A new biological plastic (L) shows obvious biodegradation compared to polyethylene (R). Polyethylene gave a estimated half-life of 48-years in the Marine Degradation studies, while the PHA bioplastic indicated a half-life of only 11-months.
For one year, marine biodegradation tests have been underway at Woods End and are revealing “important and interesting differences” in behavior of polyethylene (PE) compared to biological plastic such as PLA (polylactic acid) and PHA (polyhydroxyalkanoate) polymers. Test protocols include ASTM 7081 and ASTM-6691 which require quantifying disappearance and also use marine phytoplankton to rule out ecotoxicity effects. Decay constants determined for PE showed that it had a half-life of 48 years, according to Dr. Brinton who is leading the studies. PLA cut this in half but “that does not disappoint us since it is designed to degrade in hot composts”. The studies at Woods End are a follow-on to aerobic composting tests conducted by Woods End labs for a wide array of clients who are developing novel bioplastics for consumer markets. “There are reports that the oceans now contain 100-million tons of non-degraded plastic trash, so working towards plastics that degrade in marine environments is a big step”. The marine studies are being especially supported by Pepsico and FritoLay, who developed with Woods End the world’s first PLA-compostable chip-bag. “The big excitement” according to Woods End is how some other new bioplastics perform under marine conditions. Switching from polyethylene to PHA reduced the marine half life from 48 years to 11-months, the study reports. The researchers plan to present full results at upcoming marine biology and sustainable packaging events.