Future tech: Ballistic armor made of wood?
By processing cellulose further than has been the case to date, it’s possible to extract cellulose nanocrystals (CNC) fibrils with incredible tensile strength
Since soft body armor has been available for police for roughly 40 years, we don’t pay much attention to it. Developments in this industry are more apparent when you have the perspective of most of that history, and remember when a plain vanilla Level II vest without a trauma plate was almost as bulky as the external body armor the military presently uses.
The body armor available to today’s cops bears little resemblance to the Second Chance vests Richard Davis was demonstrating — by shooting himself, many times) for cops around the country in the 1970s.
It was a lot thicker and less flexible.
We’ve Come a Long Way
The carriers were either non-breathing plastic that left no place for sweat to go except down your pants, or made of fabric that smelled like very ripe sweat socks by the end of the week, and had to be washed frequently. Many cops in warm climates wore only the front panels, as it was just too stifling to wear front and back at the same time.
My first vest, purchased in 1979, gave the illusion I had stuffed several sheets of cardboard inside my uniform shirt (kind of felt that way, too).
Today, many body armor panels are hybrids of Kevlar, Spectra, and Dyneema fiber, combined to take advantage of the characteristics of each. Level III vests are thinner, lighter and more flexible than Level II vests of yesterday.
Cellulose occurs naturally in the walls of plants and bacteria. It’s the most plentiful biological polymer on earth. Wood is mostly cellulose bound together by lignin.
Common cellulose looks a little like wet tissue paper (not surprising, since paper is mostly cellulose), and isn’t especially strong. By processing cellulose further than has been the case to date, it’s possible to extract CNC fibrils with incredible tensile strength. Tensile strength and elasticity is measured in Pascals, and ballistic fiber most commonly in giga-Pascals (GPa). Kevlar 49 has an elasticity of 125 GPa and a tensile strength of 3.5GPa. CNC’s numbers are 150 GPa and 7.5 GPa, respectively.
The only known material stronger than CNC is a carbon nanotube, and they cost at least 100 times as much to produce. Wood pulp yields about 30 percent CNC, and costs of large-scale production of CNC are estimated at about 10 percent that of Kevlar.
The downside of CNC at the present level of technology is its resistance to water. Cellulose is highly water absorbent (which is why paper towels are made of it), and tends to swell to almost twice its dry volume. The swelling also introduces defects which severely reduce its tensile strength. CNC can be treated to be hydrophobic (water-repelling), but doing so alters the mechanical characteristics of the material.
We may not see CNC in body armor any time soon, but there are other ballistic applications where moisture contamination and flexibility aren’t as great a concern. Door panels for patrol cars could be fabricated of CNC and sealed in waterproof coverings. Kevlar panels are already available, but they’re relatively expensive, so they’re not a standard feature. The cheaper CNC may make these commonplace.
Body Armor for Women
The armed forces didn’t take a cue from law enforcement, and have been issuing only one configuration of external body armor to all troops — one that is designed for men’s bodies. Women have proportionally shorter torsos than men, so the existing models make it difficult for them to bend over.
The panels rub against their hips and cut into their thighs when they sit. Some women couldn’t get their rifles in proper position to shoot without first shifting their body armor. The new models will accommodate their different proportions and make life a little easier and more survivable for female warfighters.
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