Will today’s waste methane become tomorrow’s textiles?Nancy Ordman | June 18, 2019
Biobased plastics are neither a new idea nor a new material. British metallurgist Alexander Parkes developed Parkesine, a celluloid plastic made from cellulose with nitric acid and a solvent, in 1855. Polyhydroxybutyrate (PHB), the first bioplastic created by bacteria, dates from 1926. If the concept of producing plastics from natural materials is not new, why is bioplastic development only accelerating in the late 20th and early 21st centuries?
One impetus is to create new plastics that do not harm the environment, materials that break down when discarded or that are easily recycled into new products. Mango Materials, a California-based startup producing polyhydroxyalkanoate (PHA) and PHB, feeds methane harnessed from sewage treatment plants to bacteria, which in turn create a biopolymer that will degrade under proper conditions. Since Mango’s process uses methane, a potent greenhouse gas, Mango could ameliorate two environmental threats with one process. Textiles and plastic caps and closers are the initial target markets for the biopolymer material.
Mango co-founder Molly Morse decided as an elementary school student that she would focus on reducing plastic waste in the environment. After graduating with a Stanford Ph.D. in environmental engineering, she teamed with two other young engineers and Mango co-founders, Anne Schauer-Gimenez and Allison Pieja, to figure out how to encourage methane-eating bacteria to excrete a usable polymer material.
Mango has set up shop at a sewage treatment plant by San Francisco Bay, where the company harvests plentiful quantities of methane to feed their polymer-generating bacteria. The bacteria live in a fermentation tank, consuming both methane, oxygen and what the Mango team calls their secret sauce, an additive that maintains the process. When the bacteria are sufficiently fattened up, they are split open and the polymer is harvested, dried and pelletized.
The Mango team foresees turning the polymer into thread that can be woven into textiles for clothing. To help move forward toward this goal, the company in 2018 joined forces with Fashion for Good’s Scaling Program, whose purpose is to accelerate the commercialization of PHA biopolyester.
Does this biopolymer meet expectations?
As with much terminology intended to denote a product’s positive qualities – think “natural” foods – biodegradability lacked an operating definition until the publication of ASTM standards D6400, Test for Compostability, and D6868, Biodegradable Plastics. A biodegradable plastic only degrades under specific conditions, such as those defined in D6400:
"…plastics are designed to be composted under aerobic conditions in municipal and industrial aerobic composting facilities, where thermophilic conditions are achieved."
A plastic that breaks down only under these composting conditions will not biodegrade while lying discarded along a roadside, or on an ocean bed. And this kind of composting facility is in short supply in the U.S. The lack of an adequate waste management infrastructure will limit the impact that introducing biodegradable products might otherwise have on plastic pollution.
Independent laboratories are testing Mango Materials’ claim that their PHA will biodegrade in a couple of months, under the right conditions. The company asserts on its website that its product is expected to meet relevant ASTM and other bio-related certification tests.
Mango Materials is not alone in pursuing plastics that do not persist in the environment. Other researchers are using different materials to feed their processes, including avocado pits, and better uses of natural polymers to produce useful packaging materials.