Principal Types Of Polyester Resins Used In FRP 

FRP stands for fiberglass reinforced plastic. This is a composite material made of polymer reinforced with fibers. The fibers combine with a resin matrix to form a single unit called FRP. Common types of fibers used are glass, carbon and aramid. Many types of resin systems used in making FRP include polyester, vinyl, epoxy, phenolic, polyurethane and hybrid.

Polyester resin for FRPs exhibits better load carrying capacity as compared to conventional construction materials such as steel and aluminium. These materials also exhibit high strength to density ratio, high resistance against corrosion and low conductivity to electricity, magnetic fields and heat. FRPs are widely used in constructing walkways, stairways and platforms in industrial settings, underground piping, offshore installations, reinforcements for concrete structures and many more.

Importance of Resin

The matrix of an FRP composite is plastic resin. The plastic resin is a synthetic product which is different chemically from natural resin but exhibits some of the characteristics of natural resin. The type of resin system used in the FRP has a profound effect on its chemical, thermal and electrical properties. The resin matrix also binds the fibers in the structural unit.

Thermoset resins are commonly used in FRPs. These type of resins do not melt or flow after curing. Thermoplastic resins are uses for making FRPs for low temperature applications. There are many types of additives which can be added to the resin matrix to impart extra beneficial properties to the FRP.

Properties of Polyester Resin

Unsaturated polyester resin is a condensation polymer formed by reaction of a diol such as ethylene glycol, propylene glycol or diethylene glycolwith unsaturated or saturated dibasic acid such as maleic acid or fumaric annhydride. The resulting polyester resin for FRP is a very viscous liquid. Thus, polyester resin comesas a combination of polyester in a reactive monomer, usually styrene. The reactive monomer such as styrene lowers the viscosity of the polyester resin.

Polyester resins for FRP cure fast and are resistant to high temperatures and catalysts. They also impart high dimensional stability, high chemical resistance and good mechanical and electrical properties. Glass FRPs make up the largest segment in which unsaturated polyester resins are used.

There are two types of polyester resin used in FRPs: Orthophthalic and Isophthalic resin. Both differ in many aspects which influence the type of FRPs manufactured using these polyester resins.

Orthophthalic vs Isophthalic

Orthophthalic polyester resin is used in making low cost FRPs. This is also known as general purpose polyester. FRPs in which the resin matrix is orthophthalic polyester resin are suitable for applications not requiring high mechanical strength and corrosion resistance. Such FRPs cannot be used in chemical industries because orthophthalic polyester resin has low tolerance against chemicals. However, orthopthalic resin FRPs perform well in water including seawater.

Isophthalic polyester resin imparts higher strength and flexibility to FRPs as compared to orthopthalic polyester resin. Isophthalic polyester resin FRP panel exhibits 20% higher tensile strength and 10% more flexibility as compared to an FRP panel made of orthophthalic polyester resin. High chemical resistance of isophthalic polyester resin makes it suitable for making FRPs for use in underground petroleum tanks and other chemical applications. Isophthalic FRPs are also suitable for marine applications because of high water resistance of isophthalic polyester resin.

Advantages of Polyester Resins

Polyester resins for FRP provides high grade binding to the fibers in FRP unit. The resins can tolerate temperatures up to 80 degrees C. The shrinkage during curing is low at about 4% to 8%. FRPs made of polyester resins provide satisfactory level of resistance to water, chemicals, weathering and general wear and tear. FRPs made of polyester resins are also lower in cost as compared to FRPs using other kinds of resins.