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Bio-based plastics, environmental considerations

Biodegradability is an end of life option that allows one to harness the power of microorganisms present in a selected disposal environment to completely remove plastic products designed for biodegradability from the environmental compartment via the microbial food chain in a timely, safe, and efficacious manner.

Designing plastics that can be completely consumed by microorganisms present in the disposal environment in a short time frame can be a safe and environmentally responsible approach for the end-of-life management of single use, disposable packaging. That being said, when considering any bio-based resin, there are some environmental considerations one must take into account. These include: end-of-life management, complete biodegradation; its agriculturally-based feedstock; and, the energy required and the greenhouse gasses emitted during production.

Before I expand on these concepts below, let us quickly discuss the biological processes that degradable plastics endure during biodegradation.

Microorganisms utilize carbon product to extract chemical energy for their life processes. They do so by:

1.Breaking the material (carbohydrates, carbon product) into small molecules by secreting enzymes or the environment does it.
2.Transporting the small molecules inside the microorganisms cell.
3.Oxidizing the small molecules (again inside the cell) to CO2 and water, and releasing energy that is utilized by the microorganism for its life processes in a complex biochemical process involving participation of three metabolically interrelated processes.

If bio-based plastic packaging harnesses microbes to completely utilize the carbon substrate and remove it from the environmental compartment, entering into the microbial food chain, then biodegradability is a good end of life option for single use disposable packaging.

End-of-life management considerations:

Because biodegradation is an end of life option that harnesses microorganisms present in the selected disposal environment, one must clearly identify the ‘disposal environment’ when discussing the biodegradability of a bio-based resin: examples include biodegradability under composting conditions, under soil conditions, under anaerobic conditions (anaerobic digestors, landfills), or marine conditions. Most bio-based resins used in packaging applications are designed to biodegrade in an industrial composting facility and one should require some type of certification or standard from material suppliers, ensuring compostability.

Unfortunately, little research has been done on how many industrial composting facilities exist in the United States and how bio-based plastic packaging impacts the integrity of the compost. However, the Sustainable Packaging Coalition did perform a survey of 40 composting facilities in the U.S., which provides some insight. According to their research, 36 of the 40 facilities surveyed accept compostable packaging. These facilities reported no negative impact of including bio-based plastic packaging in the compost. Of the 4 facilities that do not accept compostable packaging, 3 are taking certain packaging on a pilot basis and are considering accepting compostable packaging in the future. Of the facilities surveyed, 67.5% require some kind of certification of compostability i.e. ASTM, BPI, etc.

In addition, because value for composters is found in organic waste, I assume most facilities would not accept bio-based plastic packaging for non-food applications because the lack of associated food waste and therefore value. In other words, as a representative of Cedar Grove Composting articulated in a presentation at the spring SPC meeting, composters only want compostable food packaging because the associated food waste adds value to the compost whereas the compostable packaging has no value, positive or negative, to the integrity of the compost product.

It is also important to note that because there are so few industrial composting facilities available, the likelihood that your bio-based plastic packaging will find its way to its intended end of life management environment is rare. While the idea of biodegradation and compostability for plastic packaging may resonate with consumers, the industrial composting infrastructure is in its infancy and requires a considerable amount of investment in order to develop to the point where it would be an effective and economical option to manage plastic packaging waste post consumer.

Complete biodegradability considerations:

A number of polymers in the market are designed to degradable i.e. they fragment into smaller pieces and may degrade to residues invisible to the naked eye. While it is assumed that the breakdown products will eventually biodegrade there is no data to document complete biodegradability within a reasonably short time period (e.g. a single growing season/one year). Hence hydrophobic, high surface area plastic residues may migrate into water and other compartments of the ecosystem.

In a recent Science article Thompson et al. (2004) reported that plastic debris around the globe can erode (degrade) away and end up as microscopic granular or fiber-like fragments, and these fragments have been steadily accumulating in the oceans. Their experiments show that marine animals consume microscopic bits of plastic, as seen in the digestive tract of an amphipod.

The Algalita Marine Research Foundation report that degraded plastic residues can attract and hold hydrophobic elements like PCB and DDT up to one million times background levels. The PCB’s and DDT’s are at background levels in soil and diluted our so as to not pose significant risk. However, degradable plastic residues with these high surface areas concentrate these chemicals, resulting in a toxic legacy in a form that may pose risks to the environment.

Therefore, designing degradable plastics without ensuring that the degraded fragments are completely assimilated by the microbial populations in the disposal infrastructure in a short time period has the potential to harm the environment more that if it was not made to degrade.

Agriculturally-based feedstock considerations:

Most commercially available bio-based resins are produced from sugar or starch derived from food crops such as corn and sugarcane. Over the past few years, the use of food crops to produce biofuels has become highly controversial; the same may happen with bio-based resins. However, this is only if the scale of bio-based polymer production grows. According to Telles VP Findlen, “If the bioplastics industry grows to be 10% of the traditional plastics industry, then around 100 billion pounds of starch will be necessary, and there is no question that that will have an effect on agricultural commodities.”

This sentiment is echoed by a representative of the World Wild Life Fund. Because sugar is the most productive food crop WWF explained, it makes an ideal feedstock for bio-based resin production; however, if all Bio-PE and Bio-PET came from sugarcane, we would need 2.5 times as much land in sugarcane. Unfortunately, this can not be done sustainably because, according to the Living Planet Report, our current demand for the Earth’s resources is 1.25 times what the planet can sustain. Put another way, on September 25th of this year our resource use surpassed what is sustainable. What this would mean as a financial issue is that we are living off our principle.

Therefore, when considering bio-based resins, one should take into consideration the feedstock from which it is derived and the various environmental requirements that go into procuring said feedstock. While the current production of bio-based resins is not to scale to compete with sugarcane production for food, it is important to understand the environmental and social ramifications of sourcing materials from agriculturally based products.

Energy requirements and fossil fuel consumption of production:

Obviously sourcing plastics from bio-based resources as opposed to fossil fuel is an intriguing option for those looking to reduce the burden of packaging on the environment. However, if the energy required to produce bio-based plastics exceeds the energy consumed in the production of traditional resins, then the sustainability profile of bio-based plastics can be compromised.

When bio-based plastics first became commercially available, the processing technologies were not developed to the point where producing plastics from bio-based sources consumed less energy than producing traditional, fossil-fuel based plastics. However, the bio plastics industry has dramatically evolved and is now able to produce certain bio-based resins with less energy when compared with traditional resins. Natureworks Ingeo PLA (2005), for instance, is processed in such a way that it actually consumes less energy and emits fewer greenhouse gas equivalents during production when compared with traditional, fossil-fuel based resins.

The Institute for Energy and Environmental Research (IFEU), Heidelberg, Germany, conducted the head-to-head lifecycle comparison on more than 40 different combinations of clamshell packaging made from Ingeo PLA, PET and rPET. Both PLA and rPET clamshells outperformed PET packaging in terms of lower overall greenhouse gas emissions and lower overall energy consumed and PLA exceeded rPET in its environmental performance.

According to the study, clamshell packaging consisting of 100 percent rPET emitted 62.7 kilograms of C02 equivalents per 1,000 clamshells over its complete life cycle. PLA clamshells emitted even less, with 61.7 kilograms C02 equivalents per 1,000 clamshells. Energy consumed over the lifecycle for 100 percent rPET clamshells was 0.88 GJ. This compared to o.72 GJ for the Ingeo 2005 resin, which is an 18% reduction in energy consumed.

Taken together, one would assume that the 2005 Ingeo PLA is a more sustainable option than traditional plastics, as manifest through this study. However, it is important to take into account the other dimensions discussed above, such as end of life management, complete biodegradation, and sustainable sourcing. By understanding the advantages and disadvantages of bio-based resins from an environmental perspective, packaging professionals can make informed material selections and truly comprehend the ecological ramifications of their packaging selections and designs.

Posted June 14, 2010

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