Epoxy-poly sulfide adhesives

These blends can take a number of different forms. The added resin may be reacted with the epoxy resin, or it may be included as an unreacted modifier. The modifier may be blended into a continuous phase with the epoxy resin (epoxy alloys) or precipitated out as a discrete phase within the epoxy resin matrix (as is generally done in the case of toughening modifiers). Epoxy hybrid adhesives are often used as film (supported and unsupported) or tape because of the ease with which formulated systems can be dissolved into solvent and applied to a carrier or deposited as a freestanding film. Some systems, notably epoxyurethanes and epoxy-poly sulfides, can be employed as a liquid or paste formulation because of the low-viscosity characteristics of the components. 

Applications of epoxy-polysulfide adhesives primarily include structural assemblies requiring some degree of resilience. Epoxy-poly sulfides are used in bonding concrete for floors, airport runways, bridges and other concrete structures, metals, glass and ceramics, wood, rubber, and some plastics. They are particularly durable in outdoor applications where temperature extremes (freeze-thaw cycles) will be encountered. Epoxy-poly sulfides can be heavily filled without adversely affecting their properties. 

Epoxy poly sulfides [10] are available as two-part liquids or pastes that cure at room temperature or higher to rubbery solids that provide bonds with excellent flexibility and chemical resistance. These adhesives bond well to a number of substrates. Shear strengths and elevated-temperature properties are low, but resistance to peel and low-temperature properties are quite high. 

Table 11.18 shows the effect of increasing the poly sulfide-epoxy ratio on impact properties the effect at concentrations of polysulfide polymer greater than 1 1 is especially significant. The combination of increased flexibility, tensile strength, and elongation is very desirable in certain adhesive applications. 

Epoxy-polysulfide systems can be formulated either as a liquid DGEBA epoxy mixed with liquid poly sulfide polymer or as an epoxy-terminated polysulfide polymer either may be cured with a tertiary amine such as DMP-30. Table 11.19 describes the formulation and shows the physical properties of these epoxy-polysulfide adhesives compared to an unmodified epoxy adhesive. 

Poly sulfide rubber was first produced in 1929, and the liquid polymers were used in sealants and as flexibilizers for epoxy adhesives around 1950. In 1952 the polysulfide sealant was introduced to the construction industry [11, p. 74]. In the 1950s the first butyl rubber caulks appeared in the construction market [11. p. 108] and latex caulks [vinyl acrylic and poly(vinyl acetate)] appeared sometime after 1956. 

Interfacial aspects and adhesion of polysulfides have been studied extensively and reported by us [3,17]. The epoxy-modified poly sulfide has improved adhesion due to chemical reactions that increase electronic attraction forces. Water has been found to be the most potent debonding agent in cured polysulfides. Formation of thiourethane is responsible for excellent adhesion of polysulfide onto polyurethane coatings. 

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