From Molecules to Heavy Lifting: The Chemistry of VECTRAN™ Fiber

Every building is chemistry you can walk through, from concrete that keeps curing for years to glass that never quite became a crystal. The American Chemical Society calls this year's National Chemistry Week theme, “Chemistry Under Construction.”

VECTRAN™ liquid crystal polyester (LCP) fiber from Kuraray America, Inc. is the part of that chemistry that never makes it into the walls. It hangs from the crane, braided into the rigging that lifts the steel.

Walk past a high-rise under construction and look up at the top deck. You might notice a couple of things.

Up there, ironworkers clip into self-retracting lifelines, and the tower crane beside them swings a bundle of rebar on a synthetic sling. Rope and sling makers have long built that rigging and lifeline from steel wire. Some now build it with VECTRAN™ fiber. Before the concrete cures and the glass goes in, nearly everything rides on rigging past workers tied off at height.

Images 1 and 2 are for illustrative purposes only and do not represent or imply the use of VECTRAN™ fiber in the equipment or applications shown.

Strength Starts at the Molecular Level

Five Times Stronger Than Steel, Pound for Pound

VECTRAN™ fiber is technically a polyester, though it has little in common with the fabric in a gym shirt.

This polyester is made from two rigid, ring-shaped building blocks, 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, which link into stiff, rod-shaped chains. The whole molecule contains only carbon, hydrogen, and oxygen, the same elements in table sugar, so its strength comes from how those atoms are arranged.

The rods line up with one another even while the polymer is molten. Melt spinning then locks that alignment in along each filament. Ordinary polyester starts out as a tangle, more like cooked spaghetti, and only partially straightens when drawn.

For certain specific grade(s), with its chains already pointing in the direction of the pull, VECTRAN™ fiber is about five times stronger than steel and ten times stronger than aluminum, pound for pound.

Kuraray America spins VECTRAN™ fiber at its manufacturing site in Fort Mill, South Carolina. Turning the polymer into consistently oriented fiber depends on know-how built over more than 35 years of production experience.

Hard to Cut, Slow to Stretch

Because the chains are tightly packed and already aligned with the load, a VECTRAN™ rope is designed for low stretch after its first loading, even when it holds that load for years. That packing also makes the fiber hard to cut, since a blade needs more force to get through stiff, closely packed chains.

Fall protection makers use it in lifelines rated for leading-edge work, built to hold up if the line runs across a slab's sharp edge. It absorbs approximately less than 0.1% moisture even at 80% relative humidity. It also holds its strength against a wide range of chemicals.

For outdoor applications, rope makers add a coating or a braided cover that can shield it from direct sunlight, and some ropes built that way have shown little strength loss after decades of service.

Some jobs call for exposure to temperatures above 200°C, direct flame, unprotected sunlight, or chemicals such as caustic soda or ammonia. For those conditions, the Kuraray America team shares its test results so customers can choose the right material for the job.

Lighter Than Steel, Easier to Rig

Depending on the application, a VECTRAN™ rope has the ability to match the strength of a steel wire rope at a fraction of the weight.

The synthetic rope offers greater flexibility to bend. This can support easier and safer handling for rigging operations. Many large contractors emphasize safety as a company-wide standard.

Construction is one stop on a long list for this fiber. The same chemistry is applicable to select medical devices, puncture-resistant bike tires, and military inflatables, and it cushioned the airbag landings of NASA's Mars Pathfinder, Spirit, and Opportunity before helping lower the Curiosity Rover to the surface on a sky crane bridle.

The next time a crane swings a load past your office window, the sling carrying it may share its chemistry with the hardware that set four rovers down on Mars.

Chemistry Under Construction, in the Most Literal Sense.