Sealants and Adhesives

Adhesives and sealants are manufactured from a variety of polymers. Their selection and their combinations used impact solvent selection. Most solvent systems are designed to optimize the solubility of the primary polymer. Adhesives can be divided into ones which bond by chemical reaction and ones which bond due to physical processes. Chemically reactive adhesives are further divided into three more categories for those that bond through polymerization, polyaddition, or polycondensation. Physically bonding adhesives include pressure sensitive and contact adhesives, melt, or solution adhesives, and plastisols. Polymerization adhesives are composed of cyanoacrylates (no solvents), anaerobic adhesives (do not contain solvents but require primers for plastics and some metals which are solutions of copper naphthenate), UV-curable adhesives (solvent-free compositions of polyurethanes and epoxy), rubber modified adhesives (variety solvents discussed below). 

Polyaddition adhesives include epoxy and polyurethane polymers which can either be 100% solids, water-based, reactive or non-reactive hot melts or contain solvents mostly to regulate viscosity. Typical solvents include methyl ethyl ketone, acetone, mineral spirits, toluene, and xylene. Polycondensation adhesives include phenol-formaldehyde resin, polyamides, polyesters, silicones and polyimides. With the exception of polyesters (which require ethanol and N-methylpyrrolidone as solvents) and polyimides (which require 

Pressure sensitive and contact adhesives are made from a variety of polymers including acrylic acid esters, polyisobutylene, polyesters, polychloroprene, polyurethane, silicone, styrene-butadiene copolymer and natural rubber. With the exception of acrylic acid ester adhesives which can be processed as solutions, emulsions, UV curable 100% solids and silicones (which may contain only traces of solvents), all remaining rubbers are primarily formulated with substantial amounts of solvents such as hydrocarbon solvents (mainly heptane, hexane, naphtha), ketones (mainly acetone and methyl ethyl ketone), and aromatic solvents (mainly toluene and xylene). 

Melt adhesives and plastisols do not contain solvents. The solution adhesives group includes products made from the following polymer-solvent systems nitrocellulose (typical solvents include solvent combinations usually of a ketone or an ester, an alcohol and a hydrocarbon selected from isopropanol, 2-butylhexanol, amyl acetate, acetone, methyl ethyl ketone), nitrile rubber (main solvent - methyl ethyl ketone), polychloroprene (which is usually dissolved in a mixture of solvents including a ketone or an ester, an aromatic and aliphatic hydrocarbon selected from naphtha, hexane, acetone, methyl ethyl ketone, benzene, toluene), and polyvinyl acetate (water). 

In addition to the solvents used in adhesives, solvents are needed for surface prepara-tion and primers. Their composition may vary and is usually designed for a particular substrate, often using fast evaporating solvents and environmentally unfriendly materials with significant adverse health effects. 

Adhesives and sealants were some of the first products to be made from block polymer thermoplastic elastomers and remain among the most important 

Many adhesives require special properties, for example, SBS polymers are often used for crosslinkable adhesives because the polybutadiene midblock is readily crosslinked by peroxides, UV light or electron-beam radiation. The vinyl content of the butadiene block of SBS polymers is often increased from the standard 8% to near 50% to make it more reactive to crosslinking. Star architectures are also used to reduce the number of crosslinks necessary to form a continuous network throughout the adhesive. For adhesives that require 

One of the most important features of SBC adhesives is their versatility. Because they are thermoplastic materials of carefully controlled molecular weight, they can be applied both as hot melts and from solvent. More importantly, adhesive manufacturers can tailor their properties to match a wide range of applications. The primary competitors for SBCs in the pressure-sensitive adhesive market are acrylic copolymers. While acrylics have better specific adhesion to polar materials, adhesive manufacturers cannot easily formulate them for varied adhesion applications. 

---

Adhesives and Sealants. Dominated by copolymers, adhesives and sealants remain somewhat of a specialty market. These polymers usually... 

R. P. Deltieure, "Polyurethane Adhesives and Sealants," Proceedings of Caulks and Sealants Short Course II, The Adhesive and Sealant Council, Rosemont, hi., 1992. 

Sealant Specifications Compendium, The Adhesive and Sealant Council, Washington, D.C., 1988. 

The total elastomer consumption in the United States in 1994 accounted for 145,000 t automotive RIM appHcations account for 63% of the total. Coatings consumption in the United States in 1994 was 95,000 t, and powder coatings accounted for about 20% of the total. Adhesives and sealants consumption amounted to another 95,000 t. 

Chlorinated paraffins are versatile materials and are used in widely differing appHcations. As cost-effective plasticizers, they are employed in plastics particularly PVC, mbbers, surface coatings, adhesives, and sealants. Where required they impart the additional features of fire retardance, and chemical and water resistance. In conjunction with antimony trioxide, they constitute one of the most cost-effective fire-retardant systems for polymeric materials, textiles, surface coatings, and paper products. Chlorinated paraffins are also employed as components in fat Hquors used in the leather industry, as extreme pressure additives in metal-working lubricants, and as solvents in carbonless copying paper. 

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. 

In the United States approximately 50% of the 40,000 t of chloriaated paraffins consumed domestically are used in metal-working lubricants. Approximately 20% are consumed as plastic additives, mainly fire retardants, and similarly 12% in mbber. The remainder as plasticizers in paint (9%) and caulks, adhesives, and sealants at 6%. 

Fig. 7. U.S. production and consumption of styrene block copolymers (104). A, Total production B, consumption C, adhesives and sealants D, polymer...

Adhesives and Sealants. Most industrial adhesives contain surface active components and additives, and air entrainment during their mechanical appHcation can significantly reduce joint strength. Defoamers are usually formulated into adhesives to protect users against such difficulties. Additional benefits, such as improved uniformity of products, increased throughput and reduced labor costs can also result from the use of defoamers during adhesive appHcation. The footwear and nonwoven fabric industries are extensive users of defoamers in this way. 

Adhesives and sealants Aluminum forming Asbestos manufacturing Auto and other laundries Battery manufacturing Coal mining Coil coating Copper forming... 

Handbook of Chemistry and Physics, Vol. 69, CRC Press, Boca Raton, EL, 1988-1989. Bascom, W.D. In Engineered Materials Handbook, Adhesives and Sealants, Vol. 3, ASM International, 1990. 

All grades of regular butyl rubber are tacky, rubbery and contain less unsaturation than natural rubber or styrene-butadiene rubber. On the other hand, low molecular weight grades of polyisobutylene are permanently tacky and are clear white semi-liquids, so they can be used as permanent tackifiers for cements, PSAs, hot-melt adhesives and sealants. Low molecular weight polyisobutylenes also provide softness and flexibility, and act as an adhesion promoter for difficult to adhere surfaces (e.g. polyolefins). 

Tanno, T. and Shibuya, L., Special behaviour of para tertiary phenol dialcohol in poly-chloroprene adhesives. Adhesives and Sealant Council Meeting, Spring 1967. 

This chapter first reviews the general structures and properties of silicone polymers. It goes on to describe the crosslinking chemistry and the properties of the crosslinked networks. The promotion of both adhesive and cohesive strength is then discussed. The build up of adhesion and the loss of adhesive strength are explained in the light of the fundamental theories of adhesion. The final section of the chapter illustrates the use of silicones in various adhesion applications and leads to the design of specific adhesive and sealant products. 

Scheme 5. Common moisture RTV condensation cure systems for silicone adhesives and sealants. R is typically methyl (CH3-) or ethyl (CH3CH2-) group.

Vedula, R. and Samms, J.B., Adhesives and Sealants Council, Spring Convention, April, 1999. 

Stamper, D., In Wake, W. (Ed.), Synthetic Adhesives and Sealants. Wiley, Chichester, 1986, Chapter 3. 

Lucas, H., Festel, G., Rainthun, I., Witowski, R. and Dormish, J., Journal Adhesion and Sealants Council. 1996 International Conference. Adhesive and Sealants Council, Inc., San Francisco, CA, 1996, pp. Tyi-TSl. 

Frisch, Jr., K., Sealants and Caulks II — Short Course, Urethane Sealants. Adhesives and Sealants Council, Ine., 1994. 

Petrie, E.M., Handbook of Adhesives and Sealants. McGraw-Hill, 2000. 

Spotnitz, W.D., History of tissue adhesives. In Sierra, D. and Saltz, R. (Eds.), Surgical Adhesives and Sealants, Current Technology and Applications. Technomic, Lancaster, PA, 1996, pp. 3-11. 

---