Biopolymers and polylactic acid (PLA) – or rather, Ingeo

27 04 2011

Synthetic polymers have experienced almost exponential growth since 1950, and today about 5% of world oil production is used for that purpose.  In fact, we will need 25% or more of the current oil production for making polymers by the end of this century.

Some synthetic polymers are used to make fibers, and they have been around for a while:  rayon was discovered in 1924 and nylon in 1939.  But synthetic use really began to take off only since about 1953,  when polyester was discovered.  Qualities like durability and water resistance make synthetics highly desirable in many applications.  Today synthetics account for about half of all fiber usage.

This, despite the fact that synthetics are made from fossil fuel, and the contaminants from the manufacturing leach into our waterways and pollute the atmosphere, and the fact that they are not biodegradable and therefore don’t break down in landfills.  So recently there has been a spotlight on bio-plastics.

Bio plastics, or biopolymers –  in other words, synthetic plastics produced from biological sources –  are derived from cellulose. Cellulose is abundant – it’s said to make up half of all the organic carbon on the planet.   The most often-used biopolymers  include:

  • natural rubber (in use since the mid-1700s),
  • cellulosics (invented in the late-1800s),
  • and nylon 11 (polyamide – or PA 11) and 6–10 (polyamide 6/10) (mid-1900s).

A recent addition to the list is polylactic acid (PLA).  PLA is made from corn starch (in the United States), tapioca products (roots, chips or starch, mostly in Asia) or sugar cane (the rest of the world).[1]  You’ve probably heard about polylactic acid (PLA),  because Cargill, one of the largest agricultural firms on Earth, has invested heavily in it.  Cargill’s wholly owned subsidiary, NatureWorks, is the primary producer of PLA in the United States.  The brand name for NatureWorks PLA is Ingeo, which is made into a whole array of products, including fabrics.

The producers of PLA have touted the eco friendliness of PLA based on:

  1. the fact that it is made from annually renewable resources ,
  2.  that it will biodegrade in the environment all the way to carbon dioxide and water  –  at least in principle, and
  3. they also cite PLA’s lower carbon footprint.

Let’s take a look at these three claims.

Plant based biopolymers do come from renewable resources, but the feedstock used presents some interesting problems.  In the United States, corn is used to make the PLA. In the US, corn-based biopolymer producers have to compete with ethanol producers of government mandated gasoline blends, raising the cost and limiting availability for both. This problem will become worse in the future as the law requires a doubling of the percentage of ethanol used in motor fuel. Nearly a third of the US corn crop previously used for food was used to replace 5% of gasoline consumption in 2008.[2]

In a world where many people are starving, many say that it seems almost criminal to grow food crops, such as corn, to turn it into cloth. Agricultural lands are often cleared to make way for the growing of crops for the production of polymers. This leads to a continuous shrinking of the food producing lands of the world.  Lester Brown, president of the Earth Policy Institute, says, “already we’re converting 12% of the US grain harvest to ethanol (anticipated to rise to 23% by 2014). How much corn do we want to convert to nonfood uses?”[3]

In addition, most of the corn used by NatureWorks to make PLA is genetically modified, which raises serious ethical issues.

Other critics point to the steep environmental toll of industrially grown corn. The cultivation of corn uses more nitrogen fertilizer, more herbicides and more insecticides than any other U.S. crop; those practices contribute to soil erosion and water pollution when nitrogen runs off fields into streams and rivers.

PLA is said to decompose into carbon dioxide and water in a “controlled composting environment” in 90 days or less.  What’s that?  Not exactly your backyard compost heap!  It’s an industrial facility where microbes work at 140 degrees or more for 10 consecutive days.  In reality very few consumers have access to the sort of composting facilities needed to degrade PLA.  NatureWorks has identified 113 nationwide – some handle industrial food-processing waste or yard trimmings, others are college or prison operations .  Moreover, PLA in quantity can interfere with municipal compost operations because it breaks down into lactic acid, which makes the compost wetter and more acidic.

It looks like most PLA will end up in landfills, where there is no evidence it will break down any faster than PET.  Glenn Johnston, manager of global regulatory affairs for NatureWorks, says that a PLA container dumped into a landfill will last as long as a PET bottle.[4]

In fact, manufacturers have changed their stance: PLA is now defined as “compostable” instead of biodegradable, meaning more heat and moisture is needed to degrade PLA than is found in your typical backyard compost bin.

So far, biopolymer producers have had problems demonstrating that their materials have smaller carbon footprints than fossil fuel-derived polymers.   The energy inefficiencies of planting, growing, and transporting biological feedstocks mean more total energy is likely consumed to produce a unit of biopolymer than to make a unit of an oil or gas-based polymer.

However, Ramani Narayan of Michigan State University  found that “the results for the use of fossil energy resources and GHG emissions are more favorable for most bio based polymers than for oil based. As an exception, landfilling of biodegradable polymers can result in methane emissions (unless landfill gas is captured) which may make the system unattractive in terms of reducing greenhouse gas emissions.”[5]

Dr. Narayan recommended that, relative to their conventional counterparts, green polymers  should:

  • save at least 20 MJ (non-renewable) energy per kg of polymer,
  • avoid at least 1 kg CO2 per kg polymer and
  • reduce most other environmental impacts by at least 20%.

From this point of view, he says,  green plastics  can be defined in a broad and target-oriented manner.

But  carbon footprints may be an irrelevant measurement, because it has been established that plants grow more quickly and are more drought and heat resistant in a CO2 enriched atmosphere. Many studies have shown that worldwide food production has risen, possibly by as much as 40%, due to the increase in atmospheric CO2 levels. Therefore, it is both ironic  and a significant potential problem for biopolymer production if the increased CO2 emissions from human activity were rolled back, causing worldwide plant growth to decline.  This in turn would greatly increase the  competition for biological sources of food and fuel –  with biopolymers coming in last place.[6]

A further problem with biopolymers (except for future PE/PP made from sugar cane) is that  they require additional sorting at commercial recycling centers to avoid contaminating other material streams, and, although segregated collection helps, it is complex and increases costs.

In the final analysis, newer biopolymers don’t yet perform as well as oil based polymers, especially in terms of lower heat and moisture resistance, so the user might feel green but gets results that are less sustainable and more limited in use.  PLA remains a boutique polymer, and some see the best value proposition for biopolymers to be where their use is based on their unique properties, such as in medical and dental implants, sutures, timed released chemotherapy, etc. , because  PLA will slowly come apart in the body over time, so it can serve as a kind of scaffold for bone or tissue regrowth or for metered drug release.  But this is a small and specialized market.

But still, the potential and need for plastic alternatives has become acute:  The SPI Bioplastic Council anticipates that the biopolymer market will exceed $1 billion by 2012 – today it is half that.   Bioplastic remains “a sector that is not yet mature but will be growing fast in the coming years,” says Frederic Scheer , CEO of Cereplast and the so-called ‘Godfather of Bioplastics.’  It has not matured because of high production costs and the restricted capacity of biomass-based polymers.

But  according to The ETC Group, there are already concerted efforts, using biotechnology,  to shift global industrial production from a dependence on fossil fuels to biomass – not only for plastics but also for power, chemicals, and more.  It sounds good – until you read their report, which I’ll cover next week.


[2] Jones, Roger, “Economics, Sustainability, and the Public Perception of Biopolymers”, Society of Plastics Engineers, http://www.4spepro.org/pdf/000060/000060.pdf

[3] Royte, Elizabeth, “Corn Plastic to the Rescue”, Smithsonian,  August 2006

[4] Ibid.

[5] Narayan, Ramani, “Review and Analysis of Bio-based Product LCA’s”, Department of Chemical Engineering & Materials Science, Michigan State University, East Lansing, MI 48824

[6] D. B. Lobell and C. B. Field, Global scale climate-crop yield relationships and the impacts

of recent warming, Env. Res. Letters 2, pp. 1–7, 2007  AND

L. H. Ziska and J. A. Bunce, Predicting the impact of changing CO2 on crop yields:

some thoughts on food, New Phytologist 175, pp. 607–618, 2007.

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Biodegradeable or compostable?

1 12 2010

There is no legal definition of “biodegradable,” so the term has been used loosely by some manufacturers.  The American Society for Testing and Materials defines the term as “a degradation caused by biological activity, especially by enzymatic action, leading to a significant change in the chemical structure of the material.”

The Biodegradable Products Institute (BPI) cites a 2006 American Chemistry Council study showing that most consumers believe a product labeled “biodegradable” will go away completely and on its own in a year or less. The BPI says many consumers also believe that these products will “biodegrade” in landfills.

Because it seems a desirable product attribute, the term “biodegradable” has been applied to a wide range of products—even those that might take centuries to decompose, or those that break down into harmful environmental toxins.   Biodegradability is definitely perceived as  a positive trait, yet it could be applied to virtually anything because anything is biodegradable, given enough time.  The Federal Trade Commission (FTC) in the U.S., however, has issued some general guidelines on what types of products qualify as legitimately biodegradable, and has even sued companies for unsubstantiated, misleading and/or deceptive use of the term on product labels.

According to the FTC, only products that contain materials that “break down and decompose into elements found in nature within a reasonably short amount of time after customary disposal” should be marketed as “biodegradable.”

But the FTC acknowledges that even products appropriately labeled as biodegradable may not break down easily if they are buried under a landfill or are otherwise not exposed to sunlight, air and moisture, the key agents of biodegradation. In fact, in landfills materials degrade very, very slowly – if at all!  This is because modern landfills are designed, according to law, to keep out sunlight, air and moisture – the very ingredients needed for materials to biodegrade. This helps prevent pollutants from the garbage from getting into the air and drinking water, and slows the decomposition of the trash. In Dr. William Rathje’s book entitled “Rubbish,” he sites that “The truth is, however, that the dynamics of a modern landfill are very nearly the opposite of what most people think…Well designed and managed landfills seem to be far more apt to preserve their contents for posterity than transform them into humus or mulch. They are not vast composters: rather they are vast mummifiers.” In his book, Dr. Rathje talks about doing excavations on 15 landfills throughout North America. From those digs, they found 40 year old newspapers that were still legible, 5 year old lettuce and a 15 year old hot dog. From these studies it seems fairly clear that even organic materials take a very long time to break down in landfills let alone plastic or other items.  The reality is if any product ends up in a landfill, it will not degrade.

But the fact that a product breaks down – if it does indeed break down – may not be as important as what the product breaks down into. In a perfect would all products would break down to CO2 and H2O. But it gets more complicated as we increase the number and kinds of chemicals. The banned pesticide DDT is hazardous and toxic in its own right. And it does biodegrade, though rather slowly. The problem is that its breakdown products of DDD and DDE are even more toxic and dangerous than the original DDT.
So just because a product or ingredient is biodegradable does not mean it is healthy or safe for people or the environment – especially if it leaches harmful chemicals into the ecosystem. Under this definition, even regular oil based plastic can be advertised as “biodegradable” because at some point, sooner or later, it is going to break down into small pieces.

“Compostable”, on the other hand, has a definition that is rigorously governed by the standards ASTM D-6400, ASTM D6868, and EN13432.   The term “compostable” covers four areas:

1.      Biodegradable – i.e.,  60 – 90% of the product will break down into CO2 within 180 days in a commercial composting facility.

2.      Disintegration – this requires that 90% of the product will break down into pieces that are 2mm or smaller

3.      Eco-toxicity – the product will not deposit heavy metals that are toxic to the soil beyond that found in typical compost.

4.      Compostable products have the added implication that when they break down they turn into humus, which provides valuable nutrients to the soil.

So, while some products are considered biodegradable, they may not be considered compostable because they either don’t meet the heavy metal requirements,  don’t break down in a timely fashion or don’t contribute valuable nutrients which improves the soil.

Composting of organic waste makes sense, but compostable plastic for shopping bags, food packaging, fabric, etc. does not, because:

1.      It is up to 400% more expensive than ordinary plastic;

2.      it is thicker and heavier and requires more trucks to transport it;

3.      recycling with oil-based plastics is impossible;

4.      it uses scarce land and water resources to produce the raw material, and substantial amounts of non-renewable hydro-carbons are burned and CO2 emitted, by the tractors and other machines employed.

5.      If buried in landfill, compostable plastic can emit methane (a greenhouse gas 23 times more powerful than CO2) in anaerobic conditions.

Many industrial composters of organic waste around the world do not want plastic of any kind in their feedstock, because it is difficult to separate biodegradable plastic from ordinary plastic. Home composting of plastic is not encouraged, as it will often be contaminated with food residues, and temperatures may not rise high enough to kill the pathogens. Compostable plastic is useless in compost because 90% of it has to convert to CO2 gas in order to comply with ASTM D6400 and the other composting Standards. It therefore contributes to greenhouse gases but not to the improvement of the soil.

Meanwhile, you can follow Dave, who  buried an advertised Paper Mate  biodegradable pencil in his backyard last summer and says he will report on it’s degradation over time.  Click here to read more and follow the story!

So how does this apply to fabrics?  Well, for starters the companies that make PLA (polylactic acid) based polymers – those corn based bio plastics – advertise that their products are biodegradable.   PLA is said by the manufacturer  to decompose into carbon dioxide and water in a “controlled composting environment” in fewer than 90 days. What’s a controlled composting environment? It’s not exactly your average backyard bin, pit or tumbling barrel. It’s a large facility where compost—essentially, plant scraps being digested by microbes into fertilizer—reaches 140 degrees for ten consecutive days. So, yes, as PLA advocates say, corn plastic is “biodegradable.” But in reality very few consumers have access to the sort of composting facilities that can make that happen. NatureWorks (the largest manufacturer of PLA, owned by Cargill Dow)  has identified only  113 such facilities nationwide.

Moreover, PLA by the truckload may potentially pose a problem for some large-scale composters.  And there is no evidence that  PLA breaks down any faster than PET or other plastics in a normal landfill environment.  (Read more about PLA and biodegradability here.)

And unless the chemicals used during processing of your fabric are such that there are no chemicals which would combine with other chemicals to form molecules of anything other than water, carbon dioxide and safe organic material – then it cannot be called compostable.  If the chemicals used during processing contain, for example, heavy metals in the dyestuffs – then those metals become available to your plants in the garden – and that again knocks it out of the “compostable” set of products.  That might be o.k. if you’re growing roses rather than radishes, but if you plan to eat those plants I’d look elsewhere as a way to dispose of your fabric.  Certified fabrics  made of natural fibers which look at the chemical inputs of processing (such as GOTS and Oeko Tex) would be o.k. for use in a vegetable garden – because they have been tested to be free of toxic inputs – and they could be called “compostable”.

Resources:

The Biodegradable Products Institute, www.bpiworld.org

US Composting Council  http://www.compostingcouncil.org