Introduction about Polyester Resins & Pultrusion process

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How Polyester Resin System Used In Pultrusion
Process
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• Fibre Reinforced Plastic profiles have a number
  of applications such as industrial flooring,
  platforms, ladders, window frames and many other
  structures. There are multiple steps through
  which fibre reinforcements are blended with a
  resin system to create a composite material known
  as FRP. Pultrusion is one such process which uses
  either Thermoplastic or Thermoset Resin systems.
  Polyester resin for pultrusionis thermoset resin.
  In pultrusion process, continuous fibre materials
  are passed through a bath containing the resin.
  The fibres get impregnated with the resin
  resulting in the addition of a lot of beneficial
  properties.

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What is Polyester Resin?

• Polyester resin user in pultrusion process is
  unsaturated. The standard and economical
  polyester resin used in the composite industry to
  make FRP is orthopthalic polyester resin.
  However, isophthalic polyester resin is being
  widely used for making FRP for marine
  applications due to its high water resistance.
  Polyester resin is a thermoset resin which means
  it can be cured from both liquid and solid state
  under the right conditions.
• Polyester resin is a solution of polyester in a
  monomer. The most common monomer used is Styrene.
  The monomer reduces the viscosity of the
  polyester. For example, 50 Styrene is present in
  polyester resin to reduce its viscosity. The
  monomer such as Styrene also cross links the
  molecular chains of the polyester, thereby
  enabling it to cure from liquid to solid state.
  Polyester resin sets by itself over a period of
  time, hence inhibitors are added to retard the
  setting process. Polyester resin can be provided
  in the basic form or with additions such as
  catalysts or accelerators. Catalyst increases the
  rate of curing of the resin without taking part
  in the chemical reaction. Accelerator also
  increases the rate of curing but is not effective
  in the absence of a catalyst.

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• Low viscosity of the polyester resin enables
  addition of fillers. Many types of fillers can be
  added to the resin to impart superior mechanical,
  physical, chemical and even fire retardant
  properties to the FRP profile manufactured by
  pultrusion. Addition of fillers also make the
  cost of manufacturing the FRP profile more
  economical. Pigments can also be added to the
  polyester resin.
• Polyester resin for pultrusion accounts for the
  largest share in terms of resin used in making
  FRP. This is because polyester has good
  processing properties and gives high yield of FRP
  profiles. Polyester resin is in liquid form when
  not cured which allows easy impregnation of the
  reinforcing fibres during the pultrusion process.
  This is another reason why polyester resin is
  widely used for pultrusion.
• Polyester resin infused FRPs are known for their
  high structural integrity and superior fire
  resistance. This is the reason why such FRPs are
  used in commercial constructions and for making
  appliances.

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Pultrusion Process

• First of all, the fibre reinforcements are
  selected. Fibre reinforcements can be glass
  fibres, metal fibres, carbon fibres, aramid
  fibres and many more. The fibre reinforcements
  are introduced in an automated system which
  passes them through an impregnating trough
  containing the resin system. Apart from
  polyester, many other kinds of resin such as
  vinyl ester resin, methacrylic resin,
  polyurethane resign, etc. can also be used.
  Additives and fillers such as strengthening
  agents, fire retardants, chemical retardants,
  pigments and others can also be added.The fibres
  get saturated with the resin.
• The resin impregnated fibres pass to the mould
  where they are subjected to heat. The resin is
  cured due to heating. The shape and size of the
  mould determines the cross section and other
  features of profile. Temperature at which the
  mould is heated depends upon the properties to be
  imparted to the FRP.
• The profile is pulled out of the mould and cut to
  the required length.

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