A new blend of thermoplastic starch (TPS) and biodegradable copolyester (PBAT) degrades more rapidly than the copolyester alone, broadening application possibilities for blown and cast film, sheet, and thermoformed and injection molded parts intended for composting, it was announced today by the Bioplastics Division of Teknor Apex Company.
With TPS content ranging up to 40%, Terraloy™ 20000 Series compounds have passed the ASTM D6400 test for plastics intended for composting in aerobic facilities. Teknor Apex recommends the compounds for replacing polyolefins and polystyrene in applications such as carrier bags, can liners, trays and plates, cutlery, and flower pots.
While the starch in conventional blends acts as a filler, compromising the properties of the host polymer, the TPS in the new Terraloy compounds is melt-mixed with the copolyester, providing a synergistic effect that retains the key properties of the copolyester, according to Edwin Tam, manager of strategic initiatives. At the same time, the higher biodegradation rate of the TPS speeds composting of blown and cast film and makes it possible to produce thicker sheet and molded parts than with 100% PBAT, while meeting requirements for compostability.
“The process employed by Teknor Apex for intimately dispersing TPS within the host polymer makes it possible for plastics processors to do more with biodegradable copolyester,” Tam said.
He cited tests in which a 100% TPS part with thickness of 0.125-in (125-mil) biodegraded in less than one month, while a 0.007-in. (7 mil) part of 100% copolyester needed more than five months to achieve the same degree of degradation. “When TPS is incorporated into PBAT, it complements this material, opening up additional application possibilities for PBAT to meet the ASTM D-6400 compostability requirement, which is otherwise unachievable due to the thickness limitation for rate of compostability,” said Tam.