Polysulfide adhesives sealants

Besides water vapor and gas diffusion, other requirements for good edge sealants are water resistance, uv resistance, heat/cold resistance (—40 to 80°C), adhesion to glass and metal, and good characteristics for appHcation. Polysulfide sealants have maintained an exceUent record in use since the 1950s. Development of new polysulfides and sealant formulations continues in order to meet market needs of the 1990s. 

Formulation. Polysulfide-based sealants are formulated with appropriate ingredients to obtain the desired properties for a particular application. A typical formulation contains liquid polysulfide polymer, curing agent, cure accelerators (bases) or retarders (acids), fillers, plasticizers, thixotropes, and adhesion promoters. 

Epoxy-polysulfide Epoxy-polysulfide adhesives and sealants have a very high degree of elongation but poor tensile strength compared to unmodified epoxies. They are used primarily as sealants or coatings in die building and construction industries. 

Polysulfide Excellent oil, solvent, and water resistance, high impermeability to gases, low strength, unpleasant odor (particularly during processing) Adhesive, sealants, binders, hose... 

Uses Coupling agent in polysulfide and PU caulks and sealants, and waterborne systems (latex coatings, adhesives, sealants)... 

Epoxy-polysulfide. Polysulfide resins combine with epoxy resins to provide adhesives with excellent flexibility and chemical resistance. These adhesives bond well to many different substrates. Shear strength and elevated temperature properties are poor, but resistance to peel forces and low temperatures is very good. The epoxy-polysulfide alloy is supplied as a two-part, llowable paste that cures to a rubbery solid at room temperature. A common application for epoxy-polysulfide adhesives is as a sealant... 

Gallagher, J. P., Recreational Vehicles—A New Market for Polysulfide-Based Sealants, Adhesives Age, 39 (Nov. 1971). 

Tetrylshows negligible reaction with Adhesive EC 1099, Dapon resin, Delrin, Epoxy 907 adhesive, Galvanoplast, conductive paint, Glastimat No. 1, Lexan, Loctite 404, Molylube No. 18, Permacel PN 112 tape. Polyesters, polysulfide mbber sealant, polyurethane EP 626/628, RTV 102 and 732 vulcanizing rubbers. Silastic RTV 731 or 732 (uncured). Silicone No SE 1201 and No Q 95-011, urea-formaldehyde. Tetryl is also compatible with the following adhesives Adiprene L-10Q, L-167 and LD-213, and Eastman 910. 

Aircraft Sealants. Polysulfides have been used for sealing fuel tanks and aircraft stmctural components since the 1940s. There are stringent requirements for these sealants. They must have outstanding resistance to fuels and exceUent adhesion to many different materials such as various metal aUoys and protective coatings used in aircraft constmction. The sealants must also perform in extremely variable weather conditions (10). The polysulfides have an exceUent performance record. 

Polyurethane sealant formulations use TDI or MDI prepolymers made from polyether polyols. The sealants contain 30—50% of the prepolymer the remainder consists of pigments, fiUers, plastici2ers, adhesion promoters, and other additives. The curing of the sealant is conducted with atmospheric moisture. One-component windshield sealants utili2e diethyl malonate-blocked MDI prepolymers (46). Several polyurethane hybrid systems, containing epoxies, siUcones, or polysulfide, are also used. 

Adhesives and Sealants. Various grades of chloriaated paraffins are used as nonvolatile iaert fire-retardant plasticizers and modifying resias ia adhesives and sealants (3). They find wide appHcation ia polysulfide, polyurethane, acryUc, and butyl sealants for use ia building and constmction. The low volatihty high chlorine types are also employed ia sealants for double- and triple-glazed wiadows. 

Polysulfides are more commonly used as sealants but are occasionally employed as adhesives as well. Polysulfides adhere well to a wide range of materials and are useful where some flexibility is needed in the joint. 

Titanates have been instrumental in the bonding of fluorinated resins to packaging films, poly(hydantoin)—polyester to polyester wire enamel, polysulfide sealant to polyurethane (a phosphated titanate is recommended), polyethylene to cellophane using a titanated polyethylenimine, and silicone mbber sealant to metal or plastic support using polysilane (Si—H) plus polysiloxane (Si—OR) and titanate as the adhesive ingredients (450—454). Polyester film coated first with a titanium alkoxide, then with a poly(vinyl alcohol)—polyethylenimine blend, becomes impermeable to gases (455). 

Polysulfides and mercaptan Moisture resistance Quick set time Flexible Odor Poor elevated-temperature performance Poor tensile strength Adhesives and sealants Civil engineering Casting and encapsulation Coatings... 

Amstock, J. S., Polysulfide and LP Polymers, Chapter 11 in Handbook qf Adhesives and Sealants in Construction, McGraw-Hill, New York, 2001. 

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