Old Plastics, Fresh Dirt

Houston had a problem. The city’s composting program called for residents to put their lawn clippings and leaves in polyethylene bags and leave them curbside. The sanitation workers who collected the bags had to cut them open and dump the contents into the backs of their trucks. It was laborious and time-consuming. Overtime was piling up.

The city decided to end the program and stop composting yard waste, recalls Gary Readore, chief of staff and recycling manager for Houston’s Solid Waste Management Department. “Everything was going to the landfill.” That system wasn’t cheap either. Houston was collecting 60,000 tons of clippings per year. With a $25-per-ton “tipping fee,” the charge for sending it to the landfill, yard waste cost the city $1.5 million per year.

In 2010, Houston resumed collecting yard waste for composting, but now residents leave it out in compostable plastic bags. The bags are translucent, allowing workers to peer inside to see if residents are cheating by commingling regular trash with the leaves. In addition to saving the tipping fee, the city gets $5.00 per ton for the material from its composting contractor, Living Earth Technology. The firm composts the bags right along with the rest of the waste; no special handling is required.

Houston’s experience illustrates the value of compostable plastics. Such materials aren’t meant to make the problem of plastic waste magically disappear. But they are intended to help municipalities and institutions divert organic waste away from the landfill and to the compost pile by making participation in composting programs convenient for consumers.

In this way, compostable plastics are addressing a bigger problem than mere plastic waste. According to the Environmental Protection Agency, plastics composed 12% of the 250 million tons of trash Americans generated in 2010. Food waste and yard trimmings, in contrast, made up 27%. Although skeptics question the value of compostable plastics, manufacturers such as BASF, Novamont, and NatureWorks see huge market potential.

In the plastics industry, terms like “biodegradable” and “compostable” are thrown around loosely. Biodegradability is an attractive selling point, and many plastics are purportedly biodegradable. “Theoretically, you can argue that any plastic could be biodegradable over a long enough period of time,” says Jack Macy, commercial zero-waste coordinator for SF Environment, San Francisco’s environmental department. “But the term biodegradable is meaningless unless you have a specific time frame and environment in which the plastic will fully biodegrade into something useful.”

Only a handful of polymers are biodegradable in a matter of months. Such polymers are consumed by bacteria as food. But for this to happen, according to Ramani Narayan, a professor of chemical engineering and materials science at Michigan State University, the polymers need to have a relatively rare confluence of structure and properties that allow them to be broken down into smaller parts that the bacteria can digest.

Biodegradable polymers have bonds that are readily hydrolyzed. Ester linkages are particularly vulnerable to esterases, microbial enzymes that hydrolyze such bonds. This is why all the important biodegradable polymers are polyesters: biobased ones such as polylactic acid (PLA), polyalkanoates (PHAs), and polybutylene succinate (PBS), as well as BASF’s petroleum-derived Ecoflex, a polyester copolymer made from adipic acid, terephthalic acid, and butanediol.

But to be biodegradable, a polymer needs more than just ester linkages. The polyesters have to be highly aliphatic so their molecular chains are flexible enough for the esterases to attack. The world’s most popular polyester, polyethylene terephthalate (PET), is not biodegradable because it is aromatic. Also, the polymers need to be water permeable. “For biology to happen, water is an essential requirement,” Narayan says.

When a polymer is said to be “compost­able,” it will biodegrade in a specific environment in a relatively short period of time. The ideal conditions occur in industrial composting facilities, where organic waste is aerated and kept warm and moist to incubate the hardworking bacteria. Narayan notes that complex chemical reactions between plant substances such as lignin and compounds found in the bacteria after they die form humic acid, the main plant nutrient in compost.

The plastics industry uses specifications published by ASTM International to determine whether a plastic article biodegrades well enough to work in industrial composting environments. According to Steve Mojo, executive director of the Biodegradable Products Institute (BPI), an industry trade group, a plastic must pass four main criteria to meet the specifications, called ASTM D6400.

The plastic cannot contain heavy metals. After 12 weeks under composting conditions, the material must have physically broken down so that only 10% of it will remain on a 2-mm sieve. In 180 days, 90% of the plastic must be converted into carbon dioxide. Finally, the resulting compost must be compared to a control of regular compost to make sure that it doesn’t harm plant growth.

If the material passes ASTM D6400, BPI licenses a logo to the manufacturer for product labeling. Labeled products have been made of Ecoflex, PLA, PHA, and other resins. San Francisco, like many towns, requires that all of the plastic articles thrown out as part of its organic waste collection program meet ASTM specifications.

Some observers are skeptical about the value proposition of compostable plastics, even if they pass all the standards. George Intille, a principal consultant with the consulting group Nexant, points out that the materials won’t biodegrade unless properly composted, and such operations are few and far between. “In order to recognize even the perceived value, you have to have situations that are not all that common. They are more rare than common,” he says.

Moreover, Intille says the environmental benefits of degrading the plastics are marginal. They turn into CO₂ when composted, the same as if they are burned. In contrast, polyethylene sitting inert in a landfill sequesters carbon for a long time, he notes.

Compost does have economic value, Intille acknowledges. But he worries about the contamination that could plague widespread curbside collection of compost­ables—the same problem that has hindered plastics recycling. “You don’t want to be selling stuff as farm fertilizer if it also has battery waste,” he notes.

The high cost of biodegradable plastics relative to conventional materials is also a barrier to broad market adoption, Intille adds. “The difference in costs is still way above the difference in value,” he asserts.

Biodegradable polymers are more expensive, a point that producers readily admit. PHA and BASF’s Ecoflex are sold in bulk at a price roughly two-and-a-half times that of the polyethylene they are meant to replace. On the retail level, a biodegradable 33-gal yard waste bag costs about four times more than its polyethylene counterpart.

But advocates of compost­able plastics assert that their materials provide enormous value by enabling the large-scale collection of organic waste such as grass clippings and food. Although the market today is relatively small, they say the potential for growth is enormous.

Rhodes Yepsen is marketing manager for Novamont North America and a former freelance environmental writer who conducts a biennial survey of municipal food waste composting programs for the composting industry magazine BioCycle. Today, more than 160 U.S. municipalities have food waste collection programs, Yepsen says, up from 95 two years ago. There are 2.3 million American households served by such programs, an increase of 300,000 in only two years.

Because organic waste is such a large share of the garbage stream, municipalities are increasingly eyeing it as a way to meet stringent waste reduction goals, says Keith A. Edwards, BASF’s North American business manager for Ecoflex. A common target is diverting more than 50% of waste from the landfill. “Just about every major city has either got a program, a pilot, or an investigation going on,” he says.

Edwards sees three key drivers. One is landfill costs. “There is a big financial incentive for a city and for the companies in that area to stop sending things to the landfill and just send them to the compost­er,” he says. On the coasts of the country, Yepsen says, tipping fees can be as high as $120 a ton. In the interior, they can be as low as $10 to $15.

Another driver, Edwards says, is culture. It is no accident that environmentally conscious college towns such as Ann Arbor, Mich., and Madison, Wis., are among the communities that collect food waste. State mandates, such as a California law requiring 50% diversion, are also responsible for many programs.

The U.S. is still behind other countries in composting. Canada has a comparable number of households participating in such programs out of a much smaller population. Novamont’s home country of Italy has more than 1,800 municipal food waste collection programs, Yepsen says.

He sees an enormous market in the U.S. if it is able to duplicate Europe’s composting habits, which he figures are 10 to 15 years ahead. Helping the U.S. implement these practices is an essential part of Novamont’s strategy.

“Novamont has been involved in shaping these programs in Europe from the start, helping to make them extremely successful,” he says. “Part of the perception in the U.S. is that we can’t set up these programs because it will cost too much, people won’t participate, or the logistics won’t work in our communities. In Europe, we’ve developed case studies and best practices to show how to overcome these hurdles.”

For the municipal and organic waste diversion programs that do exist in the U.S., compostable plastics are an essential component. San Francisco has had the nation’s largest residential and commercial food scrap collection program since 2000. SF Environment’s Macy says the city opted for the program in response to the state mandate for municipalities to divert 50% of their waste from the landfill.

“We recognized as a dense urban city that we needed to do more than the traditional recycling and yard trim composting,” he says. The city went beyond the state regulations, reaching 78% diversion by 2010. It wants to reach 100% diversion by 2020.

The city, Macy says, also recognized the environmental benefits. In a landfill, food scraps generate methane, a much more potent greenhouse gas than CO₂. They also form acids that leech out of landfills. “If you ask all these cities what the largest component of their waste going to the landfill is, it’s food,” he says. “And what is one of the worst things to go to the landfill? It’s food. The only thing worse is hazardous waste.”

Compostable plastic bags make up for their high costs by facilitating the participation of residents and institutions in the program, Macy argues. “People who insist on using plastic bags have an option that will work in composting,” he says.

Dinnerware—utensils, plates, and cups—is another market where advocates see potential for compostable plastics, especially for cafeterias, restaurants, and other institutions. When such items aren’t compostable, Macy observes, they often end up being thrown out with food waste anyway. “That creates a lot of contamination and is an impediment to effective participation,” he says.

Nonbiodegradable plastic utensils are also a hindrance to San Francisco’s recycling program, which takes in all kinds of conventional plastics. Utensils are small and hard to sort from other plastics. They also tend to be difficult to clean. “For cutlery, if it’s compostable and there is a food composting program, we think that’s a better route,” Macy says.

The suppliers of compostable plastics are the first to admit that not every product ought to be made of their materials. Yepsen points to biodegradable gift cards, like those available at Target. He says that Novamont’s resins are more valuable in products directly related to organic waste diversion.

Steve Davies, director of marketing and communications at NatureWorks, maker of Ingeo PLA, says he sees some companies making durable goods of PLA that have little chance of actually being composted. “There is this great, sexy idea of having products that disappear,” he says. “We sit on top of a long supply chain, and we’ll see consumer products that have gone out that are marketed as compostable where it makes absolutely no sense. A composter would be the first to raise his hand and say, ‘I don’t want that durable in my compost.’ ”

Outside dinnerware and films, recycling is often a better way to dispose of plastics, Davies argues. “We often shock our customers when we say that,” he says. “Why destroy a perfectly good molecule, whether it is PET or PLA or whatever? Where the plastic is relatively clean, our interest is much more strongly in recycling and preserving the energy that went into making that molecule.”

NatureWorks has been experimenting with depolymerizing PLA via hydrolysis back into lactic acid. The company has recycled about 25 million lb of “off spec” material back into virgin PLA this way at its Blair, Neb., plant. The company has also been working with BioCor, a California recycler, to aggregate relatively clean sources of postconsumer PLA, like the beer cups used in the Oakland Coliseum. Using a custom manufacturer to depolymerize the material, BioCor has shipped several truckloads of lactic acid back to Blair.

Bags and dinnerware might seem like humble beginnings for the compostable polymer sector. But the applications add up. BASF’s Edwards says the market has been growing at an annual rate of 20%. Companies have been making big moves to expand product lines and capacity to capture as much of the market as they can and reduce manufacturing costs.

Last month, NatureWorks formed a joint venture with succinic acid maker BioAmber so it can extend its Ingeo resins line. The partnership, called AmberWorks, is already testing two grades, Davies says. The objective is to further penetrate the compostable plastics market by using succinic acid-based polymers such as PBS to improve the flexibility and heat performance of PLA. “But also, we are really interested in the degradability attributes of things based on succinic acid,” he says. He notes that PBS, for example, is more easily composted than PLA and that PBS may lend attributes like biodegradability in marine and soil environments.

NatureWorks is also expanding capacity. Last November, Thailand’s PTT paid $150 million for a 50% stake in the firm. NatureWorks plans on building its second plant, in Thailand, by 2015.

Likewise, BASF has been expanding its compostable product line. Introduced in 1998, Ecoflex has properties that mimic those of low-density polyethylene, making it a natural fit for trash bag films, but some customers wanted to use Ecoflex in other applications. “We began to get requests from the marketplace for properties that Ecoflex couldn’t pull off by itself,” Edwards says. “Those mounted and we began to look at ways to formulate to meet those needs.”

The company’s answer, introduced in 2004, was Ecovio. The product blends Ecoflex with polymers such as PLA to improve stiffness, which allows the resin to break into markets such as shopping bags and injection molding. The blend also allows BASF to offer a resin with biobased content.

For many years, BASF served Ecoflex customers from a 14,000-metric-ton-per-year plant in Ludwigshafen, Germany. A year ago, the company increased capacity by 60,000 metric tons. Edwards says the new capacity was sorely needed. “Demand would outrun our ability to produce,” he says. He notes that the added capacity has helped boost economies of scale and bring down costs. Still, he acknowledges, a polymer made from butanediol, adipic acid, and terephthalic acid will have a hard time competing with polyethylene on price.

Novamont has been stepping up the use of biobased content in its compostable plastics. When the company started out in the late 1980s, its Mater-Bi product line consisted of starch blended with polycapro­lactone. In 2004, the company purchased Eastman Chemical’s Eastar Bio business, which featured a polyester made from the same monomers as Ecoflex.

Stefano Facco, Novamont’s director of new business development, says the company now uses a polyester based on the Eastman technology but modified with slightly different monomers. The company recently formed a joint venture with San Diego-based start-up Genomatica to spend $50 million to convert an idled lysine facility in Adria, Italy, into a biobased butanediol plant. Novamont will use the butanediol to make the copolyester, Facco says.

Amid the bullishness on compost­able plastics, though, a setback for PHA maker Metabolix is a reminder of the growing pains still ahead for the business.

A joint venture between Metabolix and the agribusiness giant Archer Daniels Midland opened a 50,000-metric-ton-per-year PHA plant in late 2010 at ADM’s complex in Clinton, Iowa. In January, disappointed with the slow growth rate for sales, ADM suddenly pulled out of the venture. The plant reverted to ADM, which wrote it off. Metabolix was unexpectedly left without a means of producing its polymer.

“I woke up last night at 2 AM thinking that just as we were emerging from a long, dark tunnel, with the light in view, someone slammed on the brakes,” Metabolix cofounder and Chief Scientific Officer Oliver P. Peoples told financial analysts in a recent conference call.

In the two months after the announcement, Metabolix has been regrouping. The company is still advancing plans to make C₃ and C₄ monomers by breaking down PHA. Additionally, the company paid ADM $3 million for 2,000 tons of PHA inventory to serve existing customers. It’s developing plans for a 10,000-metric-ton plant and is in discussions with other potential partners. In a conference call, Chief Executive Officer Richard P. Eno said Metabolix will target small-volume, high-value applications. “We will focus on areas where the superior biodegradation and performance characteristics of PHAs are valued,” he said.

Meanwhile, another new firm is entering the PHA market. Meredian is a Bainbridge, Ga., start-up firm that purchased PHA technology from Procter & Gamble in 2007. A Meredian sister company, DaniMer Scientific, has been making PLA-based extrusion coatings for paper since 2006 and recently launched a biobased hot-melt adhesive.

S. Blake Lindsey, Meredian’s president, says the company is building a 14,000-metric-ton PHA plant in Bainbridge that will open later this year. The company hopes to have a 90,000-metric-ton plant running by 2014.

Lindsey says Meredian’s polymers are different than other PHAs on the market and cost less to make. The company has been working with developmental partners, he says, all of whom are attracted to the polymer’s biodegradability. Despite Metabolix’ problems, he thinks the market is ready for Meredian. “We’re not afraid of where we are,” he says. “We know what we need to do.”

Compostable plastics such as PHA have a bright future because they help solve a large national problem, BPI’s Mojo says. “These materials in these applications are really designed to facilitate the composting of the large amount of food waste we throw away every year,” he says. Offering convenience and sanitation should help capture the market just as earlier generations of plastics captured the market for trash bags decades ago.

“Slowly but surely, plastic bags won out over paper bags because they worked better,” Mojo says. Compostable plastics makers are betting that their products will take that evolution one step further.