C E Rtifying Biodegradability of Compostable Plastic Bags

SEAL OF APPROVAL CE R TIFYING BIODEGRADABILITY OF COMPOSTABLE PLASTIC BAGS

HE U.S. COMPOSTING Council ern United States for BioCorp. “It talks (USCC) and the Biodegradable about bench-scale, lab-scale and full-scale Products International Institute testing. What it doesn’t say is what num- (BPI) are close to finalizing a certi- Program aims to bers you need to pass the test, which is what fication process that will award a the new specifications outline.” seal of approval to bags and other erase confusion plastic products that meet stan- and establish BUILDING CREDIBILITY Tdards for biodegradability. To earn the logo, The USCC/BPI certification program will manufacturers will have to pay a fee and be managed by BPI, a group founded last have their bags pass muster according to credibility for year by three biodegradable bag producers, specifications adopted by the American Soci- two university researchers, the council and ety for Testing and Materials (ASTM) in biodegradable the city of Montreal. A scientific review pan- April. “We hope this becomes an identifiable el will examine data submitted by manufac- seal for the public to recognize those products plastic bags. turers, with the results made public. The that have passed ASTM standards and are laboratory tests for assessing degradability manufactured by companies willing to get in- replicate well-run compost facilities, as con- volved in a program like this,” says Sharon firmed by a 1995-96 full-scale study con- Barnes, president of USCC. “This will show ducted at the RECOMP of Washington Com- people that these truly are biodegradable.” posting Facility in Bellingham, Washington. The ASTM has defined “compostable plas- (See “Assessing the Degradability of Poly- tic” as “a plastic that undergoes biological meric Materials,” March, 1998.) degradation during composting to yield car- The expectation is that the new seal will bon dioxide, water, inorganic compounds clear up the confusion caused by various and biomass at a rate consistent with other manufacturer claims and definitions, as known compostable materials and leaves no well as establish confidence in a field where visually distinguishable or toxic residues.” many bags professing to be biodegradable or Although formalized only recently, the spe- compostable have produced failure and dis- cific standards for biodegradable plastics es- appointment. (See “Degradables Tested In tablished by the ASTM are familiar ones. Compost Programs,” October, 1989.) “Con- (See “Moving Toward Consensus on Degrad- sumer confidence has been hurt a lot by dif- able Plastics,” March, 1998.) Because of the ferences in performance and claims,” says priority placed on building consensus, it has Mojo. “I think the confidence of regulators taken ASTM several years to confirm the and others in the industry will increase as standards, which essentially are the same the certification program becomes reality.” as those under consideration by the Euro- The early plastic bags claiming degrad- pean Committee of Standardization and ability were produced by companies like Mo- Germany’s standards organization. To be bil and Archer Daniels Midland as modifi- considered biodegradable, bags must: Con- cations of olefinic polymers, such as the vert to carbon dioxide at 60 percent within addition of varying amounts of corn starch 180 days when comprised of a single poly- to polyethylene. The attorneys general of mer and at 90 percent when made of a blend ten states and the FTC sued the companies of materials; Leave no more than 10 percent to drop the degradability label since the of their original weight on a three-eighths- products were not completely biodegrading inch screen after 12 weeks; and Not nega- in landfills. Since then, notable improve- tively impact plant growth. ments have been made through compound- The ASTM specifications build on the ing natural and synthetic polymers in a va- work of the 1996 ASTM Standard Guide to riety of combinations. Adds Barnes: “There Reprinted From: Assess the Compostability of Environmen- May, 1999 was quite a debacle in the 1980s when the tally Degradable Plastics. “What that did first wave of bags didn’t work. It’s going to was outline the number of tests you can do, take a learning curve for people to become depending on where you are in developing comfortable with these products.” compostable products,” explains Steve JOURNAL OF COMPOSTING & ORGANICS RECYCLING Although the recently formulated Mojo, chairman of the USCC’s Biodegrad- 419 State Avenue, Emmaus, PA 18049-3097 polyethylene degradable bags eventually able Standard and Logo Subcommittee, as 610-967-4135 • www.biocycle.net break down to a small particle size when well as senior vice president of sales, east- composted, both Barnes and Mojo don’t ex-

BIOCYCLE MAY 1999 pect them to pass the BPI tests. “I’m not a chemist, but I think the polyethylene bags may be a thing of the past,” says Barnes. “I COMPOSTABLE BAG DIFFERENCES don’t think they’ll be the choice of technolo- gy for biodegradable products. Everything’s HE BAGS marketed as suitable post site where they would be used. always open for review, but the scientists in- for composting can be placed in It is essential to test under the actu- volved in this feel that the new generation of Tfour categories, representing al composting conditions and with bags is a better performer.” the primary options: the input materials typically com- Composters using questionably “degrad- Degradable polyethylene bags — posted. To incorporate a positive able” plastic bags have seen them divide into Additives (sometimes including control, such as kraft paper, and a smaller pieces of plastic, rather than truly granular starch) are mixed with negative control, such as non- degrading. In some cases, a bag may eventu- polyethylene to accelerate the degradable polyethylene. The latter ally break down, but still presents the prob- breakdown of the polymer; the pur- ensures the bags being tested are lem of plastic pieces blowing around after the pose of the starch is to provide a di- truly degrading and not just lost. Re- first windrow turning. To be convenient for rectly biodegradable substrate to covery rates of the nondegradable composting, biodegradable plastic bags not help polymer degradation. Disinte- bags should be at least 80 percent. only should completely break down, but gration (the breakup of the plastic Some general guidelines for the should hold moisture, not be lighter than film into small pieces, sometimes de- four categories of bags can be es- composting feedstocks, and start to degrade fined by size, e.g., less than one- t a b l i s h e d : after several days. Some biodegradable plas- quarter inch ) can be achieved in Degradable polyethylene bags — tic bags on the U.S. market have been pro- many composting systems. Shelf life is normally satisfactory, but ducing favorable results in Europe, perform- Water-soluble bags — These are very long hot storage can be a prob- ing comparably to paper bags. (The based on hot water-soluble poly- lem; curbside performance is nor- accompanying sidebar reviews the four main mers, such as certain grades of mally satisfactory, although long ex- categories of bags marketed as compostable.) polyvinyl alcohol. They are de- posure in sunlight may cause some With a body of evidence to back the ASTM signed to dissolve only in a moist, breakdown; mineralization is slow, standards and successful projects abroad, hot compost pile. occurring over years in the soil; and BPI is confident that regardless of the feed- Hydrolysable bags — The poly- approximate cost is 1.3 to two times stocks involved, bags with its logo will de- mers used to make these bags are that of a typical nondegradable grade every time they are properly compost- hydrolysed in the warm moisture of polyethylene bag. ed. “The first thing I would look at in a claim a compost pile — therefore, the Water-soluble bags — Shelf life is of a certified bag’s failure to degrade is bags disintegrate — and the prod- normally satisfactory, although dry- whether the composter followed all of the ucts of hydrolysis are rapidly miner- ness obviously is vital; curbside per- guidelines in the operating guide of the alized (the breakdown of plastic film formance is normally strong; miner- Compost Council,” says Mojo. “With some into carbon dioxide, water and alization occurs over a few months people who say they’re composting, when biomass). The typical polymers for once the bag is dissolved; and ap- you look at their process and control of vari- this are based on polylactic acid. proximate cost is three to five times ables, it bears very little resemblance to Directly biodegradable polyester- more expensive, although some what we call composting.” based bags — The polymers used grades are now available at costs BIODEGRADABLE ADVANTAGES to make these bags are directly comparable to poloyethylene. biodegradable, for example, poly- Hydrolysable bags — Shelf life is The seal and improved performance caprolactone (PCL), and the bags normally satisfactory, but hot/wet should open up the market for biodegradable disintegrate as a result of this storage can be problematic; curb- plastic bags, along with food utensils and biodegradation. Sometimes starch side performance is normally satis- other applications. This would lead to (normally in its destructurized or factory, but can become brittle at greater diversion of compostable materials gelatinized form) and other directly low temperatures; mineralization is such as food residuals. “I think there’s sig- biodegradable natural materials are very rapid; and approximate cost is nificant opportunity within the U.S.,” says added to improve the properties or three to five times more expensive. Mojo. “Paper bags have had limited competi- reduce the cost. Directly biodegradable polyester- tion. In the short term, it becomes a question No standard test methods have based bags — Shelf life is normally of competing with them in terms of perfor- been developed for assessing shelf satisfactory, but PCL-based bags mance and price. Many regulations give a life and curbside performance, but can melt during hot storage; the preference for paper bags. Now they’ll be able empirical tests, such as loading the very rapidly mineralizable type can to specify kraft paper bags and those with the bags with organics and leaving break down in a few days at curb- BPI logo. As for price, as volume builds, it them exposed for two weeks, have side when filled with active organic will come down. It’s certainly not the imped- been carried out in a variety of ex- contents; mineralization can be ac- iment that it was five or six years ago.” posure conditions. Mineralization is complished in a few days or a few Certified biodegradable bags also should often tested using ASTM Method months, depending on the polyester have appeal to composters who currently de- D5338, which measures carbon used; and approximate cost is four bag and are left with small pieces of plastic dioxide evolution in a simulated to five times more expensive. in a lower quality end product. “As one who compost environment. This is — Graham Chapman has tried to break open bags, it’s the most in- sometimes referred to as a “com- efficient use of human resources I’ve ever postability test,” but it is relevant Dr. Graham Chapman has 14 seen,” says Barnes. “The other issue with a only to rapidly mineralizable mate- years of experience in the degrad - plastic garbage bag is that you’re more like- rials, and is more a measure of di- able plastics industry, including work ly to throw in trash, as opposed to one that rect or indirect biodegradability un- on the ASTM Committee to develop has a different look to it as you’re walking by der simulated compost conditions. standard test methods to determine your container.” Although conventional plas- Bags should be tested at the com- the degradability of plast i c s . tic bags are less expensive to purchase for the consumer, the added costs for the composter to deal with them are greater. — D.B. Ⅵ

BIOCYCLE MAY 1999