Importance & properties of Polyester Resin

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Principal Types Of Polyester Resins Used In FRP
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• FRP stands for fibreglass reinforced plastic.
  This is a composite material made of polymer
  reinforced with fibres. The fibres combine with a
  resin matrix to form a single unit called FRP.
  Common types of fibres 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.
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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 fibres 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.
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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
  glycol with 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.

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• 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.

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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.

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Advantages of Polyester Resins

• Polyester resins for FRP provides high grade
  binding to the fibres 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.

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