Thermoset resin processing

The work described herein relates primarily to lamination and bonding processes. However, the techniques are generic to most forms of thermoset resin processing. In the discussion which follows many of the resin systems contain glycidyl amines. The bulk of the epoxy formulations used in the aerospace industry today are based on tetraglycidylmethylenedianiline, I (TGMDA) and with diaminodi phenylsulfone, II (DOS). Systems based on... 

Time, temperature, viscosity models are another useful element in understanding the science of thermoset resin processing. They perform a number of valuable functions such as defining the proper point for consolidation pressure application in FRP lamin-... 

Predictive Models as Aids to Thermoset Resin Processing... 

The aerospace industry has had a pronounced influence on developments in thermoset resins that are also useful for other industrial applications. The efforts of the aerospace Industry in the science of thermoset resin processing will afford techniques that are applicable to a broad range of nonaerospace applications. Fabrication of resins into aerospace products is but a step away from being a complete scientifically controlled process from resin formulation to finished hardware. As this work becomes a practical reality, the entire thermoset resin industry will benefit. 

Name given to synthetic, thermosetting resins processed from polyhydric alcohols and polybasic acid or anhydrides. These unsaturated polyesters are prepared by esterification of a polyfunctional alcohol (e.g., glycerin) with phthalic anhydride in combination with fatty acids or rosin acids (molecular weight about 2,000 to 5,000). These resins are frequently modified by incorporation of, e.g., nitrocellulose, NC, or phenolics. AUcyds are used mainly as lacquers. 

Fillers, through their essentially volumetric and thermal inertness at typical thermoset resin-processing temperatures, offer a valuable means of exotherm and shrinkage control. 

Each of these processes has had wide application in mould and core production as alternatives to the cement-sand and conventional carbon dioxide processes. Another alternative is the thermosetting resin process known as shell moulding. Because of its importance it is properly considered in the next section. 

Ammonia is used in the fibers and plastic industry as the source of nitrogen for the production of caprolactam, the monomer for nylon 6. Oxidation of propylene with ammonia gives acrylonitrile (qv), used for the manufacture of acryHc fibers, resins, and elastomers. Hexamethylenetetramine (HMTA), produced from ammonia and formaldehyde, is used in the manufacture of phenoHc thermosetting resins (see Phenolic resins). Toluene 2,4-cHisocyanate (TDI), employed in the production of polyurethane foam, indirectly consumes ammonia because nitric acid is a raw material in the TDI manufacturing process (see Amines Isocyanates). Urea, which is produced from ammonia, is used in the manufacture of urea—formaldehyde synthetic resins (see Amino resins). Melamine is produced by polymerization of dicyanodiamine and high pressure, high temperature pyrolysis of urea, both in the presence of ammonia (see Cyanamides). 

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. 

Reinforced Thermoplastic Sheet. This process uses precombined sheets of thermoplastic resin and glass fiber reinforcement, cut into blanks to fit the weight and size requirements of the part to be molded. The blanks, preheated to a specified temperature, are loaded into the metal mold and the material flows under mol ding pressure to fiU the mold. The mold is kept closed under pressure until the temperature of the part has been reduced, the resin solidified, and demolding is possible. Cycle time, as with thermosetting resins, depends on the thickness of the part and the heat distortion temperature of the resin. Mol ding pressures are similar to SMC, 10—21 MPa (1500—3000 psi), depending on the size and complexity of the part. 

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). 

Newer resins include polysulfone, polyethersulfone, polyetherimide, and polyetherketone. Some of these newer materials are high temperature thermoplastic, not thermoset, resins. They are being promoted for the design of injection-molded printed circuit boards in three-dimensional shapes for functional appHcations as an alternative to standard flat printed circuit boards. Only semiadditive or fully additive processing can be used with these devices. 

Plastics are subidivided into two types thermoplastic and thermosetting. The thermoplastics can be softened by heat and hardened again by subsequent cooling. This process is reversible and can be repeated many times. By contrast, the thermosetting resins are first softened and melted and, at subsequent heating to a definite temperature, they are irreversibly hardened, becoming insoluble [53]. 

Thermosetting resins are available as powders and liquids. The powders can be molded in a similar manner to thermoplastics and are used in process plants where large numbers of small items are required (for example, packing rings). 

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