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Bioplastics Conference Learns of New Additive to Enhance PLA Performance

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19. February 2014

Innovations Take Root, the biennial conference and exhibit organized by NatureWorks LLC, Minnetonka, Minn., feels different from most plastics industry meetings. For one thing, there’s the sense of excitement among the participants in helping create something new—an entire plastics supply chain based on renewable, biobased feedstocks. And for me, at least, this event is reminiscent of a time decades ago when the big polymer producers would gather together other segments of the industry—machine builders, additive suppliers, and processors—to help each other learn how to tap the potential of an upstart family of materials that was challenging the established order. NatureWorks, supplier of Ingeo PLA (poly lactic acid) is the world's leading bioresin producer.

Participating in this year’s two-day event are 41 speakers and around 370 attendees—a new record—from 27 countries and 209 companies. In the news on the first day was a new player in additives for improving performance of PLA biopolymer.

Metabolix Inc., Cambridge, Mass., has just begun to commercialize new grades of its Mirel PHA (polyhydroxyalkanoate) biopolymer designed specifically to modify PLA. This is an extension of its recent introduction of PHA grades for modifying flexible and semi-rigid PVC (see July ’13 feature article). In both cases, Metabolix has come up with new amorphous, rubbery grades of its normally rigid and semicrystalline Mirel PHA. According to Bob Engle, v.p. of biopolymers, PHA acts as a flexibilizer and impact modifier for PLA, much as it does for PVC. It adds ductility and toughness without lowering the Tg or HDT of PLA. Mirel is inherently compatible with PLA but forms two-phase blends that remain clear at up to 20-25% PHA. The rubbery additive has a Tg of -30 to -50 C, and Engle says it is similar in efficiency and cost-effectiveness to standard impact modifiers of ABS, MBS, or acrylic in the same Tg range. A key difference, however, is that PHA retains full compostability of the compound.

Metabolix is starting with a PLA compound (designated P4004) containing its PHA modifier. The compound is designed for rigid sheet extrusion and thermoforming. The modifier reportedly makes the formed sheet cut cleanly and prevents deformation of the package during heat-seal operations. Later this year, Metabolix aims to offer the modifier separately as a masterbatch in a PLA carrier. Engel says Metabolix is also expanding capacity for modifier grades of PHA by 4-10 million lb in the near future.

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