Degradables Tested in Compost Programs

DEGRADABLES TESTED IN COMPOST PROGRAMS

AST YEAR, the people running manager’s point of view, it has solved the the yard waste composting project pesky debagging problem. However, if the for the Region of Durham (located bags take appreciably longer than it takes to How long does it near Toronto, Ontario) thought compost the yard waste, the manager has they had found the solution to the problems similar to those posed by use of take for degradable messy problem associated with de- regular plastic bags. bags to break bagging leaves. Rather than use The type of problems encountered depend standardL plastic bags for a pilot leaf collec- upon the composting system used. For in- tion and cornposting project, the Region stance, if whole bags are piled in windrows down? How safe made corn starch-based degradable plastic and turned with only a front end loader, the bags available for the collection. composting rate will be retarded if the bags are the residues? “Our supplier told us the bags would de- don’t readily degrade. The yard waste will sit grade in three months,” explained Elaine in the bags without the essential ingredients This report Collis, who heads the composting program. for composting. In fact, many involved in Unfortunately, while the bags had lost some yard waste composting suggest that even describes ongoing of their strength, even in May they were still when degradable bags are used, some means holding up and holding leaves. “We finally of breaking the bags open is appropriate. research projects had to go into the piles and remove the bags Even in programs where the degradable by hand,” remarked Collis. bags are run through a preprocessing shred- to answer these If yard waste is collected in regular plastic der, or a windrow turning machine that rips bags, at some point in the process those bags the bags open, if the residues of the plastic and other key have to be removed. Most of the options for don’t degrade along with the yard waste and removing the bags are expensive and time remains visible, a final screening will be questions, consuming. The promise of degradable plas- needed to produce a marketable product just tic bags, not worrying about removing the like with regular plastic bags. In short, why bags, is almost too good to be true in those spend the extra money for a degradable plas- Jim Glenn situations. But as the problems in the Re- tic if its performance during the composting gion of Durham illustrate, a few questions process does not enhance the operation and need to be answered. the product? Another major question about degradable WHAT QUESTIONS? plastics is what they become when they de While in applications like yard waste com- grade. One manufacturer’s promotional ma- posting there appears to be great potential terial states that, “full degradation leaves for the use of degradable plastic bags, a num- only a fine powder which is absorbed by the ber of questions have also begun to appear. environment.” Little research has been con- First, and most basic, is the issue encoun- ducted into the effect of this fine powder in tered by the Region of Durham. How long the environment. According to Dr. Susan does it take for degradable bags to break Mooney of the U.S. Environmental Protec- down in the compost pile? tion Agency, who heads the EPA’s look at de If a bag degrades at a rate that corre- gradable plastics, “In aquatic environments, sponds with the rate of decomposition of the there may be problems with animals ingest- yard waste, then from a yard waste compost ing the fine plastic particles. On land, the

28 BIOCYCLE OCTOBER 1989 question is what happens when fine plastic applications,” explains Tim Shiveley, ADM’s particles are incorporated into the soil or pos- National Sales Manager. In the spring of sibly inhaled. Are there any environmental 1989, ADM put together a new formulation or health effects?” designed to degrade at a much faster rate in Toxic materials “The size of the plastics fragments result- a composting pile. ing from degradation” is also identified in a According to Dr. George Poppe, who heads should be avoided report of the U.S. General Accounting Of- ADM’s degradable plastic research work, fice, Degradable Plastics: Standards, Re- bags using the new degradable additive when manufacturing search and Development as a safety-related should break down to one millimeter, or less, issue along with the “potential toxicity of size pieces within six months and should be degradable plastic chemicals leaching from degradable plas- unnoticeable in the compost at the end of one tics.” Some in the plastics industry also year. “We souped up the catalysts used to en- bags. There are voice those concerns. Speaking at a 1987. courage the degradation process considera- conference on Degradable Plastics sponsored bly” says Dr. Poppe. alternative coloring by the Society of the Plastics Industry, Re- St. Lawrence started selling a formulation. gina Johnson of Dow Chemical Company Ecostar Plus, for composting last year and agents and inks that noted that “Degradation products of degrad- reports from users are that the bags using it able materials are not well characterized, so perform well in yard waste compost projects can overcome any their toxicity and environmental effects are One user of Ecostar Plus, Petoskey Plastics, unknown." has sampled a number of projects and ac- potential problems. Most people who have examined the toxic- cording to Jim Craig is “seeing the plastic ity issue believe that it’s not the polyethyl- break down to dimesize pieces in six months ene molecules that could cause potential or less.” Ecostar Plus is an adaptation of the problems, but rather additives such as pig- original Ecostar formulation. According to ments used to color the bags, inks used for Peter Campbell, St. Lawrence’s Project En- the printing on the bags and stabilizers that gineer, Ecostar Plus was the culmination of keep the plastic in one piece while the bags research done in Europe that looked at vari- are in use. ous combinations of starch and photosensi- The toxins of concern to most are heavy tive additives. “The final formulation in- metals that include lead, cadmium, nickel cludes 10% starch and an iron salt additive,” and cobalt used in the additives. In 1988, the remarks Campbell. “We believe the plastic city of Lincoln, Nebraska started using bags will be unidentifiable as a plastic within yellow-colored degradable plastic bags in 12 months of being placed in a yard waste their yard waste collection pilot program. composting windrow.” When the city ran tests on the compost this While some programs, like the Region of year, samples showed trace amounts of cad- Durham’s, are experiencing trouble with mium. According to Gene Hanlon, who bags not living up to manufacturer’s claims, heads the project, the source of the cadmium at least one manufacturer believes that the was the yellow bags. “Cadmium was part of fault lies more with the operators of the com- the pigment used to color the bags.” post facilities than the bags. “Many munici- If additives using heavy metals are used, palities simply don’t know the proper way to the concern is that those metals could pose make compost,” maintains Charlie Armis- long term effects on the environment and tead of Manchester Packaging. “They pile health if they either leach into the ground- the yard waste up and only turn it every six water or are taken up by plants and then con- or eight months. Then they wonder why the sumed by humans and/or animals. bags and the yard waste haven’t broken down.” INDUSTRY’S ANSWERS While questions about using degradable PRODUCTS AFTER BREAKDOWN plastic bags in yard waste composting proj- While it appears that in a short period of ects exist, the degradable plastic industry time, the producers of degrading additives Hole after starch granule believes that it has the answers to most, if have been able to cut the time required to biodegraded out of not all, of the questions. Take, for instance, make the plastic in a composting project polyethylene film, after 11 the concern about the rate of degradation. “unidentifiable,” there remains the question weeks in a leaf compost. When degradable plastic bags were first introduced, most companies claimed that the bags would degrade to a size that was indis- tinguishable within three to five years. That length of time certainly isn’t appropriate for composting. However, now the two principal suppliers of the degradable additive - Archer Daniels Midland (ADM) and St. Law- rence Starch Co. - have introduced formulations that offer a much quicker action than the standard formulations. These two companies supply the additive, the active ingre dients of which include starch and oxidizing agents, that is used by the bag manufacturers in producing the degradable bags. “Last year, the standard formulation we used just didn’t perform well in composting

BIOCYCLE OCTOBER 1989 29 of into what the plastic degrades. Most of to these low levels at least one researcher, Dr. the manufacturers of the degradable bags Michael Cole, of the University of Illinois and the degrading additives maintain that isn’t sure if all systems can reach molecular the plastic will break down into CO, and wa- weights as low as 500, “The literature on this ter, or those two products and a humic mate subject isn’t conclusive,” notes Dr. Cole. rial. “In an active microbial setting, the plas- Even if the plastic does not completely de tics should break completely down within grade, or if it takes three to five years, or as three to four years,” contends Dr. Poppe. long as 50 years as some suggest, wiIl the Likewise, Peter Campbell of St. Lawrence be- resulting material be harmful? Many in the lieves that plastic will break down com- degradable plastics field think not. “Polyeth- pletely, but “we haven’t tested long enough ylene is a very stable material,” says Mr. Ar- to know exactly how long the process will mistead of Manchester Packaging. “It’s not take. St. Lawrence is conducting those tests going to cause problems in the compost.” now.” Dr. Richard Wool of the University of Illi- What causes these polymers to degrade nois’ Degradable Plastics Institute goes a into CO2. water and humic material in the step further. “It may be over-designing to process is the fact that the polymer chains, try and degrade plastics into CO, and water, which have a very high molecular weight, are when they are used in compost projects,” broken into smaller and smaller pieces until says Dr. Wool. “In fact, although I don’t finally when they reach between 500 and want to overstate the case, polyethylene par- 3000 molecular weight, microorganisms can titles may enhance the compost by adding metabolize the material. While some degrad- structure to it.” ing technologies can break the plastics down The final issue is that of toxins being re

A BRIEFING ON DEGRADABLE PLASTIC

ATERIALS deteriorate or de- ing organisms. grade via physical, chemical Biodegradation is catalyzed by en- and biological actions. They zymes and its rate depends greatly mayM be physically stressed, chemi- upon environmental conditions such cally attacked, or consumed by mi- as temperature, moisture, oxygen, crobes. All three of these actions have and a population of suitable microor- been studied in efforts to accelerate ganisms. These microorganisms se- photodegradation or to impart biodeg- crete enzymes which require a very radation in plastics, the two kinds of moist environment to reach the food degradation suggested for removal of source. With plastics, the enzyme plastic products from litter or solid must breakdown the polymer mole- waste. cules to products small enough to be Photodegradation is degradation assimilated by the microorganisms for resulting from exposure to light. In the digestion. While natural polymers like case of plastics polymers, photodeg- starch are biodegradable, most syn- radation results from the UV portion of thetic ones are not. the spectrum, the erythmal radiation which also causes sunburn of the skin. Attack of the molecules may be by UV energy alone or may require Very pure polymers are not sensi- the presence of oxygen, in which tive to that portion of the sun’s UV ra- case, the process is called photoxida- diation which reaches the earth, tive degradation. namely wavelengths of 280 to 400 nm. Plastics owe their toughness and in- As a result, very pure polymers are tegrity to their molecular structure not susceptible to photodegradation. which consists of large, usually very In real life, however, plastics articles long chain molecules. If these large contain some molecular alterations or molecules are reduced in size, the imperfections created during process- plastic article loses strength, becomes ing and fabrication. In polyethylene, brittle, and may fall apart if stressed. thermal processing results in some UV radiation can cause a chemical re- carbonyl impurity which does absorb action resulting in chain scission of UV light from the sun. For greater sen- the long polymer chains, and physical sitivity, photo-sensitive additives stress from wind or weight may break might be used. It is this susceptibility it apart. Molecular modification and of impurities and additives to UV ab- Polyethylene film after 18 the use of photosensitive additives sorption, leading to polymer degrada- months of soil burial without have both been shown to accelerate tion, which forms the basis for the sys- de radable additive (top), tems which have been offered witll standard degradable photodegradation. additive (center), and with Biodegradation is the assimilation commercially. A discussion of these compost grade degradable or consumption of substances by liv- systems follows. additive (bottom).

30 BIOCYCLE OCTOBER 1989 leased when the bags degrade. Most scien- lead, cadmium and the like, should not be used in producing bags,” declares Peter not be used as additivea. Ramani Narayan of Campbell of St. Lawrence Starch. “Likewise Purdue University who heads the Environ- we want to see the bag manufacturers using mentally Degradable Plastics Subcommittee non-toxic inks in any printing that is done” of ASTM states that ‘toxic materials should Many of the bag manufacturers, particu- be avoided when manufacturing degradable larly those that produce a composting bag, plastic bags.” Lyle Schwartz of the National have followed this advice. For the most part, Institute of Standards and Technology be- compost bag manufacturers are now market- lieves there are alternatives to toxic coloring ing either clear or opaque bags that require agents and inks that can overcome any po- no heavy metal pigments and use either car tential problems. Those sentiments are bon black-based or vegetablebased inks. echoed by Dr. Michael Tempesta of the Uni- “Clear bags make a lot of sense,” states Jim versity of Missouri. “We concluded early on Craig of Petoskey. “Not only don’t you have in our research that manufacturers should to worry about heavy metals, but the clear not use heavy metals when they were pro bags help collectors identify yard waste for ducing cornposting bags,” relates Dr. Term- pick up and allow for visual inspection of the pesta contents.” Apparently the degradable additive manu- The other potential source of heavy metals facturers agree, because they have made an in degradable plastic bags are photodegrada- effort to keep toxins from being put into the tion catalysts, particularly nickel and iron. bags. “In our technical literature, we tell our While these materials are indeed heavy customers that toxic pigments containing metals, some in the industry maintain they

TECHNOLOGY n Ketone Carbonyl. Carobonyl sky will not photodegrade as rapidly n PHBV-Blodegradable Plas- groups absorb UV energy in the range as one that is not. Similarly, latitude tic. PHBV is an acronym for poly of 270 to 360 nm. If the pure polymer and the seasons have a substantial ef- (hydroxybutyrate-valerate). These are molecule is modified by introducing fect. Except at lower latitudes, winter aliphatic polyester copolymers pro- carbonyl groups (simply, a carbon time rates will be slower than summer. duced during fermentation of sugars. monoxide molecule) it can be made Articles will degrade more rapidly near Their existence has been known for photosensitive to UV radition reach- the equator than in northern latitudes. more than 50 years, but extraction ing the earth. With carbonyl molecules and purification from fermentation distributed at intervals along the long n Antioxidant-Photoacti- bacteria has only recently been per- polymer chain, it can be postulated vator. During thermal processing, fected. that UV energy could break the chain plastics may be degraded by oxygen at each carbonyl and make the poly- by the formation of peroxides. To pre- mer brittle. This range of wavelengths vent this thermal oxidative degrada- n Starch-The technology utilizes is not present in incandescent light, tion, additives known as antioxidants starch which is treated with a silane only barely in fluorescent light, but ap- are incorporated in the plastics resin coupling agent to provide compatibil- preciably in the sun’s rays. Window formulation. These antioxidants scav- ity with the synthetic polymer, such as glass screens most of this range of enge the oxygen so it cannot degrade polyethylene. To this is added a small wavelengths. Plastics modified by this the polymer molecule. Interestingly, amount of an unsaturated ester, such method should, therefore, not be ex- some antioxidants containing certain as corn oil, to serve as the autooxi- pected to photodegrade under artifi- metal salts act to stabilize polyolefins dant. In a buried article made of this cial light or behind window glass. if present at higher concentrations, mixture, the starch is consumed by but act as photodegradation catalysts soil fungi leaving a porous structure, n Carbon Monoxide Carbonyl. An- at lower concentrations. while the corn oil reacts with metal other method of incorporating car- In practice, UV energy is absorbed salts in the soil to form peroxides. Al- bonyl groups, which is applicable to by the metal complexes (iron, cobalt, legedly, the peroxides break the syn- only low density (not linear low) poly- or nickel compounds are generally thetic polymer chains into fragments ethylene, is to copolymerize carbon used), thus releasing the metal ions small enough so that they too can be monoxide with ethylene in the poly- which then act as catalysts to break biodegraded. Following burial, a polymer manufacturing process. The level the polymer chain. ethylene film containing 15 percent of carbon monoxide incorporated is starch decomposers in six months typically less than 2 percent. The pho- POLYMER BIODEGRADATION and one with 6 percent starch in three todegradation reaction is similar, al- TECHNOLOGY to five years. n though not identical, to that with ke- Efforts to make plastics biodegrad- tones. Again, the polymer chain able have pursued two courses, one (Adapted with permission from a paper breaks at the CO groups to form to make the polymer itself susceptible “An SPI Overview of Degradable Plas- shorter, weaker chains. to enzyme attack, and the other to in- tics” presented by Regina Johnson, The intensity of UV radiation ab- corporate biodegradable additives. Dow Chemical Corp. at the Society of sorbed by the material determines the The second approach does not neces- the Plastics Industry, Inc. June 70, rate at which chains will be broken. sarily make the polymer biodegrad- 7987 Degradable Plastics Confer- Thus, a plastic article shaded from the able. ence.)

BIOCYCLE OCTCOBER 1989 31 tests will be conducted on the strength and degradation rate of the bags and the leachate will be analyzed for heavy metals content. “Last year when we did our testing, there was virtually no loss of strength in the bags,” notes Dr. Wilfred Hanna of the Uni- versity of Nebraska, who heads up the research team. “The six percent ADM formulation (not ADM’s new composting formulation) that we rue testing this year is showing some loss of strength, but it’s a slow process.” In addition to performing strength tests and tests on the leachate, Dr. Hanna’s team is also doing microbiological studies to determine how the microbes on the surface of the bags change over time. Two independent tests are being conducted at Urbana’s yard waste composting site. In one research project, Drs. Michael Cole and Karen Leonis of the University of Illinois are studying the degradation rates “It may be over-designing are present in such low concentrations that and loss of strength in three types of bags - to try and degrade plastics they cause no harm. For instance, research the bags produced by Petoskey and Man into CO2 and water, when at Iowa State Universitv showed the 50 vear Chester and a third type that utilizes a photo- they are used in compost loading of nickel on agricultural land from degradation process, the Plastigone technol- proiects,” says Dr. Richard one formulation was just over 1% of the ogy developed by Ideamasters. Dr. Richard Wool of the University of EPA’s proposed nickel level from sewage Illinois. Wool is also conducting degradation rate ex- sludge applications. periments at Urbana testing an expanded number of degradable plastic films. DEGRADABLE PLASTIC BAG RESEARCH In addition, projects planned by Michigan Whether the questions that surround the DNR will include a full range of toxicity use of degradable plastic are valid or not, tests. “We’ll be sampling a number of pro- asking them has spawned a bevy of research grams that have utilized several different projects that are attempting to answer them types of bags,” reports Wayne Kosar, DNR’s one way or another. Unfortunately, at this Composting Specialist. “The tests will be juncture, most of the research and tests that conducted on both compost piles that in- relate to composting is ongoing and won’t be clude the degradable bags as well as those completed for several months. Several places that had yard waste brought in by other where tests on the performance of the bags methods. We want to be sure of these bags are currently being conducted include Lin- before we give them a clean bill of health.” coln, Nebraska; Urbana and Chicago, Illi- Similarly, Minnesota’s Pollution Control nois; and Composting Concepts’ project in Agency and its Department of Agriculture Minnesota. Michigan’s Department of Natu- are testing the degradable bags at Compost- ral Resources also plans tests in the near fu- ing Concepts for much the same reason. ture at a number of sites throughout that In addition to the independent experi- state. ments, many companies involved in produc- While most of the research and tests have ing degradable bags are also conducting not been completed, one thing becoming tests of their own. Petosky Plastics is doing clear is that the degradable formulators are a series of toxicology tests looking at both improving their products to the point where final compost products. Tests are also being the bags are breaking down at a rate condu- done on the bags alone. Other companies cive to composting. According to Tom Waf- that have or are sponsoring toxicology tests fen, manager at the Southeast Oakland include Manchester Packaging, Ideamasters County (Michigan) Resource Recovery Au- and St. Lawrence. St. Lawrence is also run- thority’s yard waste project, Petoskey bags ning tests to determine exactly into what the put in the piles in April had become brittle bags degrade. within six to eight weeks and were easily bro- While these and other tests may not an- ken open. “These bags are breaking down swer all questions relating to using degrad- quite nicely,” states Mr. Waffen. Similar sen- able bags in yard waste composting projects timents about the bags are expressed by they certainly will add to the limited amount John Maroney of Composting Concepts. of information available at this point. Al- “We’re very pleased with the Polar Plastic ready the research has moved the industry bags. They are breaking down at a rate that away from using heavy metals in pigments should make them unidentifiable in less than and inks, as well as helping to improve a year.” breakdown of the bags. This year’s tests in Lincoln follow up some For their part, a private yard waste collec- rudimentary testing in 1988 that turned up tor or municipality intent on using degrad- the cadmium in trace amounts. That cad- able bags should make sure the bags it pur- mium was believed to have come from yellow chases are designed specifically for bags. “This year we’re using clear bags,” composting and are produced without heavy notes Gene Hanlon. According to Hanlon, metals in the pigments and inks.

32 BIOCYCLE OCTOBER 1989