Einsatz von Faserstoffen aus chemisch-thermisch aufgeschlossenen, gebrauchten Faserplatten zur Herstellung von mitteldichten Faserplatten (MDF)

Ohne Zusammenfassung     

Formaldehydabgabe von mitteldichten Faserplatten (MDF) unter hydrolytischen Bedingungen

Subject Using a modified version of the WKI-bottle-method formaldehyde release from pine-MDF bonded with TF- and MUPF-resin was measured after 3, 24 and 48 hours at 40°C, 50°C and 60°C.The results reveal: With increasing time and increasing temperature the release of formaldehyde increased. Boards bonded with MUPF-resins emanated at 50°C and 60°C, in general, more formaldehyde than those bonded with TF-resins. From the preliminary results it can be assumed that MUPF-resins are less resistant to hydrolysis than TF-resins at high temperatures.

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Die Förderung des Forschungsprojektes erfolgte teilweise durch die AiF über die DGFH.     

Abbau von UF-Harzen beim TMP- und CTMP-Aufschluss von mitteldichten Faserplatten (MDF)

Thermo-mechanical (TMP) and chemo-thermo-mechanical pulping (CTMP) of UF-bonded MDF induce considerable degradation of the UF-resin in the board and lead to a conspicuous increase in the content of water extractives of the fibres. Moreover, the water extractives of the fibres have a higher pH-value and a lower buffering capacity as well as higher acetate and formate ions content than the extractives of the original board. However, the lignin content seems rather to increase than to decrease. This is possibly due to reaction between lignin and formaldehyde from the resin.     

Benetzung von TMP und CTMP aus Holz sowie gebrauchten mitteldichten Faserplatten (MDF)

TMP (thermo-mechanical pulps) and CTMP (chemo-thermo-mechanical pulps) were made from pine wood and recycling MDF, which has been prepared from pine wood too. The fibres were tested for their wettability using the method developed by Roffael et al (2002). The results reveal that TMP are much less wettable in comparison to CTMP from the same wood. Moreover, fibres made from UF-bonded MDF by the TMP- and CTMP-process are of much higher wettability compared to TMP and CTMP prepared directly from wood. No significant difference in the wettability between TMP and CTMP from UF-bonded MDF was detected. This behaviour has been attributed to the fact that the UF-resin in MDF degrades during thermohydrolytic pulping leading to the formation of ammonia and free urea. Therefore, pulping of UF-bonded boards takes place under chemo-thermo-mechanical conditions (CTMP).     

Die Prüfung von Faserplatten

Zusammenfassung Es wird ein kurzer überblick gegeben über die wichtigsten Prüfverfahren, die Aufschlu? geben über die Güte und auch Verwendungsf?higkeit von Faserplatten. Hervorgehoben wurden Untersuchungen, die sich für Betriebsüberwachung mittels einfacher Einrichtungen eignen.     

Die Ausbeute bei der Herstellung von Faserplatten

Zusammenfassung Die Ausbeutezahlen zeigen, da? bei der Verarbeitung von Holz auf Faserplatten eine sehr wirtschaftliche Ausnutzung dieses Rohstoffes erzielt wird. Sie liegt wesentlich über den Ausbeuten, die sich in der Sperrholz- und Schnittholzindustrie ergeben und verbessert durch Verarbeitung eines Teils ihrer Abf?lle auch deren Holzbilanz. Noch günstigere Zahlen werden natürlich in L?ndern oder Anlagen erreicht, die Rundholz als Ausgangsstoff verwenden, wie dies vielfach in den nordischen L?ndern und USA. der Fall ist. Verschiedene bisher in das Schrifttum eingegangene Ausbeutezahlen erscheinen demgegenüber ziemlich willkürlich. Sie lassen vor allem Angaben über Holzart und -güte vermissen, sowie darüber, ob sie die gesamten Herstellungsverluste darstellen oder sich nur auf Teilvorg?nge beziehen.     

Zur Abgabe von flüchtigen Säuren aus mitteldichten Faserplatten (MDF)

Wood and wood-based panels emanate formic and acetic acid. The amount of acetic acid release is high in comparison to its concentration in cold water extracts of wood-based panels containing both formic and acetic acids. This is most probably due to the fact that formic acid is a stronger acid (pK_a 3.77) than acetic acid (pK_a 4.76). Insofar the dissociation of acetic acid is suppressed by the presence of formic acid and the undissociated acetic acid emanates in higher amounts than formic acid in the vapour phase.     

Einfluß von Holzaufschlußverfahren (TMP-, CTMP-Verfahren) und Aufschlußbedingungen auf die physikalisch-technologischen Eigenschaften von mitteldichten Faserplatten (MDF)

Ohne Zusammenfassung     

Mitteldichte Faserplatten (MDF) aus gebrauchten Oriented Strandboard (OSB)

Zusammenfassung Die Ergebnisse zeigen, dass durch den alkalischen Aufschluss von Oriented Strand Boards (OSB), die in den Mittelschichten PMDI und in den Deckschichen MUPF als Bindemittel enthalten, Fasern gewonnen werden, die bei der MDF-Herstellung zur Verringerung der Dickenquellung und zur Erhöhung der Querzugfestigkeit führen. Die Biegefestigkeit der MDF nahm bei Zusatz von 25% OSB-Recyclingfasern kaum ab. Erst bei einer Ersatzmenge von 50% verringerte sich die Biegefestigkeit von ca. 60 N/mm² auf rund 50 N/mm².

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Medium density fibre boards (MDF) from recovered oriented strand boards (OSB)

Fibres for medium density fibre boards (MDF) were made from oriented strand boards (OSB) bonded with PMDI in the core and MUPF in the surface. Chips from OSB were pulped with sodium hydroxide. The fibres obtained therefrom were used for partial substitution of fresh fibres in MDF. The preliminary results reveal that recycled fibres decrease the thickness swelling enormously and has also a remarkable positive effect on the internal bond strength as well. However, the use of higher amounts (50%) of recycled fibres negatively impacts the bending strength.

     

Chemische Eigenschaften von TMP und CTMP, hergestellt aus Kiefernholz und UF-Harz-gebundenen mitteldichten Faserplatten (MDF)

Thermo-mechanical (TMP) and chemo-thermo-mechanical pulps (CTMP) were prepared from pine wood and from UF-bonded MDF made from pine wood. For preparing TMP pine chips as well as UF-bonded MDF were digested under pressure at 170 °C. Thereafter, the digested chips and MDF were defibrated at 170 °C using a single disc refiner. CTMP was prepared from pine wood with 0.25% NaOH (based on dry wood) under the conditions set forth above. CTMP was also made from MDF under two conditions using 0.15% sodium hydroxide (% based on dry MDF) and a mixture of sodium sulphite (1%) and sodium hydroxide (0.25%). The pulps show distinct differences in their properties: TMP from UF-bonded MDF shows lower extractive content in cold and hot water, lower pH-value and higher buffering capacity towards alkali of the cold water extractives than the CTMP counterpart. Moreover, CTMP prepared by using sodium hydroxide alone as a pulping agent increases the content of formate and acetate ions in the cold water extractives. The use of a mixture of sodium sulfite and sodium hydroxide as a pulping agent decreases, however, significantly the content of formate and acetate ions in the cold water extractives. This may be due to the buffering action of sodium sulfite. In general, CTMP decreases the formaldehyde release of the fibres, as measured by the flask method. In presence of sodium sulfite as a pulping agent for recycled MDF, the formaldehyde release is slashed to almost 30% of its original value. The formaldehyde release of CTMP from UF-bonded boards seems to be in the same range as that of TMP from virgin wood.      

Einfluß der Trocknung von thermo-mechanischem (TMP) und chemo-thermo-mechanischem Holzstoff (CTMP) der Fichte auf die physikalisch-technologischen Eigenschaften von daraus hergestellten mitteldichten Faserplatten (MDF)

Ohne Zusammenfassung     

Das Verhalten von Faserplatten gegen holzzerstörende Pilze

Zusammenfassung Die Versuche geben einen allgemeinen überblick über das Verhalten von Faserplatten, vorzugsweise von Holzfaserplatten, und zwar von D?mmplatten und von Hartplatten, gegen verschiedene holzzerst?rende Pilze. Es wurden dabei auch Platten berücksichtigt, denen verschiedene Abwehrstoffe einverleibt waren. Auf den Einflu? der holzzerst?renden Pilze bei der praktischen Anwendung der Platten wird eingegangen.     

Über die Eignung von thermo-mechanischem (TMP) und chemo-thermomechanischem (CTMP) Holzstoff aus Buchen- und Kiefernholz für die Herstellung von mitteldichten Faserplatten (MDF)

Medium density fibreboards (MDF) were made from thermomechanical (TMP) and chemo-thermo-mechanical pulps (CTMP) derived from pine wood. As a binder a melamine reinforced urea formaldehyde resin (UF-resin) and diisocyanate polymers (PMDI) were applied. The mechanical-technical properties of the boards as well as some of their chemical properties were evaluated. The results of the investigation led to the following conclusions: MDF from CTMP showed in general higher mechanical properties (bending strength) compared to MDF from TMP. Moreover, the formaldehyde release of the CTMP-boards was lower. This may be due to the formaldehyde scavenging properties of the used pulping chemicals during the process of CTMP. MDF from CTMP showed much higher release of acetic acid compared to MDF from TMP. This is likely to higher deacetylation of the wood substance during CTMP process compared to the TMP technique.     

Zur Hydrophobierung von mitteldichten Faserplatten (MDF) mit Paraffinen Teil 3: Methoden zur Erfassung der Hydrophobierung von Faserstoffen durch Paraffine

The first part of this publication deals with the influence of chain length and amount of n-paraffins as well as the chemical composition of technical paraffins (chain length and amount of n- and iso-alkanes) on the thickness swelling, water absorption and internal bond strength of MDF (Roffael et al. 2005a). The second part reports on the effect of resination process (blender- and blowline-technique) as well as different methods of adding paraffin dispersion in both resination processes on paraffin sizing of MDF (Roffael et al. 2005b). This paper describes two different methods for evaluation of paraffin sizing on thermo-mechanical pulps (TMP). In one method the sizing degree was measured by determining the wettability of handsheets made from paraffin sized TMP as previously described by Roffael et al. (2002). In the other method paraffin sizing of fibres was determined by using the well known Cobb test which quantifies the water absorption of handsheets. Industrial produced TMP of Scots pine was resinated in the blender by using an MUF-resin together with n-paraffin dispersions of different chain length (C₂₀, C₂₈, C₃₆). The MUF-resin was not cured. Handsheets were manufactured from the MUF-resinated TMP and kraft pulp (ratio 1:1). On using 0.25% n-paraffin (based on dried fibres) wettability of handsheets decreased with increasing chain length of n-paraffins (C₂₀ to C₃₆). Also the results of the Cobb test (Cobb₃₀) showed that water absorption of handsheets decreased by using n-paraffins with higher chain length. Further investigations were carried out on handsheets, manufactured from kraft pulp and TMP resinated in the bowline (ratio 1:1). Within the blowline-process three technical paraffins with different chemical composition were applied in two different ways. In one case the paraffin dispersion was added to the chips before thermo-mechanical pulping. In the other case the paraffin dispersion was added to the fibres together with the resin in the blowline. Results of wettability and of water absorption of handsheets (Cobb test) showed that adding paraffin dispersion to the chips prior to thermo-mechanical pulping leads to more effective paraffin sizing than applying the paraffin dispersion to the fibres together with the resin in the blowline. Moreover, the influence of type of softwood (Scots pine and Norway spruce) on the paraffin sizing of TMP was investigated. Irrespective of the chemical composition of the used technical paraffins it was found, that handsheets manufactured from TMP of Norway spruce showed better wettability and higher water absorption than handsheets manufactured from TMP of Scots pine. The lower water absorption of handsheets manufactured from TMP of Scots pine may be due to the higher content of hydrophobic extractives in pine.     

Vergleichende Untersuchungen an mittelharten Faserplatten (MDF) und Spanplatten

Mechanical and physical properties of commercial medium density fiberboard (MDF) and particleboard were determined and compared. The investigation showed that bending strength and face strength for MDF were considerably higher than corresponding particleboard properties. Concerning internal bond strength and screw holding ability no remarkable differences were found between the two board types. Medium density fiberboard showed lower hygroscopicity and thickness swelling but higher linear expansion than particleboard. Both board types were found to have higher bending strength and lower linear expansion parallel rather than perpendicular to feeding direction. Furthermore MDF showed lower surface roughness than particleboard.     

Über die Eignung von thermo-mechanischem und chemo-thermo-mechanischem Holzstoff (TMP und CTMP) aus Buchen- und Kiefernholz für die Herstellung von mitteldichten Faserplatten (MDF)

A condensed review on the state of the art of the producton of medium density fibreboards is given. Thereafter, results of investigations on pulping beech and pine wood under differnet conditions according to the TMP- and CTMP-process are presented. The pulps derived from both wood species were analysed for some of their physical and chemical properties. The results reveal: Within the TMP- and CTMP-process, both the chemical and biological oxygen demand increase with increasing pulping temperature. In general, however, waste water from the CTMP-process has higher chemical and biological oxygen demand. The CTMP-process seems to be milder than the TMP-process as it leads to pulps with higher fibre length, especially in case of beech. The content of acetyle groups is much lower in CTMP-pulps than in TMP-pulps, CTMP-pulps emit also more acetic acid than TMP-pulps. With increasing pulping temperature the pH-value decreases and the buffering capacity towards alkali increases. MDF were prepared from TMP- and CTMP-pulps and their properties were evaluated. The results are included in the next parts of the publication.     

Über die Abgabe von Ameisen- und Essigsäure aus Deck- und Mittelschichten von aus CTMP hergestellten mitteldichten Faserplatten (MDF)

Volatile acids (formic and acetic acid) from the surface and core layers of medium density fibre-boards (MDF) made from chemo-thermo-mechanical pulps (CTMP) were measured following the flask method technique. The results indicate explicitly that the emission of acids from the core layer is much higher than from the surface layer. The results are indicative of the influx of the steam distillable volatile acids from the surface layers to the core layer during pressing operation.