C. Behn

On the formaldehyde release of wood particles

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.ZusammenfassungDie 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.

Influence of fibre preparation method and wood species on the VOC-emissions from MDF boards

Abstract Emission of volatile organic compounds (VOCs) from medium density fibreboards (MDF) containing different proportions of softwoods (SW) and hardwoods (HW) was evaluated. The results reveal that decreasing the proportion of HW in MDF elevates the emission of terpenes and aliphatic aldehydes. The pulping method (TMP, CTMP) seems to have no significant influence on the emission of terpenes or aldehydes from MDF. On using the TMP process, the emission of acetic acid elevates remarkably with increasing the amount of HW in the boards. Compared with the TMP process, the CTMP process leads to a decrease of acetic acid emission at 40°C with more than 15% at 35% HW content of the boards and 40% at 65% HW content.

On the influence of binder content in particleboards bonded with resins of high and low molar ratio on the formaldehyde release measured by the perforator method

A comprehensive literature survey and the results of investigations clearly show that the influence of resin level in particleboards on the perforator value (EN 120) depends on the molar ratio of the resin used as a binder. In case of high molar ratio resins (F:U 1.6:1) increasing the binder content in the boards leads to an increase in the perforator value of the boards. In contrast, boards bonded with very low molar ratio aminoplastic resins with molar ratio F:U of 1:1 (F:NH2 0.5:1) or even lower do not show any noticeable increase in the perforator value on raising the binder level. On the contrary, the measured perforator values may sometimes decline due to increase in the resin content in the boards. The perforator test seems to include two main processes taking place alongside each other: the physical extraction of free formaldehyde and the chemical hydrolysis process of the resin itself, induced by the moisture content of the boards. In case of low molar ratio resins, particularly at very low molar ratios (F:U 1:1 or even lower), free urea may also be present in the resin or added to the resin as a scavenger. Urea seems to react with extracted formaldehyde at high temperature during the extraction process. This lowers the perforator value without necessarily decreasing the emission at ambient conditions. Insofar, inextricably intertwined chemical processes seem to unfold during the extraction process. Additionally, the results show that subtle differences in the perforator value in the very low formaldehyde emission region may remain without noticeable impact on the emission measured by the chamber method (EN 717-1).ZusammenfassungDie Literaturauswertung und eigene Untersuchungsergebnisse lassen deutlich werden, dass das Molverhältnis des verwendeten Harzes in Holzspanplatten Einfluss auf die Beziehung zwischen Bindemittelgehalt und Perforatorwert (EN 120) nimmt. Im Bereich hohen Formaldehydgehalts im Harz bzw. hohen F:NH2-Verhältnisses steigt – Literaturangaben entsprechend – der Perforatorwert mit zunehmendem Bindemittelgehalt in der Platte an, bei Verwendung von Harzen mit einem Molverhältnis F:U von 1:1 oder darunter bleibt der Perforatorwert in Abhängigkeit vom Bindemittelgehalt der Platte entweder unverändert oder nimmt sogar geringfügig ab. Während des Prozesses der Formaldehydabgabebestimmung aus Holzspanplatten nach der Perforatormethode scheinen folgende Vorgänge stattzufinden: Zum einen die physikalische Extraktion des Formaldehyds und zum anderen eine Hydrolyse des verwendeten Harzes, induziert durch die Feuchte der hergestellten Platten. Die Hydrolyse scheint zur Bildung von Harnstoff und Harnstoffderivaten zu führen, die mit dem extrahierten Formaldehyd reagieren. Der Formaldehyd kann in der Platte auch mit Harnstoff, der als Formaldehydfänger zugegeben wird, reagieren. Das Ausmaß dieser Reaktionen scheint vom Molverhältnis des Harzes abzuhängen. Geringe ermittelte Unterschiede im Perforatorwert können deshalb ohne Bedeutung für die Emission in der Prüfkammer nach EN 717-1 bleiben.

Influence of pulping technology on the release of formaldehyde and volatile organic acids from oak fibres and medium density fibreboards (MDF) prepared therefrom

Chemo-thermomechanical pulps (CTMP) from oak wood release more formic and acetic acid than thermomechanical pulps (TMP) made from the same wood. In contrast, the emission of formaldehyde from CTMP is lower than that from TMP. Medium density fibreboards (MDF) made from TMP and CTMP emit less formic and acetic acid compared to the fibres, from which they are made. The formaldehyde release from MUF-bonded MDF made by using TMP and CTMP is higher than from the fibres (TMP and CTMP) used to make the boards.

On the release of formic and acetic acid from surface and core layers of medium density fibreboards (MDF) made from CTMP.

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.

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.

Über die Abgabe von Ameisen- und Essigsäure aus Deck- und Mittelschichten von aus CTMP hergestellten mitteldichten Faserplatten (MDF)@@@On the release of formic and acetic acid from surface and core layers of medium density fibreboards (MDF) made from CTMP

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.

Influence of aging of UF-bonded particleboards on the release of volatile organic acids.

ZusammenfassungDie Abgabe an flüchtigen Säuren von UF-Harz gebundenen Kiefernholzspanplatten wurde nach der Herstellung sowie nach einer Alterungsdauer von 13 Jahren bestimmt. Die Ergebnisse lassen erkennen, dass die Abgabe an Ameisensäure durch die Alterung der Platten deutlich abgenommen hat, während die Abgabe an Essigsäure signifikant zugenommen hat. Auf diesen Zusammenhang scheint der bei der Plattenherstellung verwendete Härtertyp (Ammoniumnitrat, Ammoniumchlorid) und die eingesetzte Härtermenge keinen entscheidenden Einfluss zu nehmen. AbstractThe release of volatile organic acids from UF-bonded particleboards made from Scots pine was assessed after production as well as after aging for 13 years. The results reveal that aging significantly decreased the release of formic acid and substantially increased the emanation of acetic acid. The change in the release of volatile acids by aging seems to be highly independent of the hardener type used (ammonium chloride, ammonium nitrate) as well as of the amount of added hardener.