Biodegradable polymers crop up all over again.

Unlike earlier offerings, biodegradables now do what their name suggests. But it may be what else they can do that ensures them a future.

Just when it seemed biodegradable polymers would fade from view, never getting their chance to dissolve in our compost heaps, they've sprung up again. As an answer to environmental problems, short-lived polymers may still pale next to more popular "green" solutions like recycling and source reduction. But don't count out the latest versions. In spite of hefty price premiums, at least three of these materials recently wound up in new commercial applications. Even brighter hopes for biodegradables rest on a future that embraces composting more fully.

So why didn't degradables catch on earlier? Suppliers blame a perception problem in part, noting that efforts in the '80s degraded only partially. These resins still left small pieces of conventional polymers after a biodegradable binding had dissolved. "Companies have gotten a black eye promoting these kinds of resins as biodegradable," notes Scott Johnson, development manager for Vinex resins from Air Products and Chemicals Inc. Unlike their forebears, today's biopolymers break down completely into non-plastic constituents--substances like water, C|O.sub.2~ and biological materials.

An even bigger obstacle for biodegradables remains. Never cheap, biodegradables can cost as much as $10/lb--a far cry from the commodity resins they often compete against. Whether the drive to reduce the environmental toll will get strong enough to offset this price differential is unclear. In the meantime, suppliers admit it's not easy selling green. Yet, a niche for these materials has already sprung up wherever biodegradability can impart advantages that transcend environmental concerns. And at least three divergent biodegradable technologies fall into that category now.

As for the future, suppliers argue large-scale composting will soon provide the ideal disposal environment for spent biodegradables, a place where they easily outperform conventional polymers. Warner-Lambert's Novon Products Group, for instance, points to a recent Roper study showing that 96% of waste-management professionals anticipate significant growth in composting over the next decade. And at ICI BioProducts and Fine Chemicals Div., marketing manager William Luzier also expects composting to create more opportunities for the company's Biopol polymer. Yet rather than replacing other environmental solutions altogether, biodegradable materials will likely play a single role in a more comprehensive waste-management picture. "Manufacturers realize the need for a combination of solutions," notes Rhonda Brooks, marketing v.p. for Novon Products Group.

STARCH FOR THE FUTURE

One of the starch-based polymers from Novon Products recently found a place in injection molded golf tees from Terra Form Inc. of Dalton, Mass. Aside from being the first commercial domestic molding application for two-year-old Novon, the tees illustrate how biodegradability can overcome a price premium by addressing non-environmental needs. Degradable tees may be nice from an ecological perspective, but perhaps not enough to offset the $1.50-3/lb cost of the biodegradable resin. In this case, however, Novon resin primarily tackles another problem--the maintenance headaches caused by leftover tees. Rain and overnight course watering dissolves the tees. The resin itself breaks down into water, C|O.sub.2~, and biological material at the same rate as wood or leaves, according to the company.

Novon Products makes its polymers from starch, proprietary biodegradable additives and naturally occurring minerals (see PT, Sept. '91, p. 19). Starch content ranges between 60% and 98%. Specific gravities fall between 1.30 and 1.45, or 30-40% higher than commodity resins. With a glass-transition temperature of 140 F, Novon resins soften and melt at lower temperatures than commodity plastics but remain stable to 300 F. The polymers have worked in the full variety of extrusion and molding processes, the company reports. The grade chosen for the tees, Novon 3001, won out over other grades because it degrades quickly in a soil environment and can be injection molded. The company recommends molding temperatures between 265 and 410 F. Other commercial uses for Novon so far include foam-packing material and votive candle cups.

Potential composting frenzy aside, Novon Products emphasizes the concept of designing resins for other disposal methods as well. "We'll see a series of grades tailored to specific disposal methods," Brooks says of Novon resins planned for the near future. For a cotton-swab manufacturer, Novon Products has already come up with a grade designed specifically for flushing. Brooks adds that the next generation of Novon grades, by contrast, will offer more water resistance, opening up wetter applications like baby diaper film.

Novon Products has also worked toward the marriage of biodegradables and recycling. Brooks says a developmental film grade will soon be available as a tie layer for laminated packaging. As this layer degrades, recyclers could easily separate the laminated structure into paper, aluminum and plastic.

PUTTING BACTERIA TO WORK

Employing a biological manufacturing process, ICI actually leaves the polymer production to bacteria. The company make its Biopol family of biodegradable polyesters through a proprietary fermentation process. A single species of bacteria converts corn and potato feedstocks into a copolymer of polyhydroxybutyrate (PHB) and hydroxyvalerate. By manipulating the agricultural feedstocks, ICI can vary the proportions of these two naturally occurring homopolymers to arrive at different Biopol grades.

All offer moisture resistance while still degrading fully, ICI reports. In the presence of oxygen, the PHB/V decomposes into C|O.sub.2~, water, and some biological material. In anaerobic settings, it breaks down into molecule-sized pieces.

Biopol may suffer the most from the bane of all biodegradable resins--it costs a lot. For the time being, prices range between $8-10/lb. Nonetheless, ICI chalked up its first North American application just two months ago. The Berlin Packaging Corp. has chosen Biopol to bottle a new line of hair-care products.

Marketing manager William Luzier expects Biopol prices to come down now that ICI produces more of the resin at its new 300 metric ton/yr production facility in Billingham, England. "We're in the process of ramping up capacity relative to demand," he explains. In fact, ICI projects production to reach 5000 metric tons/yr by the middle of this decade.

Even at its current price, Luzier says biodegradability and "naturalness" make the product appropriate whenever packaging costs are low relative to the product's retail cost. He cites personal-care goods as the chief example, and European manufacturers already use Biopol to package such products. Biopol has also gone into bottles for hair-care products in Japan.

WATER SOLUBLE SELLS

Air Products takes yet another tack with its Vinex series of synthetic biodegradable polyvinyl alcohol (PVOH) resins. Johnson explains that at $2.50/lb, Vinex would be a tough sell on biodegradability and composting ability alone. "We don't really promote it on the environmental aspect," says Johnson. Instead, the company stresses two of the physical characteristics it provides: water-solubility and barrier capabilities. Vinex customers pay mostly for these properties, not biodegradability. Still, the company doesn't discount the fact that the resins decompose completely into water and C|O.sub.2~.

Applications so far have come where solubility makes products easier or safer to use, Johnson says. For pesticides, ink, and other chemicals, Vinex bottles provide the barrier properties to protect the contents. At the same time, Vinex allows unit does of a given chemical to be administered with the toss of a soluble bottle into any application where water is present. Fibers made from Vinex have seen use as bales for binding wood pulp. These straps then degrade to release the pulp. Otherwise, a person would have to risk cutting steel bales.

As for processing, Vinex products have also been injection and blow molded. Other extrusion applications have included foam and coated paper as well as blown and cast film. Vinex resins have a specific gravity of 1.25 and melt flows ranging between 5 and 30 g/10 min. The company offers grades soluble in either cold or hot water. Johnson says the only special requirement for processing Vinex is tight temperature control since it has a processing window of only 30-40|degrees~.

Currently, the Vinex 1000 Series offers the highest dissolution temperatures at 100 F while the 2000 Series exhibits the highest tensile strength at 5200 psi. In the coming months, however, a special blown film grade with even better physical properties and higher dissolution temperatures will come on the market, Johnson adds.

BIOLOGY MARCHES ON

Biology's inroads into the world of polymers stretch beyond the companies already mentioned. Novamont North America, for one, sells the MaterBi family of starch-based resins for the full range of molding and extrusion processes. Other sources, meanwhile, have come up with biodegradable polymers based on lactic acid. Du Pont's EcoChem, for instance, has developed such a polylactide from cheese whey and corn (see PT, Sept. '91, p. 23). And Kyowa Hakko U.S.A. recently obtained a license for polylactide technology developed by the Argonne National Laboratory in Illinois.

FOR MORE DETAILS ON ITEMS IN THIS ARTICLE, USE READERS' SERVICE CARD

Air Products and Chemicals Inc., Polymer Chemicals Div., Allentown, Pa. (CIRCLE 65)

Du Pont/EcoChem, Wilmington, Del. (CIRCLE 66)

ICI BioProducts and Fine Chemicals Div., Wilmington, Del. (CIRCLE 67)

Kyowa Hakko U.S.A., N.Y.C. (CIRCLE 90)

Novamont North America, New York, N.Y. (CIRCLE 68)

Warner-Lambert's Novon Products Group, Morristown, N.J. (CIRCLE 69)