Polyethylene and Body Armor

Polyethylene and Body Armor
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Polyethylene, in simple terms, is a fancy word for plastic. Considering this, one might think it’s the last thing a company would use for body armor. But, this is where things get a bit more technical. Yes, polyethylene is a type of plastic. And when I think of plastic, I think of every plastic fork I’ve broken trying to eat at a family bbq. Luckily, this isn’t what happens in your body armor. It’s a much stronger material, and when engineered correctly as ballistic protection, it can save your life. So, in this particular blog, we’re going to dive into the properties of polyethylene—what it is and why it makes for excellent body armor.

What is Polyethylene?

We’re going to get a little technical here, but I’ll try to keep things as simple as possible. Polyethylene is a synthetic (artificial) resin. This resin is created from something known as the polymerization of ethylene. 

POLYMERIZATION

Polymerization is when these little molecules—think middle school science—combine with larger molecules. These small molecules are called monomers, and the larger molecules are called polymers. Basically, the little guys molecularly bond with the larger guys.

Ethylene is a type of gas, it’s what you get naturally from plants, and it’s an industrial organic chemical. We can create ethylene by heating natural gas, such as petroleum. When this happens, ethylene is separated.

Now, this is how the polymerization of ethylene happens. Remember the little guys joining up with the bigger guys? This same thing is happening, but they are all repetitively joining (polymerization) of ethylene to produce polyethylene. 

And this is where things get a bit more interesting for those who may have dozed off in chemistry class.

Polyethylene is a polymer. If you know anything about holsters, magazines, or various firearm parts, you might be familiar with the term polymer. It’s often associated with being lightweight. What’s so great about polymer is that it’s so versatile. It’s used in various products, from those associated with the tactical realm to squeeze bottles.

But, you don’t want a squeeze bottle protecting you from shots fired—it won’t work. You want reliable, lightweight body armor.

When the repetition of small molecules joining large molecules (polymerization) occurs at high pressures and high temperatures, you get something known as low-density polyethylene. But, you don’t want low-density; you want high-density when it comes to body armor.

HIGH-DENSITY POLYETHYLENE

High-density polyethylene (HDPE) is the result of the polymerization of ethylene, just like low-density. However, unlike the low-density stuff, high-density is formed from low pressures and low temperatures—yes, we know that sounds a bit backward. This is important because it makes all those molecules pack in real close together, making the material stronger.  When we say stronger, we mean in the ballistics world stronger in tensile strength.

Think of it like this. If you have a sheet of paper, it’s easy to rip in half. However, take a pack of paper and try the same thing. It’s near impossible. When polymerization of ethylene happens at these low pressures and temperatures, you’re getting a solid, packed together material that’s hard to “rip down the middle” without machinery or super-human strength.

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This gets quite a bit more technical because HDPE uses something known as Ziegler-Netta and metallocene catalysts (activated chromium oxide, known as Phillips catalyst). To save you the headache, just know, this is how polymer chains are packed so tightly, which gives you density, strength, and a moderate level of stiffness.

ULTRAHIGH-MOLECULAR-WEIGHT POLYETHYLENE

We’re still not quite to the stuff that gets us to body armor; for that, we need a really long chain of words known as ultrahigh-molecular-weight polyethylene or UHMWPE—to make things easier.

UHMWPE occurs when polymers of HDPE are spun into fibers and stretched into a highly crystalline state. This state results in a much higher stiffness level than that found in HDPE—strength greater than steel.

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The yarns made from these fibers can create bullet-resistant vests, often through a process known as gel-spinning. The advantage of gel-spinning is that it can be used to create a composite for flexible, lightweight ballistic protection or hard plates.

Why Does Polyethylene Make for a Great Material in Body Armor?

Now that we’ve gone over how you get from polyethylene used in your ketchup bottle to what’s needed for ballistic protection, let’s cover why body armor companies go through all this work to get to the final product.

Since polyethylene in body armor is made by bonding unidirectional UHMWPE over HDPE sheets, it’s easy to mold and cut to shape. When it’s compressed under high pressure and high temperature, you end up with a cohesive hard armored plate, which most might associate with heavy—fortunately, that’s not the case here.

As stated earlier, polyethylene is a type of polymer. Polymer is known for its lightweight properties. If you’ve worn body armor, you know how important it is to add as little weight as possible to your already heavy gear.

All that weight adds up, and pounds equal pain

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We want to create a product that not only protects those defending our communities and our nation, but we want a product that isn’t going to result in long-term back and knee pain. And that’s what using our patented Duritium® UHMWPE does for the body armor we’ve created at ShotStop®.

Not only do you get lightweight body armor, but you also get functional armor. Ballistic protection you can maneuver better in because it’s thin without compromising strength.

HOW DOES POLYETHYLENE WORK IN BODY ARMOR

UHMWPE works great for use in body armor because of its reaction to the spinning bullet.

When you fire a round, it spins. This spinning—when it hits body armor—causes friction. That friction is essential because it’s what causes polyethylene to melt. When polyethylene melts, it grabs the bullet, cools down, hardens back up, and prevents further penetration. This is especially important for backface deformation, which I wrote in our previous blog, Backface Deformation, What is it and Why is it Important?

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And to review what I wrote in that article, “UHMWP works by use of high modulus fibers with unusually strong tensile strength. Those fibers prevent or create less backface deformation, which means the bullet’s energy is diffused and dispersed much more efficiently by the plate system compared to other rifle plate technologies like ceramic or steel.”

UHMWPE also has a significant advantage when considering its strength-to-weight ratio. Not only is it strong and can potentially take more hits than ceramic or steel plates, but it’s also much lighter.

If you’re interested in learning more about our lightweight body armor, send us an email at sales@shotstop.com.


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