PHA Modifiers for PLA Fiber

Metabolix (Cambridge, Massachusetts, USA) recently introduced newly developed polyhydroxyalkanoate (PHA) copolymer technology.

This development has extended the range of Metabolix’s PHA portfolio with crystallinity ranging from 0% or 60% to include fully amorphous products. The glass transition temperature (Tg °C) of these PHAs now extends from +5°C down to ~-30°C. Like the more crystalline products in its portfolio, these amorphous PHA products are 100% renewable and widely biodegradable in most environments where microbial activity is present. Metabolix sees exciting opportunities for using these new copolymers to modify and improve the performance of PLA and thereby expand the market potential of PLA fibers and filaments.

At Natureworks’ 2014 ITR conference, Metabolix showed early results for modifying PLA using these new PHA copolymers. Metabolix is grateful to Natureworks for their support in this development effort. This work focused on the ability to improve PLA ductility  without negatively impacting the PLA glass transition temperature (a common problem with using miscible plasticizers). Metabolix then demonstrated this effectiveness in PLA films by developing a much softer PLA blown film with flex modulus and toughness approaching HDPE. By varying modifier loads, flexibility and toughness in PLA blown and cast film can be adjusted across the range spanning from paper to HDPE. A series of these film prototypes were highlighted by Metabolix at Interpack 2014.

More recently, Metabolix is excited by very interesting results in improving PLA fibers using with these new PHA modifiers. These developments were also highlighted at the 3rd PLA World Congress in Munich.

Benefits of Modifying PLA fibers with PHA

  • Ductility; Drape
  • Improved touch and feel; Hand & Elongation
  • Reduced Boiling Water Shrinkage

The ductility improvement that characterized PHA modified PLA films is also clearly seen in PHA modified PLA fibers. Textile and nonwoven applications for skin contact require a gentle touch and feel. With only a very low loading (< 5%) of PHA the Hand of the PLA fibers was reduced by 60% (Fig. 3). A soft, silky feel was imparted into the PLA fibers by modulus reduction as well as improved elongation leading to finer filaments and to improved Drape. Furthermore, after drawing and heat set, the PHA enabled hot water shrinkage to be significantly reduced and tenacity improved.

By improving the softness characteristics of PLA nonwovens, expanded potential is possible in medical, personal hygiene (where skin contact comfort is important) and home care applications where single use is expected. The PHA modifier doesn’t compromise the 100% renewable makeup of these non-woven single-use materials.

In textiles, touch and feel comparable to PET is also an important aesthetic factor for success and PHA copolymer modifiers can enable this softness in PLA filaments (Fig. 4). Furthermore, being polyesters in their backbone chemistry, PHA modifiers are compatible with typical fiber treatments for dying and sizing.

  • Distinct Advantages of PHA modifiers in PLA fibers
  • Efficient improvement of touch and feel
  • Compatibility with fiber treatments
  • 100% Renewable (bio-based)
  • Fully Compostable

Metabolix is prototyping these PHA modifiers on a pilot scale in nonwoven and monofilament applications and expects to launch several modifier Masterbatches this year and into 2015 when expanded production of the new PHA copolymer products is expected to be available. These products will take advantage of the extended range of PHA copolymer technology that Metabolix has developed and a variety of PLA base resins to provide solutions for expanding the market potential of PLA fibers.

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