Читать книгу Metal Oxide Nanocomposites - Группа авторов - Страница 24

A composite material is obtained by merging two or more materials (wood, minerals, plastic co-polymers and/or metals alloys,) to give a unique blend of physico-chemical properties. The concept of composites was mimic from the Mother Nature. The naturally available, wood, is a composite material which is composed of cellulose fibers in a matrix of lignin which is also called as natural glue. Also, the shell of snails and oysters are also a composite material. Recently, the studies have revealed that the strength of spider’s web fibers is many-folds better than man-made processed fibers. The concept was also used in ancient civilizations wherein clay consisting of husks or straws was widely utilized to build houses that withstand for hundreds of years [1].

The composite consist of matrix materials (metals, plastics, or ceramics) which are formed by reinforcing materials (fibers, particulates, or whiskers) in a matrix resin (Figure 2.1(a)). The fibers can be of any dimension i.e. continuous, long, or short. The function of reinforcing material in a composite is to provide stiffness and mechanical strength, while matrix induces the rigidity and resistance to environmental effects [2]. The reinforcing materials can be of any type such as mat, short chopped fibers and a woven fabric. The style by which the fibers are fitted in the composites can induce different properties in the composite [3]. The composite materials composed of polymer matrix are easily processable and readily available and therefore widely used in various industries. In composite materials, the fiber acts as load carrier wherein its strength is most along the axis of the fiber. The fibers which are long and continuous can be aligned in the direction of the load thereby leading to the formation of composite with much enhanced properties than the pure matrix material. Figure 2.1(b) shows that the chopped fiber with continuous fibers shows better properties than short lengths fibers. Therefore, the targeted application together with the manufacturing method leads to the selection of the continuous fibers or long fibers (structural applications) and short fibers (nonstructural applications) [4]. The short fibers are needed in the process of injection and compression molding, whereas continuous fibers are required in the process of roll wrapping, pultrusion and filament winding.