Epoxy resins: properties, applications, types / Articles

Epoxy resins (epoxy oligomers) are a class of thermosetting synthetic resins containing at least two epoxy groups in their molecule. Under the action of curing agents, they are capable of transforming into crosslinked (network) polymers with a unique combination of physical, mechanical and chemical properties. Thanks to high adhesion to most substrates, excellent chemical resistance, low shrinkage during curing, and high dielectric characteristics, epoxy resins have found wide application in all industries — from aerospace to construction.

Chemical Structure and Synthesis

Epoxy resins are oligomeric products with a molecular weight ranging from 300 to 3500. The key structural element is the epoxy group (glycidyl group) — a strained three-membered ring containing an oxygen atom and two carbon atoms.

The most common method for producing epoxy resins is the polycondensation reaction of epichlorohydrin with compounds containing an active hydrogen atom: phenols, alcohols, acids and others. The main type is resin based on bisphenol A and epichlorohydrin — the so-called diglycidyl ether of bisphenol A (DGEBA).

Cycloaliphatic epoxy resins are obtained by epoxidation of unsaturated compounds with peroxyacids or hydrogen peroxide. These resins do not contain hydroxyl groups, which provides them with high arc resistance, tracking resistance and hydrolytic stability.

Depending on the grade, epoxy resin can be a transparent yellow-orange liquid or a solid brown mass.

Classification of Epoxy Resins

By chemical structure and method of production, epoxy resins are divided into several main types:

Bisphenol A (DGEBA) epoxy resins — the most common and high-volume type, forming the basis of global production. They offer an excellent balance of properties and affordable pricing.
Bisphenol F epoxy resins — characterised by lower viscosity, making them preferred for solvent-free coatings and highly filled compositions.
Novolac epoxy resins — provide increased thermal and chemical resistance, sought after in high-temperature applications.
Cycloaliphatic epoxy resins — possess high arc resistance and weather resistance.
Glycidyl ethers and glycidyl amines — specialised types for high-performance applications.

Based on physical state, epoxy resins are classified as liquid, semi-solid and solid. By application, they are divided into resins for adhesives, coatings, electrical insulation, composite materials, and others.

Curing of Epoxy Resins

Epoxy resins are thermosetting — they cure (transform into an infusible and insoluble state) only in the presence of curing agents. The curing process can occur over a wide temperature range — from room temperature to 200 °C.

Main types of curing agents:

Amines (polyethylene polyamine, PEPA) — the most common type of curing agent for cold curing at room temperature. Curing with PEPA takes about one day.
Acid anhydrides (phthalic, maleic, pyromellitic) — used for hot curing at elevated temperatures (up to 180 °C, holding time up to 10 hours).
Tertiary amines and Lewis acids — used as curing catalysts.

An important feature of epoxy resins is low shrinkage during curing (less than 2%), which ensures excellent dimensional stability of products.

Physical, Mechanical and Chemical Properties

Epoxy resins possess a unique combination of properties:

Adhesion. Epoxy resins have exceptionally high adhesion to metals, glass, ceramics, concrete and many polymers. Due to the presence of polar groups, they wet most surfaces excellently.

Mechanical Strength. Cured epoxy resins are characterised by high tensile, flexural and compressive strength, as well as good impact resistance.

Chemical Resistance. Epoxy resins are resistant to acids, alkalis, halogens, oils and many organic solvents.

Thermal Resistance. Special grades can withstand temperatures up to 290 °C. The glass transition temperature varies widely depending on the type of resin and curing agent.

Electrical Insulation Properties. Epoxy resins are excellent dielectrics with high volume resistivity.

Low Shrinkage. Minimal shrinkage during curing ensures high dimensional accuracy.

Water Resistance. Epoxy resins are resistant to moisture.

Applications

Thanks to the unique combination of properties, epoxy resins find application in almost all industries:

Coatings and Paints. The largest consumption segment (about 48% of the market). Epoxy coatings provide anti-corrosion protection for metal structures, pipelines, ships, automobiles and industrial equipment. They are used as primers, topcoats, electrical insulation and anti-corrosion varnishes.

Adhesives and Sealants. Epoxy adhesives offer record strength and are used for bonding metals, composites, ceramics and plastics in automotive, aerospace, shipbuilding and construction.

Composite Materials. Epoxy resins serve as binders for high-strength reinforced plastics: carbon fibre composites, fibreglass and textolite. They are widely used in aerospace for aircraft and rocket structures, in wind turbine blade production, boat hulls and automotive parts.

Electronics and Electrical Engineering. Epoxy resins are used for encapsulation and protection of electronic components from moisture and dust, as insulating materials, for casting transformers and cable joints. They protect electronic components, extending their service life.

Construction. Epoxy resins are used in floor coatings, for concrete structure repair, as waterproofing materials, for injection strengthening of foundations and in the production of plastic cements.

Wind Energy. One of the fastest-growing segments. Epoxy composites are used for wind turbine blades due to their light weight, high strength and fatigue resistance.

Aerospace. Epoxy resins with carbon fibre form composites for aircraft, satellite and rocket structures.

Household Appliances and Consumer Goods. Used for coatings, adhesives, repair compounds and decorative products.

Global Epoxy Resin Market

The global epoxy resin market shows steady growth. In 2025, the market was valued at USD 13.55–14.32 billion. It is projected to grow to USD 21.66–23.89 billion by 2032–2034 at a CAGR of 5.7–9.7%. In physical terms, the market was approximately 3.52 million tonnes in 2025 with global production capacity of about 5.1 million tonnes.

The Asia-Pacific region is dominant with a market share of about 68.9% in 2025, driven by strong manufacturing bases in China, India, Japan and South Korea.

China is the world's largest producer and consumer of epoxy resins. In 2025, China's total capacity exceeded 4 million tonnes, and production volume reached 2.205 million tonnes, up 15.11% year-on-year. The average annual capacity utilisation rate was about 51%. By 2025, production is expected to reach 2.205 million tonnes.

Key market trends include growing demand for bio-based epoxy resins — manufacturers are replacing 20–50% of petrochemical content with renewable materials such as lignin, vegetable oils and tannins. Technologies for reducing volatile organic compound content, solvent-free systems and low-bisphenol A formulations are also being actively developed. Growing sectors include wind energy, aerospace and electric vehicle battery production.

Conclusion

Epoxy resins represent one of the most versatile and sought-after classes of polymer materials in modern industry. The unique combination of high adhesion, chemical resistance, mechanical strength, excellent electrical insulation properties and low curing shrinkage makes them indispensable in coatings, adhesives, composites, electronics, construction and renewable energy. The development of bio-based and environmentally friendly technologies opens new prospects for this critically important class of materials, ensuring their continued growth and expansion of applications.