More on Kevlar

In a previous post, it was mentioned that Stephanie Kwolek discovered Kevlar, the miraculous material that was five times stronger than the same weight of steel. How exactly is this possible? One needs to examine the properties of Kevlar to find out.

Kevlar is an aramid, which is a fire resistant and strong synthetic fiber, which consists of long polymer chains that are aligned parallel to each other. Its strength lies in its strong inter-molecular hydrogen bonds (see Dr. Crane's website and accompanying picture), and aromatic stacking interactions. These interactions are much stronger than simple London Dispersion forces found in other synthetic polymers. Thus, because of these interactions, Kevlar has high mechanical strength and remarkable heat resistance.

These are some other properties of Kevlar:

High Tensile Strength at Low Weight
Low Elongation to Break High Modulus (Structural Rigidity)
Low Electrical Conductivity
High Chemical Resistance
Low Thermal Shrinkage
High Toughness (Work-To-Break)
Excellent Dimensional Stability
High Cut Resistance
Flame Resistant, Self-Extinguishing


And here are some applications of it:
Ropes that secure the airbags in the crucial landing apparatus of the Mars Pathfinder
Small-diameter, lightweight ropes that hold 22,000 pounds and help moor the largest U.S. Navy vessels
Shrapnel-resistant shielding in jet aircraft engines that will protect passengers in case an explosion occurs
Run-flat tires that allow for greater safety because they won't ruin the rim when driving to the nearest assistance
Gloves that protect hands and fingers against cuts, slashes and other injuries that often occur in glass and sheet metal factories
Kayaks that provide better impact resistance with no extra weight
Strong, lightweight skis, helmets and racquets that help lessen fatigue and boost exhilaration

Click here for more applications of Kevlar

Commercializing Nylon

After DuPont discovered nylon, they wanted to make a profit from it. Of course, since the most obvious idea was to incorporate it into clothing, they decided to substitute it for silk in women's hosiery. Although this idea became a reality in 1937, there were two problems with it: breaks formed due to bubbles and extrusion holes had to be unclogged due to fouling. Fouling is the accumulation of inorganic particles, microorganisms, macromolecules, and corrosion products on a surface. Today, the bubble problem has been solved but the fouling of extrusion holes is still a big problem.
Soon after that, a pilot plant was started in Seaford Delaware, which started producing 1/10 of DuPont's expected production. It slowly increased its production, and today it produces about a million pounds a day. Another plant was authorized in Martinsville, Virginia, where DuPont's experience with cellulose based products, such as Rayon and acetate, helped them succeed in commercializing nylon.
Nylon has come a long way since Charles Stine, Vice President of DuPont, introduced nylon:

"This textile fiber is the first man-made organic textile fiber prepared wholly from new materials from the mineral kingdom. I refer to the fiber produced from nylon. . . . Though wholly fabricated from such common raw materials as coal, water, and air, nylon can be fashioned into filaments as strong as steel, as fine as a spider's web, yet more elastic than any of the common natural fibers."

For pictures of factories, advertisements, and more in-depth information on the commercialization of nylon, click here

From Space Technology to Food Wrap

From space to food wrap Mylar has been there. Mylar developed out of the early 1950s compound Dracon and Cellophane of the 1960s. It showed that polyester could be oriented not only into long threads, which are woven, but also thin sheets, which are extremely strong and flexable. These thin sheets, much like long threads of polyester, have molecules aligned so that the durability of the material is increased.
The Mylar compound itself was impressive enough to be used on the lunar lander captained by Neil Armstrong. As stated in the fly and the ointment, “The lander was wrapped in a lustrous gold material.” Now a days you may find that Mylar is more commonly found wrapping food produce in the grocery market, than on our modern space shuttles. Yet, so far the polyester based Mylar has proved its usefulness, since its development back in 1960. Here you can see a thin layer of Mylar suspending a car from a crane, showing the strength of this material.

The Secret Behind Perspiration-fighting Athletic Gear

Sweat-fighting athletic gear, known as “performance apparel,” is a multibillion-dollar business. Sweat cools your body when it evaporates from your skin. However, too much sweat gets soaked up by the cotton shirt, which becomes damp. Performance apparel solves this problem by absorbing the sweat and drawing it upward. How does this work? It works because of polyesters. The sweat-removing shirts. With their polyester-blended fabrics, pull sweat away from the skin and push it through the clothing’s surface, which then evaporates. The result is a comfortable and dry shirt.
Brooks Sports’ Pulse T is a shirt that comes with “moisture transfer polyester” and heat release panels in the armpits and chest. It actually works. One would receive a cold sensation when wearing that polyester shirt. These polyester shirts do absorb the sweat thus leaving an athletic with a dry comfortable shirt ready to play his game.

Biodegradable Polyester: US Entering the Race

Global suppliers have commercialized a broad range of synthetic biodegradable resins, which is based on aliphatic polyesters. The demand for biodegradable polyesters is growing at a rate of 30% per year. The US is catching up with Europe and Asia in exploring the potential of biodegradable polyesters in flexibility and rigid packaging. The US is trying to find packaging applications for these materials. Synthetic polyesters are made in modified PET (mentioned in an earlier post) polymerization facilities. Polyesters, compared to other materials that take centuries to degrade after disposal, break down rapidly to carbon dioxide and water. It takes about twelve weeks to break down. Synthetic biodegradable polyesters can break up into two categories. One is highly amorphous (lacking shape), and has flexibility and clarity. The second is more rigid with properties close to that of PET. Julian Jensen, an Eastman Chemical’s business market manger, states:

"The emphasis is now on using biodegradable polyesters as specialty materials for paper coating, fibers, and garbage bags"

Companies such as Japan’s Showa Highpolymer, part of the Showa Denko group, and Korea’s SK Chemicals have small plants producing aliphatic (polybutylene succinate) and aliphatic-aromatic (polybutyrate adipate terephthalate) polyesters. It is becoming evident that polyester is indeed part of our future.

Polyester...Nylon... Now What?

Chemists at DuPont were still not satisfied after they discovered nylon. They wanted yet another stiffer and tougher nylon-type of material. But this time the new material was not discovered by Carothers; instead, it was found by Stephanie L. Kwolek.

What was the new material's name? Kevlar. This miraculous new material was five times stronger than the same weight of steel. Kwolek discovered Kevlar when she developed a liquid crystal polymer that could be cold-spun. This polymer that she synthesized was known as an aromatic polymer, which means one that is spun with a solvent rather than melt spun. As a result of this, DuPont spent over $500 million towards research on this. It won the National Medal of Technology in 1996, and Forbes magazine called it "a miracle in search of a market." Thus, DuPont found a use for this material in tires at a plant in Virginia, but today Kevlar is well known as the body armor that policemen and soldiers wear.

Performance Polyester

Polyester had a great run during the 70s with the infamous leisure suit era, which unfortunately ended disastrously. Yet, the wonder material is on the rise again. Since the 70s craze, polyester has evolved past the disco floor into the realm of performance athletic wear. Here, in this niche of the market, polyester has remained favorable for its heat retaining and moisture transferring properties.

DuPont has invested in its own polyester based performance wear product, which is advertised to offer superior warmth with extremely reduced weight. DuPont’s Thermolite Base delivers just what its advertisement claims. Thermolite utilizes a unique hollow structure variation of polyester thread, which maintains heat due to the air trapped inside the core.

DuPont explains that, “Hollow-core fiber technology provides the most warmth at the lightest weight.”

Due to its airway capillary design, Thermolite is one of the most breathable materials on the market. The constant flow of moisture away from the body maintains a comfortable body temperature even on the coldest days. Additionally the drying speed of this fabric beat out materials ranging from cotton and wool, to ordinary polyester and silk.

Powder Coating

TGIC (Triglycidylisocyanurate) polyester and urethane polyester are the two main groups of polyester powder coatings. They both have “flexibility and durability, including outdoor UV-resistance.” In addition, they have outstanding weathering properties.
TGIC, more specifically, is a low molecular weight epoxy (oxygen attached to two different atoms that is already united) functional cross-linker that is employed in polyester powder coatings. A cross-linker allows the polyester TGIC to have 90 plus percent resin within the binder system. Powder coating is any coating that is applied as a dry, fine solid which sticks to the substrate as a continuous film when melted and fused.
TGIC is used for the following: outdoor furniture, farm equipment, fence poles, air-conditioning units, automotive trim and accessories, and transformers. Some applications for urethane-polyester powders are fluorescent light fixtures, steel and aluminum wheels, patio furniture, chrome wheels and tires, air-conditioner cabinets, ornamental iron, electrical housing, range hoods, lawn and garden equipment, and automotive exterior trim. Research is now being done on polyester amide powders; polyester amide powders are going to be a powder coating in addition to the two primary types.

Polyester and Odorama

Some may be able to recall the 1981 film Polyester, in which director John Waters pokes fun at middle class, suburban life style and culture. However, more so than the actual film, some may be surprised by the fact that it was the first movie ever coordinated with Odorama. You guessed it! Smells were incorporated into the plot of the film via the magic of Scratch and Sniff cards. Dr. Schwarcz reminisces about his experience with Polyester, stating:

“There were oven fumes, pizza, ‘new car,’ and sweaty gym sock smells, and I’ll leave it to you to guess which odor filled the theater when the number 2 appeared on the screen.” (Schwarz, 165)

Yet, how can such a variety of different smells be triggered at different times and work so effectively? Once again polyester plays a fundamental role in this product. First the chemical makeup of whatever scent, for example moldy gym socks, is devised. The next step is the most astonishing. The scent molecules are encapsulated into incredibly tiny polyester beads through the process of microencapsulation (learn more here.) The beads are then ruptured when scratched, releasing the scent. Approximately one square inch of Scratch and Sniff paper can hold up to 50 million beads. This explains why Scratch and Sniff stickers seem to never lose their scent.