Moldable PP/glass fabric makes headway in composites.

Several new automotive and non-automotive applications for a compression moldable resin/glass fabric are under development by Vetrotex CertainTeed Corp., Valley Forge, Pa. The firm introduced the Twintex line of thermoplastic composite materials about a year and a half ago. These reportedly unique materials consist of commingled glass-fiber rovings and thermoplastic filaments. These soft, drapable fabrics can be placed in a mold and hot pressed, causing the resin to melt and wet out the glass reinforcements.

Until now, commingled fabric composites have tended to combine high-end reinforcements and thermoplastics, such as carbon fiber and PEEK, notes Twintex marketing manager Bill Mcgill. Twintex, by contrast, combines conventional E-glass rovings with low-cost polypropylene. The company is also developing grades using PET, PBT, and polyethylene filaments.

Key properties are said to be excellent impact resistance, uniform distribution of glass and thermoplastic filaments, and ease of processing. Twintex is available as basic rovings or in plain, twill, or satin weaves, and in unidirectional, oriented, and three-dimensional fabrics. Depending on the application, glass content can be 40% to 75% by weight. Besides compression molding and vacuum forming, Twintex can be used in pultrusion and filament winding.

TARGETING METAL

In general, Twintex is aimed at applications that currently use steal and aluminum, rather than existing composites such as BMC and SMC, notes Susan Blake, a Detroit-based sales engineer for the Twintex line. She adds that the continuous glass strands give higher impact strength and overall toughness than chopped-glass materials. Specific property data should become available by the beginning of November, says Blake.

Initial industrial applications include a thermoformed fireman's helmet that is produced in a 42-sec cycle. Other non-automotive applications include stadium seats, kayaks and other marine products, and center structures for highways.

Vetrotex CertainTeed also says Twintex can be pultruded at higher speeds than traditional thermosets. Twintex PP rovings have been pultruded into unidirectional strips for roofing and shelving reinforcement.

The company is working with Honda to develop a rear bumper beam for a 2000 model-year car. Twintex is the only composite material tested that withstands 5-mph impact without sustaining cracks or other damage, Blake reports.

In addition, a compression molded modular interior door panel has been developed by Vetrotex CertainTeed's sister company Sekurit Saint-Gobain, Troy, Mich., for Chrysler Corp.'s 1999-model Viper roadster. It's said to weigh less than comparable BMC, SMC, or injection molded parts and to mold at lower pressures.

Meanwhile, Blake says skid plates are being developed for a 1999 General Motors vehicle. Other potential automotive applications include pick-up box liners and a cross-member structure for the rear of a vehicle.

Ford Motor Co. is presently doing research on compression molding Twintex in order to optimize processing methods and cycle times.