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New clear, food-grade styrenic goes from freezer to microwave.

New Clear, Food-Grade Styrenic Goes From Freezer to Microwave

New thermoformable food grades of an engineering styrenic copolymer from Arco Chemical Co., in Newtown Square, Pa., have thermoformers excited. The new resins include what may be the first clear, microwavable styrenic tray material on the market. Opaque impact grades are also available.

The resins are new versions of Arco's Dylark styrene maleic anhydride (SMA) copolymer, previewed at the recent PMMI Pack Expo in Chicago. Dylark has been used mostly in automotive applications like foamed head liners, injection molded instrument panels and trim. These are apparently the first food grades of SMA on the market, though Arco has other clear Dylark materials. The new food grades--Dylark 232-FG, 332-FG and 378-FG--target clear and colored microwavable trays> 232-FG and 332-FG can also be foamed. But the impact-modified 378-FG, targeting freezer-to-microwave trays, is causing the most excitement.

Rumors of a new clear microwavable styrenic have been circulating for months, building anticipation among tray formers, who find PP, PET and CPET difficult to form, or perhaps face capital investment to modify existing machinery for tighter process and temperature control. By contrast, Arco's impact-modified Dylark 378-FG is formable on any standard PS forming equipment at comparable cycle times, says Edward Passarelli, president of Clear Pack Co. In Franklin Park, Ill., which is doing development work with the new Dylark on a Brown 821HD. "It's hard to tell the difference from PS," he says. Clear Pack is prototyping a two-compartment oblong tray for nacho-cheese snacks in red, yellow, or black, using Milliken Clear Tint colorants. Clear Pack is also working on an application to be pasteurized at 190 F, then quick-frozen to -40 F in 15 min.

Arco's commercial development manager for the new resins, Joseph Paolucci, says the Dylark-FG materials are FDA approved for conditions H through B, and Arco is pursuing condition-A approval for two of the grades, 332-FG and 378-FG (for retorting). Paolucci says early results show that 378-FG appears reliable in freezer conditions. He notes that it can also be down-blended with high-impact PS to increase low-temperature impact strength and cost-effectiveness, without significant loss of high-heat properties.

Paolucci says Arco hasn't changed the molecular structure of its original Dylark to produce the food grades, but only "tuned the process for better taste and odor properties."


Single-portion trays of Dylark resins are competitive with PP at a cost of 6[-11[/tray, but use 25-30% less material, says Clear Pack. They're formed from 20-mil sheet, compared with 25-30 mil for a comparable PP tray. Dylark's ability to down-blend with lower cost materials like HIPS also reduces cost. Clear Pack's prototype freezer-to-microwave tray, for example, is a 60:40 blend of SMA with HIPS, at half the cost of pure SMA.

Cycle time is also a cost saver relative to PP. "Processing is close to half the total tray cost, so 20% faster cycle times equate to overall savings of about 10%," says Clear Pack sales director Art Hagg, noting that Clear PAck's high-heat prototype tray runs at 22-23 cycles/min, whereas "18 cyles/min is considered acceptable for PP."

Commercial production of the new grades is to start this year. The resins will be sold as pelletized natural product for under $1.40/lb, depending on quantity and grade. Besides forming trays, Clear Pack will sell all three grades down-blended with HIPS, as 9-70 mil sheet, at $1.32-1.48/lb, depending on quantity and grade.
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Author:Schut, Jan H.
Publication:Plastics Technology
Date:Jan 1, 1991
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