type of curing agent will modify the physical properties of the polymer and can change the processing methods. Matrix suppliers will assist in the choice of materials and processes for a given application.

Thermoplastic matrix materials differ from thermoset in that they are not crosslinked materials that require hardeners and heat. Thermoplastic materials are solids that are formed to shape by heat and pressure. When combined with a fibrous reinforcement, the composite is pressed or molded into the final desired shape. The differences in manufacturing methods can sometimes result in savings of time and equipment cost. Property differences in the final product exist and are usually the determining factor in the selection of the resin type. Many types of thermoplastic matrix materials exist. Conventional materials such as polyesters, polystyrene, nylon, and the like are not usually thought of as advanced thermoplastic matrices even though they are widely used in automotive, medical, and other commercial applications.

1.2.3 Prepregs

Composites are manufactured by combining fibers and resin in a mold or on a form that defines the final product shape. This can be done in one step by a wet lay-up method or through the use of an intermediate product known as a prepreg. A prepreg is a product form in which the reinforcing fibers are preimpregnated with the polymer matrix resin and partially cured to form a sheet or tapelike material. Many fiber and resin suppliers also supply prepregs. Other companies are just prepreg suppliers. The prepreg allows precise control over the relative proportions of resin and fiber in the composite and allows fiber orientation to be controlled. The development of this intermediate product form has had a large impact on the expanding use of polymer composite structures. While there are generic types of prepregs available, almost any fiber-resin combination is possible. The reinforcements can be contained in the prepreg as parallel fibers (unidirectional), woven fabrics of textile types, nonwoven cloth, or braids. The choice of a particular product form is closely related to the manufacturing process to be used and to the complexity of the final product.

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