Prepregi

Prepregi are pre-impregnated composite materials in which reinforcing fibers are already coated with a resin system. The term is used in some languages as the plural of prepreg. A prepreg consists of fibers such as carbon, glass, or aramid embedded in a resin matrix that is partially cured (B-stage) to give a tacky, sheeted material. The resin systems are typically thermosetting epoxies, cyanate esters, or BMI resins, though thermoplastic prepregs using polymers like PEEK or PEI also exist. Resin content and cure chemistry are specified by the manufacturer, affecting handling and performance.

Prepregs offer controlled fiber volume content and resin distribution, enabling high strength and stiffness with low void content. They require careful handling due to moisture sensitivity and limited shelf life. Storage is usually at low temperatures (often -18 to -20 C) to extend life; thawing and outlife management are important to prevent degradation.

Manufacture and use involve laying the prepreg onto molds or tooling, followed by curing with heat and pressure, commonly in autoclaves or ovens, according to defined cure cycles. Vacuum bagging is used to remove air and consolidate layers. Prepregs are widely used where high performance is required, including aerospace, race cars, wind turbine blades, and high-end sporting goods.

Types and properties: epoxy-based prepregs are the most common, with resin contents ranging roughly from 25 to 70 percent by weight, influencing stiffness, glass transition temperature, and damage tolerance. Thermoplastic prepregs can be melted and fused, offering different processing and potential recyclability.

Limitations include higher cost, limited shelf life, specialized handling, and challenges in recycling and disposal.