Thermosets processing methods

The processing methods will be selected according to the importance of the series, part sizes and targeted properties. Table 6.1 suggests some processes, for thermoplastic and thermoset composites, according to the part sizes and production outputs. 

Injection moulding is by far the most frequently applied technique for manufacturing end-products directly from a thermoplastic raw material. In this process articles are formed by injecting the molten polymer into a cooled mould. Also on rubbers and thermosets this method is applied, though at a smaller scale in these cases the mould is heated rather than cooled in order to promote the vulcanisation or curing reaction. 

As a binder system polymers are utilized. If the binders contain energy or gas-producing molecular groups (-N02, -N3), one classifies the binders as Active Binders (e.g. polynitropolyphenylene, glycidyl azide polymer, polyvinyl nitrate and nitrocellulose). If these substances are not present, then the binders are classified as inert binders. Depending on available processing methods, binder types such as thermoset material, thermoplast or gelatinizers can be used. They can then be formed and cured by chemical or physical means. 

Depending on available processing methods, binder types such as thermoset material, thermoplast or gelatinizers can be used. They can then be formed and cured by chemical or physical means. 

The effects of cure on the viscosity of thermoset resins are monitored on the catalysed resin and are associated with the late injection, packing and curing cycles of a thermoset process. There are essentially two types of test methods, namely isothermal and non-isothermal tests, which are usually performed in dynamic or steady shear. 

Polyesters A broad class of polymers usually made by condensation of a diol with dicarboxylic acid or anhydride. Polyesters consist of chains with repeating carbonyloxy group and can be aliphatic or aromatic. There are thermosetting polyesters, such as alkyd resins and unsaturated polyesters, and thermoplastic polyesters such as PET. The properties, processing methods, and applications of polyesters vary widely. Also called Polyester Resins. 

The matrices used in sisal fiber-reinforced composites include thermoplastics (polyethylene, polypropylene, polystyrene, PVC, etc.), thermosets (epoxy, polyester, and phenol-formaldehyde resin, etc.), rubber (namral rubber, styrene-buta-diene mbber, etc.) gypsum, and cement. The effects of fiber length, fiber orientation, processing methods, fiber volume fi-action and fiber surface treatment on the mechanical and physical properties of sisal fiber reinforced composites have been smdied. 

Rader and Richwine have [34] identified various processing methods and advantages of TPEs over thermoset rubber. Two of the most important advantages of TPEs are the economics and ability to produce complex parts. 

Table 1.1 Principal processing methods for thermoplastics and thermosets.

With regard to methods of fabrication, all processes in Table 1.1 that are applicable to unfilled, unmodified thermoplastics can also be used for discontinuous systems (with the exception of expandable bead molding). In addition to thermoforming, hot stamping of reinforced thermoplastic sheets mostly containing randomly oriented continuous or discontinuous fibers is used for the production of large semistructural parts. Fillers can also be used in the thermoset processes in Table 1.1, often in combination with the primary continuous fiber reinforcement. The content and inherent properties of the additive, as well as its physical/chemical interactions with the matrix, are important parameters controlling the processability of the composite. 

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