Continuous-fiber Extrusions Make Strong Thermoplastics

Continuous-fiber thermoplastic (CFT) materials are a new family of engineered extruded composites that combine the cost advantages of extrusions with the high-strength, lightweight capabilities of composites. CFTs are viable alternatives to conventional metal extrusions and highly filled extruded plastics that have mechanical performance limitations.

The key feature, as the name implies, is that this new process produces parts with continuous reinforcing fibers running axially from end to end. Short and long-fiber-filled thermoplastic extrusions, on the other hand, have discontinuous reinforcing fibers. CFTs also have higher fiber volume. The result is better modulus values, impact strength, and overall durability than possible with other filled-plastic extrusions.

CFTs are manufactured through a hybridization of extrusion and pultrusion processes. Pultrusion techniques create a high-glass-content fiber architecture, and extrusion delivers molten thermoplastic to the reinforcing fibers.

Thermoplastics include polypropylene, polyurethane, PET, nylon 6, and PEEK, with other materials to be available in the near future. Reinforcing fibers are primarily glass or carbon fiber, but the process is suitable for aramids, metaramids, and other fibers.

Here's a closer look at some other features and capabilities:

Part size. The manufacturing process places few limits on part dimensions. Current production parts have a maximum envelope of about 12 in., but larger parts are certainly possible. Thickness is not an issue because the process does not involve exothermic thermosets that could cause thick profiles to crack. The reinforcing fiber determines minimum thickness, and the process places no practical limits on part length.

Mechanical properties. The composites can have a wide range of mechanical properties depending on the thermoplastic, the type and volume of reinforcing fiber, as well as whether or not the extruded profile is composed entirely of CFT.

Typical flexural modulus values range from 3 to 6 million psi. Transverse mechanical properties are typically 2.5 to 4 times better than equivalent fiberglass pultrusions. Overall system durability is fundamentally better because thermoplastic resins have superior elongation characteristics versus thermosets.

Targeted reinforcement. A proprietary process called inSERT technology strategically embeds high-strength CFT material within an extrusion. This two-stage process combines CFT with conventional overextrusion technology. A symmetrical or asymmetrical profile is extruded over a CFT insert, resulting in finished profiles with high-strength materials only where needed.

For example, CFTs can improve the mechanical properties and lower costs of a PVC patio-door frame. Adding four CFT reinforcements in the corners of the extruded profile increases stiffness by 30 to 45%, with the same wall thickness and minimal added cost. Higher stiffness also makes it possible to reduce the wall thickness and save on materials. For instance, using CFT inserts while maintaining the original stiffness reduces PVC volume by more than 35%.

Dual and triextrusion. CFT offers the ability to selectively place material over, around, or in a portion of the extruded profile. As an example, a coextruded TPE strip can create a handgrip on a tool without secondary assembly. Selectively extruded materials can also increase bond-line integrity, provide an electrically conductive path, or perform many other functions within the CFT profile.

Surface effects. As with many extruded materials, CFT permits various surface effects in the host material. In-line knurling, embossing, logo imprinting, or other surface effects can be added at high speeds.

Postforming capabilities. Because CFT materials are based on thermoplastic resins, limited postforming is possible. The high fiber volume of CFT material, however, means postforming capabilities are more limited than with filled thermoplastic. Because the CFT profiles contain continuous axial fibers, postforming geometries must not overstress individual fibers.

For more information:
A CFT design guide introducing the material concept and product capabilities is available by e-mailing Polygon at [email protected].