Selected Thermoset Resins

Probably about 90% of all thermoset resins used are polyester resins because they are relatively cheap to make and about three quarters of this production are used with some form of reinforcement. Only the resins with better mechanical and high temperature performance are, however, used with the relatively expensive carbon fibers (Table 13.1). 

The next most important class of resins used are the epoxide resins, developed over 50 years ago. They are more expensive than polyester resins but have superior mechanical properties and good resistance to alkaline conditions. Epoxides are by far the most widely used polymer matrix for carbon fibers and currently constitute over 90% of the matrix resin material used in advanced composites [1]. 

The vinyl ester resins have properties that are intermediate between polyesters and epoxides, are easier to process than epoxides, coupled with a better chemical resistance than polyester resins. 

Phenolic resins are cured by a condensation reaction using hot press molding and are relatively cheap, having good high temperature performance (230°C), excellent fire and smoke resistance and good resistance to acids. 

Bismaleimides and polyimides have good thermal stability, extending the working temperature range of epoxides from about 200°C to 280°C. In the UK, polyimide is not widely used due to the high cost and difficulty in processing. However, bismaleimides are now becoming an important class of thermoset resins. 

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The function of the resin matrix material in filament-wound structures is to help distribute the load, maintain proper fiber position, control composite mechanical and chemical properties, and provide interlaminar shear strength. Either a thermosetting or a thermoplastic resin material may be selected. Thermosetting resins may be selected for application in a wetwinding process or as part of a prepreg resin system. 

The decorative laminates described in the previous chapter are made with selected thermosetting resins while resins of this type can be moulded and extruded by methods similar to those outlined in the present and the next chapter the materials employed for these processes predominantly are thermoplastic. Many such plastics can be moulded and extruded under suitable conditions, the most important in terms of quantities used being those that combine properties satisfactory for the purpose with convenience in pro-cessing-especially the polyolefins (polyethylene and polypropylene), poly(vinyl chloride), and styrene polymers and blends. Other plastics with special qualities, such as better resistance to chemical attack, heat, impact, and wear, also are used—including acetals (polyformaldehyde or polyoxymethylene), polyamides, polycarbonates, thermoplastic polyesters like poly(ethylene terephtha-late) and poly(butylene terephthalate), and modified poly(phenylene oxide),... 

If a thermoset resin is selected for wet winding, desirable characteristics include ... 

The most common advanced composites are made of thermosetting resins, such as epoxy polymers (the most popular singlematrix material), polyesters, vinyl esters, polyurethanes, polyimids, cianamids, bismaleimides, silicones, and melamine. Some of the most widely used thermoplastic polymers are polyvinyl chloride (PVC), PPE (poly[phenylene ether]), polypropylene, PEEK (poly [etheretherketone]), and ABS (acrylonitrile-butadiene-styrene). The precise matrix selected for any given product depends primarily on the physical properties desired for that product. Each type of resin has its own characteristic thermal properties (such as melting point... 

Asymmetric hydrogenations have been reported with palladium on silk 123>, palladium on modified cellulose 124> and on modified ion exchange resins 125 >. Also with Raney Nickel modified with amino adds 126> and peptides, 27>. Platinum-carbon catalysts exhibiting shape selectivity have been made by coating them with a thermosetting resin, which is carbonized. In such a way an organic molecular sieve skin is formed over the original catalyst 128>. 

Table 3 summarizes the key properties of selected major types of thermosetting resins. Their cross-linking reactions can occur by radical chain addition... 

Kimura [37] selected three kinds of thermosetting resins—furan, diphenylether-formaldehyde and polyimide resins—as matrix precursors to fabricate carbon fiber reinforced carbon composites (C/C composites). After heat treatment at 2000-3000°C, the graphitization process of the matrix was examined by optical microscopy and X-ray diffraction. In the C/C composite derived from a polyimide, the graphite structure was not as well developed as the others. This retarded development is attributed to less internal stress between fibers and matrix as well as to less stretching of the matrix. 

As a result activated carbon fiber is produced through a series of process consisting of stabilization, carbonization, and activation of precursor fibers. It is important to improve the efficiency of the production process as well as to select low cost precursors [42]. The stabilization process, air oxidation of precursor fibers at 200-300 °C, is the process required to prevent the precursor fibers from melting during the subsequent carbonization process [61, 62]. It is essential for PAN and pitches, but is not essential for phenolic resin and cellulose, because the latter precursors are thermosetting resins. Phenolic resin is known to produce higher surface area ACF as compared with other precursors. It is, therefore, very advantageous if we could improve the production efficiency of phenol resin based ACF by, possibly, simple and cost effective methods. 

Surfactants are added to a thermoset resin system to promote the dispersion of fillers in the resin matrix. Recently, surfactants have been used to disperse carbon nanotubes in polymer matrices [48-50]. Surfactants are of two types neutral and ionic. Surfactants have many applications in coating industries for the development of a water-based resin system [51]. Surfactants are added to phenolic or polyurethane foam formulation in which they facilitate formation of small bubbles. The size and uniformity of bubble formation results in a fine cell structure. A surfactant reduces the surface tension of resin formulations and provides an interface between the highly polar resin and the non-polar blowing agent. The surfactant for a particular resin system must be selected carefully so that it is compatible with the resin and resistant... 

The plastic is often selected based on its inherent properties, product need, availability, cost, and the manufacturer s familiarity with the material. Small amounts of thermoset resins such as PF or diphenyl methane diisocyanate, as mentioned before, are also sometimes used in composites with a high wood content [38]. 

In this article we describe the distinguishing characteristics of thermosetting materials the more common thermosetting resins including their cure chemistry thermoset nanocomposites cure and properties, including cure kinetics the development of residual stress as a result of curing cure monitoring and conclude with a description of selected thermoset processes. 

As a consequence, thermoset resin selection to ensure optimum cost-effective component performance, demands careful comparison of the many high-quality competitive systems now available. Following from that, there was a need for a comprehensive volume to permit that rapid comparison. 

The use and acceptance of buried large-diameter glass fiber, plastic reinforced, filament-wound pipe has increased steadily since the 1950s. Such RP was selected for its superior corrosion-resistance characteristics and installation-cost savings. ASTM standards use the term Reinforced Thermoset Resin Pipe (RTRP). Filament-wound pipe with a double helical angle of continuous-glass reinforcement (discussed later) is but one of several types of RTR pipe constructions. 

There are two alternates in matrix selection, thermoplastic and thermoset, and there are many matrix choices available within the two main divisions. The basic difference between the two is that thermoplastic materials can be repeatedly softened by heat, and thermosetting resins cannot be changed after the chemical reaction to cause their cure has been completed. The two alternatives differ profoundly in terms of manufacture, processing, physical and mechanical properties of the final product, and the environmental resistance of the resultant composite. 

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