In the recent past, increasing attention has been paid to the use of natural adhesives as a binder in the wood-based panel industry. Nowadays, two German companies are using Quebracho tannin and Wattle tannin for the production of particleboards and medium density ®berboards (MDF), respectively. To date no serious attention has been given to bond ®berboards using tannin derived from spruce bark. Results of research work on the use of spruce tannin as a binder for medium density ®berboards carried out in the last two years are presented. The results reveal that spruce tannin can be used to partially substitute Quebracho tannin in MDF up to about 60%. Such boards still meet the speci®cation of moisture resistant MDF (according to EN 319 and EN 321). Moreover, spruce tannin can be used to 100% as a binder for the production of MDF for indoor use (type MDF EN 622-5).
Fichten-Tannin alsKleber fu Èr Spanplatten und MDF Seit kurzem wird natu Èrlichen Klebern als Bindemittel fu Èr Spanplatten auch in der Industrie erho Èhte Aufmerksamkeit gewidmet. Zur Zeit verwenden zwei deutsche Firmen Quebracho-und Akazientannin fu Èr die Produktion von Spanplatten und MDF. Bisher wurden Tannine aus Fichtenrinde hierfu Èr noch nicht ernsthaft in Betracht gezogen. Die vorliegende Arbeit stellt Ergebnisse eines Forschungsprojektes zur Verwendung von Fichtentannin fu Èr MDF vor. Mit Fichtentannin kann bis zu 60% des Quebrachotannins in MDF ersetzt werden. Solche Platten erfu Èllen die Richtwerte der EN 319 und 321 fu Èr die Feuchteresistenz. Daru Èberhinaus kann bei Platten fu Èr Innenverwendung (Typ EN 622-5) bis zu 100% Fichtentannin verwendet werden.
IntroductionUtilization of bark is one of the utmost pressing problems facing the wood industry. The quantities of bark available are substantial, since approximately 10±15% of the volume of every log consists of bark. In Germany, about 2 million tons of bark are produced annually. Dealing with such enormous quantities of bark has created thorny disposal problems, particularly with the outcome of more stringent environmental regulations regarding air and water pollution enacted in the recent past. It has become imperative that the industry no longer considers bark as a waste. Bark is a low cost material with a limited market for diverse applications such as a high-quality mulch or as energy source. However, the current uses do not require bark in suf®cient quantities to consume the supply available.Bark and heartwood of limited wood species contain large quantities of water soluble extractives of polyphenolic nature suitable as a starting material for the production of adhesives. The extractives are mainly concentrated in the inner layer of the bark (Fig 1). Figure 2 shows the extractable amounts by water at about 100°C from different barks and wood species. In general the hot water extract of bark or heartwood comprise about 60±80% of polyphenolic tannin polymers as measured by the so called``hide powder'' method. The remainder is a mixture of many polymeric and monomeric compounds, such...
Summary
Thermomechanical (TMP) and chemo-thermomechanical pulps (CTMP) were prepared from spruce under different pulping conditions. The fibres were dried at 70 °C and medium density fibreboards (MDF) were made therefrom in pilot plant scale using urea-formaldehyde resins as a binder. The results of testing the physical-mechanical properties reveal that the pulping temperature has a significant influence on the thickness swelling and water absorption of the boards. MDF prepared from fibres produced at high pulping temperature (180 °C) generally show lower thickness swelling and water absorption than MDF made from fibres produced at low pulping temperature (140°C and 160 °C). However, high pulping temperature may have a negative effect on the internal bond strength of the boards. In general, CTMP leads to MDF with higher internal bonding strength compared to those derived from TMP. In addition, the influence of different drying conditions (150 °C and 170 °C) of TMP and CTMP on the physical-mechanical properties of MDF was assessed. MDF made from CTMP showed lower thickness swelling when dried under high temperature.
The emission of formaldehyde from softwood particles, as measured by the flask method (EN 717-3), depends highly on the particle size. Therefore, no definite value for the formaldehyde release from wood can be given.
Die Formaldehydabgabe von HolzspänenZusammenfassung Die Formaldehydemission von Nadelholzspänen verschiedener Größe wurde nach der Flaschenmethode (EN 717-3) bestimmt. Es zeigte sich, dass die Formaldehydabgabe sehr stark von der Partikelgröße abhängt. Demzufolge kann für die Holzspäne kein definierter Formaldehydabgabewert angegeben werden.
The paper describes a method to measure the wettability of thermomechanical pulps (TMP) from wood. Handsheets were made from pine TMP produced at different pulping temperatures (140 °C, 160 °C and 175 °C). A coloured waterdrop (0.1% aniline-blue solution) is added on the surface of a handsheet. The wettability is defined by the time elapsed from applying the waterdrop on the handsheet until its total penetration. The results reveal that pulping temperature influences the wettability of the TMP. The wettability of the TMP decreases with increasing pulping temperatures during the refining process
Cold water extracts from pulps produced by the chemo-thermomechanical technique (CTMP process) contain higher amounts of formate and acetate ions compared to cold water extracts from pulps produced by the thermo-mechanical process (TMP process). The CTMP shows a higher emission of acetic acid than the corresponding TMP. However, the release of formic acid is lower than that from TMP due to the higher pH-value of CTMP. Furthermore, the release of formaldehyde from CTMP is lower than that from TMP due to Cannizzaro reaction catalysed by alkali. Moreover, binderless fibreboards from CTMP are significantly lower in the formaldehyde release compared to binderless boards from TMP. The use of MUF-resin increases the formaldehyde release of the boards from TMP and CTMP. Furthermore, MUF-bonded boards from TMP and CTMP are of higher pH-value and lower emission of formic and acetic acid
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