Thermoformable thermoplastic composites

This table lists, by supplier, some commercially available thermoformable reinforced thermoplastic composite (TPC) materials. Suppliers use several methods to impregnate fiber reinforcements with thermoplastic polymers.

• Prepregs are made using solvent impregnation or hot-melt impregnation methods similar to those used to make thermoset prepregs. Fibers are wetout during prepreg manufacture,
• Semipregs affix a thin film of the matrix system to a fabric, using heat and pressure. During the forming process, the film or melts and wets out the fabric.
• Powder impregnation coats the fibers or fabrics with the matrix in powder form and then heat-sets it to affix the granulated matrix. During the composite forming process, the powder melts and wets out the fibers.
• Commingled fibers/yarns intermingle the matrix in a fiber form and the reinforcement fiber into a single strand, which then can be processed further to form woven, nonwoven and other textile formats. During the forming process, the TP fibers melt and wet out the fibers.
• Fiber Integrated Thermoplastic (FIT) spreads fiber bundles and then draws them through a wet bath or dry bath of powdered matrix and then closes the bundles, using an extrusion system with the same matrix.
• Self-reinforced polymers are formed from fabrics made with fibers spun from polymer material similar to the liquid matrix with which they are impregnated, but possessing a higher melt-temperature. During processing, the matrix and fibers bond, but the fibers retain some integrity and, therefore, function as a reinforcement.

As the chart indicates, stretch-broken fibers can be used to enable conformability for complex curvature with only a slight knockdown in tensile strength (~85 percent of continuous fiber), as the separate fiber lengths are still maintained in a straight-line load path within the textiles. For more about stretch-broken fibers, click on  "Aligned discontinuous fibers-come of age" under "Editor's Picks," at right.