Redelf Kraft

Einfluss der thermischen Modifizierung von Holz auf das Wasserrückhaltevermögen (WRV-Wert)

Thermal modification of wood (ash, beech, spruce) leads to a remarkable decrease in the Water Retention Value (WRV). In case of beech wood the WRV-value decreased after immersion in water for 72 h from 55.5% to 40.5% (about 27%) and in case of spruce wood from 49.3% to 34.5% (about 30%). The decrease in the WRV of ash wood was relatively low (about 19%). The WRV-method seems to be useful to follow up the process of thermal modification of wood.

Extrahierbarer Harnstoff in MDF, hergestellt nach dem Blowline- und Blender-Verfahren

Extractable urea was determined in water extractives of medium density fiberboards (MDF), prepared using the blowline- and blender-technique. The results reveal: higher amounts of urea are extractable from boards resinated in the blowline than in the blender. Therefore, it seems that less cross-linking of the resin takes place in the blowline than in the blender.

Zur quantitativen Bestimmung von Harnstoff mittels Indophenolmethode (Berthelot-Reaktion)

ZusammenfassungDie Indophenolmethode (Bergmeyer 1983) wird zur quantitativen Bestimmung des Harnstoffes nach dessen enzymatischen Abbau zu Ammoniumionen angewendet. In diesem Zusammenhang wurde untersucht inwieweit Harnstoffderivate, die bei der Hydrolyse von Harnstoffformaldehydharzen entstehen können, mit erfasst werden und die Messergebnisse beeinflussen. Untersuchungsergebnisse deuten darauf hin, dass eine quantitative Harnstoff- bzw. Stickstoffbestimmung durch Harnstoffderivate beeinflusst wird, insofern ist die Methode querempfindlich.AbstractUrea in water extracts of wood-based panels can be measured quantitatively using the indophenol-method after enzymatic hydrolysis by the enzyme urease. The results reveal, however, that urea derivatives like dimethylolurea, a degradation produkt of UF-resins may set urea free due to hydrolytic degradation and leads to higher values. Therefore, the method is prone to error.

Extractable urea in MDF prepared using the blowline- and blender-technique

Extractable urea was determined in water extractives of medium density fiberboards (MDF), prepared using the blowline- and blender-technique. The results reveal: higher amounts of urea are extractable from boards resinated in the blowline than in the blender. Therefore, it seems that less cross-linking of the resin takes place in the blowline than in the blender.

Effect of some treatments on emission of volatile organic compounds (VOC) from chips used in pellets making processes

Abstract Emission of volatile organic compounds (VOC) from wood during processing to pellets – significance of wood extractives. Cellulose, hemicelluloses and lignin are the main components of the cell wall in wood. Moreover, wood contains different amounts of extractives, depending on the wood species. Extractives in softwoods play an important role during processing of wood to different wood products. This work studies the influence of storage on the change of extractives as well as on the emission of monoterpenes (primary emission) and aliphatic aldehydes, as degradation products of fats and fatty acids (secondary emission). In case of pine wood storage for 2 days at 80°C proved to be more efficient in the reduction of emissions of terpenes and aldehydes than 4 weeks at 40°C. Quantitative differences between pine (Pinus sylvestris) and spruce (Picea abies) wood chips in the emission were evaluated and discussed. Pinewood emits about 10 times higher amounts of terpenes and aldehydes than spruce wood. The results indicate that the intense of change in primary and secondary emissions due to storage depends on the wood species as well as on the boundary conditions under which storage is carried out. In general, storage at high temperature (80°C) is much more effective than at low temperature (40°C). The results also reveal that removal of wood extractives from pine wood by extraction with ethanol-cyclohexane or treatment with sodium hydroxide decreases the emission of primary and secondary volatile organic compounds drastically. Nevertheless, after such treatments minute amounts of volatile organic compounds are still detectable.

Storage-induced emissions from different wood species

Abstract In this study, the extractive contents and the storage-induced emissions from chips of Salix alba, Betula pendula, Populus tremula, and Alnus glutinosa are compared with emissions from Pinus sylvestris chips. Soxhlet extraction was performed, and carbon monoxide (CO) and O2 concentration in the gas phase as well as gas chromatography-mass spectrometry analysis of volatile organic compounds were analyzed. Pinus sylvestris showed the highest extractive content in the petrol ether fraction and emitted CO in the highest concentration. Salix alba, B. pendula, P. tremula, and A. glutinosa have lower extractive contents in the petrol ether fraction and the CO concentrations decreased in the headspace accordingly. The emission of aldehydes was lower in the case of woods with lower petrol ether contents (P. sylvestris, S. alba, and B. pendula), but the situation was not as clear for P. tremula and A. glutinosa. The origin of CO and aldehyde emissions is discussed in view of the possible oxidative degradation processes of lipids and terpenes.

Zum thermohydrolytischen Abbau von UF-Harzen in Holzspanplatten

ZusammenfassungÜber den thermohydrolytischen Abbau von UF-gebundenen Holzspanplatten ist umfangreiches Schrifttum bekannt geworden (vgl. z. B. Fleischer 2001, Kirchner und Kharazipour 2002). Einige der entwickelten Verfahren werden inzwischen in der einschlägigen Industrie praktiziert (Michanickl, Boehme1995). Durch den thermohydrolytischen Abbau der UF-Harze in Gebrauchtspanplatten entzieht sich ein Teil des UF-Harzes hartnäckig der Hydrolyse und verbleibt in den Hydrolyserückständen (vgl. Franke und Roffael 1998a, b).AbstractDuring thermal hydrolysis of UF-bonded boards more urea is dissolved than is equivalent to the molar ratio (F:U) in the used resin. Therefore, the molar ratio F:U of the resin in the hydrolysis residues increases.

Verringerung der Emission von Thermoholz durch nachträgliche Behandlung mit Ammoniak

ZusammenfassungThermisch modifiziertes Holz (TMT) gibt hohe Mengen an Aldehyden (Furfural und Formaldehyd) sowie an flüchtigen organischen Säuren (Ameisen- und Essigsäure) ab. Die Abgabe von Aldehyden und Säuren lässt sich mit Hilfe der Flaschenmethode (EN 717-3) bestimmen. Die Ergebnisse zeigen, dass die Emission an flüchtigen Säuren und Aldehyden durch nachträgliche Ammoniakbehandlung erheblich reduziert wird. Der pH-Wert der Absorptionsflüssigkeit im Flaschenverfahren erhöht sich durch die Ammoniakbehandlung. Dies ist ein Hinweis auf die Abpufferung der Säuren im Holz.AbstractThermally modified timber (TMT) emits a high amount of aldehydes (furfural, formaldehyde) and volatile organic acids (formic and acetic acids). The release of aldehydes and acids, as assessed by the flask-method (EN 717-3), can be reduced significantly by ammonia fumigation. The emission of formaldehyde is attenuated by more than 90%. Emission of furfuraldehyde decreased in most cases by more than 70%. The pH-value of TMT increased due to ammonia fumigation above the neutral point indicating buffering of the volatile acids.

Thermohydrolytischer Abbau von Mitteldichten Faserplatten

Mit dem Inkrafttreten der Altholzverordnung am 1.3.2003 erhalt die stoffliche und energetische Nutzung von gebrauchten Holzwerkstoffen eine hohe Umweltrelevanz. Im Rahmen eines Forschungsvorhabens uber die Nutzung von gebrauchten mitteldichten Faserplatten (MDF) als Rohstoff fur die Herstellung von neuen Holzwerkstoffen wurde der Einfluss der Thermohydrolyse auf mit Harnstoff-Formaldehydharzen (UF-Harzen) gebundene MDF systematisch untersucht.

Über den Einfluss des Bindemittels auf das Wasserrückhaltevermögen (WRV-Wert) von Recyclingfasern und Recyclingspänen

ZusammenfassungDer hydrophobierende Einfluss des in Gebrauchspänen und -fasern vorhandenen Bindemittels ist bekannt (vgl. Roffael und Schneider 1978, 1979). Erste Untersuchungsergebnisse deuten darauf hin, dass dieser Einfluss durch die ohne großen Aufwand durchführbare Messung des WRV-Wertes erfasst werden kann.AbstractThe hydrophobing influence of binders on the equilibrium moisture content (EMC) of wood and fibers is well known in the literature (Roffael und Schneider 1978, 1979). Preliminary experiments reveal, that this effect can be assessed by measuring the water retention value (WRV) of glued recycling fibers and chips.