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New polymer solves crazing problem

At a press conference held during K 2007, Eastman Chemical (Kingsport, TN) introduced its next-generation copolymer, tradenamed Eastman Tritan. Based on a new molecular structure, the material is said to have a higher heat resistance than traditional copolyester, better toughness, and lower in-mold stresses without giving up any of copolyester?s noted chemical resistance.

Together, these improvements will enable Tritan to outperform polycarbonate in appliance and housewares applications, according to Deborah Baum Crain, director of Copolyester Innovation, Eastman Specialty Plastics.

?The housewares and appliance segment drove the development of this new material,? she explained. ?Most dishwasher-safe parts are currently molded from either SAN [styrene acrylonitrile] or PC. SAN is brittle, while PC parts develop crazing after repeated exposure to hot water. Raising the heat resistance of the copolyester, which has much better hydrolytic stability, solves both problems. It has been tested at 500 commercial dishwasher cycles with no crazing.?

Tritan?s heat resistance reaches 108°C, or 226°F, roughly 65 deg F higher than traditional copolyester materials. ?In addition, an enhanced toughness gives Tritan materials a notched Izod performance comparable to polycarbonate,? said Crain. ?When we tested quarter-inch-thick sections, ductile failures for Tritan were actually occurring above the limits of polycarbonate performance.?

Gregory Nelson, Eastman executive VP and head of the Polymers Business Group, explained that another driver for developing the new material is the increasing competition among brand owners who seek to differentiate their products.

?This new material gives brand owners several advantages in performance, aesthetic, and processing categories,? Nelson said. ?Traditional copolyesters have no residual stress but cycle times are longer than PC. Tritan has cycle times comparable to PC, and can be dropped into existing PC tooling. Shrinkage is the same as PC, so tooling modifications are not required.?

The inherent low inmold stresses of copolyester are also the key to the design freedom that Tritan offers, according to Dante Rutstrom, VP and general manager for Eastman Specialty Plastics. ?Parts that were formerly impossible due to residual stress are now able to be molded,? said Rutstrom. ?And the chemical and heat resistance, combined with toughness and durability, mean these materials will apply to a wide range of products.??MM

Eastman Chemical Co.
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