Though 75 percent of the resins consumers use are unsaturated polyester resins (uses for saturated polyester resins are limited to coatings), epoxy resins stand out as superior for reliability and multiple uses. Though both resins do well above and below water, epoxy completely resists moisture where polyester does not. Knowing the properties, advantages and limitations of these two bonding agents can assist you in choosing which fits the project best.
The principal advantage of polyester resin is the mechanical, chemical and electrical stability of its properties. The primary advantage of epoxy resin is its superior mechanical properties in making high-functioning composites of different materials. Epoxy wins over polyester resins in its resistance to acidic liquids and locations. With its better electrical properties, outstanding performance at higher temperatures and ability to bond with multiple types of surfaces, epoxy resin again outdoes polyester.
Fracturing easily and lacking durability, polyester is best suited to building lighter weight objects. In tension and flexibility strength, epoxy resin is the better of the two and is especially useful for high-strength bonding.
Compatible with only fiberglass materials, polyester resins have limited use for laminating, seaming and repairing. Both the epoxy and polyester resins are popular in the marine industry, but epoxy strength and durability make it the first choice. Epoxy resins reinforce such materials as glass, carbon and aerospace materials.
Epoxy resins have an extraordinary ability to bond dissimilar and already cured material. Polyester resins have the poorest adhesion power. Superior epoxy resins have a 2,000 p.s.i. (pounds per square inch) adhesion strength over polyester resin at 100 p.s.i.
The shelf life for polyester is 18 to 24 months and a minimum of two years for epoxy. Epoxy has a longer cure time, with five to seven days, versus six to eight hours for polyester. Epoxy costs more than polyester resin. Polyester allows 20 to 30 minutes working time. Depending on the catalyst used with the epoxy resin, the working time ranges from 30 minutes to 6 hours.