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What are the Benefits and Drawbacks to Oxo-degradable Bags?


RAPID RESPONSE QUESTION: What are the benefits and drawbacks to oxo-degradable bags?

Request by: City of Portland, Oregon

Introduction

The city of Portland, Oregon wanted to understand more about oxo-degradable bags with respect to using them as receptacle liners.  Specifically:

  • Do they cause problems for plastics recyclers
  • Under what conditions do the material biodegrades?
  • Can they be included in the city’s commercial composting program?
  • If used oxo-degradable bags that end up in the landfill, do they offer an environmental benefit over traditional plastic bags?

Background

Degradable bags and plastic films are readily available and marketed by producers for environmental benefits, such as biodegradation.  There are at least four different types of “degradable bags”.

Starch-based films and bags (heretofore referred to as “biobags”) are made of a starch or fiber, typically corn, soy or potatoes.  These decompose in a controlled composting environment in 10-45 days.   Bio-based plastics meet standards set by the American Society for Testing and Material (ASTM) for compostability, breaking down 60 percent or more within 180 days or less.   In order to do this, bio-based plastics need water, heat, and aeration.  Biobags are used in many food waste collection programs; oxo-degradable bags are not compostable.

Oxo-degredable bags, the subject of this document, are different than biobags.  They are additive based biodegradable films/bags (including oxo-degradable) rely on additives to the resin to hasten degradation upon exposure to different conditions. Oxo-degradable films degrade by oxidation; hastened by the chemical additives.  Degradation of oxo-degradable plastic begins with a chemical process followed by a biological process.   Examples of product that may use oxo-degradable plastic include: agricultural sheeting, blister packaging, bottles, caps/closures, carryout bags, clamshells, labels, landfill covers, lids, milk pouches, pallet and shrink wrap, and trays.

Two other types of degradable plastics, also additive-based, include, hydro-biodegradable plastics which degrade by hydrolysis, and thermal-based biodegradable plastic which degrade with exposure to heat.

At the time of the initial request for information on the oxo-degradable bags, the City of Portland had compiled some information about oxo-degradable bags and plastics.   They had worked with hydro-biodegradable plastics but not yet with oxo-degradable suppliers. The oxo-degradable plastic manufacturers claim the material is recyclable and compostable, and degradable in the landfill.  However, studies show these bags are not compatible with recycling or composting.  Thus, the City was looking for answers regarding use of these bags

Findings

Do the oxo materials cause problems for plastics recyclers?

A 2007 study [1] which evaluated two brands of oxo-degradable and hydro-degradable bags, indicates that neither type of bag are perfectly compatible with the traditional plastic grocery bag recycling stream, which is typically low-density polyethylene (LDPE).

Another study by the Loughborough University in 2010, concluded the following:  “Oxo-degradable plastics are not suitable for recycling with main-stream plastics. The recyclate will contain oxo-degradable additives that will render the product more susceptible to degradation. Although the additive producers suggest that stabilisers can be added to protect against the oxo-degradable additives, it would be problematic for recyclers to determine how much stabiliser needs to be added and to what extent the oxo-degradable plastic has already degraded. On this basis it seems unreasonable to claim recyclability of oxo-degradable plastics in existing recycling streams” [2].

A study commissioned by the California Integrated Waste Management Board (CIWMB), Performance Evaluation of Environmentally Degradable Plastic Packaging and Disposable Food Service Ware [3] states, “Degradable plastics can negatively affect the quality and mechanical properties of recycled plastics if they are mixed with the recycled plastics. The contamination of degradable, biodegradable, and oxo-degradable plastics can be treated as other contamination to plastics. The effects of the degradable contamination can be evaluated by measuring physical properties and mechanical properties of the plastics.” One specific test conducted was on the effects of mixing oxo-degradable material with post-consumer low-density polyethylene (LDPE) at a ratio of 1:5. Researchers found that the introduction of the additive containing oxo-material increased specific gravity of the LDPE and altered the melt index of the LDPE.

A rebuttal, on the CIWMB study results, comes from the Chairman of the Scientific Advisory Board of the Oxo-biodegradable Plastics Association, and claims that “The studies referred to above [in the CIWMB 2007 report) show that oxo-biodegradable polyethylene(PE)  can be collected with regular PE waste for recycling without any adverse effects on the quality of the recycled products. [4]

The industry group’s (Oxo-Biodegradable Plastic Association) Scientific Advisory Board argues that combining post consumer oxo-materials with other plastics is feasible, with rationale that recycling post-consumer oxo-degradables with virgin or recycled resins effectively dilutes any additives, rendering them ineffective [5].  This position paper suggests they are recyclable “without significant detriment the newly formed plastic product.”

These differing claims and study results, that the material is recyclable with PE streams, or is not compatible and may affect the properties of the final product, are not fully resolved in the literature.  Further, the Biodegradable Plastics Institute (BPI) says that the formulation of additives in oxo films varies greatly [6], which introduces even more variability in the recycling process.

Since processing conditions and quality or property requirements of reprocessed PE varies at every processor, the most real and local answer will be identified by the recycled plastic processor that may be taking that material.  They can test samples in their process to see impacts on the final product.

Here is one company’s story, that started using oxo-bags, and returned to non-oxo-degradable plastic:

Dave’s Killer Bread researched oxo-degradable bags for their bread products, and knew that many oxo-degradable plastics are not recyclable.  However, they did find one film that had been verified by a third party to be recyclable.  After also verifying that this plastic would have no effect on the food product it was enclosing, and that the FDA had approved it for packaging, they switched to oxo-biodegradable bags in early 2009.   After finding out that plastic recyclers had concerns about their bags, because of concerns over their unknown effects on the long term viability of products containing recycled oxo-biodegradable plastic, along with other new information about oxo-degradable plastics, they discontinued use of oxo-degradable bags in 2012 [7].

Here is another company’s statement on using oxo-bags in their recycled-content wood:

TREX plastic lumber company, a large volume user of recycled PE films, stated in 2008, “Unless and until the long term durability testing concludes that the oxo-biodegradable polyethylene plastic (OBPE) will not have an adverse effect on our product, Trex cannot support the introduction of OBPE materials into traditional recyclable polyethylene streams.” [8]

More recently, Trex told us that it is still their position that biodegradables are, by definition, non-recyclable.  They offer a 25 year Residential Warranty on their composite lumber.  If the raw materials used to manufacture this product are designed to disintegrate, they are uncertain whether their boards will bare that impact.

Should oxo plastics be included in our commercial composting program?

The literature, again, has differing study results on whether oxo-degradable bags are compostable.  As an example, see the citations in this Intertek (May 2012) report, (pages 10 – 11) [9].

Currently, oxo plastics are not approved by the Biodegradable Products Institute (BPI) because they do not meet the ASTM specs for compostability (ASTM D6400 – “Specifications for Compostable Plastics”). This standard requires that a product degrade within 180 days.  The oxidation process for oxo-degradable bags tends to take longer in most conditions.  While the bag may fragment within this time period, full degradation is not likely to occur.

Cedar Grove (a large commercial composter in the Pacific Northwest) does not accept, nor even typically test materials for suitability in their process if they are not BPI Approved for compostability to ASTM D6400.   For those composting with companies other than Cedar Grove, the question of the suitability for composting of a particular product will be dictated by the compost operation in the area.  If Cedar Grove is considering accepting an incoming material for composting, (in this case, oxo-degradable bags), they will test the material in their exact process before approving the material for compost collection.

An additional challenge that composters face is determining plastic type as plastic shoots down the conveyor belt at 50 tons per hour.  If an oxo-degradable bag looks like LDPE (e.g., grocery bag), the operator is hard pressed to be able to tell the difference in the time given, and may just pull the material off the line for other disposal whether it is LDPE or oxo-degradable.

If the bags just end up in the landfill (as in trashcan liners) is there an environmental benefit to it degrading in the landfill?

Based on the literature, there seems to be no significant benefits to degradation in the landfill.  Oxo-degradable products require oxygen to degrade, so decomposition deep in a landfill, with anaerobic conditions, is not likely to occur due to the absence of oxygen and UV light, where these bags are completely inert .

Conceivably, most commercially available oxo-biodegradable plastics will begin to disintegrate in the surface layers of a landfill if oxygen is present.  Oxygen levels will vary according to factors such as how loose or compressed the waste was when it was buried, how much ultraviolet light is available, and how quickly additional waste materials or daily cover is added on top of the bag.   One potential advantage of landfilling these, over traditional bags, is that the oxo-degradable bag will fragment sooner when conditions allow (such as loose upper layer conditions).  It would then settle more easily than an ordinary plastic bag with trapped contents or air, and occupy less space.

A landfill study carried out by the University of California [10] reported that oxo-biodegradable plastic did not undergo anaerobic biodegradation during the study period of 43 days, while a control sample of paper did biodegrade under the same anaerobic conditions, and produced methane. Thomas at al (2010) concluded that these findings supported the claims from the producers of oxo-biodegradables that these products will not emit methane in anaerobic conditions in landfill sites.

Under what conditions does it decompose, and how long does it take?

Oxo bag degradation depends heavily on the surrounding conditions.  According to Powell & Leineweber’s article [11], many manufacturers promote oxo-degradable products based on the assumption that full decomposition occurs between 18 and 24 months, but other studies indicate it may take five years to decompose. Critics of oxo-bags say that the oxo-degradable bonds require a hot arid environment to break, and the polymeric fractions require a warm, wet, microbe-rich environment to decompose.

Although the exact brand or resins studied are unknown, the CIWMB study [4] tested degradation rates of biodegradable plastic samples in lab, landfill, and compost settings and found that the biodegradable samples decomposed within 180 days, but no measurable degradation occurred for the selected oxo samples, using ASTM D6400 standard specifications.

One company, EcoSafe Oxo-Biodegradable Trash Bag products are said to be engineered to degrade and totally fragment in 90 to 120 days and 60% mineralize / biodegrade in a further 12 to 24 months after disposal [12].  Another company, EcoBio® products are engineered for disposal in a landfill and under these conditions will degrade and fragment at a slower rate (12 to 18 months) [13].

References

[1] Grenier, D., and Cote, L. 2007. Evaluation of the Impact of Biodegradable Bags on the Recycling of Traditional Plastic Bags.

[2]  Loughborough University.  2010.   Assessing the Environmental Impacts of Oxo-degradable Plastics Across Their Life Cycle.

[3] California State University, Chico Research Foundation. June 2007. Performance Evaluation of Environmentally Degradable Plastic Packaging and Disposable Food Service Ware – Final Report. June 2007.

[4] Scott, G.  2008.  Comments on “Performance Evaluation of Environmentally Degradable Plastic Packaging and Disposable food Service Ware – Final Report”.  California State University for CIWMB

[5] Oxo-Biodegradable Plastic Association .  2012.  “Recycling of Plastics

[6]  BPI.  2003.  BPI Assessment of Oxo-Degradable Films

[7] Dave’s Killer Bread.  2012.  Press release.

[8] Greener Package.  2009.  Feedback on Oxo-Biodegradables

[9] Edwards & Parker.  Intertek.   May 2012.   A Life Cycle Assessment of Oxo-biodegradable, Compostable and Conventional Bags

[10] California State University, Chico Research Foundation. 2007. Evaluation of the Performance of Rigid Plastic Packaging Containers, Bags, and Food Service Packaging in Full-Scale Commercial Composting

[11] Powell & Leineweber, 2009. Breaking Down Oxo-Degradables. Resource Recycling. April. Iv

[12] Eco-Safe Bags (website)  http://www.dirtworks.net/Biodegradeable-Plastic-Bags/EcoSafe-Information-Dirt-Works.html

[12] EcoBio® (website)  http://www.all-greenjanitorialproducts.com/EcoDegradable-Garbage-Bags-33-Gallon-p/1075.htm

Additional Resources

OxoBiodegradable Plastics Association FAQs:       http://www.biodeg.org/faq.htm#1

The Biodegradable Products Institute:                     http://www.BPIworld.org

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