Evaluating the Durability of Sealants

Five silicone based sealants were subjected to heat aging, humidity and ultraviolet radiation over an eight thousand hour period. Changes in the tensile characteristics of the sealant products were determined and investigated on the molecular level using infrared and thermoanalytical techniques. Tensile testing revealed that specimens subjected to direct UV radiation were, in certain instances more susceptible to loss in elongation capacity than when shielded from radiation. Furthermore, the reduced elongation capacities were dependent on sealant type with the largest losses in the order of 53%. There were also noticeable changes in the modulus with decreases of 40–70% and for one product, an increase of 43% after 8000 hours of accelerated aging. It is surmised that modulus decreases are due to chain scission; however, it was not possible to strictly verify this from the analytical work carried out in this study. However, TG/DTA did confirm the susceptibility to loss of PDMS as well as other sealant components at elevated temperatures. PAS-FTIR was instrumental in detecting the presence of absorbed water as well as filler modifiers, such as calcium carbonate treated with stearic acid, which potentially play a role in the change in mechanical properties of aged silicone products.