Polymer and Plastic Composites

Polymer and plastic composites are strengthened with fibers, fillers, particulates, powders and other matrix reinforcements to provide improved strength and/or stiffness. Examples of polymer and plastic composites include fiber reinforced plastics (FRPs), sheet molding compounds (SMCs), bulk molding compounds (BMCs), pre-preg materials, and fabricated composite parts. Fibers are usually chopped, wound or woven and made of materials such as fabric, metal, glass, or fiberglass. Solid, self-lubricated, and bearing grade fillers are commonly available. Particulates vary in terms of shape and size. Powders are usually made of carbon, graphite, silicates, ceramics, and other organic or inorganic materials. Some matrix reinforcements provide improved electrical conductivity. Others offer improved thermal conductivity. 

Polymer and plastic composites use many different matrix types and resins. Some matrices contain acetals, acrylics, elastomers, natural or synthetic rubbers, epoxy resins, silicone compounds, or vinyl systems. Others contain cellulosic thermoplastics, ethylene copolymers, fluoropolymers, ionomers, ketones, phenolics, polyamides, polyimides, or styrenes. Commonly used chemical systems for polymers and plastic composites include polybutadiene, polycarbonate (PC), polyethylene, polyester, polyetherimide, polyolefin, polyphthalamide, polypropylene (PP), polysulfide (PS), polysulphone, and polyurethane (PUR). Resins are available as compounds, liquids, pellets, and powders. Molding-grade compounds and extrusion-grade resins are designed for specialized applications. 

There are several curing technologies for polymer and plastic composites. Typically, thermoplastics and hot melt adhesives are cured using heat or heat and pressure. Vulcanization, a thermosetting reaction, uses heat and/or pressure in conjunction with a vulcanizing agent to produce materials with greatly increased strength, stability, and elasticity. Some polymer and plastic composites cure or vulcanize at room temperature. Others cure with radiation, electron beam irradiation, visible light, or ultraviolet (UV) light. Single component curing systems consist of a resin that hardens through the application of heat or a reaction with surface moisture. Two-component and multi-component curing systems consist of two or more resins and a hardener, crosslinker, activator or catalyst. 

Selecting polymer and plastic composites requires an analysis of physical, mechanical, electrical, and thermal properties. Physical properties include viscosity, melt flow index (MFI), and water absorption. For semi-finished or stock shapes such as films, plates, and rods, measurements such as thickness, width, length, inner diameter (ID), and outer diameter (OD) are important. Mechanical properties for polymer and plastic composites include tensile strength, tensile modulus, and elongation. Electrical properties include electrical resistivity, dielectric strength, and dielectric constant. Use temperature, deflection temperature, thermal conductivity, and the coefficient of thermal expansion (CTE) are important thermal properties. 

Polymer and plastic composites vary in terms of features. Products that are designed for electrical and electronics applications often provide protection against electrostatic discharge (ESD), electromagnetic interference (EMI), and radio frequency interference (RFI). Materials that are electrically conductive or resistive are also available. Thermal compounds, insulators, and interfaces are used between heat-generating devices and heat sinks. Polymer and plastic composites that use a phase change provide enhanced thermal characteristics. Some products are available as molded stocks. Others are flame retardant. Dampening products are used to form a layer that will not crack or delaminate. 

Polymer and plastic composites are used in many industries and applications. Some products are used in aerospace, automotive, or marine applications. Others are designed for use with electrical power products, high voltage applications, semiconductors, or integrated circuit (IC) packaging. Materials that are suitable for medical, pharmaceutical and food processing applications meet requirements established by the Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA). Polymer and plastic composites that meet military specifications (MIL-SPEC) are also available. Original equipment manufacturers (OEMs) and repair, maintenance and overhaul (MRO) organizations also use polymer and plastic composites.

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