Polyester (UPE)

Unsaturated polyester resins are the most commonly used for the composites industry. Polyester resins have a good balance of mechanical, electrical and chemical properties. The polyester resins are mainly used in glass fibre profiles. Typical mechanical properties of the polyester/glassfibre profiles are described in the following table.

  Unit Structure = UCU Structure = U
Typical glass content [%-vol] 55-58 % 58-65 %
Tensile strength [Mpa] 600-900 1000-1200
Tensile modulus [Gpa] 38-42 42-45
Flexural strength [Mpa] 700-1000 1000-1300
Flexural modulus [Gpa] 35-40 40-43
Coefficient of thermal expansion [10-6/K] 9-11 6-8
Density [kg/dm3] 1.9-2.0 1.9-2.0

Structure: U = unidirectional, C = Cross-wound

Polyester resins can be modified so that they are flame-retardant of self-extinguishing.

The polyester resins have good chemical resistance properties. The chemical environment have to be known before a polyester or vinylester resin can be chosen. Polyester resins are good in weak alkalis and excellent in weak acid conditions.

The maximum recommended operation temperature is 80°C for the basic grade polyesters. Modified versions are also available

Vinyl esters (VE)

Vinyl ester resins combine the best features of polyester- and epoxy resins. The strength is good and the resin has a very good chemical resistance in acids and alkalis environments, especially at high temperatures. The glass fibre vinyl ester profile has good electrical and thermal insulation properties.

Epoxy based vinyl ester resins have good chemical resistance at elevated temperatures.

The maximum recommended operating temperature is 90-150°C. Modified versions are also available.

Epoxies (EP)

Epoxy resins have very good properties and are commonly used with high performance reinforcements, e.g. carbon of with glass fibres when the reinforcement content is very high.

Different specific properties can be created by changin hardener systems.

Polyurethanes (PU)

Polyurethane resin can be tailor made for many applications. In the pultrusion the PU can be an excellent alternative to epoxy for mechanical high performance applications like springs, thanks to good physical properties and the possibility to use a high fiber volume content. The high fiber volume content also ensure high stiffness of the material, allowing to use thinner wall sections – thus saving weight.
Especially toughness of the PU composite is superior compared to UPE/VE, and screw retention is outstanding even without the use of crosswise reinforcement.
PU is compatible with both standard glassfiber and high performance carbon fiber grades. 

Other resins

Exel can offer a wide range of other resin system for your applications. For example resin systems for very high temperatures, fire retardent systems or systems for very aggressive environments.

Resin comparison table

  Polyester Vinylester Epoxy Other
Cost 1 2 3 2-4
Strength 2 2 1 2
Chemicals 2 1 1 2
Electrical 2 2 1 1-3

(Legend: 1= superior | 2= excellent | 3 = good)

Exel Oyj, Vantaa head office, Mäkituvantie 5, FI-01510 Vantaa, Finland, Tel +358 20 7541 200, Fax +358 20 7541 201