Aimee Ruth I. Dagupon
15 January 2013
CHEM 171 SYNTHESIS OF KEVLAR® Discovery and Historical Background
Stephanie Kwolek, a female research scientist at DuPont Company, was the first one to develop Kevlar in 1965 by polymerizing and solubilizing para - aminobenzoic acid. Spinning the resulting opaque solution, fibers were obtained. Results on the physical test of the product were unbelievable that the process was repeated several times before they concluded that the data were correct. Kevlar fiber was concluded to have extreme stiffness and heat resistance, many-fold higher than existing fibers (Tanner, 1995). Kwolek’s team was originally tasked to invent a polymer that can replace steel in radial tires (Smith et al , 1998). Kwolek patented her invention in 1966. Kevlar was first sold in the market in 1971. The next challenge was the cost of the raw materials for its production, after having found the potential uses for Kevlar and how it can contribute to the economy. This matter was addressed by producing PPD – T, a suitable polymer that became the basis of Kevlar. Another concern was the spinning solvent which was supposedly 100% sulfuric acid. Using such amount and concentration of solvent, the mixture was too viscous, making it had to spin; and also considering that sulfuric acid is difficult to handle. A deliberate solution to this matter was spearheaded by Herb Blades. Blades. He addressed this by using twice twice the amount of the solvent at an elevated temperature. The result was a formation of a crystalline complex. In addition to this, Blades suggested that an air gap between the spinneret and cold water should be established. This resulted to the formation formation of a fiber with excellent tensile tensile properties. These discoveries and addressed problems led to the scaling up of the production of Kevlar (Tanner, 1995). Synthesis of Kevlar
Kevlar
is
actually
DuPont
Company’s
brand
name
for
poly-paraphenylene
terephthalamide fiber. It is most popular in the weaponry as bullet – proof vests. It can also be
1 A term paper paper submitted in partial fulfillment fulfillment of of the course requirements requirements in CHEM 171; 171; 2 nd sem. A.Y. 2012-2013.
used in sports equipment, cars, fire suits, yacht sails, animal handling protection and many more. Kevlar is synthesized via the condensation polymerization of terephthaloyl chloride and p – phenylenediamine (Jingsheng, 1981). Below is the general reaction.
The mechanism of the above reaction is as follows (Baltimore, 2012):
It is a condensation polymerization since two monomers are involved. The by- product is HCl. The
polymerization
solvent
is
hexamethylphosphoramide
(HMPA).
Condensation
polymerization produces cross - linked and networked polymers such as Kevlar. The fibers are obtained via mechanical drawing called spinning. The use of concentrated sulfuric acid keeps the polymer in the solution during synthesis and spinning (Callister, 2000).
2 A term paper submitted in partial fulfillment of the course requirements in CHEM 171; 2 nd sem. A.Y. 2012-2013.
Different types and properties of Kevlar
Kevlar is claimed to be five times stronger than steel considering the same weigh t. It has half the density of glass. It is lightweight, flexible and comfortable. It is very heat and cut O
resistant. It can decompose above 400 C without melting. It can be degraded when wet, thus it needs to be specially waterproofed (Callister, 2000). Furthermore, it has low electric conductivity and high chemical resistance. Some of the disadvantages of Kevlar include its cost. It has poor compressive qualities and is very sensitive to the environment since it absorbs water. It is very stiff, thus it limits movement when used in bulletproof vests (Tanner, 1995). The most common types of Kevlar are Kevlar® 49 or also known as composites grade and Kevlar® 29 or ballistics grade. Kevlar® 49 is used with epoxy, vinyl ester or polyester resins, forming ridigd laminates which are most commonly used in kayaks, high speed boats, aircraft panels and many more. They are rigid and are used in wet applications to maximize its physical properties (Smith et al ., 1998). Kevlar® 29 is for ballistic protection or hard armor applications such as protective vests, gloves, armor helmets and many more. It is made of tough yarn and its ballistic level is tested based on the type of weapon, caliber, bullet type, testing range and projectile velocity. It is used in dry applications (Smith et al ., 1998). Commercial Scale production of Kevlar
Actions to avoid environmental and health issues were pointed out during the early commercial scale production of Kevlar. Such matters include the following. The disposal of used sulfuric acid is carried out by converting it to calcium sulfate or gypsum which can be used in the manufacture of wallboard and cement. HMPA is found to be the ideal polymerization solvent since it has no unusual toxic effe cts (Klowek et al., 1962). The industrial scale production of Kevlar today is carried out such that the materials are efficiently used in order to maximize production. The following patent presents a method for
3 A term paper submitted in partial fulfillment of the course requirements in CHEM 171; 2 nd sem. A.Y. 2012-2013.
spinning and washing aramid fiber while recovering sulfuric acid. The following is the schematic diagram of the process (Bruining et al ., 2012):
Figure 1. Schematic diagram for the spinning and washing of aramid fiber and recovering sulfuric acid (Bruining et al., 2012). The process involves first, spinning the aramid polymer from the sulfuric acid spin and doping it to a yarn. While the yarn is being coagulated, it is washed with water. All washings are saved and their sulfuric acid contents are enriched via evaporation. This gives off 98% sulfuric acid and water. Finally, oleum is added to obtain 98- 105% sulfuric acid. The solution can now be recycled or reused at this stage. Latest Kevlar Innovation
One of the popular issues today is the production of genetically modified organisms (GMO). With the use of harsh and great amounts of pesticides, herbicides and insecticides, agriculturists have shifted to using heavy duty tractor tires made of Kevlar. The chemicals and the presence of stalks which are sharp and weapon – like likely destroy ordinary tires or shorten their span of efficiency and durability (Gucciardi, 2012). Another one is the manufacture of bulletproof backpacks and vests for kids. The demand for these products abruptly boomed after the massacre in Connecticut. Worried 4 A term paper submitted in partial fulfillment of the course requirements in CHEM 171; 2 nd sem. A.Y. 2012-2013.
parents are willing to buy expensive bags and clothes to keep their children safe (France-Presse, 2013). References
BALTIMORE, E. 2012. Kevlar Synthesis. Park School of Baltimore. BRUINING, W.J. et al. 2012. Method for spinning and washing aramid fiber and
recovering
sulfuric acid. Patent No. US 8273134 B2. App. No. 12/739,643. th
CALLISTER, W.D. 2000. Materials Science and Engineering: An Introduction. 5 Ed.
New
York: John Wiley and Sons, Inc. FRANCE – PRESSE, A. 2013. Back-to-school accessories, US style: the bulletproof backpack. Brisbane Times. GUCCIARDI, A. 2012. Kevlar Tires Now Required to Traverse ‘Spear – Like’ GMO Crops. The Natural Society Newsletter. JINGSHENG,
B.
1981.
Studies
on
the
Semirigid
Chain
Polyamide-
Poly(1,4
Phenyleneterephthalamide) . J. Of Appl. Polym. Sci., 26, 1211.
KLOWEK, S. et al. 1962. Process for making wholy aromatic polyamides. Patent No. US 966.
3,063,
SMITH, A.P., et al. 1998. Quantitation of the Lateral Orientational Order within Various Grades of Kevlar High Strength Fibers with X-ray Linear Dichroism Microscopy. Department of Physics, North Carolina State University. TANNER, D. 1995. The Kevlar Innovation. #184 from R&D Innovator Volume 4, Number 11.
5 A term paper submitted in partial fulfillment of the course requirements in CHEM 171; 2 nd sem. A.Y. 2012-2013.
