Composites

Composites are combinations of (at least two) materials, a polymeric matrix and reinforcing elements, particles, or fibers. The matrix material surrounds and supports the reinforcing elements by maintaining their relative positions. The reinforcements are arranged in specific internal configurations to obtain mechanical or other properties tailored to specific applications. Over the last few decades, composites have been rapidly developed to meet the demand for materials that provide higher standards of performance and in-service reliability. The reinforcing materials consist of one or more chemically distinct constituents and can be metal, ceramic, biopolymer, or a synthetic polymer. Due to the broad diversity of matrix and reinforcement materials available, the properties of the composite materials can combine the best features of each constituent to maximize a given set of properties (stiffness, strength-to-weight ratio, toughness, etc.) and minimize others (e. g., weight and cost). Typically, the reinforcing materials are stiff and strong – inorganic particles, fibers, or carbon nanotubes – while the polymer matrix is either a ductile, tough material or a brittle epoxy. The advantages of composites can be summarized as: ■ high strength-to-weight ratio (low density at high tensile strength) ■ high tensile strength at elevated temperatures ■ high creep resistance ■ reduced shrinkage and good shape stability also at elevated temperatures ■ improved liquid and gas barrier properties ■ flame retardancy ■ high toughness.