Aramid fibre (AF)

15-80 usd/kg
Circularity potential
Low
Strength
Extreme
Production energy
Extreme
Stiffness
High
Embodied CO2
High
Density
Medium

Aramid is a very high performance material. There are two distinct groups: para-aramids are strong and resistant to penetration and cutting; and meta-aramids are prized for their superior resistance to heat and fire. They are commonly referred to by their trademark names. P-aramids include Kevlar, Twaron and Technora; and Nomex is an M-aramid. Production is very expensive, which limits applications somewhat – finer yarns are more expensive per kg and the cost of meta-aramid varies greatly.

It can be described as a type of nylon (PA), but rarely is, because its polymer structure is quite different. Nylon is aliphatic – the polymer chains are branched and only semi-organised. By contrast, aramid consists of an aromatic polymer structure (closed rings of atoms), which produces a highly crystalline (oriented) structure. The strength of aramid is the result of inter-molecular hydrogen bonds between these long and highly oriented polymer chains, and the stacking of the aromatic structure. This is very different from the typical van der Waals interactions (weak molecular-level electrostatic attraction) found in regular plastics like nylon, which is the reason why they can be melt-processed at relatively low temperatures. Aramid does not melt and cannot be processed in the same way – it will eventually breakdown at around 450 degC – and therefore is only available as a spun fibre, or as part of a fibre-based composite.

Aside from all its benefits and life saving attributes, aramid has some weaknesses. It has much lower resilience compared to nylon and other plastic fibres, and repeated bending and flexing will cause the linear fibre structure to breakdown (fibrillate). It is also very vulnerable to UV degradation and must be protected from exposure to daylight.


Sustainability concerns
Non-renewable ingredients
Raw material generates polluting by-products
Low circularity potential
Microplastics


These high performing fibres are used in demanding applications, such as car tyres, bullet-proof body armour, shielding for sports equipment and fibre reinforcement for lightweight composites used in aerospace and transportation. Its very high resistance to penetration is due to the relatively high strength bonds acting between the oriented polymer chains – and the many layers of polymer inside a fabric structure make it difficult for bullets and other objects to push through.

Compared to carbon fibre, aramid is not as strong in tensile or compression, but it is lighter, tougher and non-conductive – three very useful properties. Compared to glass fibre, it is stronger for the same weight. As a result, it is used as fibre reinforcement in a range of demanding applications and protective apparel. It is applied as both continuous and short fibre in thermoset and thermoplastic matrices, especially where high temperature performance is required. There are several grades available – each has unique benefits. While Kevlar is only available as yellow fibre, Technora and Twaron are available as dope-dyed black. The black yarn is typically only used where the colour is important, such as racing sails and protective clothing. Due to difference in chemistry, Technora is a darker yellow than Twaron and Kevlar.


Design properties
Cost usd/kg
25-35
Embodied energy MJ/kg
1650
Carbon footprint kgCO2e/kg
8.7-13
Density kg/m3
1440
Tensile modulus GPa
100-140
Tensile strength MPa
2700
Hardness Mohs
2
Thermal expansion (µm/m)/ºC
-4
Thermal conductivity W/mK
0.09
Temperature min-max °C
-150 to 250
Thermal
good insulator
Electrical