Polymer adhesives thermosetting

Both thermoplastics and thermosets can be used in four of the five major application areas plastics, elastomers, coatings, and adhesives. But, only thermoplastics can be used in making fibers. During the spinning and drawing process of fiber processing, it s necessary to orient the molecules. Only unbranched, linear polymers (not thermosets) are capable of orientation. 

Achieving Glass-to-Matrix Adhesion. This subject has been expanded upon in several papers and is summarized well by Sterman and Marsden (13). A review of some of the key concepts in glass-to-polymer adhesion as it relates to thermosets and thermoplastics will serve the purposes of this paper. 

Thermoplastic and Thermosetting Polymers. Polymer adhesives that dissolve in solvents, or that soften and flow on heating and... 

Apart from the synthetic thermosetting polymer adhesives, other polymers such as polyvinyl acetate and polyamides are used in... 

Thermoplastic Adhesives. The polymer adhesives described in the following sections are not used as extensively with wood as the thermosetting adhesives discussed earlier. However, they do illustrate many interesting principles of the chemistry of adhesion through organic polymers. 

Polymer adhesives may be further classified as either thermoplastic or thermosetting, depending on whether their molecular structures after curing are linear or crosslinked. The linear polymers maybe straight chains... 

Certain general categories are also listed, such as alloys, aromatic polymer, conductive, delayed-tack, elastomeric adhesives, anaerobic, film and tape adhesives, hot-melt adhesives, inorganic glues, microencapsulated adhesives, rubber-based adhesives, solvent-based systems, thermoplastic resin adhesives, thermosetting-resin adhesives, and water-based adhesives. 

In most widely used two-polymer adhesives, the thermosetting component is phenolic. Phenolic resins are generally compatible, although not easily miscible, with a number of thermoplastic polymers. Particularly good compatibility is demonstrated between conventional alcohol-soluble phenolic resins and polyvinyl esters and acetals. Epoxies are important in two polymer adhesive systems. The most important thermoplastic components are the polyvinyl acetals (polyvinyl formal and butyral) and synthetic rubber, particularly nitrile rubber. Soluble nylons are also an important class. ... 

Rubber to metal adhesives contain polymeric materials that are compatible with the ingredients in the primer, as well as the rubber compound to be bonded. Many are based on halogenated polymers. Halogenated polymers or resins are known to wet metals efficiently and can be used in both the primer and adhesive formulation. They provide effective barriers to chemicals that can undermine the adhesive bond. The adhesive also contains very powerful curatives that react with both the polymers in the rubber and the polymers in the adhesive [19]. Difunctional and polyfimctional chemicals are capable of making the film forming polymer a thermoset as well as reacting across the interface of the film to link into the rubber. 

Two other important classes of polymer are thermosets and elastomers. Thermosets harden when the temperature is increased due to crosslinking and cannot be processed by melting. Thermosets are often formed by resins such as epoxy adhesive which, when mixed with hardener, becomes solid ( sets ) very rapidly if heated. Elastomers are rubbery materials that can be stretched to many times their original dimension and that recover... 

Maleate esters such as dimethyl maleate, diethyl maleate and dibutyl maleate are extensively used in the production of latex emulsion polymers, thermoplastic and thermosetting plastics. Dimethyl maleate has found use in applications where improvement in hardness and toughness of polymer films are desired. This includes, in particular, the improvement of anti-blocking properties of copolymers of vinyl acetate with dimethyl maleate. It is also used as an internal modifier to increase the glass transition temperature of styrene or vinyl chloride polymer. The intermediate in esterification of maleic acid with methanol, monomethyl maleate provides plastsizing effect, as well as promotion of improved polymer adhesion due to the carboxylic group. It can be copolymerized with a variety of vinyl and acrylic monomers to provide coatings with improved stiffness and adhesion and reduced tackiness or tendency to block. Monoesters of maleates are used to provide carboxylic acid functionality in emulsions and water-soluble polymers. 

Garton et al. (1989) discussed stiff polar molecular additives which interact strongly with the (thermoplastic or thermoset) matrix polymer adhesive, thus decreasing the composite free volume, /, as given by the equation... 

Synthesis of adhesives, thermosetting polymers Often burned... 

Polymers are characteri2ed as thermosetting and thermoplastic with respect to the methods by which they are joined. Thermosetting polymers are permanently hard and do not soften upon the apphcation of heat they are joined by mechanical fasteners and adhesives. Several methods have been devised to join thermoplastic polymers, as weU as thermoplastic composite materials, which soften upon heating. 

Poly(vinyl alcohol) is employed as a modifier of thermosetting resins used as adhesives in plywood and particle board manufacture (314,315). The polymer is added to urea-formaldehyde or urea—melamine—formaldehyde resins to improve initial grab, to increase viscosity, and, in general, to improve the characteristics of the board. 

---