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Composite Resin Basics - Polyester and Vinyl Ester

Polyester and Vinyl Ester Resin - The Foundation of FRP Composites

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Blue Barrels
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Thermoset polyester resin and thermoset vinyl ester resin are the two major “work horses” of the composites industry. They are low-cost, easy to work with, and are commonly used in FRP composites. These versatile resins are commonly used in a wide variety of composite applications, including:
  • Marine and boat building
  • Industrial tanks and pipes
  • Marble counter tops
  • Bath tubs, showers, and spas
  • Building panels and construction
  • Surfboards and recreational sporting goods

Polyester and vinyl ester resins are unique, and can be chemically tailored to be flexible or rigid. The resins can be reinforced, pigmented, and filled. When working with these composite resins, manufacturers can cure them at ambient temperature, or in a oven up to 400 degrees F.

When working with polyester and vinyl ester resins, nothing beats experience. However, understanding the basic building blocks of these composite resins is equally important.

Chemical Background of Polyester and Vinyl Ester Resin

The chemical foundation of polyester and vinyl ester polymer resins is derived from petroleum. Polyesters are composed of three types of compounds:

  • Dicarboxylic Acids
  • Glycols
  • Monomers/Diluents

Vinyl ester polymers are comprised primarily of:

  • Diepoxides
  • Monocarboxylic Acid
  • Monomers/Diluents

Polyester resin is made under high heat, the dicarboxylic acids and the glycols react and form a polymer chain. When an acid and a glycol react together, and ester is formed. This is known as an esterification reaction. The acids and glycols are heated together for long periods of time (14-24 hours) and at temperatures up to 430 degrees F.

Vinyl esters are formed by a reaction between diepoxides and unsaturated monocarboxylic acids. The process of creating vinyl ester polymers takes less time (8-14 hours) and at lower temperature up to 240 degrees F.

Both vinyl esters and polyesters in their raw form are solid chunks. To turn the polymer into a liquid form, usable by manufactures, a monomer is added. The most common monomer used is styrene.

Once in the liquid polymer resin state, all that is required is a peroxide initiator (catalyst), to create a chemical reaction which cross-link the polymer molecules. The polyester or vinyl resin will become rock solid, and permanently stay that way, even when heated to high heats.

Polyester and vinyl ester resin, when reinforced with a structural fiber such as fiberglass, a strong composite material is formed. This combination helps create long-lasting products used in our everyday life.

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