[+]Enlarge Credit: DSM Dyneema

The technology for producing ultra-high-molecular-weight polyethylene (UHMWPE) fibers has existed for nearly four decades. Two companies, DSM and Honeywell, use it to manufacture most of the world’s supply of the lightweight fibers, which are twice as strong as steel and are used in bulletproof clothing, armor, marine towlines, and other applications.

Now ﻿﻿Paul Smith﻿ and ﻿﻿Theo Tervoort﻿ of the ETH Zurich and coworkers have found a way that might greatly improve the manufacturing process (﻿Macromolecules 2015, DOI: 10.1021/acs.macromol.5b02211).

The new study proposes replacing the solvent currently used, petroleum-based decalin, with environmentally benign vegetable oils. This solvent switch, according to the study, could increase fiber strength nearly 100% or cut production costs by more than 50%.

“This is a revolutionary discovery in the field of high-strength fibers and will have a very significant societal impact,” says ﻿Macromolecules Associate Editor Alan D. English of the DuPont Experimental Station. “It’s the most significant discovery in fiber science in nearly a half-century.”

Conventional polyethylene, the world’s most common plastic, is weak because its fibers are short. To make UHMWPE fibers, manufacturers polymerize ethylene monomer into chains about 30 times as long as those of conventional polyethylene. Those chains are initially entangled with one another, which also weakens the polymer, so manufacturers dissolve them in decalin and then draw them out lengthwise to remove some entanglements. The solution used commercially is 10% polyethylene and 90% decalin by volume—meaning that for every kilogram of UHMWPE fiber produced, 9 kg of decalin has to be recovered.

Sign up for C&EN's must-read weekly newsletter Email Address * Subscribe » Contact us to opt out anytime

In the new study, the researchers found they could prepare UHMWPE by using 25% polyethylene and 75% vegetable oil, so only 3 kg of environmentally benign—in fact, edible—solvent needs to be recovered for every kilogram of ­UHMWPE produced, lowering production costs. A solution of 10% polyethylene and 90% vegetable oil enabled further disentanglement and yielded stronger fibers than those made with the decalin-based method.

Pieter Lemstra, a professor emeritus at Eindhoven University of Technology (TUE), who codiscovered the current UHMWPE manufacturing process with Smith, notes that changing the current industrial process could prove challenging. Nevertheless, the new study is “a scientific breakthrough,” he says.