Topeka, KS — Bioplastic bags that say they are compostable are more likely to degrade in industrial compost settings than home compost, according to a recent study of bioplastic bags.
The biggest problem discovered by the tests is that the product packaging and labels do not adequately explain the conditions needed for the products to degrade.
The study, commissioned by Mother Earth News and conducted by Woods End Laboratories, also found that three products labeling themselves as oxo-biodegradable did not degrade at all in industrial compost settings, home compost or when left in soil.
Five bioplastic shopping bags and two bio-based foam plates were tested. Three of the bags came from Novamont (which makes Mater-Bi, a polyvinyl alcohol/cornstarch blend), Bag-To Nature by Indaco (which uses NatureWorks' polylactic acid) and BioTuf by Heritage (made of a blend including polyhydroxyalkanoate, a biopolymer created by bacteria). The remaining two were plastic grocery bags that label themselves as oxo-biodegradable, one of which was manufactured by EPI. The foam plates came from Dyne-a-pak (which also uses polylactic acid from NatureWorks) and Cascades, whose plate was labeled as oxo-biodegradable.
Products were left in three different environments for 180 days: 140 degrees F compost (60 degrees C, similar to an industrial setting), 77 degrees F compost (25 degrees C, similar to a home compost pile) and in 25 degree soil. Only some bags that claim they degrade in soil were tested in the soil. The industrial compost setting was set up to replicate the conditions used by the ASTM D6400 standard for compostability.
At the end of the 25-week test, Woods End Laboratories found that most of the products degraded in the industrial setting, but less action happened in the home compost and soil settings.
Novamont's Mater-Bi material fared the best, biodegrading within nine weeks in industrial compost, halfway degrading in the home compost and slightly tearing in soil.
In the industrial test, the Dyne-a-pak plate degraded in six weeks, the BioTuf bag was gone in nine weeks, and the Bag-To Nature bag disappeared in 17 weeks.
In the home compost test, no product fully degraded within the test timeframe. Novamont's halfway degraded, BioTuf has some holes and tears, Bag-To Nature had almost no change and Dyne-a-pak's plate had slight change.
The only other bags tested in soil were the BioTuf bag, which has only slight change, and the oxo-biodegradable bags. The oxo-biodegradable bags and plate did not degrade at all in any of the settings.
Most of the products carry various certifications, whether from the U.S. Composting Council or European standards. The oxo-biodegradable bags, however, have no certification labels, but state on them that they are oxo-biodegradable.
The problem with the oxo-biodegradable bags might be that they needed longer to degrade. As EPI, one of the bag makers, explains on its website, its oxo-biodegradable bags are formulated to degrade at various rates, from a few weeks to a couple years. Nevertheless, the study concludes the bags are misleading by not specifying the specific conditions under which they will degrade.