Mechanical and chemical analysis of structural silicone adhesives with the influence of artificial aging

Abstract Structural sealant glazing systems, or bonded glazing, refers to facades in which the glass is structurally bonded to a facade frame and which is typically used in large facades for office buildings. The structural silicone bond lines are an essential element of such facades and a variety of environmental influences and aggressive media interact with the adhesive and may affect its performance. The ETAG 002 is commonly used for the verification of the technical applicability taking these effects into account. In this study, samples of an approved standard silicone adhesive and a high-modulus silicone adhesive are artificially aged according to ETAG 002 and exposed to a climate change test. The aim of this study is to determine the essential mechanical properties and to explain the changes due to aging by means of chemical analysis. Polymer degradations are determined by evaluating the molecular structure with Fourier-transform Infrared Spectroscopy and Thermo-Gravimetric analysis. In addition, water absorption is investigated with Karl Fischer titration. Changes in the chemical structure are particularly identified after aging in SO2 atmosphere as well as after UV exposure. Increased water contents are detected for all specimens conducted to high moisture. The mechanical properties as well as their characteristic temperature ranges are determinate by the Dynamic Mechanical Analysis and Differential Scanning Calorimetry. The results of the study show significant loss of the adhesive stiffness up to 30% after artificial aging, mainly after storage in cleaning agent and after climate change test. However, there are no significant chemical effects of both aging methods on the adhesives. On the other hand UV-radiation as well as the acid attack, interact with the polysiloxane and the filler of the adhesive. This shifts the crystallization temperature a bit but it does not influence the adhesive stiffness at room temperature. Finally, tensile tests and shear tests are performed on both reference and aged bonded glass–aluminum specimens. These test confirm the good durability of silicone adhesives and the results meet the requirements of the ETAG 002.