Dated from 1993, By Monks, Richard.

The recent annual composites conference of ASM International, Materials Park, Ohio, and the Engineering Society of Detroit covered a range of timely topics, including advanced thermoplastic composites, thermoset recycling, so-called “3-D” fabric reinforcements, and real-time process monitoring of liquid composite molding (LCM) processes such as SRIM and RTM. Here is a synopsis of some of the more newsworthy presentations.

HIGH-PERFORMANCE RTP SHEET

Du Pont Co., Wilmington, Del., described an aerospace-grade formable thermoplastic sheet based on its “XTC” technology. Du Pont XTC sheet of long-glass-reinforced PET was introduced for cost-sensitive automotive uses last year (see PT, April ‘92, p. 15). This sheet is produced in a papermaking type of process that results in a porous scrim scrim of fibers coated with resin. The porous quality facilitates rapid hot-air heating of the sheet to forming temperature.

For high-performance applications, Du Pont has made XTC-type sheet of 1/4-in. AS4-type carbon fibers and its polyetherketoneketone (PEKK) thermoplastic resin. Offering fuel and flame resistance, as well as static dissipation, Du Pont considers this compression moldable composite to be a lower cost alternative to aluminum in semi-structural aircraft parts. Physical properties of an isotropic panel containing 30% by volume of carbon fiber include a density of 1.44 g/cc, tensile strength of 39,440 psi, tensile modulus of 3.52 million psi, compressive strength of 47,415 psi, shear strength of 17,110 psi, and surface resistivity of 519 ohm/sq.

ADVANCES IN RECYCLING

Researchers at Union Carbide Chemical and Plastics Co. Inc., Danbury, Conn., reported that incorporation of small amounts of organosilicon chemicals increased mechanical properties in polypropylene filled with reground SMC scrap, in recycled Azdel PP/glass-fiber sheet (from GE Plastics, Pittsfield, Mass.), as well as in virgin PP/glass-fiber mixtures. The additives were Carbide’s Ucarsil PC-1A or a blend of Ucarsil PC-2A and PC-1B at a 3:1 ratio. Adding 2% of the organosilicon mixture to reground Azdel containing 38% glass boosted tensile strength in injection molded parts from 6850 psi to 9650 psi. Flexural strength rose from 11,240 psi to 15,350 psi; and notched Izod impact strength increased slightly from 1.0 ft-lb/in. to 1.3 ft-lb/in.

Rogers Corp., Manchester, Conn., discussed its work in recycling phenolics. According to Rogers, cured phenolics can be ground and used as filler in fresh phenolic compounds, resulting in mechanical properties that range from unaffected to significantly increased. Rogers incorporated 4-15% phenolic regrind containing approx. 50% glass content. Rogers found that the smaller the particle size of the regrind, the better the results. Production-scale trials used a virgin phenolic with 40% glass and 10% regrind. Tensile strength at 302 F increased from 8279 psi to 9265 psi, while flexural strength at the same temperature jumped from 17,660 psi to 18,995 psi.

In an effort to make lighter weight yet stronger building materials, the Department of Civil and Environmental Engineering at Michigan State University in East Lansing has experimented with replacing as much as 50% of the aggregate in concrete with recycled HDPE. Using a sulfonation process that helps adhere the recycled plastic to the cement matrix, the MSU team was able to stop microcracks in the concrete and improve its impact resistance. The quality of the sulfonation-induced bonding with the cement matrix, the study showed, was more important to the ultimate results than the recycled HDPE characteristics. Therefore, the researchers concluded, it is probable that different types of plastics would produce comparable results.

Pages: 1 2