What is Epoxy? Types, Production and Uses

Epoxy is a resin family that carries at least two strained three-membered oxygen rings (oxirane/epoxide group) in its molecule. When this ring is opened by a hardener, a densely cross-linked, hard and extremely well-adhering network structure forms. Epoxy is the first solution that comes to mind wherever bonding, protection or structural reinforcement is required.

What is epoxy?

Epoxy is not a single product on its own, but a two-component system: component A is the epoxy resin, component B is the hardener (amine, anhydride, polyamide). When mixed, a chemical reaction begins — this is not drying but an irreversible curing process. The final properties depend not only on the resin but also on the hardener chosen; the same resin can yield either a flexible coating or a brittle structural adhesive depending on which hardener is used.

The distinguishing advantage of epoxy is its low shrinkage. Since no by-product (water, alcohol) is released during curing, volume loss is very small; this means dimensional stability and high adhesion strength.

How is it produced?

Standard epoxy resin (DGEBA) is produced by the reaction of bisphenol A with epichlorohydrin in the presence of sodium hydroxide. Molecular weight is adjusted by varying the bisphenol A/epichlorohydrin ratio: low molecular weight products are liquid, while higher molecular weight ones are solid and used in powder coatings.

Other production routes include novolac epoxies (epoxidation of phenol–formaldehyde condensate, for high heat resistance), cycloaliphatic epoxies (UV-cured systems) and bisphenol A-free alternatives (from bio-based building blocks such as cardanol and sorbitol). The latter group is developing rapidly due to regulatory pressure on food-contact packaging linings.

Types and varieties

Which sectors use it?

• Construction chemicals: industrial floor coating, concrete repair, anchoring, carbon fiber reinforcement.
• Paints and coatings: corrosion primer, pipe interior and exterior coating, marine paint. Since it yellows under UV, it is generally used as a primer for exterior facades, with a polyurethane top coat applied over it.
• Composites: carbon and glass fiber structures — wind turbines, aviation, sports equipment.
• Electrical–electronics: printed circuit board laminate, transformer encapsulation, chip coating.
• Adhesives: metal-to-metal and metal-to-composite structural bonding.
• Packaging: interior lining of metal cans.

The Turkish market and production

Epoxy resin production in Turkey is limited; the majority of base resins and hardeners are imported. The formulation side, however, is strong: numerous domestic companies producing floor coatings, construction chemicals and protective paints convert imported resin into their own systems and sell it together with application services.

Current topics in the sector include: the bisphenol A debate and the shift to BPA-free linings in food-contact applications, low-VOC/solvent-free flooring systems, demand for protective coatings linked to infrastructure investments, and the impact of wind energy investments on demand for composite epoxy. Current developments can be found in the news feed below.

Technical properties

The most frequently overlooked parameter is Tg. The Tg of a room-temperature-cured system is typically around 50–60°C; for a floor or part that will operate above this temperature, either a post-cure heat treatment must be applied afterward, or a hardener with a higher Tg must be selected from the outset.

Points to watch during application

• Apply the mix ratio by weighing it. Eyeballing the ratio or the assumption that "a bit more hardener cures better" disrupts the system's chemistry.
• Measure substrate moisture. A coating applied without measuring the concrete's moisture content and vapor transmission from below will blister; this is the most common site error.
• Check ambient and surface temperature separately. If the surface is close to the dew point, a surface defect (amine blush) will form during curing.
• Observe the recoat window between layers. Adhesion weakens if an intermediate coat has been left too long before recoating; sanding is essential in such cases.
• Select Tg according to service temperature. Systems cured at room temperature may soften in warm environments.

Frequently asked questions

Should epoxy or polyurethane be chosen?

Epoxy offers adhesion, hardness and chemical resistance; polyurethane offers flexibility, abrasion and UV resistance. The common solution in industrial flooring is to use both together: an epoxy primer and body coat, with a polyurethane top coat over it. Used alone outdoors, epoxy yellows and chalks.

Why is the mix ratio so critical?

Epoxy and hardener react stoichiometrically; this is not a catalyst relationship. Excess hardener leaves uncured amine residue (stickiness, yellowing, surface blushing), while insufficient hardener means low cross-link density and poor chemical resistance. The ratio must be measured by weight or volume as specified by the manufacturer.

What is pot life?

It is the period during which the product remains workable after the two components are mixed. The reaction is exothermic — the heat released further accelerates the reaction. For this reason, the pot life of epoxy mixed in a large volume is much shorter than that of epoxy spread out in a thin layer, and once the mixing container starts to heat up, the application window has closed.

Can epoxy be applied to damp concrete?

Not with standard systems. Moisture in concrete disrupts curing, and more importantly, residual moisture underneath creates vapor pressure that causes the coating to blister. Moisture measurement is a mandatory preliminary step in floor applications; in cases of high moisture, moisture-tolerant special primers or vapor barrier systems are used.

Why does epoxy yellow outdoors?

The aromatic rings in the DGEBA structure absorb UV light and break down over time; the result is yellowing and surface chalking. This is more of an appearance issue than a loss of strength, but the protective film does begin to thin. The solution is to stop UV exposure with an aliphatic polyurethane or acrylic top coat.