B-+Structure+of+Bulletproof+Fabrics

Q&A Wednesday Assignment What is the structure of bulletproof fabrics? Wilfred Ho =What is Kevlar? = - The most common bulletproof material is Kevlar, a man made polymer similar to nylon which can be made into strong, tough, stiff, extremely high-melting fibre that is five times stronger than steel. - There are generally 2 types of Kevlar. Kevlar 29 is used to make bulletproof vests, while Kevlar 49 is more ridged and is used also in tires, heat/flame resistant fabrics, and fibre-reinforced materials like aircraft panels, boat hulls, and golf club shafts

 Kevlar is an aromatic polyamide. Its full name is poly-para-phenylen terephthhalamide

= = = =

Figure 1.1- Structure of poly-para-phenylen terephthhalamide
=Strength of Kevlar = - What makes Kevlar so strong is because it is made from a polymer that is spun from hot, solutions of concentrated sulphuric acid. The fibres are then heat-drawn, which means that the while the material is being formed, reactions are happening in an environment over 400oC. - Because of Kevlar’s resistance to heat and inability to melt, it is also used in firefighting as a product known as Nomex - Poly-para-phenylen terephthhalamide has very strong intermolecular forces, like H-bonding between each monomer subunit and chain as well as highly stable benzene rings - The material is also woven into a spider web like pattern that interlock and overlap to maximize strength and the dispersion action on impact.

=Fabrics in bullet blocking action = - Kevlar is effective at stopping ballistic damage from high velocity objects because it only causes localized deformations, uncrimpling(damage to intermolecular bonds) and micro fractures(damage to intramolecular bonds). - However, ballistic damage from low velocity objects damage the structure of Kevlar more because the fibres uncrimple and translation as well. Fibre translation causes the intermolecular forces to lose the ability to reform. The damage also causes the fibres to lose their folding pattern, which in turn causes loss in bulletproof properties <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">- Impact from blunt projectiles also causes severe damage to the structure of the fabric like low velocity projectiles. <span style="font-family: 'Times New Roman',Times,serif; font-size: 120%; margin-left: 0.5in; text-indent: -0.25in;">- Ballistic resistance in these fabrics also decrease when they are wet and exposed to high temperatures

<span style="font-family: 'Times New Roman',Times,serif;"> __<span style="font-family: 'Times New Roman',Times,serif; font-size: 120%;">Citations __

=
<span style="font-family: 'Times New Roman',Times,serif; font-size: 90%;">Kirkwood, J., Kirkwood, K., Lee, Y., Egres, R., al, E. (2004, November 01). Yarn Pull-Out as a Mechanism for Dissipating Ballistic Impact Energy in Kevlar¿ KM-2 Fabric: Part II: Predicting.... Textile Research Journal, (11), 939, Retrieved from [|http://elibrary.bigchalk.com] ======

=
<span style="font-family: 'Times New Roman',Times,serif; font-size: 90%;">Kevlar. (2010). In Encyclopædia Britannica. Retrieved November 06, 2010, from Encyclopædia Britannica Online: [] ======

=
<span style="font-family: 'Times New Roman',Times,serif; font-size: 90%;">Litherland,. (2010). eHow. Retrieved October 28, 2010 from What is Kevlar Fabric: http://www.ehow.com/​about_5114619_kevlar-fabric.html. ======