Determining minimum curing time and temperature for a phenolic formaldehyde/epoxy adhesive

Alfa Laval has been using its unique adhesive mixture for over 50 years for bonding of rubber gaskets to the corrugated plates used in their heat exchangers. The adhesive mix is designated GC6 and is composed out of an epoxy component and a phenolic component. GC6 has throughout the years shown exceptionally good performance in both adhesion to the rubber gasket and to the plate with minimal pre-treatments of the surfaces required. The manufacturer of the phenolic component recently announced that they would discontinue this product. Thus, a replacement with a similar composition was identified. This new component showed to have a faster cure rate which as a result meant that the same curing temperature and time could be used as for the old component. However, data on the minimum curing conditions with respect to time and temperature to obtain a well performing adhesive bond had not yet been established. Thus, the aim of this project was to investigate this. The adhesive showed sufficiently good performance when samples were cured to a residual enthalpy of <2.3J/g, both in initial bond strength and chemical resistance. This required a curing of at least 1h at 120°C and showed no decrease in bond strength after ageing for one week in a humidity chamber. For curing temperatures under 110 °C, in addition to reduced performance also a separation of the individual components. These findings suggest that the current minimum curing recommendations of 120°C for 3h are well above the findings in this report. This also opens the possibility for Alfa Laval to optimize their curing conditions to lower the energy consumption and environmental impact of each cycle. (Less)