Plastics additives suppliers are playing a major supporting role in the evolution of biopolymers.
Plastics additives improve the usefulness of sustainable resins. As in their usage in conventional polymers, additives aid processing and boost mechanical properties and, in the case of colorants, provide a palette of hues.
``The challenge is defining the problem and identifying meaningful targets,'' said Jim Gray, director of business development for biomaterials with PolyOne Corp. of Avon Lake, Ohio.
Additives makers are working to improve the mechanical properties of the biopolymer polylactic acid. In its natural state, it can lack melt strength, impact strength and heat resistance.
Biopolymer polyhydroxyalkanoate also relies on additives for strength and performance. Impact strength, flow, thermal stability, lubrication and nucleation are among the properties PHA supplier Metabolix Inc. wants to improve, according to Sally Kline, the firm's director of technology. Boosting strength, while maintaining degradability, is a tall order for most additives, she said in a telephone interview from Metabolix headquarters in Cambridge, Mass.
``It's an opportunity for additive suppliers to develop new chemistry,'' Kline remarked. Metabolix is promoting degradability for all its PHA applications so any additives it recommends need to meet that criterion.
Kline said she has seen a lot of technology development but additive suppliers still have some work to do to get the full potential out of PHA. Colorants, thermal stability and nucleation are among the areas needing the most work.
``We're always looking to improve, to help us expand the performance envelop,'' Kline stated.
Additives are not necessarily interchangeable for PLA and PHA, according to Kline.
Choosing an additive for a biopolymer might entail finding one that is degradable as well as modifies a property. The biopolymer's end use often dictates the additive choice.
``It all depends on the application, approval requirement of the item and the claims the manufacturer willl make on the final part,'' said John Politis, director of marketing for Teknor Color. Co. of Pawtucket, R.I.
For a part to be designated as biodegradable, for example, the resin and additive must allow the product to pass tests such as ASTM 6400 tests for compostability. The same argument applies in choosing a carrier resin in additive and colorant masterbatches.
``When the plastic breaks down, everything is released to nature,'' explained Chris Pandis, global head of the packaging market segment for Clariant Masterbatches. Degradable additives don't persist in the environment as traditional ones might.
To address brittleness, Rohm and Haas Co. has developed a new impact modifier aimed at bioplastics. It is designed to make PLA more effective in packaging.
Rohm and Haas of Philadelphia claims its modifier does the job without hurting clarity. Based on dispersible nanoparticles, the additive shows less than 10 percent haze at loadings of 5 percent.
Plastics Color Corp. of Calumet City, Ill., is one firm using the new modifier in a masterbatch.
DuPont Co.'s packaging business has an additive that strengthens PLA — an ethylene copolymer that boosts impact strength, flexibility and viscosity. The pellets are well-suited for rigid applications such as cast sheet for thermoforming, and in injection molding. It, too, has minimal impact on clarity at usage levels of 5-10 percent, said Wilmington, Del.-based DuPont.
Arkema Inc. has impact modifers and a melt-strength enhancer for PLA. One modifier is designed for translucent or clear applications, the other is higher efficiency for opaque uses. The melt-strength enhancer is an acrylic copolymer that also enhances processability of PLA in sheet extrusion, calendering, blow molding, thermoforming and foaming.
New from Philadelphia-based Arkema is a metal release lubricant for PLA. The lubricant allows a wider processing window in extrusion, injection molding and calendering of PLA and other biopolymers.
Variations in processing temperatures and shear are minimized with the lubricant, according to Arkema.
``Heat distortion is an issue with PLA,'' PolyOne's Gray said in an interview.
PolyOne has developed a compounded blend of PLA with an undisclosed polymer that hikes PLA's heat resistance from about 131° F to more than 212° F. For the higher temperature, PLA comprises 35 percent of the compound. The blend is not transparent.
PolyOne recently introduced colorants and process aids based on sustainable materials that complement the firm's line of additive concentrates for biopolymers. Gray said impact modifiers and rheology modification additives are among the latest, and bolster the company's lineup of ultraviolet protectors, anti-statics, slips/anti-blocks, anti-fogging agents, blue-tone additives and denesting agents.
Several more companies have introduced or are developing additives and colorants that are degradable or otherwise suited for use in biopolymers.
``As the market grows, more additive suppliers are fine-tuning their products,'' said Gray.
Clariant Masterbatches of Holden, Mass., is expanding its line of Cesa-natur renewable additive masterbatches. The company has commercialized masterbatches based on slip/anti-block agents, UV/light stabilizers, antioxidants and anti-stats. The company is developing an all-natural antimicrobial additive, impact modifiers and a metal deactivator, Pandis said in a telephone interview.
Clariant's Renol-natur colorant masterbatches also are based on renewable, biodegradable ingredients such as chlorophyll and curry. The colors aren't as intensely bright as, say, cadmium pigments, but muted colors are in vogue for most biopolymer applications.
Teknor Color recently debuted color concentrates for use with PLA resins. They are designed for clear or opaque bottles, film, sheet, profiles and injection molded items. One concentrate, with a PLA carrier, is for all biodegradable applications. Another has a biodegradable copolyester carrier aimed at biodegradable blown film where greater flexibility is needed than is possible for 100 percent PLA carrier. The third series has PET as a carrier and is geared to nonbiodegradable applications such as toys and housewares. All three are available in a range of colors, according to Politis.
Polyvel Inc. has concentrates for PLA including slip, nucleation, anti-block, matte, impact-modification, and a plasticizer for film and extruded foam, according to the Hammonton, N.J., firm.
One challenge facing additive and concentrate developers is getting enough biopolymer to conduct development work, according to Gray. Supply constraints ``limit short-term development,'' he said. Gray also questioned the consistency of biopolymers from lot to lot.
``So far there are not too many problems,'' said Clariant's Pandis, regarding biopolymer supply.
``Big food companies are treading slowly, so there isn't massive demand.''
Pandis said sustainability also benefits from using additives in the three R's: reduce, recycle and reuse.
Reduced resin weight is possible through foaming agents.
Recycling gains from chain extenders that help regain strength in PET. Optical brighteners help overcome color problems in recycled resins and antioxidants help them last longer.
Reuse is becoming more important as items shift away from disposability. Heat stabilizers and antioxidants provide greater durability for molded and extruded goods.