Typical Formulation Ingredients
Phase
Ingredient
Parts by weight
A
Liquid polysulfide (LP-3, Thiokol)
A
Kaolin pigment (Hydrite 121, Imerys)
A
Curing agent (EH 330 or DMP30, 2,4,6-tri (dimethylaminomethyl)phenol)
B
Epoxy resin (Epon 820, Momentive)
B
Kaolin pigment (Hydrite 121, Imerys)
Typical Properties
Ratio of Part A to Part B
Setting time for 0.25 mm, hrs
Cure time for 0.25 mm, hrs
Resulting Properties
Typical properties of several polysulfide-epoxy adhesives are shown in the table above. Room temperature tensile shear strength will depend 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.
The source of Epoxy-Polysulfide Sealant (B) formulation is Pizzi, A. and Mittal, K.L., Handbook of Adhesive Technology, p. 538.