Sunday, September 14, 2014

ALD coating offers Kevlar(R) bullet proof armour better stab resistance

Chemistry World reposrts "Oxide armour offers Kevlar better stab resistance":

Scientists in the US have synthesised an ultrathin inorganic bilayer coating for Kevlar [abstract below] that could improve its stab resistance by 30% and prove invaluable for military and first-responders requiring multi-threat protection clothes.

Developed in 1965 by Stephanie Kwolek at DuPont, poly(p-phenylene terephthalamide) (PPTA), or Kevlar, is a para-aramid synthetic fiber deriving its strength from interchain hydrogen bonding. It finds use in flexible energy and electronic systems, but is most commonly associated with bullet-proof body armour.

The ALD TiO2/Al2O3 bilayer coating adds protection but the fibers still retain good durability and flexibility (Picture by Chemistry World)

However, despite its anti-ballistic properties, it offers limited cut and stab protection. In a bid to overcome this drawback, Sarah Atanasov, from Gregory Parsons’ group at North Carolina State University, and colleagues, have developed a TiO2/Al2O3 bilayer that significantly enhances the cut resistance of Kevlar fibers. The coating is added to Kevlar by atomic layer deposition, a low temperature technique with nanoscale precision.

Full Story:

Improved Cut-Resistance of Kevlar® using Controlled Interface Reactions during Atomic Layer Deposition of Ultrathin (<50Å) Inorganic Coatings

Sarah Elizabeth Atanasov, Christopher J Oldham, Kyle A. Slusarski, Joshua Taggart-Scarff, Shalli A. Sherman, Kris J. Senecal, Shaun F. Filocamo, Quinn P. McAllister, Eric D Wetzel and Gregory N Parsons

J. Mater. Chem. A, 2014, Accepted Manuscript
Conformal atomic layer deposition (ALD) of Al2O3 and TiO2 thin films on Kevlar®, poly(p-phenylene terephthalamide) (PPTA) fibers at 50 and 100°C affects the fiber cut resistance. Systematic studies of ALD coatings between 10 to 400Å thick formed at 50 and 100°C revealed excellent conformality, and trends in cutting performance depended on materials and process details. A 50Å/50Å TiO2/Al2O3 bilayer formed at 50°C increased cut resistance of PPTA by 30% compared to untreated fiber materials. In-situ infrared analysis shows that trimethylaluminum (TMA) Al2O3 precursor reacts sub-surface with PPTA and tends to degraded mechanical performance. The TiCl4 TiO2 precursor reacts to form a barrier that limits TMA/PPTA interactions, allowing a harder Al2O3 layer to form on top of TiO2. The thin ALD coatings do not substantially affect durability, flexibility, or weight of the PPTA, making ALD a potentially viable means to enhance the protective properties of Kevlar and other polymer fiber systems.

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