A biopolymers bonanza is seen beyond degradables.

Nowadays, executives at Cargill, Inc. in Minneapolis are the first to admit that the domestic market potential for biodegradable resins is somewhat limited. As the world's biggest producer of polylactic acid (PLA) resins made by bacterial fermentation of cornstarch or sugar beets, Cargill says PLA will have to compete on properties and cost with other commodity resins in uses where degradability is a secondary or negligible attraction. Within 10 years, such uses reportedly could push global PLA demand over the billion-lb/yr mark for cast and oriented films, blown films, fibers and nonwovens, foam sheet, rigid containers (blown, thermoformed, and injection molded), and paperboard extrusion coatings.

A NEW PARTNERSHIP

Such a forecast would have sounded outlandish a year ago, but it has gained credibility from the announcement last month of the formation of Cargill Dow Polymers L.L.C., a 50/50 joint venture of Cargill and Dow Chemical Co., Midland, Mich. The two firms had quietly conducted a 15-month joint-development program to evaluate PLA's potential. Dow brings to the venture its global marketing resources and know-how in materials formulation and processing. Cargill contributes nine years of PLA R&D experience and its 8-million-lb/yr semi-works plant near Minneapolis. Capacity there will be doubled by the end of this year. The partners expect to build a world-scale PLA production facility of 250 million lb/yr by 2001.

PLA is a polyester made from lactic acid that is produced by fermentation. PLA can be fully compostable and is recyclable. The only current commercial application in North America is compostable bags for yard waste and food waste (see sidebar). In Europe and Japan, applications are being developed for thermoformed yogurt cups, extrusion-coated paper cups, cellophane replacement, bin liners, nonwoven agricultural mulch fabric, and cast film for consumer packaging. Current PLA prices range from $1.30 to $3/lb. Once a world-scale plant is built, Cargill Dow officials foresee prices closer to 50[cents]/lb.

COMPETES ON PROPERTIES

Jim Stoppert, formerly Dow's global director of polystyrene issues and development and now president of the new venture, voices confidence that, degradability aside, PLA will ultimately compete on cost/performance with PE, PP, PS, and PET, as well as paper and cellophane. Currently, PLA's biggest potential appears to be as a lower-cost competitor for PET in films, fibers, and bottles for water and other noncarbonated liquids. PLA reportedly offers clarity and gloss superior to PET and comparable to PS. Also superior to PET are PLA's printability (more like that of PE), heat-sealability (more like PS), and ability to be metallized and barrier coated. Many PLA properties are similar to those of PET: stiffness, tensile strength, oil and grease resistance, crimp properties, and flavor and odor barrier.

Other advantageous characteristics reportedly include lower heat-seal and processing temperatures than many polyolefins, processability similar to PS, and memory (deadfold) properties like cellophane. Moisture and gas permeability are in the same range as those of polyolefins.

Stoppert says processing of PLA has been demonstrated on a large commercial scale with only minor modifications to equipment. PLA must be predried. It appears suited to virtually all processes, including ones involving orientation, which improves its properties.

One of the most promising aspects of PL& says Pete Hawthorne, Cargill's general manager for emerging businesses, is its unusual range of properties from amorphous to crystalline. These can be tailored by manipulating molecular weights and the mix of right- and left-handed stereo-isomers, as well as through copolymerization. Today, Cargill Dow's seven grades of "EcoPLA" resins (see table) are copolymers with epoxidized soybean oil, though the company plans to explore a wider range of random and block copolymers.

Typical properties of today's grades include a Tg of 140 F, crystalline melting point of 266-356 F, processing temperature of 374-500 F, and HDT of 133-279 F at 66 psi.

ANOTHER PLAYER SCALES UP

Cargill Dow (whose personnel will remain at Dow and at Cargill locations) has a few PLA competitors with smaller production capacities. According to Hawthorne, Mitsui Chemicals and Shimadzu Corp. of Japan (both have offices in N.Y.C.) have a combined capacity of around 1.3 million lb/yr. In North America, the only other PLA producer is Chronopol Inc. of Golden, Colo., which is developing technology originally from Battelle, Adolph Coors, and DuPont. This month, Chronopol will start up a 2-million-lb/yr semi-works plant in Golden. The next step will likely be a 100-150 million-lb plant to come on stream in 2002. "We've got markets identified to easily fill that plant up," asserts director of marketing Stephen Cox. "Many of the people we're selling to today have 10- to 20-million-lb applications waiting. They expect us to build a large plant for resin that will cost them $1.50-2/lb in 2002." Today's prices for Chronopol's Heplon Polylactide are around $5/lb or more. At the 500-million-lb production level, Cox thinks the price could get down to $1/lb.

Cox is enthusiastic about PLA's wide range of properties. It reportedly can be as hard as acrylic or soft as polyethylene, stiff as PS or flexible as an elastomer. It can be formulated in a variety of impact strengths. PLA is gamma sterilizable and uv stable. It can have glass-transition temperatures from 44 to 140 F and melting points from 266 to 356 F. Crystallinity can be from 0 to 40% in linear or branched homopolymers and random or block copolymers. The company is concentrating on linear, highly crystalline homopolymers for now, though it has explored several copolymers, including ones made with caprolactone. Cox says Chronopol has an advantage over others in its ability to produce 100% pure stereo-isomer whose properties exceed those of isomer mixtures that are only 93-97% pure.

Properties that Cox finds particularly exciting are softness and surface hardness. The former would be attractive in applications next to the skin, such as adult incontinence diapers. Scratch and scuff resistance could allow PLA to replace acrylic-coated OPP films or acrylic films that are laminated onto paperboard packaging. PLA could provide mar-resistant labels for returnable softdrink bottles. It could also make longer-lasting bristles for street sweepers (now of PP). High gloss and odor barrier suggest perfume or cosmetics packaging, Cox notes. Very fine-denier PLA fibers could prove superior for [TABULAR DATA OMITTED] filtration. Cox predicts that PLA monofilaments can be oriented to achieve twice the tenacity of PP filaments, suggesting the ability to make high-strength twine with less material at competitive cost. He also says PLA processes easily on conventional screws and equipment for PE, PVC, PET, and nylon.

Cox acknowledges that PLA's compostability and renewable-resource pedigree offer small domestic market potential, though they are more highly valued abroad. But even at home, he says, a biodegradable clamshell hamburger pack might be worth a penny more to a player seeking a marketing edge.

RELATED ARTICLE: First Domestic PLA Application

The only real commercial use of PLA in North America is 33-55 gal compostable bags for yard and food waste, which have been made since 1996 by Duro Bag Manufacturing Co. in Ludlow, Ky. The translucent bags hold up to 50 lb. Dave Davis, v.p. of marketing, believes that Duro will get the price down closer to that of paper waste bags in 1998. "This year well probably sell 34 million bags," he predicts.

The bags are a 1-mil, three-layer, blown-film coextrusion with a center layer of plasticized EcoPLA resin from Cargill Dow and thin skins of a biodegradable aliphatic polyester from another producer. The skins act as a plasticizer barrier to prevent blocking. Cargill Dow supplies both types of pellets to Duro as a material system.