Polyesters also thermosets

One class of such materials is the fluorinated alkyl esters of acrylic and methacrylic acid, a number of which have been prepared [1]. One of these esters, poly(l,l-dihydropentadecafluoro-octyl methacrylate), has a 11 dynes per cm.—less than Teflon TFE or even FEP [4]. Such materials, and others within the general class of unsaturated, appropriately fluorinated, polyesters warrant investigation for use either as thermoplastic hot-melt adhesives, or for cross linking in situ to form rigid thermoset adhesives. The saturated, appropriately fluorinated polyesters also warrant investigation as thermoplastic hot-melt adhesives. 

Tapes for component supply in loading installations usually consist of an acrylate- or rubber-based adhesive (also thermosetting) on a paper or polyester foil carrier (dependent on the mass of the components). Depending on the type of application, different materials are used for the adhesive and the carrier for covering tapes. Most important carrier materials are foils (PVC, polypropylene, cellulose, polyester, polyimide), papers, and woven and nonwoven fabrics (cotton, glass). Adhesives frequently used are based on rubbers, silicones, and acrylates. Carrier less adhesive foils are used, for example, for the bonding of copper foils and polyimide films to get special base materials for circuit boards. 

Thermosets arc plastics that undergo chemical crosslinldng during processing to become permanently insoluble and infusible. Phenohc, amino, epoxy, and nnsaturated polyester resins are typical thermoset plastics. Natural and synthetic rubber such as latex, nitrile, millahle poly(uiethane), sUicone, butyl, and neoprene, which attain their properties throngh a process known as vulcanization, are also thermoset plastics. 

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 stmcturaHy demanding appHcations. 

Many different thermosetting polymers are used in pultmsion, eg, polyester, vinyl ester, epoxy, and urethane. Reinforcements must be in a continuous form such as rovings, tows, mats, fabrics, and tapes. Glass fibers are the low cost, dominant composition, but aramid and carbon fibers are also used. 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

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. 

The largest user of phenol in the form of thermosetting resins is the plastics industry. Phenol is also used as a solvent and in the manufacture of intermediates for pesticides, pharmaceuticals, and dyestuffs. Styrene is used in the manufacture of synthetic rubber and polystyrene resins. Phthalic anhydride is used in the manufacture of DMT, alkyd resins, and plasticizers such as phthalates. Maleic anhydride is used in the manufacture of polyesters and, to some extent, for alkyd resins. Minor uses include the manufacture of malathion and soil conditioners. Nitrobenzene is used in the manufacture of aniline, benzidine, and dyestuffs and as a solvent in polishes. Aniline is used in the manufacture of dyes, including azo dyes, and rubber chemicals such as vulcanization accelerators and antioxidants. 

Important thermosetting plastics include the phenolics, melamine-formaldehyde, epoxides and polyester resins used in glass-reinforced plastics. (See also Sections 14.5 and 14.9.)... 

Pettersson and Sorensen have described a number of different thermoset resin structures based on hyperbranched aliphatic polyesters [123]. Their results can best be exemplified by a study on hyperbranched alkyd coating resins. A comparative study was performed between an alkyd resin based on a hyperbranched aliphatic polyester and a conventional high solid alkyd, which is a less branched structure. The hyperbranched resin had a substantially lower viscosity than the conventional resin of comparable molecular weight, that is, less solvent was needed to obtain a suitable application viscosity. The hyperbranched resin also exhibited much shorter drying times than the conventional resin, although the oil content was similar. These achievements would not have been possible without a change in architecture of the backbone structure of the resins (Figs. 12,13). 

This process is generally used for thermosets, such as polyurethane, polyisocyanurate, phenolic, unsaturated polyester and silicone foams, but it is also used for plastisols or PVC... 

Results are presented of experiments undertaken by Gaiker in the manufacture of sandwich panels containing foam cores based on PETP recycled by a solid state polyaddition process developed by M G Ricerche. Panels were produced with glass fibre-reinforced unsaturated polyester and epoxy resin skins, and allthermoplastic panels with PE, PP, PS and glass fibre-reinforced PETP skins were also produced. EVA hot melt adhesives and thermoset adhesives were evaluated in bonding glass fibre-reinforced PETP skins to the foam cores. Data are presented for the mechanical properties of the structures studied. 

Unsaturated polyesters are relatively brittle and about 70% are used with fillers, of which glass fiber is easily the most popular. Glass fiber-reinforced polyester for small boat hulls consumes one quarter of unsaturated polyesters. Automobiles, furniture, and construction also make use of this thermoset resin. 

The crosslinking of unsaturated polyesters (Sec. 2-12a) is carried out by copolymerization [Selley, 1988]. Low-molecular-weight unsaturated polyester (prepolymer) and radical initiator are dissolved in a monomer, the mixture poured, sprayed, or otherwise shaped into the form of the desired final product, and then transformed into a thermoset by heating. Styrene is the most commonly used monomer. Vinyltoluene, methyl methacrylate, diallyl phthalate, a-methylstyrene, and triallyl cyanurate are also used, often together with styrene. 

In most applications, polyester and vinyl ester resins are used as the matrix materials. Epoxies are also used, although they require longer cure times and do not release easily from the pultrusion dies. Hence, thermosetting resins are most commonly used with pultrusion, although some high-performance thermoplastics such as PEEK and polysulfone can also be accommodated. In addition to the resin, the resin bath may contain a curing agent (initiator, cf. Section 3.3.1.2), colorants, ultraviolet stabilizer, and fire retardant. 

The typical resin systems include thermoset polyesters, vinyl esters, epoxies, polymi-dies, bismaleimide, and phenolics. Thermoplastics are also finding their way into filament winding. Wet thermoset filament winding requires a resin with viscosity in the range of 1000-3000 cpoise. Resin components are chosen on the basis of pot life, winding temperature, viscosity, gel time, and cure time. 

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