How to Make Epoxy Resin: A Quality Inspector's Guide to Olin Chemicals, Wrap Resins, and Reflector Enhancer Epoxy

The short answer

People often search “how to make epoxy resin” and expect a simple recipe. The industrial version is a controlled reaction between bisphenol A and epichlorohydrin, with caustic soda used to close the epoxide rings. After the reaction, the resin is washed, stripped, filtered, and tested. The product that arrives in your drum is not a single molecule; it is a distribution of oligomers, and that distribution decides whether the material works as a basic casting resin, a wrap resin, or a reflector enhancer epoxy. Buyers who ignore the distribution end up with rework.

If you ask me, the spec sheet matters more than the brand name. And the spec sheet has numbers that need context.

Who I am and why I can say this

I’m a quality and brand compliance manager at Olin Chemicals. My job is to review epoxy resin lots before they are shipped—roughly 300 unique lots a year. In 2025, I rejected about 6% of first deliveries for reasons like off-spec viscosity or hydrolyzable chlorides. Those rejections delayed customers, annoyed production, and taught me a simple lesson: most problems are visible in the certificate of analysis if you know where to look.

When I first started this role, I assumed “epoxy resin” was one product with different purities. It’s not. Two lots can have the same epoxy equivalent weight and still behave differently because of molecular weight distribution, chloride content, and color. My first job in quality almost ended with a batch of reflector enhancer epoxy that looked fine by viscosity but failed clarity after cure. That’s how I learned to respect the COA.

How to make epoxy resin, step by step

The most common liquid epoxy resin is made from bisphenol A and epichlorohydrin. The chemical name is diglycidyl ether of bisphenol A, usually shortened to DGEBA. Here is the core process:

1. Bisphenol A is charged into the reactor with an excess of epichlorohydrin. Excess epichlorohydrin matters: it prevents chain growth too early and keeps the product fluid.
2. Caustic soda is added in stages. The caustic drives the dehydrochlorination reaction that forms epoxide rings. Salt and water are byproducts.
3. The organic resin layer is washed to remove salt and other water-soluble contaminants.
4. Excess epichlorohydrin and water are stripped under vacuum. The recovered epichlorohydrin is recycled.
5. For solid or advanced epoxy resins, the liquid resin is further reacted with additional bisphenol A and a catalyst to increase molecular weight.
6. The resin is filtered to remove particulates, tested against the specification, and packed under conditions that keep it dry and clean.

That’s the skeleton. The real skill is in temperature control and addition rates. If caustic is added too quickly, the chloride number climbs. If stripping runs too hot, the resin turns amber and the viscosity drifts. The manufacturing process is as important as the recipe.

What I check before approving a lot

On a certificate of analysis from Olin Chemicals, the four values I always check first are epoxy equivalent weight, viscosity, hydrolyzable chlorides, and color.

• Epoxy equivalent weight (EEW) tells you the stoichiometric ratio with the curing agent. If EEW drifts, your crosslink density changes. That changes glass transition temperature and chemical resistance.
• Viscosity is reported at a set temperature, usually 25°C or 23°C. It controls how well the resin wets glass or carbon fiber, how fast it releases air, and how thick a film you can apply.
• Hydrolyzable chlorides are residual reactive chlorine compounds from the caustic step. They can cause corrosion, premature gelation, and optical haze.
• Color is measured in Gardner units. For a clear coating or reflector enhancer epoxy, a one-unit color shift is already a warning.

Don’t assume a high viscosity means higher quality. Viscosity is a process specification, not a status symbol. The right value is the one your application needs, not the biggest number available.

Why wrap resins are a different conversation

Wrap resins are formulated epoxy systems for composite wrapping, pipe repair, and structural reinforcement. They need to wet out fiber quickly, stay in place while the wrap is applied, and cure at the intended service temperature. A general-purpose liquid epoxy can be too viscous, too slow, or too fast depending on the formulation.

The neat resin values are not enough. In my role, I test wrap resins as a mixed system with the recommended hardener. Mixed viscosity at 23°C, gel time at 25°C and 60°C, and cured glass transition temperature are part of the review. A resin can look good alone and fail when mixed because of reactivity shifts.

One of the most common avoidable problems is treating a wrap resin like a casting resin. It’s not the same. Wrap resins are built for contact with fiber, not for a free-pour into an open mold.

Reflector enhancer epoxy: the quality bar is higher

Reflector enhancer epoxy is the most demanding of the three categories. It has to hold glass beads or prismatic reflectors in place while maintaining optical performance. That means the cured system has to be clear, low-color, and free of voids or haze-forming contaminants.

The same hydrolyzable chloride level that causes no visible problem in a floor coating can cause clouding in a reflector enhancer epoxy. A viscosity swing of five percent might be acceptable for some adhesives; it is not acceptable when the resin must form a thin uniform layer around reflectors.

In my first year, I almost approved a reflector enhancer epoxy lot based on EEW and viscosity only. The cured clarity test failed. We quarantined 12 drums, reworked the batch, and added cured-clarity testing to the acceptance criteria. That was a lesson learned the hard way.

Use the Olin Portal to verify your lot

A generic datasheet is not the same as a certificate of analysis. The generic datasheet describes a typical product. The COA describes the specific lot in your drum. At Olin Chemicals, lot-specific COAs are available through the Olin Portal. You can look up the measured EEW, viscosity, chloride content, and other values for the exact lot number you shipped.

If you’re buying Olin chemicals, make it a habit to check the Olin Portal before the material arrives or at least before you use it. It’s also the right place to confirm specification changes and product status. If your supplier cannot provide lot-level traceability, that is a red flag.

Three questions to ask before you order epoxy resin

1. What are the lot-to-lot tolerances for EEW and viscosity? “Typical” is not a specification.
2. What is the mixed viscosity and gel time with your recommended hardener? The neat resin number is not enough.
3. For wrap resins or reflector enhancer epoxy, does the supplier have cured-property data for this grade? Not for a similar grade.

If the answers are vague, I’d keep digging. An informed customer asks better questions and makes faster decisions.

When this guide doesn’t apply

Not every epoxy resin uses bisphenol A. Novolac epoxy resins, cycloaliphatic epoxies, and glycidyl amine resins use different chemistries. If you need high temperature performance or UV stability, the DGEBA route might not be the right starting point.

“How to make epoxy resin” is also a phrase used by hobbyists who mean “how to mix resin and hardener.” That is not manufacturing epoxy resin. Mixing is a different process with different safety rules. Don’t confuse the two, and never follow a manufacturing guide to set up a cure schedule.

To be fair, not every application needs the same level of scrutiny. If you only need an internal part with no optical or structural requirements, a standard liquid epoxy may be fine. But for wrap resins and reflector enhancer epoxy, the tolerances are tighter and the cost of a wrong lot is much higher than the time spent asking questions.