An amino-alkyl siloxane oligomer as hydrophobation agent for particleboards used under high humidity conditions

In this study, an amino-alkyl siloxane oligomer was used as a hydrophobation agent in order to improve the behaviour of particleboards under moist and outdoor weathering conditions and to be compared to conventionally used paraffin waxes. Melamine-urea-phenol-formaldehyde (MUPF, 15.0 %) was used as adhesive and mixed with the hydrophobation agents at concentrations of 1, 3, and 5 % related to the dry particle mass. The siloxane oligomer improved the water-related properties (thickness swelling, water uptake, internal bond strength (IBS) and IBS after boil test) in comparison to a control without hydrophobation agent. It also tended to enhance bending strength, modulus of elasticity, and IBS compared to specimens containing wax. IBS after boil test was significantly higher at addition of 3 and 5 % siloxane than that of wax-added reference boards. Specimens with siloxane oligomer, however, displayed higher thickness swelling and water uptake than those with wax added. It is assumed that the siloxane oligomer is able to contribute to bonding via hydrogen and covalent bonds and particularly enhance wet strength, while waxes exclusively act by their non-polar nature and, thus, water repellent behaviour.