Back To Basics: Resin Selections – Part 1 – Epoxy Resins

From the many choices of different resins, the main categories for high performance composites are Epoxy, Polyester, and Vinylester. These three resin types are responsible for fabrication in billions of aerospace,  automotive, and marine applications but are not limited to home repairs or even infrastructure to buildings and bridges. Possibilities are nearly endless as resins are engineered to change the perspective on speed, efficiency, and strength.

Not all resins are created equally. Though visually sharing similarities in cured parts, resin types differ heavily by their molecular formula. These chemical differences effect the composite’s final properties heavily. Curing parameters, modulus, total strength, primary & secondary bonding properties, shear strength, chemical compatibility and many other aspects are affected by the resins’ type.

To start off our deep dive into the three main types of resins, we’ll start off with the most recognizable one, our old friend Epoxy Resin.

Epoxy resins when used in traditional methods are made of two parts; the liquid resin and a selected hardener, based on desired pot life (work time) and cure time. Through proper mixing and application of this resin, epoxy will yield the highest in strength to weight ratios of compared resins. Epoxy resins will simply outperform other resins on many applications. One reason it is placed in everything from general artwork, aerospace grade engine components, and some marine applications.Possibilities are nearly endless up to a service temperature up to 350F on some designed epoxies. Epoxy resin provides strength, better primary and secondary
bonds than other resins, also making it ideal for small repairs. However, it is consequently more expensive. For larger parts, such as a boat hull or kayak, a different resin may need to be considered if cost is a factor of design.

Optimal Epoxy Usage: When used with Carbon Fiber, Kevlar, or Fiberglass woven or unidirectional fabrics, epoxy provides strength advantages over any other resin. However, when used with Fiberglass CSM (Chopped strand mat) the resin can be tough to wet out completely, especially without assistance of a vacuum bag. This can lead to a resin starved condition that will not meet expectation or needed strength characteristics.

On the surface, it is simple to say that epoxy is superior to vinyl ester & polyester. In many ways this is the case; In aerospace applications especially, epoxy is hard to beat where having the strongest, lightest composite is desired with cost being implicated with efficiency. However, there are many applications in which polyester & vinyl ester are better for a given process. We’ll dive into applications more as we look at those two other types of resins next week.