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Einfluss des Prüfverfahrens auf die Beurteilung der Feuchtbeständigkeit Tannin-Formaldehydharzgebundener MDF
: Boehme, C.

MDF-Magazin. Supplement zu Holz-Zentralblatt (2002), pp.32-36
Journal Article
Fraunhofer WKI ()

The Wilhelm Klauditz Institute of Wood Research (WKI) in Braunschweig, Germany, tested the wet tensile strength perpendicular to surface of tannin formaldehyde resin-bonded MDF in accordance with Z-9.1-234 (based on the particle board standard). The tests were conducted on three industrially manufactured board specimens measuring 7.8 mm, 11.8 mm, 13 mm, 14.8 mm and 22 mm thick supplied by Kronospan GmbH in Sandebeck, Germany. With few exceptions the tests resulted in relatively low wet strength values in spite of a high level of dry tensile strength perpencular to surface. This was due to microstructural damage with cracking, which was caused during the test-in-duced water absorption process but does not arise in practice. Such test-induced microstructural damage did not occur, however, when the specimens were first subjected to vacuum pretreatment in order to accelerate the saturation process. The strength values were then found to be up to 3 times higher. It is thus proposed to always conduct these tests with advance vacuum pretreatment. Temperature and moisture have the same effect on the stability of the gluing when vacuum pretreatment is performed. In the test of moisture resistance in accordance with the European standard for MDF the specimen is stored in the hot water without a yoke being glued on first. In this case there were no signs of microstructural damage with cracking. Advance vacuum pretreatment resulted in a relatively small increase of the strength values. It is proposed to use this method as well for the testing of tannin formaldehyde resinbonded MDF in accordance with 7-9.1-234.