AuTx - Intellectual Property
AuTx Know How, Patents & Licences - Soft Body Armour
AuTx is a complex co-polymer aramid, this means that its physical properties can be altered within quite a wide range by altering the chemical formulation. Properties such as strength, modulus, elasticity, thermal resistance, etc. can all be modified to produce a yarn that is “optimized” for a specific applications such as composites, soft armour, fire resistant clothing. This is however a property trade off as for example as the fire resistant properties are reduced the stronger the fibre becomes, etc. AuTx can be made 200-300% dynamically stronger then Kevlar, or more fire resistant that PBI). The gel formulation development is advancing and the work in the lab is giving significant increases (100%+) in strength over what is being made “commercially”. Samples of some of the new higher strength yarns have been sent to a leading US University where AuTx filament was tested last year with a 197% increase in strength in comparison to the best Kevlar KM2.
This performance or specific optimisation is not possible in the chemical nature of other aramids such as Kevlar, Nomex, Twaron, etc. and the performance limitations have been reached in the actual chemistry of the simple aramids like Kevlar & Twaron.
The gel that is produced is “spun” like a spiders threat, it comes out of spinerettes that are like a miniature showerhead, each hole produces a filament and a number of filaments make a yarn (called fibres in a natural yarn). The size, shape and orientation (twist) of the holes in the spinarette also impart specific physical characteristics to the yarn, that are important in ballistics, especially in stopping small high speed fragments. Kevlar KM2 & Twarom Microfilament both use this know how (and patents). The difference in spinning is that Kevlar & Twaron are spun at higher speeds, from lower viscosity gel, and from larger, simpler spinarettes. The finer AuTx spinning process enables us to produce finer more specific filaments and yarns. The texs that (grams / km of yarn) AuTx is spun in is approximately 6.5tex, 14.5 tex and 30 tex, and multiples greater. Kevlar & Twaron start at 42 tex.
This is significant because to stop fine fragments efficiently (here we refer to “areal density” mass {kgs or lbs} per area {m2 of ft2} with low areal density systems (often refered to as higher performance systems) you need to wrap the fragment in fine filaments / yarns as its hitting the armour system to stop it cutting through whilst dissipating the energy as fast as possible across the armour system. The more filaments & greater their density combined with more yarns and & greater their density the lighter the armour system can be. However as the size of the fragments increases you also need to have thicker yarns to stop their penetration, so thicker yarns (higher tex) such as 30 tex are also used. This is a gross over simplification but it does enable you to see why asymmetric complex systems are more efficient / higher performance.
The gel as it comes out of the spinarettes is either drawn or flows into either a dry (air gap) and then into a solvent / reagent bath or wet (strait into a solvent / reagent bath), then wound around rollers under specific tension and temperature so that the filaments cure/set. This process imparts on the yarns the ratio of their strength : modulus : elasticity in part by determining the degree of molecular orientation in the filaments. Because the spinning process is slower than the Kevlar / Twaron one and the chemistry is more complex this enables finer tuning of the yarns properties. As mentioned above to stop the small fragments you need to wrap them (like an American baseball glove) to stop them penetrating, if these filaments / yarns were stiff (high modulus) they would break and the fragment would slice through, so in the initial few layers of our soft armour systems we would use fabrics that have lower modulus, higher elasticity filaments in them. Likewise towards the rear of the soft armour system we would have higher modulus, less elastic yarns to “brake” the encapsulated fragments penetration.
Once the filaments in the yarn have been optimally set on the rollers they are spun / twisted onto bobbins and this process has a significant effect on the ballistic performance of the fabrics. The degree of filament entanglement and twist of the yarn is used in soft armour systems. Low entanglement and low twist are used in yarns in the fabrics that are used to encapsulate / smother the fragments at the front of the back and high entanglement, higher twist yarns are used in fabrics in the centre of the back as they cause higher inter filament friction that is used to dissipate energy from the fragment as well as higher static strength that enables breaking of the filaments that “absorbs” a lot of energy.
After the yarn has been wound onto the bobbin the bobbins are then annealed (unlike other aramids) in a high temperature (250oC+) autoclave which leads to a number of key physical performance benefits. The annealing greatly increases the strength of the filaments and it makes them very chemically and thermally stable.
Lastly in normal environmental conditions such as in storage and in body armour in the field the stresses and strains within the filaments even out and combined with other slow chemical reactions over year the yarns slowly increase in strength. Although not greatly, but in military service over a decade it has been found that the yarns increase about 2%.
Thick yarns make thick fabrics, thin yarns make fine fabrics, fine fabrics stop fine fragments at less areal densities. Often in the weaving industry this is measured in grams per m2 or gsm. AuTx fabrics are woven using a number of patented processes that give them isotropy, the ability to spread energy rapidly across / through the fabric. Finer, looser fabrics (≤100gsm) are used at the front of the soft armour systems so that they wrap / entrap the fragments or bullets. Medium weight, high density fabrics (≤150gsm) are used I the middle to “absorb” as much energy as possible and then thicker (≥200gsm) fabrics are used to halt the penetration and reduce trauma.
Kevlar and Twaron yarns are generally supplied in thick yarns that are simply woven into simple fabrics that are thick and heavy.
Once woven the fabrics are colanderised (run through rollers at specific temperatures and preasures) to reduce their thickness (for thinner less bulky armour) and increase the surface density of the filaments (more filaments per mm2 to engage the fragments).
The fabrics are given a water / solvent repellant treatment so that they are minimally effected ballistically by exposure to oils, hydraulic fluids and water.
The fabrics are placed within protective systems that are optimised to defeat specific threats under specific conditions.