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Publication Citation: The Surprising Affects of Strain on the Long Term Rheology of Filled Viscoelastic Solids (Building Joint Sealant)

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Author(s): Donald L. Hunston; Kar T. Tan; Christopher C. White;
Title: The Surprising Affects of Strain on the Long Term Rheology of Filled Viscoelastic Solids (Building Joint Sealant)
Published: May 07, 2008
Abstract: Filled viscoelastic solids, have been used for the last 40 years as building sealants to separate indoor from outdoor environments.  The most important property of the sealant is the ability to respond to imposed strain while maintaining the critical moisture-barrier properties for decades.  During this decades long service life, chemical and molecular changes within the sealant are accelerated by the weather and give rise to changes in the rheological and adhesive properties.  At some point, the sealant is no longer able to withstand the imposed strain and will fail.  The three  factors have generally been considered critical to influencing the changes that occur within the sealant are: ultra-violet light, temperature, and humidity.   Recent studies have shown that imposed strain on the sealant during the exposure has a significant affect on the measured rheological properties.  Cyclic strain on the sealant in the presence of other weathering factors such as heat or high humidity result in significant modulus changes not present in samples with similar exposure without the cyclic strain.  The direction and type of these changes areas formulation dependent and several examples from all the major chemistries will be presented and discussed.   In outdoor experiments it is shown that dynamic strain, such as that encountered in an installed building environment is much more challenging for the sealant than the equivalent static strain.  Also presented are results that show that imposed strain affect the solubility of water in the sealant.  Sealant under strain will either increase or decrease in solubility depending on the base chemistry.  Consequently, strain and strain history are critical factors for understanding the long-term rheological properties of the sealant.
Conference: The XVth International Congress on Rheology
Proceedings: Proceeding of The XVth International Congress on Rheology
Location: Monterey, CA
Dates: August 3-8, 2008
Keywords: Elastomer, Durability, Outdoor Weathering, Service Life Prediction, Stress Relaxation, Sealant,Rheology
Research Areas: Service Life Prediction