if the ®nal product is toxic or not, and to what extent. Nonetheless, the amount of polynuclear aromatic hydrocarbon-type derivatives should be quanti®ed and related to the type of heat treatment process undertaken before assigning to this type of wood treatment a completely clean health safety label. Hitzebehandeltes Holz: Mo Ègliche toxische Nebenprodukte und Ausmaû des ZellwandabbausRelativ milde Hitzebehandlung mit einem Ein-SchrittVerfahren fu Èhrte zu verbesserter Dimensionsstabilita Èt und verbessertem Schnittverhalten. Dieses Holz wurde mit organischen Lo Èsemitteln extrahiert um mo Ègliche toxische Nebenprodukte des Verfahrens zu bestimmen. Zu diesem Zweck wurden die Extrakte mittels GC-MS und 13 C NMR untersucht. Einige toxische polykondensierte Aromaten vom Phenantrentyp und andere Polyaromaten wurden gefunden. Es ist mo Èglich, daû diese zur bekannten Widerstandsfa Èhigkeit des hitzebhandelten Holzes gegen Pilze und andere Mikroorganismen beitragen. Gefunden wurden auch andere, vorgeblich nicht-toxische Aubbauprodukte der Holzkomponenten, insbesondere aufgrund der Ligninpyrolyse. Die Substanzen wurden nicht quantitativ bestimmt; ihr Anteil ist jedoch sehr gering. Daraus kann man allerdings nicht schlieûen, ob diese Produkte tatsa Èchlich toxisch sind oder nicht. Denn dazu mu Èûten diese Abbauprodukte quanti®ziert werden und den verschiedenen Methoden der Hitzebehandlung zugeordnet werden, bevor ein Gesundheitsrisiko ausgeschlossen werden kann.
ABSTRACT:The variation of leather color as a function of aging time on prolonged irradiation with UV light of the leather produced by tanning with different polyflavonoid and hydrolyzable vegetable tannins is reported. A predictive model and two equations for the variation of leather color as a function of UV-irradiation time and as a function of the different vegetable tannins used was also established. This technique appears to describe well the overall phenomenon of oxidation and color change in situ observable in vegetable-tanned leathers. The variation of leather color as a function of aging time on prolonged irradiation with UV light of the leather produced based on different vegetable tannins was found to be composed of two main effects: The first one of these is the darkening reaction of the leather. This is due to the formation of quinones on the phenolic structure of the vegetable tannin. The second one is the leather-lightening reaction due to the photodegradation of the system. These two phases were equated and correlated with the radical uptake reaction and radical stabilization/decay reaction observed by ESR for UV-irradiation of pure tannin in the solid form and of the leather produced using the same. Thus, correlation among the antioxidant capability of tannins in the solid form, their antioxidant capability once included in the leather, and the color variation (darkening and lightening) of leather by colorimetry was established.
Glue-lines in boards made of wood particles using high moisture tolerance tannin-based adhesives were observed to present the unusual behaviour of producing a melting effect of the wood cell walls directly in contact with the adhesive. The high moisture content of up to 29% used in the preparation of these exterior grade particleboard and OSB industrial panels at standard pressing times causes considerable flow of the amorphous lignin and hemiceUuloses in the wood directly in contact with the adhesive leading to a composite, compact interphase in which almost loose wood fibers are drowned in a hardened adhesive matrix. In this interphase the anatomical characteristics of the wood cell walls appear to be lost. This considerable flow is apparently due to the marked decrease of the glass transition temperature of hemicelluloses and lignin at the very high moisture contents used. This effect was replicated in boards prepared with a synthetic MUF adhesive using also a moisture content level much higher than what normally this resin is capable of tolerating by just lengthening considerably the pressing time used. Verbesserte Viskoelostizit~t von Leimfugen durch feuchtetolerante hitzeh~rtende KlebstoffeOSB-Platten wurden mit Hilfe hoch feuchtetoleranter Kleber auf Tanninbasis hergestellt. An den Leimfugen zeigte sich die ungew6hnliche Eigenschaft, daff die unmittelbar an den Kleber grenzenden Zellw/inde Schmelzerscheinungen aufwiesen. Die hohe Feuchte yon bis zu 29% in diesen Industrieplatten fiir Auffenverwendung verursacht bei Standard-Preffbedingungen einen betr~ichtlichen Fluff yon amorphem Lignin und Hemicellulosen im Holz unmittelbar neben dem Kleber. Dadurch werden die zum Tell aufgelockerten Fasern mit dem aush/irtenden Kleber getr/inkt und bilden so einen kompakten Werkstoff. In dieser Zwischenschicht scheinen die anatomischen Holzstrukturen aufgel6st zu sein. Verursacht wird dies offensichtlich durch eine stark herabgesetzte Glasumwandlungstemperatur des Lignins und der Hemicellulosen. Derselbe Effekt tritt auch bei MUF-Platten auf, wenn Holzfeuchten eingesetzt werden, die normalerweise nicht toleriert werden, die aber durch betr~ichtlich verl/ingerte PreSzeiten iiberspielt werden k6nnen.
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