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Eco-conscious cleaning with polymer beads

Dyeing fabric entails transferring color—so does removing stains.

The Xeros washing machine looks like your standard washer, but those “suds” peeking out of the door are anything but soapy. Xeros, a company based in Rotherham in the UK, is looking to revolutionize domestic and industrial laundry alike with “bead cleaning.” The technology, the company claims, is not only superior to traditional soap and water but also environmentally friendly. Already with customers in Europe and the US, Xeros may be poised to make a big splash in the world of laundry with its washload full of lentil-sized polymer beads.

Xeros is a six-year-old spinoff from the University of Leeds, where textile chemist Stephen Burkinshaw had the original inspiration to reverse the dyeing process. Instead of adding pigment to textiles, Burkinshaw and his students experimented with removing pigment—that is, stains. Nylon readily takes up dye, and forming the polymer into round beads yielded the most effective stain extractor. The beads' surface area, weight, and chemistry have since been engineered with regard to four independent factors—temperature, chemistry, time, and mechanics—that affect the washing process.

The beads used in the Xeros washing process. CREDIT: Xeros

The beads used in the Xeros washing process. CREDIT: Xeros

The proprietary Xeros washer looks like a standard front-loading machine (the domestic version, slated for a 2015 US launch, will have a smaller footprint than the current commercial instantiation). About 50 kilograms of beads, held in a wet sump below the machine, are pulsed in with water through the top of the drum. The beads fall out of the drum and then recirculate. The company's chief science officer, Stephen Jenkins, likens the process to laundry taking a shower—not a bath—in beads. The shower analogy is apt in terms of water savings as well. Xeros claims a 70% reduction in water usage compared with standard washing. And because bead cleaning works in cold water (20 °C), heating is not required, which cuts energy use in half by Xeros’s estimate. The amount of special detergent used in the wash is also about 50% of what would normally be used, Jenkins says.

The one and a half million or so beads used per load constitute the fundamental ingredient in the cleaning cocktail. Xeros now has two main bead compositions—polyester (specifically, polyethylene terephthalate) and nylon (nylon 6,6). The mechanical action of the beads passing over clothing removes soil, and the weight of the beads reduces creasing by pinning the fabric down. But it is the beads' polymeric structure that attracts and traps dirt. Thanks to the presence of polar groups, the beads adsorb solubilizable stains. Nylon excels at “vagrant dye capture” because of a negative glass transition temperature that creates free volume within the polymer’s structure and allows absorption and diffusion of stains into the bead itself. In that way, Xeros washes are also resistant to dye transfer between colors and whites. In retail dry cleaning, "the ability to mix colors and whites can save considerable sorting time,” says Jenkins. “With the chemistry that we are developing for generation-two beads, we can get the dye capture to be almost perfect.”

A commercial Xeros washing machine. CREDIT: Xeros

A commercial Xeros washing machine. CREDIT: Xeros

Because the beads are particularly good at clinging to dirt and grease, they might require a periodic wash themselves—perhaps once a month when used in lightly soiled washes. The beads are reusable and have been tested to last through 500 washes. But does the cleaning performance come with a downside, say, nuisance stray beads trapped in clothing? Getting the beads in and out of a tumbling drum was a problem that had to be solved after the cleaning properties of the beads had been established, says Jenkins. “G-force, the drum size, the washload size, and the beads all work together so that the bead can interact with the cloth but then also fall away from it. No more than 20 beads should be left at the end of a washload.”

Crest Cleaners, a retail laundry and dry cleaner in the Washington, DC, metro area, says its customers now encounter stray beads in garments less than 1% of the time. Crest has been testing the Xeros process for the past year, and the company intends to fully replace its wet water washing machines with Xeros machines in the near future. “We are convinced this is the way to go,” says Crest CEO David Slan. “The rare fugitive bead that may be left over is a reminder of how cool the process is.” Crest also uses up to 90% less water with the Xeros process, says Slan. “This is the best way to reduce [the use] of what is a finite commodity.”

Shoulder pads and teddy bears

Reducing water use in nonlaundry applications is also on Xeros’s radar. Tanning and dyeing leather consumes even more water than laundry does, and the same four factors that determine the effectiveness of a laundry technology—temperature, chemistry, time, mechanics—all show savings with the Xeros process, says Jenkins. Using a different type of bead to get chemicals onto the material, rather than out of it, is the key. “We can reduce the effluent from tanning to virtually zero, and get a more uniform surface finish and dyeing with our process.” Crest also expects it can expand cleaning to nontraditional items, such as athletic padding or stuffed animals, with the Xeros system.

Commercial laundries are already using Xeros’s machines in the UK and Poland. Hotels and dry-cleaning stores like Crest Cleaners in the US are testing the system. Xeros also plans to enter the Chinese market. The company’s stable of patents now numbers 25 and covers not just the original bead cleaning idea, but also its associated washer, detergent, and other treatment processes. Also covered are ways to reuse the beads—for example, they can be remolded into automotive parts. Other recycling applications are being explored as part of a recently signed three-year joint development deal with BASF, the world's largest chemical company. Under the agreement, alternative bead chemistries that will work hand in hand with Xeros’s tailored detergent will also be investigated. “Being a polymer physicist at Xeros,” says Jenkins, “is like being a kid in a candy store.”

Amanda Alvarez is a science writer at the Institute of Molecular Biology in Mainz, Germany.

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Scitation: Eco-conscious cleaning with polymer beads
http://aip.metastore.ingenta.com/content/aip/magazine/physicstoday/news/10.1063/PT.5.5008
10.1063/PT.5.5008