Plastics Recycling and Biodegradable Plastics
Susan E. Selke, Ph.D.
Michigan State University
East Lansing, Michigan
The attention the public gives to environmental issues has long been recognized to wax and wane through time. For plastics, the first signif- icant environmental pressure came during the mid- to late 1970s, when oil prices rose dramatically. At first, plastics were targeted as made from oil and, therefore, environmentally suspect. As time went on, how- ever, the attributes brought by plastics in terms of energy efficiency became more widely recognized. In the recycling area, however, the rise in oil prices and, consequently, in the base price of plastic resins had a significant impact. The scrap from plastics manufacturing processes became too valuable to simply discard. Use of regrind in manufactur- ing of plastic products increased. The literature of this time has a vari- ety of publications addressing the concerns which arose from this practice, and they look at the effects of degradation and, to a lesser degree, of contaminants in the feedstock. Slowly but surely, the use of regrind in plastics manufacture became routine, just as the use of in- house cullet in glass manufacture and edge trim in paper manufacture had become routine. Even when oil prices fell again, the economic ben- efits of using regrind were now recognized, and such use continued.
The next significant wave of environmental concern to impact the plastics industry began in the mid-1980s, and it had a considerably different focus—solid waste. There was a perception in the United States that, as a nation, we were running out of landfill space, and fur- ther that plastics were a particular problem because their non- biodegradable nature meant they were occupying the limited landfill capacity available for seemingly an eternity. This also brought about an interest in plastics recycling, although this time the interest was primarily in recycling of products at the end of their useful lives, rather than of manufacturing scrap. Use of regrind, in fact, had become such a normal practice that it was no longer considered true recycling; rather it was just good business practice. At this same time, there was pressure for use of biodegradable plastics as a replacement for the synthetic nonbiodegradable polymers that were perceived as filling up valuable landfill space.
As time went on, landfill costs in the United States, which had risen dramatically, declined again. Fewer but bigger landfills relieved the capacity crunch. Studies about what really goes on in modern landfills demonstrated that even readily biodegradable materials, such as food, often degraded only very slowly. Further, some plastic products which had been marketed as biodegradable proved to have only very limited degradability. Interest in biodegradability decreased, while pressures and opportunities for recyclability increased. Nonetheless, technical progress toward the production of a greater variety of truly biodegrad- able plastics continued. Also, plastics recycling continued to grow. More and more U.S. households had access to curbside recycling pro- grams which accepted a few or many plastics, primarily bottles.
By the mid-1990s, critics of plastic recycling began to get more attention. The high costs of adding plastic to curbside recycling pro- grams were cited. Burgeoning production of virgin resin at different times caused falling prices for the two most widely recycled plastics, high-density polyethylene (HDPE) and polyethylene terephthalate (PET). The economic viability of plastics recycling was called into question. Nonetheless, the general public remained supportive of plastics recycling. Few communities dropped curbside recycling or dropped plastics from their recycling programs. In fact, interest in recycling plastic materials began a significant spread beyond packag- ing materials to the durable goods arena. The American public, by and large, has become convinced of the value of recycling. Many feel that it is one thing they, on a personal level, can do to help the envi- ronment, and they feel good about participating. Thus, though the sol- id waste “crisis” was over in the United States by the mid-1990s (and some argue it was never real in the first place), recycling seems to be here to stay.
During the 1990s, attention to recycling of postindustrial plastics also grew. While it got little public attention compared to recycling of postconsumer plastics, many producers of resins with recycled content relied heavily on industrial waste as feedstock. These waste streams were not the clean single-resin regrind, but rather typically consisted of multiresin materials, materials which combined plastics and non- plastics, or materials which were contaminated in some other way, and which therefore had been going to disposal rather than being reused in house. While some of these streams were heavily contaminated and difficult to use, many were relatively clean, uniform in content, and more economical to collect than postconsumer materials. Producers of such scrap found that they were able to avoid paying for disposal of these materials by arranging to feed them to a recycler, and often could make a little money on the exchange as well.
Along with the changes in public concern about plastics use and recycling, there were changes during this time period in legislative pressures. During the “solid waste crisis,” the first wave of legislation often focused on bans of materials or products, particularly plastic packaging, which were seen as a particular problem. For example, nondegradable ring connectors for beverage cans were banned, first by a variety of states, and then throughout the United States. Mandatory recycling programs were instituted, sometimes at a statewide level and other times in individual communities. Taxes on plastic packaging were proposed and sometimes instituted. Grant and loan programs were instituted to help facilitate new recycling businesses as well as community education about recycling. Some states banned disposal of recyclable materials. Many of the legislative initiatives which were proposed never passed, but their sheer number was overwhelming. Most major plastics and packaging companies found it necessary to designate one or more people to devote all, or at least a substantial amount, of their time to environmental and recycling issues.
As time passed, the tenor of legislative initiatives became focused more on recycling. An interest in bans and taxes gave way to efforts to push for markets for recycled materials, including plastics. The pace of legislative activity decreased, but the issues did not go away.
In Europe, where in many countries the issue of landfill scarcity was much more real, a very different approach emerged than in the United States. First in Germany, and then throughout the European Union, the producer responsibility principle was adopted. This says, in essence, that the manufacturers of products are responsible for the disposal first, of the packaging for the products, and increas- ingly for the products themselves. Further, landfill disposal or incin- eration are not to be the main methods of disposal. Mandatory recycling quotas are imposed. This approach was first applied, afterpackaging, to the automotive industry, and it is now spreading to a variety of consumer products. In the United States, we have had up to now only a few isolated attempts to institute the producer respon- sibility philosophy, but it has spread, in modified form, from Europe to Canada and to some parts of Asia, and is making i nroads in Latin America as well.
On the biodegradability side, along with the technical work to devel- op truly biodegradable plastics, the growth of composting as an accepted companion to recycling has opened at least limited opportunities to make use of biodegradability of materials as an asset in their ultimate disposal.
Along with all of these changes, the last 10 years have brought an increasing recognition of the complexity of environmental decision making. Most experts now agree, at least in principle, that decisions on what is best to do from an environmental perspective cannot be based on a single attribute, but must instead be based on an analy- sis of all the environmental impacts from the decision through the whole life cycle of the products or processes involved. This type of cradle-to-grave analysis is termed life-cycle assessment. While there is general agreement on the philosophy, turning that philosophy into a useful decision-making tool is not an easy task. Despite the current existence of several competing computer models which will produce an analysis on demand, there are a number of fundamental questions which have not yet been adequately answered. Simply put, how does one balance x amount of impact A against y amount of impact B, when A and B differ significantly. On a more concrete basis, how many grams (micrograms? picograms?) of dioxin emitted into the Mississippi River is equivalent to how many grams (kilograms?) of suspended particulates (and what kind of particulates?) emitted into the air (how high up?) over Salt Lake City? Thus life-cycle assess- ment must be regarded as a still-emerging tool for help in decision making.
In this chapter, we will attempt to portray the current status of envi- ronmental issues as they relate to plastics recycling and biodegradable plastics, the current status of legislative requirements which have an impact in these areas, how we are doing and where we are headed in recycling of plastics, and the current status and prospects for biodegradable plastics. Issues related to the technique and practice of life-cycle assessment, except in the general context of our look at envi- ronmental issues, are beyond the scope. Similarly, in our look at plas- tics recycling we will focus primarily on postconsumer plastic (plastic which has served its intended use and been discarded), with some attention to postindustrial plastics. Routine use of scrap in the form of regrind will not be addressed.
12.1.1 Solid waste issues
As already mentioned, in the mid-1980s solid waste disposal emerged as a “crisis” in the United States. Many major metropolitan areas, par- ticularly on the east coast, were very close to being out of disposal capacity for municipal solid waste (MSW). Disposal costs were rising astronomically, reaching over $100/ton in New Jersey for tipping fees (the amount charged by the disposal facility for accepting the waste) alone. The public’s attention was captured by the voyage of the garbage scow Mobro, which sailed from Long Island around a good part of the western hemisphere, searching for a home for its cargo, before finally ending up back on Long Island, with the garbage sent to an incineration facility.
Governments at various levels, from individual communities to whole states, were struggling to find ways to deal with ensuring con- tinuation of the necessary public service of garbage disposal, while containing the costs that were threatening to ruin their budgets—and the chances of re-election for the responsible officials. Acronyms such as NIMBY (not in my backyard), NIMTO (not in my term of office), and PITBY (put it in their backyard) were coined.
Some communities and states solved at least their immediate prob- lem by shipping their garbage to adjoining communities or states—or even farther. Garbage from Long Island, N.Y., reached landfills as far away as Michigan. Predictably, “host” communities were not always happy with their role. Many states tried to write laws to prohibit the import of “outsiders’” waste, only to have them struck down based on the free trade between states provisions in the U.S. Constitution. A number of incineration facilities for municipal solid waste were built, but public resistance to these facilities soon became even greater than resistance to landfills, and their costs were typically much higher than landfills as well. Recycling programs were started up around the coun- try, first in the hundreds and then in the thousands. In contrast to incineration, recycling proved to be very popular politically.
At the same time, slowly but surely, new landfills were sited and built. Due to new regulations, these landfills were constructed much differently than the old landfills which were being shut down. They contained liners—often double liners—to protect against groundwater pollution, and caps to help prevent ingress of water. More care was given to locating them in geologically appropriate areas as well. The cost of these new landfills was also higher, but with increase in capac- ity and decrease in demand (as recycling increased), the average tip- ping fees in landfills actually declined in many areas from the record highs set in the early 1990s. For example, in New Jersey the average landfill tipping fee in 1997 was $61/ton.1 While the absolute number of landfills in the United States continued to decline, to 2514 in 1997,
capacity increased. In 1988, 14 states reported having lessthan 5 years of disposal capacity remaining. In 1997, only one state (Vermont) reported less than 5 years of capacity, and over half the states report- ed 10 years capacity or more.1 The average landfill tipping fee in the United States was $31.75/ton in 1997.1
Incineration increased in the last half of the 1980s, but then leveled off in the face of growing public resistance. New York City, for exam- ple, at one time planned to build five large incineration facilities, but found its plans tied up for years because of public opposition, and eventually scrapped the idea. Incineration rates have been relatively steady at about 16 to 17% since 1990.2
Recycling rates have increased steadily in the United States since the mid-1980s, as many new recycling programs were begun. In 1997, the number of curbside recycling programs in the United States reached 8937.1 The proportion of municipal solid waste which was recycled reached nearly 22%, with an additional 5% recovered by com- posting, for a total recovery rate of over 27%.2
During the mid- to late 1990s, another factor also began to reduce the amount of MSW destined for landfill. The overall generation rate for MSW began to fall. Initially, the decline could be seen on a per capi- ta basis only, as the rising population made overall MSW generation go up, even when the amount generated per person declined slightly. By 1995, however, declines were seen in total tonnage as well. The U.S. Environmental Protection Agency (EPA) estimates that, in 1996,
209,660 thousand tons of municipal solid waste were generated in the United States, down from 214,170 thousand tons in 1994. Discards to landfill fell to 116,240 thousand tons, down from 139,730 thousand tons in 1990.2 Historical trends in generation and disposal of MSW in the United States are shown in Fig. 12.1.
In much of Europe, as mentioned, the lack of landfill capacity was more real than in the United States. Many countries had been heavi- ly dependent on incineration for a long time, since space for landfill was very hard to find. However, public resistance to incineration was increasing. These ongoing problems led to increased reliance on com- posting and recycling as alternatives to incineration and landfill.
Other parts of the world, too, have experienced problems with con-
tinuing to dispose of materials as had been done in the past. In much of the developing world, the usual method of waste disposal is open dumps. A considerable amount of unorganized recycling is common in these societies, with individuals scavenging reusable materials from the dump sites. As more modern forms of waste disposal are imple- mented in efforts to curtail the problems resulting from open dumping, recycling in a more organized fashion is becoming part of the solid waste management strategy.
Figure 12.1 Historical trends in MSW generation and disposal in the United States.2
Thus, around the world there is increasing reliance on recycling, not as the only method for handling solid waste, but as an important part of what has become known as integrated solid waste management—the mix of strategies used to handle disposal of the wastes we generate.
An important consideration is how significant plastics are in con- tributing to problems with solid waste generation and disposal. There is no doubt that the amount of plastics entering the municipal solid waste stream has increased markedly in the last two decades, and con- tinues to increase, as illustrated in Fig. 12.2 for the United States. It should be noted that the proportions shown are based on weight (see Fig. 12.3). When landfill is the disposalmethod most commonly used, the desired measurement is contribution by volume rather than weight. For a variety of reasons, such estimates are exceedingly diffi- cult to determine accurately. The EPA has estimated the volume per- cent of plastics in materials going to disposal (that is, including landfill and incineration but excluding recycling and composting) as 25.1% in
1996 (Fig. 12.4).
12.1.2 Other environmental considerations
As was mentioned earlier, solid waste disposal is not the only environ- mental impact that should be considered when evaluating process or product alternatives. One environmental concern is resource deple- tion. Are we using up irreplaceable natural resources? During the flurry of environmental interest in the mid-1970s, when oil prices were rising, one of the key concerns was that we, as a planet, were running out of oil. Plastics were attacked as representing an unnecessary use of this valuable resource. As time went on, and the benefits of plastics in conserving energy were realized, this concern diminished. As new
Figure 12.2 Historical trends in plastics contribution to MSW.2
Figure 12.3 Materials in United States MSW by weight, 1996.2
reserves of oil were discovered, it died away still more. The fact remains, however, that the supply of petroleum on the planet is limit- ed, and petroleum, along with natural gas, is the major feedstock in the manufacture of most plastics. Processes have been developed to substitute renewable resources (biomass) for petroleum as a plastics
Figure 12.4 Volume percent of materials in United States MSW remaining after recy- cling, 1996.2
feedstock. At present, they are not economical, but they are available should petroleum supplies diminish and/or prices rise significantly.
Pollution is another environmental issue. Does the production, use, transportation, or disposal of the material result in damaging emis- sions? No human activity (including breathing) is totally free of such emissions. The important questions are what is the amount and type of the emissions, to what extent can they be controlled, and what are their effects on the environment, in comparison to the alternatives. As time passes, legislative controls on emissions of pollutants have tend- ed to become more and more stringent. For example, in 1997, contro- versial new standards for particulates and ozone in the air were issued.3 In 1998, the U.S. EPA modified methods for estimating styrene emissions in certain industries, and drew attention to overall increases in such emissions, with the message that new regulations could be coming if industry failed to reduce emissions of styrene.4
At the present time, there is considerable concern about the effects of two categories of pollutants which overlap considerably, but are not identical. One focus is emissions of organic chemicals containing chlorine. The other is on emissions of chemicals which are mimics or antagonists of natural hormones, particularly estrogen. Within the plastics industry, polyvinyl chloride (PVC) and polyvinylidene chlo- ride (PVDC) are the polymers most affected on both fronts. Many of the suspected hormone-like chemicals are chlorinated, and some of those which are not chlorinated are used as plasticizers in PVC. The vinyl industry has been attacked by Greenpeace and some other
organizations for its contribution to what they portray as an extremely serious threat to environmental and human health. The scientific evidence needed to reliably evaluate the risk, or lack of risk, of the thousands of chemicals in these categories is still being developed. Epidemiological evidence is limited and largely inconclu- sive. At the time of this writing, the issue has receded somewhat but has not disappeared. For example, in August 1998, Greenpeace reported that Nike Inc. plans to phase out its use of PVC because of environmental concerns about its manufacture and disposal.5
Another controversial environmental issue is related to CO2 emis- sions. Many believe that man-made emissions of carbon dioxide and other greenhouse gases are leading to an overall warming of the planet, which could have a variety of adverse effects. Others dispute these claims, or that the effects would be detrimental, but this is a minority opinion. The United Nations convened a large panel of experts, result- ing in a consensus opinion that greenhouse warming is real, and steps need to be taken to curb it.6 A subsequent meeting in Kyoto resulted in an international agreement to reduce greenhouse gas emissions. This agreement has not yet been ratified by the U.S. Congress, although a number of other countries have agreed to abide by it, and some call for even more stringent measures. The potential impact on the plastics industry of energy conservation measures is hard to evaluate. Increased taxes on oil and natural gas would drive up costs. On the other hand, efforts to achieve more energy efficiency might lead to increased use of plastics, as their light weight and relatively energy efficient production could make them highly competitive.