Thermal and rheological comparison of adhesives

In some industrial sectors such as naval construction, the use of adhesives is still limited to some specific applications. However, shipbuilders, academia and classification societies are cooperating to expand the field of certificated applications of adhesive joints. As a part of a validation study, thermal and rheological studies of the curing process and of the cured adhesives should be included. While a neat glass transition and other relaxation processes can be normally identified by ramp temperature tests performed both on a differential scanning calorimeter or on a rheometer, there are some adhesive systems in which several glass transitions or melting or crystallization processes overlap. Applying a thermal treatment to delete the thermal history and conditioning are common practices to clarify what happens in complex systems. However, although that practices usually help, there are still some complexities due to overlapping processes that cannot be easily understood. An important point of this work is to show how differential scanning calorimetry and rheology complement to each other in order to demonstrate several thermal relaxations and to obtain a better understanding of the cure process. The use of two different techniques along with a careful election of the setup parameter values allows to better interpret the thermal events. In addition, thermogravimetry helps to understand some rheological behaviors. In the end, this work shows how a good insight of the adhesive properties can be obtained by means of the combined use of DSC, rheology and TG.