Liquid polysulfide polymers are normally associated with sealants for construction, marine, insulating glass, automotive, and aircraft industries. The liquid polysulfide polymer can be transformed from a liquid state into a solid elastomer, even at low temperatures.
Polysulfide adhesives and sealants have been successful in applications requiring good moisture, solvent and ozone resistance, and good weathering and low temperature properties. However, the chemical linkages that provide these properties also contribute to poor high temperature stability and high compression set because of stress relaxation.
RESULTING PROPERTIES
Typical properties of several polysulfide-epoxy adhesives are shown in the table above. Room temperature tensile shear strength ranges from about 500 to 3000 psi, depending on the substrate and the adhesive formulation. Generally, tensile strength properties reach a maximum at about 10-30% polysulfide concentration. Peel strength can be as high as 20 lb/in. The heat distortion temperature is only slightly affected by the incorporation of 20% polysulfide polymer, but at a 1:1 ratio the drop becomes significant. This property prevents the use of polysulfide-epoxy adhesives at elevated temperatures.
Polysulfide-epoxy adhesives can be used in various chemical and solvent environments, even under immersion conditions. The systems exhibit low permeability to water and water vapor, which provides improved water and corrosion resistance. Polysulfide-epoxy adhesives also cure with very low shrinkage, in contrast to unmodified epoxy resins, which may exhibit volume shrinkage as high as 5%. Polysulfide-epoxy adhesives provide resistance to thermal shock and cycling as well as resistance to low temperature environments.
