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What is an epoxy?

Epoxies are a type of plastic formed from the polymerization (smaller molecules joining together to become longer molecules) of polymers or pre-polymers containing epoxide groups. Plastics (polymers) fall into two categories, either thermoset or thermoplastic. Thermosets cure through a chemical reaction that results in the formation of cross-links.


Figure 1. Unreacted polymer units (left), as they become linked (middle) to fully cross-linked (right)

The formation of cross-links is an irreversible, or permanent reaction. This means that a cured thermoset will not melt when reheated and will remain solid. Technologies are being developed to break down these types of plastics for recycling, or via other biodegradation methods but are not readily accessible. Consequently, cured epoxy resin is not bio-degradable nor recyclable.

When mixed at the stoichiometric ratio, all the reactive groups will be consumed, and the cured resin will form an inert solid.

Consumer vs. Industrial

Resins are formulated with specific characteristics for the intended market of the product. Consumer resins have more aesthetic requirements such as colour, clarity, and ease of use. Development of these formulations may trade off mechanical performance to obtain better colour and clarity that are important for users.

In contrast, industrial resins often have more defined performance specifications such as high strength or stiffness, wear resistance or flame resistance. These formulations could be used as structural adhesives, composite resins or specialty coatings in automotive or aerospace. They are developed to meet performance criteria but may have compromised aesthetics and are less user friendly.

For example, FlowCast is a consumer resin and has been developed for clarity and low viscosity but is not suitable for structural applications. In contrast, GelCoat is a light industrial resin. It has been developed for high performance in composite applications and is a durable protective coating but does not have a simple 2:1 or 1:1 mix ratio.