Metabolix highlights PLA modification using PHA at PLA World Congress

At last week's third PLA World Conference in Munich, Germany, many of the presentations addressed the challenges of modifying PLA such that improved properties are obtained that will make a broader ranges of applications within reach.

The talk delivered by Metabolix Vice President of Biopolymers Bob Engle was also along these lines, with a focus on technology developments in which PHA is used as a modifier for polylactic acid, or PLA as it is more commonly known. Metabolix has developed new polyhydroxalkanoate (PHA) copolymer technology that extends the range of its Mirel PHAs, he said.

"There is a significant opportunity to expand the range of applications addressable by PLA, the current industry-leading biopolymer material, by rubber toughening it with PHA modifiers," Engle said. "We are developing proprietary PHA copolymer technology that is compatible with PLA and can modify PLA's properties to provide significant improvement in toughness and ductility, while still satisfying the market need for high bio-content and compostable solutions in applications such as single-use nonwovens, blister packaging and film."

These recent PHA polymer innovations underscore the strategy currently employed by Metabolix, which focuses on demonstrating the performance and value that its Mirel PHA polymers can bring to target applications, in the form of improved physical properties such as crystallinity and rheology.

Now, Metabolix is demonstrating the value in using PHA polymers to enhance the performance of PLA. Not only is PLA perhaps the most widely used bioplastic in the world today, projections suggest PLA demand growth as high as 20% per year into a broad range of applications, from food to packaging, and more recently into 3D printing and automotive uses.

But PLA is a brittle polymer that is often modified to improve its ductility. Plasticizers are one way of doing so, but these are associated with such adverse effects as reduced toughness, a lower the glass transition temperature (Tg) resulting in lower heat resistance and a narrowing of the processing window.

"At Metabolix, we have demonstrated the effectiveness of using amorphous PHA copolymers to 'rubber toughen' PLA bringing both ductility and toughness. Not being a miscible plasticizer, PHA modifiers will not significantly lower the Tg of the PLA nor compromise the processing window," said Engle.

Moreover, Metabolix PHA modifiers will not compromise the high biocontent or compostability of PLA. Inherent compatibility with PLA also means blending is relatively straightforward and clarity can be maintained without the need to tune refractive indices.

"We have seen very promising results thus far in 2014 as we prototype PHA modifiers for the PLA market across a range of PLA applications and converting technologies," Engle continued.

In PLA fibers, PHA modifiers added at levels at or below 5% have improve the "hand," a complex measure of softness, pliability and feel, by as much as 60%. This effect is a combination of ductility enhancement and elongation leading to thinner filaments and reduced shrinkage. Improving the softness characteristics of PLA nonwovens, expands the range of potential uses in personal hygiene, home care and medical applications where skin contact requires a gentle touch and feel. In these single use applications, the renewability of PLA measured in high biocontent (and potential for compostability) is important and uncompromised by PHA modifiers.

In PLA sheet, PHA modifiers have demonstrated the ability to eliminate the brittle edge trimming issues, thus improving safety and reducing scrap. The combination of ductility enhancement and elongation leads to the potential for a significant improvement in impact strength. Similar benefits are now realized in injection molded single-use items. In blown film, improved flexibility and toughness approaching HDPE has become a reality with PLA-based films.

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