Carbon fibre (CF)

15-90 usd/kg
Circularity potential
Low
Strength
Extreme
Production energy
Extreme
Stiffness
Extreme
Embodied CO2
Extreme
Density
Medium

Carbon fibre (CF) is prized for its strength, stiffness and stability coupled with high resistance to weathering, humidity and chemicals at ambient temperatures. The main limiting factor is cost – CF is only commercially viable in applications where the relatively high cost of the fibre is justified by weight savings, such as aerospace, or in applications where long-term strength retention is essential, such as pressure vessels. Huge growth in these types of applications is helping to reduce the cost of carbon fibre and so bring it inline with a broader range of applications, from automotive to sports products, consumer goods and even fashion.

It tends to be used as part of a composite – either surrounded by a resin matrix, such as epoxy, laminated between thin layers of plastic, or as the core of braided polyester rope, for example – because on its own it is quite brittle and its strength relies on fibre orientation. There are many standard formats available, including tow, spread tow, chopped (staple), woven, uni-directional, multi-directional and nonwoven.

Carbon fibre tow (untwisted bundle of continuous filaments) is the primary form of carbon fibre, before it is converted into fabric or composite part. As a standalone product, it can be used to make filament wound parts, pultruded parts, or chopped as a local reinforcement. It is available in many different sizes but most commonly 1k, 3k, 12k and 24k. The “k” refers to the number of thousands of individual carbon fibre filaments that make up the tow. So, a 3k tow consists of 3,000 filaments and a 24k tow, 24,000 filaments, for example. Spread tow is made by flattening out the bundle into a tape, with air jets or rollers, which can then be wound, woven or laid.

Each ultra-fine filament is made up of crystalline carbon, which is formed through the controlled oxidisation (heated to 200‐300 degC in air for 30‐120 minutes) and cooking (1,000-2,000 degC) of a precursor fibre. The most common is polyacrylonitrile (PAN), acrylic, which makes up about 90% of CF production. Another important type is pitch, which is a resinous by-product of coal tar or heavy oil leftover from petrochemical production. The difference in precursor governs the base structure of the carbon fibre. Graphite fibre, which offers a range of high strength and high modulus (stiffness) properties is produced by cooking the carbonised precursor at 2,000-3,000 degC in an inert atmosphere, such as nitrogen.

Sizing is polymer coating added to the carbon fibre to improve handling and processing (reduce breakage), as well as improve compatibility with the composite matrix. Sizings have been developed to maximise bond strength between various polymer or concrete systems and the surface of the carbon. This means, however, that new and emerging matrix systems, such as potentially recyclable thermoplastics, are not immediately compatible with all types of carbon fibre; first, the sizing must be adapted to suit its chemistry.

Based on properties, carbon fibre is graded as follows:
– Ultra-high-modulus, UHM (modulus above 450 GPa)
– High-modulus, HM (modulus between 350-450 GPa)
– Intermediate-modulus, IM (modulus between 200-350 GPa)
– Standard modulus and high-tensile, HT (modulus below 200 GPa, tensile strength below 3 GPa)
– Super high-tensile, SHT (tensile strength above 4.5 GPa)

Based on final heat treatment temperature, carbon fibres are classified as:
– Type I, high heat treatment carbon fibres (HTT), where final heat treatment temperature is above 2,000 degC, producing high modulus types fibre.
– Type II, intermediate heat treatment carbon fibres (IHT), where final heat treatment temperature is around 1,500 degC, and produces high strength type fibre.
– Type III, low heat treatment carbon fibres, where final heat treatment temperatures is below 1,000 degC, yields relatively low modulus and low strength fibre.


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


T1100 carbon fibre has exceptional strength and enhanced compatibility with conventional composite manufacturing techniques, including weaving, pre-prep, laminating, filament winding and infusion. It is sized for compatibility with thermosetting resin systems, such as epoxy, phenolic, polyester and vinyl ester. It is used in very demanding applications, including defence weapons systems and next-generation aircraft.


Design properties
Cost usd/kg
19.5-27
Embodied energy MJ/kg
207-287
Carbon footprint kgCO2e/kg
12.5-19
Density kg/m3
1430
Tensile modulus GPa
185
Tensile strength MPa
3460
Flexural modulus GPa
159
Flexural strength MPa
1920
Compressive strength MPa
1870
Hardness Mohs
2.5
Temperature min-max °C
-40 to 100
Thermal
insulator
Electrical
static dissipative