Last month’s Packaging column introduced sustainable packaging, an offspring of the spectacular 2000s movement to save our planet by implementing cradle-to-cradle materials philosophies, policies, attitudes, and practices. Packaging appears to have been selected for special attention by sustainability advocates, perhaps because packaging is visible on retail shelves, in home pantries, on tables, in litter, and in solid waste streams. Food packaging is particularly apparent, because it represents nearly 60% of packaging.
Noteworthy is the notion that companies must expand or even abandon their ages-old objectives of generating financial profit/returns for their shareholders. Today, companies are directed to the triple bottom line: financial profit, social input, and environmental impact. Previously, companies were urged to be cognizant of their social and environmental responsibilities as they strove to generate the fiscal assets to permit meeting all stakeholder objectives. The difference is hardly subtle to companies, brand owners, and other food-producing/marketing entities which must sustain themselves and grow (fundamental tenets of business) and comply with the new demands.
When a company is extraordinarily successful, as is Wal-Mart, it can afford to build and exercise power and dictate innovations such as sustainability, which translates in large measure into reducing packaging costs. Many Wal-Mart suppliers and allied companies, including food processors and packagers, have acceded to the initiative, and many others have envisioned a better world as a result of the concept.
Objectivity in the sustainability landscape is difficult, if not impossible, because of the participating constituents and the traction they have gained in the past three years. Recoverable bio-based materials have been in laboratories for decades but have had trivial commercial acceptance because of functionality and economics. Many a company has invested heavily in one or more versions and been financially shattered on its rocky shoals. Avoidance of petrochemical-derived package materials has been an objective of many environmentalists almost since their overt debut on the packaging space about 40 years ago. The overdrive today is biomass materials, because in theory they fulfill the sustainability objective.
Biomass package materials may be of animal, marine, agricultural feedstock, or microbiological origin. Animal materials might include collagen and gelatin. Chitosan is the heavily studied marine package material, with possible antimicrobial properties to supplement its basic claims. Lipid and hydrocolloid compounds fall into the agricultural feedstock category. Hydrocolloids include proteins such as zein and whey. Polysaccharides, including cellulose (think paper), starch, and gums such as carageenan, alginates, and pectins continue to be studied. Microbiologically sourced are polylactic acid (PLA), polyhydroxyalkanoate (PHA), polyhydroxybuyrate (PHB), and other polyesters.
Among the suppliers prominent in this arena are DuPont, Eastman, EPI, Indaco, Novamont, Procter & Gamble, Showa Highpolymer, AET, Rohm & Haas, ADM, Innovia, and Cargill. AET offers calcium carbonate–filled polypropylene; ADM, PHB film; Rohm & Haas, polyols; Innovia, cellulose biofilms; and Cargill, PLA.
Without diving into all the many offerings that have arisen from the basic notion of sustainable packaging, I will focus on PLA, the current comet flashing through our professional consciousness.
• Source. PLA is synthesized from lactic acid as its monomer. Starch is hydrolyzed into dextrose, which is fermented into lactic acid, which is converted into a cyclic intermediate dimer lactide polymerized into PLA. The starch may be wheat, potatoes, or, today’s favorite, corn. Other sources may include sucrose from beet or cane, by-passing the starch-to-sugar conversion. Cargill’s NatureWorks LLC (www.natureworksllc.com) is the United States’ major producer and chief proponent of PLA, competing with polystyrene and/or polyester thermoplastic.
• Benefits. PLA is noteworthy for its ability to be composted, i.e., reverted to lower-molecular-weight carbohydrates, carbon dioxide, and water by natural fermentation. For millennia, the end products have been effective moisture retainers in agricultural ground applications. Because the plastic returns to the earth, the polymer is "sustainable."
As a plastic, PLA is high gloss and transparent; is readily extruded to thermoformable sheet or orientable film (analogous to polypropylene); and may be extrusion blow molded into bottles, injection molded, and/or injection blow molded. The thermoforms closely resemble polystyrene or polyester versions, and bottles appear like polyester containers. PLA is reported to be an excellent flavor barrier.
NatureWorks claims that the processing of PLA requires 20–50% less energy than the thermoplastic polymers for which it is proposed as a substitute. It also claims that PLA is "the world’s first greenhouse-gas-neutral polymer to comply with the Kyoto protocol for reduction of greenhouse gases." The company says it achieves this objective by "purchase of renewable energy certificates (RECs) to serve as an offset to cover all of the emissions from the energy used" for PLA production. "The certificates ensure that production of renewable energy in an amount equal to that of non-renewable energy used by the company. The net result is … a 68% reduction in fossil fuel use compared with traditional plastics." PLA manufacturing operations themselves represent "a 30–55% reduction in greenhouse gas emissions versus petroleum-based polymers," the company says.
• Applications. Commercial applications of PLA in the U.S. include produce trays, bakery goods trays, water bottles, drinking cups (not really a packaging application), and others. Even before its recent initiatives, Wal-Mart challenged its suppliers to convert thermoformed trays into PLA, and a number of such packages are found in these supercenters. Wild Oats and Whole Foods have also joined the parade.
• Drawbacks. Processing characteristics of PLA are not too different from those of polystyrene, and other properties are also similar: water vapor and gas barrier are negligible to nil. Temperature resistance is near 41°C, which limits its applications to cold-filled products and containment of products distributed under refrigeration; secondary packaging such as labels and shrink sleeves; and use as a non-food substitute for the much-maligned polyvinyl chloride (PVC). The absence of specifications might lead to conclusions that the polymer is not useful for frozen food packaging.
Concerns About PLA
In an article entitled "Corn Plastic to the Rescue?" in the August 2006 issue of Smithsonian magazine (www.smithsonianmagazine.com/issues/2006/august/pla. php), Elizabeth Royte asked, "Is this really the answer to America’s throwaway culture?" and addressed various concerns about PLA.
• Compostability. The author begins with a brief on compostability: The product must enter a "controlled composting environment," of which only about 150 facilities exist in the U.S. Only about one-quarter accept municipal scrap. Most landfills and their associated composting operations cannot handle PLA, especially in the minute quantities calculated to be in today’s or foreseeable waste streams. Wild Oats accepts PLA back in only half of its retail stores. Despite its advocacy, Wal-Mart says it’s not "about to take back used PLA for composting. . . . We’re not in the business of collecting garbage. . . ."
• Interference with Solid- Waste Disposal Systems. Some composting experts suggest that PLA can interfere with conventional composting (of plant debris) because of the large quantities of lactic acid, which reduces pH. When and if PLA quantities become a very large proportion of solid waste, composters can convert to anaerobic digesters that ultimately produce methane useful as fuel.
A reversal can occur in solid waste recycling, she continues, when consumers cannot or do not differentiate between PLA and its visual analog, polyester (PET). Under these circumstances, PLA is a PET contaminant, i.e., it interferes with PET recycling. And when PLA enters conventional sanitary landfills, PLA will not break down any faster than petroleum-based plastics.
• More Questions. Other objections the author uncovered might be regarded as more profound than the relatively mundane challenges depicted above. Why, environmentalists ask, would we wish to divert corn acreage, even low-grade animal feed corn, to non-food applications when so many people suffer from hunger, an argument that might also be applied to corn-to-ethanol conversion. Furthermore, she states, PLA is made largely from genetically modified corn, a highly controversial source. And corn cultivation uses more nitrogen fertilizer, herbicides, and insecticides than any other American crop—the pollution and erosion consequences of which are the subject of too many debates to enumerate.
Is This the Starting Line or What?
And to raise the entire issue to galactic proportions, there are ecologists who proclaim that PLA legitimizes the use of packaging—which they contend should be eliminated. But the ultimate criticism comes from a Zero Waste movement, saying that PLA is sort of okay but we should leapfrog the present and future packaging/capture/recycle/compost systems, all of which are clearly deficient, and aim directly for perfection.
Frankly, I am baffled by these mystical visions. Have any of these self-anointed wise men/women incorporated food preservation into their magical equations? And if, by some Nobel Prize breakthrough, we resolve the food packaging bit of the equation, what then of the other three-fourths of plastics that do not become packaging, or of the more than 90% of petroleum that is burned for fuel to warm, cool, light, and transport us? Now might you share my bewilderment over sustainability and its offspring, PLA?
by Aaron L. Brody,
Ph.D., Contributing Editor,
President and CEO,