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Effect of Particulate Fillers on Properties

Although thermoset polymers are significant users of particulate fillers, the scientific literature is much scarcer than for other polymer types. This is because they are usually used in combination with glass fibers, which then dominate the properties of the composite. The following concentrates on the effects that are observed in the absence of fibers.

The principal property enhancements of importance that are produced by fillers in thermoset polymers are:

  • • Cost reduction
  • • Exotherm control and reduced cure shrinkage
  • • Increased modulus
  • • Reduced thermal expansion
  • • Enhanced thermal conductivity
  • • Flame retardancy
  • • Aesthetics
  • • Abrasion resistance
  • • Toughness

The main properties which may be negatively affected are:

  • • Rheology of the pre-cure mix
  • • Transparency

Cost Saving

In assessing materials cost savings, one needs to take into account the volume cost of the filler compared with the polymer, not the weight cost. This is because most fillers are significantly denser than polymers and hence proportionally more is needed to fill the same volume. While this consideration weighs heavily on cost saving opportunities in commodity thermoplastics, it is less of an issue for thermosets which are generally more expensive and have a higher specific gravity. Fillers are also easier to incorporate, and all these factors mean that there is a much better case for using them for cost reduction. The most widely used fillers for this are the carbonates, especially calcium carbonates.

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