When worn, washed, and dried, clothing sheds - tiny fibers scattered throughout houses, soil, and waterways that can take centuries to degrade. These fibers, usually made of polyester, are often too small to see and are a major source of microplastic pollution - if invisible at all. Polyester clothing fibers are estimated to be responsible for nearly half of all microplastics in the natural environment, exacerbating a growing environmental and public health hazard.
Preventing clothes from falling off may be impractical, if not impossible. But, according to Katrina Knauer, a polymer scientist at the National Renewable Energy Laboratory (NREL-Golden, Colorado, USA), it is possible to address this challenge at the source: replacing today's petroleum-derived polyesters with non-toxic, biodegradable alternatives made from PHAs.
"PHAs, as a therapeutic agent, have been shown to be very compatible with human tissue," said Knaul, chief technology officer of the U.S. Department of Energy's Biooptimized Technology and Environment (Bottle) Alliance. "PHAs can also break down naturally in composting environments that are not highly controlled."
A team from NREL and Colorado State University - has developed a range of PHAs with different properties, some of which are similar to traditional polyesters but are bio-based, biodegradable and easily recyclable.
Now, the team is working with North Face (Denver, CO, USA) to introduce these sustainable materials to the outdoor apparel industry. Over the next 12 months, BOTTLE will scale up the process to produce several pounds of PHA fibers, which North Face will test and evaluate for use in its product line.
Textile Bottle Tailor PHA
Just a few years ago, research on the feasibility of manufacturing textiles from PHA was inconclusive. Early production methods extracted PHA from bacterial synthesis, in which many bacteria naturally produce polymers when digesting plant-derived products such as glucose and fatty acids. However noteworthy at the time, this method made it difficult for scientists to control the backbone and properties of PHA.
As part of its mission to create more sustainable plastics, a team of Colorado State University researchers developed alternative technologies to convert succinic acid (made from glucose) and other biobased building blocks into PHA via a synthetic route.The chemocatalytic approach allowed the team to customize the PHA's chemical backbone to achieve key attributes such as melt-processability, crystallinity, and ductility. With support from the U.S. Department of Energy's Office of Bioenergy Technologies and the Office of Advanced Materials and Manufacturing Technologies, BOTTLE reports prototypes of PHAs with a wide range of properties - from rigid PHA polymers for transparent food packaging to tough polymers that can be spun into fibers.
"We actually showed that we can control the microstructure so that PHA behaves like polyester fibers and textiles," says Knauer.
Unlike traditional polyester - a petroleum-based textile that accounts for more than half of the fabrics produced each year - bottled PHA is also designed for recycling. At the end of a product's useful life, BOTTLE's chemical recycling technology breaks down PHA and other polymers into chemical building blocks pure enough to be reused in the manufacture of the highest quality plastics.
The material's recyclability depends on specific changes to the PHA's chemical backbone, says Ravikumar Gowda, a researcher at Colorado State University. By replacing reactive hydrogen atoms with stabilized alkyl groups, Gowda and other CSU researchers significantly improved the PHA's thermal stability, making it melt-processable - a key advantage over microbially sourced PHAs. Importantly, the change also allowed the team to deconstruct the polymer at will.
"Our redesigned PHA structure greatly improves the mechanical toughness and allows the new PHA to be chemically recycled into its building monomers by simple catalyzing and heating", he said. "In principle, the recycled monomer can be infinitely reused to produce the same PHA again."
Toward a better apparel industry
The Bottle's collaboration with The North Face comes at a time of growing concern about the environmental footprint of making and wearing clothing. The textile production supply chain accounts for approximately 8-10% of global CO2 emissions.
To this end, the project is prioritizing analyses to understand the energy and carbon intensity of manufacturing and recycling PHA fibers. The team will also simulate microfiber shedding and measure their biodegradation rates in various environmental scenarios. Overall, the results will allow North Face to understand the sustainability of PHA textiles and compare them to traditional polyesters.
We are committed to making products that perform at their best while reducing our impact on the planet," said Carol Shu, senior manager of global sustainability at North Face. "Material innovation is at the pinnacle of our brand, and this program not only opens up new possibilities for synthetic textiles, but also supports our focus on achieving product recycling."
After reviewing the initial results of the bottles, The North Face aims to test prototype fibers with suppliers to evaluate a range of more sustainable products.
For clothing that looks good, feels good, and can be worn in the harshest outdoor conditions, the goal is to find the perfect PHA fiber to match or even improve upon the qualities consumers value most. Most importantly, it should enable adventurers to climb mountains, run and explore cities with the confidence that it won't leave traces of microplastics behind in the process.
