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Additives

Additives

  • The foreign substances added to polymers intentionally enhances or modify their properties and are called additives.
  • Thus addition of additives to polymer enhances its mechanical, optical, electrical and acoustic properties.
  • The additives include fillers, stabilizers, plasticizers, colorants and flame retardants.

Fillers

  • Among the naturally occurring fillers are cellulosics (such as α-cellulose,starch, wood flour) and proteinaceous fillers (such as soyabean residues).
  • The fillers are divided into two categories, those that reinforce the polymer and enhances its mechanical performance and those that are used to take up space and thus reduce the amount of actual resin to produce a part - is reffered as extenders.
  • The third less common category of filled polymers is that in which filler is dispersed in the polymer to increase its electrical conductivity.
  • The polymer which contain filler that reinforce its mechanical performance is often called composites.
  • The composites are further divided into two categories namely; composite with high performance reinforcement and composite with low performance reinforcement.
  • In high performance composites the reinforcement are placed in a polymer in such a way that optical mechanical performance is achieved such as unidirectional glass fibres in epoxy resins.
  • In high performance composite the polymer contains 50-80% reinforcements by volume.
  • The filler used to reinforce a polymer is glass fibre.
  • Wood fibre which is used as an extender is also used to increase the mechanical performance of a polymer.
  • The bonding between the polymer matrix and reinforcement is increase by coupling agents such as silanes and titrates.
  • The extenders are often in particulate form.
  • The filler in particulate form are clay and fibre.
  • It is important to note that polymer with extenders are less tough than unfilled resins.

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