Resins commercial applications, thermosets

On the other heind, the linear unsaturated polyester resins find use in memy commercial applications, such as in producing solventless lacquers, and thermosetting molding compounds. The resin is normally prepcured by the reaction of a saturated diol with a mixture of an unsaturated dibasic acid and a modifying dibasic acid or its corresponding anhydride. It is commonly referred to as... 

Organic matrices are divided into thermosets and thermoplastics. The main thermoset matrices are polyesters, epoxies, phenolics, and polyimides, polyesters being the most widely used in commercial applications (3,4). Epoxy and polyimide resins are applied in advanced composites for structural aerospace applications (1,5). Thermoplastics Uke polyolefins, nylons, and polyesters are reinforced with short fibers (3). They are known as traditional polymeric matrices. Advanced thermoplastic polymeric matrices like poly(ether ketones) and polysulfones have a higher service temperature than the traditional ones (1,6). They have service properties similar to those of thermoset matrices and are reinforced with continuous fibers. Of course, composites reinforced with discontinuous fibers have weaker mechanical properties than those with continuous fibers. Elastomers are generally reinforced by the addition of carbon black or silica. Although they are reinforced polymers, traditionally they are studied separately due to their singular properties (see Chap. 3). 

Table 3 Typical thermosetting resins of commercial applications... 

Polymeric nanocomposites are a class of relatively new materials with ample potential applications. Products with commercial applications appeared during the last decade [1], and much industrial and academic interest has been created. Reports on the manufacture of nanocomposites include those made with polyamides [2-5], polyolefins [6-9], polystyrene (PS) and PS copolymers [10, 11], ethylene vinyl alcohol [12-15], acrylics [16-18], polyesters [19, 20], polycarbonate [21, 22], liquid crystalline polymers [8, 23-25], fluoropolymers [26-28], thermoset resins [29-31], polyurethanes [32-37], ethylene-propylene oxide [38], vinyl carbazole [39, 40], polydiacethylene [41], and polyimides (Pis) [42], among others. 

Polymers in their raw state are usually technically unsatisfactory in one respect or another, such as their stability to light or heat, or their processability, or flammability, or colour, or opacity, or antistatic characteristics, etc., and they simply could not be used in commercial applications successfully without the incorporation of one or more additives [2] to modify behaviour. The additives are often present at very low concentrations (0.1-3 parts per hundred of resin, by weight) and are called stabilizers, UV absorbers, viscosity modifiers, lubricants, fire retardants, pigments, etc. Fillers may be present at 50 or even 150 parts per hundred of resin, by weight. Thermosetting resins tend to have fewer additives of the kind... 

Thermosets can be divided into several classes depending on the chemical composition of the monomers or pre-polymers (resins). Important thermosetting resins in current commercial applications are the condensation products of formaldehyde with phenol (phenolic resins), urea or melamine (amino resins). Other major classes are epoxy resins, unsaturated polyester resins, allyl resins and isocyanate resins. 

The previously described properties of the resin types make thermosetting resins much more useful for civil engineering structural applications, and in fact they have been used in almost all commercially available FRP pultruded products. Table 9.2 presents the basic properties of the thermoset resins most commonly used in pultrusion polyester, vinylester, epoxy and phenolic. 

HMT is commonly used by the plastics industry as the crosslinking agent for novolac phenol formaldehyde thermosetting resins. These molding resins are used in many commercial applications. 

Differential scanning calorimetry (DSC), DMA and TG were used by Tabaddor and co-workersl l to investigate the cure kinetics and the development of mechanical properties of a commercial thermoplastic/ thermoset adhesive, which is part of a reinforced tape system for industrial applications. From the results, the authors concluded that thermal studies indicate that the adhesive was composed of a thermoplastic elastomeric copolymer of acrylonitrile and butadiene phase and a phenolic thermosetting resin phase. From the DSC phase transition studies, they were able to determine the composition of the blend. The kinetics of conversion of the thermosetting can be monitored by TG. Dynamic mechanical analysis measurements and time-temperature superposition can be utilized to... 

Thermoset moldable compounds can be mixed with a very wide variety of fillers to modify their properties to meet the requirements for a given application. Adding suitable fillers can produce coefficients of thermal expansion and elongation behavior virtually identical to those of copper. Once thermoset materials have cured, moreover, their three-dimensional molecular network structure gives them a very high level of dimensional stability. Consequently, in terms of temperature resistance to soldering many of the materials in this class are potentially suitable as MID substrates. Table 2.5 summarizes some of the important thermal properties of commercially available thermoset moldable compounds. Thermoset moldable compounds, moreover, have economic potential because in some cases the cost of the material Is low. Phenolic resin moldable compounds in particular are available at a price of less than about 7 (EUR 5) per kg and could therefore be considered an economical alternative to LDS high-temperature thermoplastics. 

Interesting developments were also taking place in the field of thermosetting resins. The melamine-formaldehyde materials appeared commercially in 1940 whilst soon afterwards in the United States the first contact resins were used. With these materials, the forerunners of today s polyester laminating resins, it was found possible to produce laminates without the need for application of external pressure. The first experiments in epoxide resins were also taking place during this period. 

Of the various amino-resins that have been prepared, the urea-formaldehyde (U-F) resins are by far the most important commercially. Like the phenolic resins, they are, in the finished product, cross-linked (thermoset) insoluble, infusible materials. For application, a low molecular weight product or resin is first produced and this is then cross-linked only at the end of the fabrication process. 

Polyesters are one of the most versatile classes of polymers ever produced, covering a wide range of properties and applications. Polyesters are present in fibers, engineering thermoplastics, and high-performance polymers as well as in thermosetting resins and elastomers. Table 2.1 lists the chemical structure, abbreviations, and uses of some commercially important thermoplastic polyesters. 

A variety of thermosetting resins are used in SMC. Polyesters represent the most volume and are available in systems that provide low shrinkage and low surface profile by means of special additives. Class A automotive surface requirements have resulted in the development of sophisticated systems that commercially produce auto body panels that can be taken direcdy from the mold and processed through standard automotive painting systems, without additional surface finishing. Vinyl ester and epoxy resins (qv) are also used in SMC for more structurally demanding applications. 

Plastics. Almost all commercial plastics find some use both dry and lubricated for sliding at low speeds and light loads the most commonly used thermoplastics are nylon, acetal resins, and polytetrafluoroethylene (PTFE). Typical thermosetting resins for bearing applications are phenolics, polyesters, and polyimides. Table 8 compares the characteristics of plastic bearing materials with those of graphite, wood, and rubber which find use in somewhat similar applications. 

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