Biodegradable plastics fit with recycling strategies

Oct. 30, 2007
Truly disposable biodegradable plastics could change people’s perceptions on recycling, says Mike Spear, editor at large, in November's End Point column.

Recycling waste, whether inside a plant or further down the product chain, is something to be encouraged — as we all know from both a process engineering perspective and the wider environmental view. Our recent reports on EU waste directives such as RoHS and WEEE (see Industry tackles a grave issue) have highlighted the increasingly international initiatives being made to impart a recycling mentality across industry and its customers. The difficulty is turning that mentality into sound practice — moving from perception to practicality, if you like — because the perception of recycling can differ significantly from the reality, as a recent nationwide online survey has shown.

Commissioned by "natural plastics" producer Telles, a joint venture between Metabolix, Cambridge, Mass., and Archer Daniels Midland, Decatur, Ill., the survey suggested that, on average, most people thought around 40% of plastic is recycled in the U.S. The actual figure is 5.7% nationally, according to the U.S. Environmental Protection Agency.

And, perhaps of more concern — although quite encouraging for Telles and its biodegradable polymers made from corn sugar and other renewable sources — around 40% of the survey’s respondents thought conventional, oil-based plastics were already biodegradable. Most alarming, mind you, were the 72% who didn’t know conventional plastics were made from oil!

Such benign ignorance of the realities of plastics recycling is understandable in a way. When we are now coaxed, if not actually compelled, to separate all our household waste into an ever-increasing number of "recyclable" categories, people can perhaps be forgiven for assuming that "recycling" is what actually happens to all their waste.

Here in my U.K. neighborhood, for instance, every household is supplied with three recycling boxes (for paper, plastics and glass, respectively) and two mini-dumpster type bins, one for garden waste and similar compostable materials, the other for anything leftover. Well, almost everything. Such is the average household’s accumulation of waste that most people still have to make regular trips to the town dump — sorry, environmental waste transfer station — to dispose of the general detritus that the curbside refuse collectors can’t cope with.

But at least this is where you see recycling in action, or at least the beginnings of the process. Instead of just three or four receptacles to put your segregated waste in, the number of  large containers on offer runs well into double figures. There are ones for fluorescent light tubes, scrap metal, solvents and paints, timber, textiles, batteries and so on, not to mention those for WEEE-type products like consumer electronics.

And yes, one for all things plastic, even though very little plastic is recycled anywhere in the true sense of the word. Some can be ground up and remolded into lower cost products, but true recycling processes — such as GE Plastics’ route to polybutylene terephthalate (PBT) based resins and polymers that uses PET plastic bottles for feedstock (see Chemical industry sees green) — remain few and far between.

More interesting in the long-term are biodegradable plastics that don’t really need recycling at all. By the middle of next year Telles, for example, should be producing 50,000 ton/yr of such plastics at its Clinton, Iowa, plant currently under construction. Taking starch from an adjacent ADM wet corn mill as its feedstock, the Clinton plant will produce polyhydroxylalkanoates (PHAs). Marketed under the trade name Mirel, these are high-performance biodegradable plastics that can be used in place of oil-based polymers in injection molding, paper coating, cast film and sheet, blown film and thermoforming. Metabolix says it already has more than 40 prospective customers working on more than 60 applications such as packaging, consumer products, agricultural products, and single use disposables (see Disposable equipment earns lasting role).

Biodegradable polylactic acid (PLA) polymers, such as those produced by NatureWorks at its corn-based 140,000-metric-ton/yr plant at Blair, Neb., have already moved into the mainstream of consumerism following retail giant Wal-Mart’s 2005 decision to use PLA packaging for fruit and herbs in its stores. Another reason why so many people think more plastics are recycled than is actually the case?

They may not free up much room in my garage — home to our own mini-recycling center with its five containers — but truly disposable biodegradable plastics could change people’s perceptions on recycling in general. And perhaps even confirm their belief that plastics don’t really come from oil at all.

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