The Truth About Biodegradable Plastics

In an effort to stymie plastic pollution, several companies have engineered so-called compostable “bioplastics.” But are biodegradable plastics really what they claim?

| June/July 2010

biodegradable plastics - composting test

Of the purportedly biodegradable plastics we tested, only Novamont's Mater-Bi (top left), was compostable in typical home compost pile conditions.


Most of us are aware of how long-lived petroleum-based plastic bags and packaging are — we’ve seen the trash along roadsides and in our lakes and oceans. Some new “bioplastics” claim to be “100 percent compostable,” but testing commissioned by MOTHER EARTH NEWS reveals that most of these claims are misleading at best.

Basically, there are two kinds of “composting.” Composting at home usually involves small-scale piles with low temperatures and less-than-optimum humidity. Then there’s large-scale commercial composting, in which materials are shredded, mixed, and maintained at 140 degrees Fahrenheit — a much higher temperature than that of typical home compost piles. Many cities compost yard waste, but only a few sites — about 100 in the entire nation — will also accept these “biodegradable” plastics.

We tested five types of bioplastic bags to see how well they would compost. None of them broke down completely after 25 weeks in home compost conditions (77 degrees). A product from Italian bioplastic manufacturer Novamont came closest to what we would call truly compostable, with a product called Mater-bi. Mater-bi is “made of corn starch, vegetable oil derivatives, and biodegradable synthetic polyesters” In our tests, only Mater-Bi was compostable at typical home compost pile conditions.

Three other brands did fairly well in commercial composting conditions, but they showed little or no degradation in home compost conditions. One type, Oxo-Biodegradable, did not begin to break down even after 25 weeks at 140 degrees.

Most bioplastic products currently being marketed carry incomplete and/or misleading labeling, according to composting expert William Brinton of Woods End Laboratories, who conducted the testing for MOTHER EARTH NEWS. One exception is the packaging developed by Frito-Lay for its Sun Chips. The new bag (which we did not test) proclaims “100 percent compostable” on the front, and on the back it states the bag is made from “90 percent renewable, plant-based materials and it breaks down completely into compost in a hot, active home or industrial compost pile.” We applaud Frito-Lay for its accurate labeling and its ongoing efforts to develop better packaging. The company’s bags may well be more compostable than their competitors’. But what most consumers won’t realize is that most of these bags, at this point, are unlikely to reach a “hot, active home compost pile.”

The bottom line: Most plastic packaging that claims to be “biodegradable” or “compostable” will only partially break down under the conditions typical of most residential compost piles.

5/9/2013 11:04:37 PM

The problem is that 25 weeks for composting a product is too long. Many composting faciities reject the use of compostable plastic, including the USDA. In Europe the time is 90 days as well as in the State of California, unless there are BioSolids(Human Waste) added to the compost. The Human waste aspect is allowed for longer periods of time to break down, but they still are shorter than 25 weeks. The other point to take in is that only a couple(1-5) compost facilities actually exist in the United State to take compostable plastic products.

This should be taken to heart as most of these compostable plastic products are not compostable at all.

Jack Roberts

BioSphere Plastic

10/5/2010 12:32:26 PM

Cheryl Long, Editor in Chief Regarding the post below by “Eco-Oxo” which was critical of the Woods End/Mother Earth News report about biodegradable plastic, the editors emailed Eco-Oxo and asked for information about his/her background and qualifications. EO’s reply was “At this point I cannot state who I am or which company I work for but I can tell you that I do work with 3 of the leading scientists in the biodegradable industry.” Why would a company have someone posting anonymous, highly critical comments when a magazine publishes a research report they disagree with? Why would “leadings scientists” be associated with such behavior? EO’s criticism of our report was harsh: “It is unfortunate that things like this get published by people that do not do the proper research before conducting studies or writing articles.” But notice that in the remainder of his/her post below, EO never really tells us what he/she believes was incorrect in our report. If companies want the public to trust their claims about their products, then they should not have their employees going around bashing reports about legitimate research by highly qualified scientists such as those at Woods End Laboratories. There are factions within the biodegradable plastics industry right now, and each side is trying to present their products in the best possible light. But as EO’s anonymous comment and Dr. Brinton’s post indicate, the Oxo faction is sometimes resorting to less than honorable tactics.

10/5/2010 12:32:24 PM

Cheryl Long, Editor in Chief P.S. Woods End researchers are running a Plastic Bags Degradation Comparison, which you can find here: They have placed a regular plastic shopping bag and an Oxo bag side by side on a fence and they are posting photos every 4 to 6 weeks so we can all watch just how these two kinds of bags do or do not degrade over time in the open air.

will brinton_1
6/23/2010 5:56:23 PM

Proponents of Oxo-degradable plastic have a reputation for uncivil attacks on scientists who objectively report results that raise obvious questions. Oxo-plastic is likely an invention looking for a market. While most plastics do not degrade at all, Oxos are designed to shatter into fragments - basically the absolutely worst scenario. Fragmenting is triggered by "TDPA" pro-oxidant additives - heavy metals restricted in some countries. So far, Oxo has been shown to work only under 3-tiered lab conditions. New evidence shows that humidity even inhibits Oxo fragmenting. An Italian study reports that with perfect conditions Oxo takes 1-2 years for 60% degradation, and only after high temperature oven treatment and moving to moist warm soil. Ironically, Oxo proponents are now claiming these artificial lab conditions exist in nature - in hot compost piles (all the while critical of testing in compost). In fact, Oxo proponents put the ASTM D6400 (the hot compost standard) into their own ASTM D6954 just to keep their options open. Meanwhile Oxo fans keep criticizing composting pioneers, probably because Oxos are not reasonably degradable. It makes no sense to compost Oxo-bags (due to the need for oven treatment), and it is senseless to put Oxo-bags in landfills. So the question remains: What on earth are they meant for? The best suggestion is to promote breakup of litter in arid deserts, but only if you pick up the pieces afterwards and move them to a moist soil. How crazy is that?

4/30/2010 9:52:03 AM

It is unfortunate that things like this get published by people that do not do the proper research before conducting studies or writing articles. While it is true that compostables are to be tested according to ASTM 6400 however you will not get an accurate test sample for Oxo-biodegradable products because they are not intended to be used in a composting situation. Oxo products have to be tested to their own standards which are ASTM 6954. Composting products need a composting environment with high levels of heat and moisture to activate the degradation process and completely break down. Oxo-biodegradable or biodegradable products will not break down in a composting environment however they do break down in the presence of oxygen and heat causing fragmentation. If you want to do a simple test take an oxo bag and lay in on the ground or tape it to a fence and watch what happens over the next few months. If it is a true oxo bag then you can witness the process taking place. Once this stage has occurred then the biodegradation begins to occur and the fragments are consumed by microbes leaving a biomass which in turn creates will help sustain plant life. Just because you read an article on the internet doesn't make it true or accurate information.

doug lass_3
4/13/2010 2:40:00 PM

Has anybody heard of recycling? I know the Wal-Mart's in my area will accept used plastic bags for recycling! I don't know if any other stores do this, but it would be a great way to keep the plastic going around in circles.

roland green
4/13/2010 3:07:02 AM

Surely the crux of the matter here is that the plastic eventually bio-degrades and disappears. Hoping that a plastic bag will do the same thing in your backyard compost pile as a cabbage leaf, is, I think, a bit optimistic. If you want to stem the rise of plastic bags, try something like Ireland did, they slapped a levy 15 eurocents at the start, on every standard plastic shopping bag (bigger bag, bigger levy)and suddenly paper bags were everywhere and now you literally have to ask for a plastic shopping bag.

4/12/2010 11:32:07 AM

Josh, nothing breaks down in a landfill at this point. Layers of rubbish are spread out, compressed with equipment, and then a layer of 'daily cover' is packed on, watered, and that layer winds up (like the ones before it), sealed in. And then I need to comment a bit about the article. Insofar as biodegradability of petroleum-based plastics (and I wish this had been addressed), we really do not need plastic films to do that, because those particles of plastic wind up being persistent pollution which is ingested by wildlife, ends up in bodies of water, etc. For something to biodegrade, fairly specific conditions need to be there. Sunshine, water, heat, exposure to the elements. A plastic bag in a street gutter is exposed to these conditions, but that is the last place we'd want this to happen, needless to say. 'Biodegradable' is actually one of the plastic industry's first attempts at greenwashing the plastic grocery bag. If you're looking to get away from petroleum-based plastic bags, look for the word 'compostable' on the packaging, as opposed to 'biodegradable'. Or just reuse a paper bag a bunch of times and then use it for your trash for its last use. One problem w/ bioplastics is we're essentially replacing one class of rubbish with another, and both are energy-intensive to produce. How about not generating this kind of trash to begin with?

4/12/2010 9:29:52 AM

This is good to know, but more importantly, what happens when you landfill them? I think that would be more relevant since that's where the vast majority of these bags end up-although I know some people use them exclusively for plant material. Do they at least break down to the point that they can be considered better than conventional plastic bags?

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