New Grades Improve Weatherability, Molding

Thermoplastic elastomers are copolymers that exhibit advantages of plastics and rubber, usually for specialized applications such as sealing. They are potentially recyclable, yet — like rubber — they are elastic and can absorb shocks. Their ability to stretch and bend without losing properties makes them valuable companions to thermoplastics, which can provide structure. One example is a new sports boot made with the thermoplastic polyester elastomer, which can absorb energy. Elastomers are often co-molded with rigid thermoplastics to provide a tactile feel on a grip handle on products such as razors.

DON'T BREAK A LEG

The Genius MX Boot was developed by Scott Sports to prevent lower-leg injuries among motocross riders. The Scott Pivot System allows the boot to flex while retaining its solid construction. It's made of DuPont Hytrel thermoplastic polyester elastomer, which has good fatigue resistance, damping properties and high-impact strength over a wide temperature range. “Under excessive loads, such as during jumps or falls, the Hytrel structure absorbs energy and thereby reduces the amount transmitted through to the rider's foot or leg, discouraging fractures and ligament strains,” says Hervé Maneint, project leader at Scott Sports. Also, the hood of the boot, injection-molded in Hytrel 6356, incorporates a soft over-molded section, combining Hytrel 7246 with polyurethane. The external, copper-colored pad is positioned in the shifting area at the top of the boot and transfers shifter lever pressure through ridges on the interior of the boot, allowing the rider to feel it without compromising protection of the boot.

CUT STABILIZERS, REDUCE COSTS

A family of lower-yellow-index thermoplastic polyurethane (TPU) elastomers will be commercialized by Dow Chemical under the Pellethane brand by the end of the year. These new products are said to offer “best-in-class” color performance and deliver significant aesthetic, weatherability and processing benefits. Dow will offer both ether and ester grades at various hardness levels. Advantages of the new materials include: increased color consistency of final fabricated parts; cost savings due to reduced use of UV stabilizers; better weatherability and improved thermal stability for higher-heat applications, as well as those that use regrind.

FLOW RATES SPEED MOLDING CYCLES

New vulcanized thermoplastic elastomers (TPVs) exhibit high-melt flow rates, allowing a speedup in molding times and a capability to fill more complex cavities. There are currently six grades in the 9500 SHF series, ranging in hardness from 55 to 85 Shore A. “The new SHF grades flow so much better that injection molding cycles can be as much as 15 percent shorter than with traditional vulcanized thermoplastic elastomers,” says Hamid Tavakoli, product manager for Solvay Engineered Polymers. Solvay says these elastomers can be processed in a wide temperature window up to 500F without showing signs of degradation. One of the prospective applications is encapsulation of glass.