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HCFC-resistant styrenic alloy challenges ABS, HIPS in refrigerators.

HCFC-Resistant Styrenic Alloy Challenges ABS, HIPS in Refrigerators

A developmental, extrusion-grade styrenic alloy specifically designed to provide improved chemical resistance to HCFC-blown polyurethane foam insulation in refrigerator and freezer liners is now being test marketed by the Dow Plastics unit of Dow Chemical Co., Midland, Mich.

The unnamed, proprietary alloy would be used to extrude sheets for thermoforming. It's formulated to overcome stress-cracking and blistering problems that have been encountered with traditional ABS and HIPS materials. Evidently, the HCFC blowing agents that have been developed as more "ozone-friendly" alternatives to CFCs in urethane insulation foams tend to be more aggressive against ABS and HIPS liner materials. The higher environmental stress-crack resistance of the new alloy reportedly would eliminate the need for added coextruded or laminated film barriers to protect the thermoplastic liner.

Dow officials cautiously refer to the new alloy only in generic terms as a "styrenic material." It's now undergoing field evaluations with several unnamed customers. The alloy already has been tested under full-scale commercial processing conditions with several appliance manufacturers, Dow says. Steve Swartzmiller, Dow senior development engineer for thermoplastic resins, says the styrenic alloy is at least a year away from full commercial introduction.

If proven commercially successful, the new alloy would displace ABS and HIPS as materials of choice for this appliance application. Both ABS and HIPS require additional polymer barrier layers to protect against chemical attack by HCFC-blown foams, which are slated for widespread commercial use in the 1993-94 time frame. "We see the new styrenic alloy as a |drop-in' replacement for traditional styrenic resins in refrigerator liner applications, without having to add special barrier films," Dow officials say.

THERMOFORMS LIKE ABS, HIPS

Although data-sheet information is not yet available regarding mechanical and thermal properties, Swartzmiller says the material extrudes much like HIPS and thermoforms similar to ABS or HIPS. The alloy's mechanical and thermal properties are similar to HIPS while offering greater toughness, he says. Swartzmiller says that, like current HIPS liner materials, the new styrenic alloy will require an additional PS gloss layer to meet the standards of U.S. manufacturers. Most ABS grades typically can meet gloss requirements without an additional cap layer of PS.

Douglas Kunnemann, market manager for the U.S. Appliance Group of Dow Plastics, says Dow has taken the unusual step of locking in the price of the styrenic alloy at 90[cents]/lb tl through 1993. He says this move illustrates Dow's confidence in the resin's growth and a willingness to control costs during market testing while manufacturers ramp up in utilization of the material.

Along with chemical resistance, the new alloy is being formulated for optimal adhesion to PU foam. Swartzmiller points out HIPS bonds poorly to PU foam, while ABS bonds well. Current development efforts to fine-tune the alloy include controlling its adhesion level to meet appliance manufacturers' requirements. Dow's capability as a producer of polyurethane foam proved to be a valuable technical resource throughout the two-year development of the styrenic alloy, he says.
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Title Annotation:hydrochlorofluorocarbons; foam insulations; high impact polystyrene
Author:Gabriele, Michael C.
Publication:Plastics Technology
Date:Dec 1, 1991
Words:499
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