Heat & Humidity Resistance

In some applications such as kitchen furniture and sports shoes, adhesives have to stick firmly, even in very hot and humid conditions. Polyurethanes adhesives are the material of choice for such applications thanks to the heat and humidity resistance of the urethane bonding. For example, when submitted to a EN 204 standard test, used to classify non structural wood adhesives, many of the aliphatic isocyanates can lead to a D4 classification, which corresponds to adhesives submitted to extreme conditions. D1 Adhesives have to withstand a dry resistance of 10 MPa minimum. This corresponds to dry conditions such as interior furniture or decoration. D2 Adhesives should withstand a 3 hours immersion in water at 20°C, followed by drying and the test requires a minimum resistance of 8 MPa after drying. D3 Adhesives must withstand several cycles including several 4-day immersion in water at 20°C and then drying, and the requirements are: initial resistance 10 MPa, wet resistance 2 MPa, and after drying 8 MPa. These requirements correspond to outside windows and doors. D4 Adhesives should withstand several cycles including several 6-hour immersion in boiling water, and then drying. The minimum requirements are: initial resistance 10 MPa, wet 4 MPa and after drying 8 MPa. This is a very severe test which corresponds to extreme heat & humidity conditions: outside building parts, ship decks, kitchen and bathrooms furniture. Table 1: Classification of non structural wood adhesives