Epoxy

10-85 usd/kg
Circularity potential
Ultra low
Strength
Medium
Production energy
High
Stiffness
Low
Embodied CO2
High
Density
Medium

Epoxy is a high performance thermosetting resin, which is the product of a one-way chemical reaction. The reaction takes place between a resin and hardener, and is triggered by the mixing process, or as is the case with one-part systems, the reaction is accelerated with heat.

It is a diverse family, including adhesives, coatings, casting resins and laminating resins. On top of this, there are many different types of hardener and a wide range of additive available, which creates the opportunity to tailor the resin to a range of applications. Key properties include high strength, low shrinkage, excellent wet-out and adhesion with other materials, insulating, and resistance to solvents and chemicals.

One downside of epoxy is that it uses some nasty ingredients that are harmful to people and the environment, in particular bisphenol A (BPA) monomer. BPA is a key ingredient of epoxy resin, alongside epichlorohydrin (ECH) – most epoxy systems are derived from reacting these two ingredients. Bisphenol A (BPA) has been at the centre of numerous studies, because it poses a risk to people and the environment (it is an endocrine disruptor and oestrogen-mimicker). The concern is that small amounts of the chemicals present in food packaging materials migrate into the contents.

Even so, certain grades of epoxy are certified as food safe and considered non-toxic by organisations such as the US Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA). As a result, they can be utilised in food contact applications. Examples include coatings on steel water storage tanks and steel food packaging (tin cans), chocolate moulds and table tops.

Another downside is that as a thermosetting resin, it is not recyclable. Bio-based alternatives are emerging that attempt to reduce the negative impacts of this versatile resin by replacing a portion of the petrochemical derived ingredients with potentially renewable ones.


Sustainability concerns
Non-renewable ingredients
Raw material generates polluting by-products
Low circularity potential
Potentially toxic in use


Epoxy is the most important commercial composite matrix resin, used in a range of applications, including construction, civil engineering, aerospace, automotive, transport, furniture, products, sports and industry. It is more expensive than commodity thermosetting systems, such as polyester and vinyl ester.

On its own, it is quite brittle. When combined with functional additives and reinforcement fibres, such as carbon, glass, aramid and basalt, it can attain impressive strength and stiffness far superior to metals. It produces no volatile byproducts – all of the ingredients are consumed in the reaction – and so yields consistent structures free from voids and bubbles.

Over the years it has made a significant contribution to lighter weight structures and progress in aircraft efficiency, racing speeds and vehicle electrification. However, design with composites is much more challenging than with predictable isotropic materials, like metal. Even though composites perform very well under tension – when the fibres align with the stress – there are a multitude of complex potential failures to consider, such as matrix cracking, fibre breakage and delamination.

Epoxy are versatile resins that can be optimised for the composite process. For example, where as vacuum resin infusion requires a high flow two-part system with long pot life to ensure all parts of the fibre are reached, pre-preg (pre-impregnated fibre) laminating uses a one-part system that is triggered with heat and requires autoclaving (positive pressure) or compression moulding to achieve optimum performance. Other manufacturing processes used in the production of epoxy composites include injection moulding, filament winding, pultrusion and resin transfer moulding (RTM).

Thermosetting composite systems tend to be a bottleneck in manufacturing. So called snap-cure systems – such as by photocuring by infrared light or UV light, for example – have been developed that harden very rapidly, allowing epoxies to be used in high rate manufacturing and 3D printing. Even so, composites present many challenges in mass production applications, due to difficulties in producing complex geometries, labour-intensiveness, and high cost of the process and materials.


Design properties
Cost usd/kg
10-15
Embodied energy MJ/kg
76-137
Carbon footprint kgCO2e/kg
8.25
Density kg/m3
1100
Tensile modulus GPa
1.2-4
Tensile strength MPa
30-120
Flexural strength MPa
70-95
Shear modulus GPa
0.98
Compressive strength MPa
70-150
Hardness Mohs
2.5
Brinell hardness HB
30-40
Poissons ratio
0.35
Thermal conductivity W/mK
0.2
Temperature min-max °C
-40 to 200
Thermal
insulator
Electrical
insulator