Acrylic beats alcohol problems

New York -What plastic is least like a naughty frat boy?

Until recently, acrylic would have been a good answer, given its aversion to alcohol and shocking conditions. But Cyro Industries (Rockaway, NJ) has set out to eliminate these two long-standing sensitivities with the introduction of new acrylic-based terpolymers at the Medical Design and Manufacturing Show. One new grade, intended mostly for medical applications, stands up to alcohol, while a shock-fighting grade dissipates electrostatic discharge (ESD) without sacrificing clarity. Both new materials injection mold much like conventional acrylic terpolymers.

For parts needing alcohol and lipid resistance, the company has introduced Cyrolite Med. According to Cyro Medical Specialist Mike Gibson, the new material "far outperforms lipid resistant polycarbonate" in terms of elongation retention. In one test, he says, Cyrolite Med samples exposed to isopropanol for five hours at 20C under a 2% strain had an elongation retention of 130% versus 4% for lipid-resistant PC. In a lipid-solution exposure under the same temperature and stain conditions, Cyrolite had an elongation retention of 94% versus 3% for the polycarbonate, Gibson reports. Other properties include an 80% light transmission, a haze value of 8, a tensile strength of 6,660 psi, a tensile modulus of 298,000 psi, and a notched izod of 1.7 ft-lb/inch in a 1/8-inch bar.

Though intended mostly for medical applications-such as filter housings, luers, IV connectors, valves, and catheter adapters-Gibson adds that the material could also see use in any industrial or consumer-product part exposed to alcohol.

For ESD sensitive components that require some clarity, Cyro has come up with Clearstat C-37. According to Rob Shiely, a technical service engineer for Cyro, the Clearstat's ESD properties spring from a liquid additive formulated to match the acrylic's refractive index, making the treatment permanent. "It lasts over time, not for days," says Shiely, noting that ESD properties previously imparted to acrylic relied on applied treatments that would degrade.

According to Gibson, Clearstat offers a surface resistivity of 2.6x10 ⁹ ohm/sq and a volume resistivity of 8.9x10 ¹⁰ ohm-cm (23C and 12% RH). At the same time, the material really is clear, with Gibson reporting that it has a haze value of 10 and 77% light transmission in 1/8-inch samples. Its mechanical properties include a tensile strength of 4,880 psi, a tensile modulus of 222,000 psi and a notched izod of 1.5 ft-lb/inch in a 1/8-inch bar.