2.3 - Additives & Fillers

How can we enhance polymers properties or reduce their cost?

By adding additives or fillers

What’s the point of using additives & fillers in polymers?

• to enhance properties

• To reduce costs

What are additives & fillers?

Substances added to polymers to enhance their properties or reduce the cost

List different additives/fillers and explain shortly their use

• plasticisers → make the plastic softer, more flexible, easier to process

• Fillers → add bulk (volume), improve mechanical properties, reduce costs)

• solvents → help dissolve/disperse other substances during processing

• Colours → aesthetic or functional colouring

• Antistatic agents → prevent the plastic from having static electricity on its surface

• Flame retardants → reduce flammability, slows down combustion

What do plasticisers do when added to a plastic?

• make the material softer, more flexible, more elastic

• Lower the temperature range of use (at which the material can be processed)

What are the 2 types of plasticisers? What’s the difference between them?

• Internal plasticisers

  • incorporated into the polymer chains (via copolymerisation)

  • Do not diffuse out over time because monomers are chemically bonded to the polymer chain

• external plasticisers

  • Lie between the polymer chains, not chemically bound to them

  • Can diffuse out over time, which can affect long-term performance

How do plasticisers make the material softer, more flexible and elastic?

They increase the distance between the molecular chains, which reduces the intermolecular forces that hold the chains together

What are the reasons to use fillers? (What do they do?)

• improvement of mechanical, electrical & thermal properties

• Cost reduction

• Density adjustment

List a few examples of fillers

• calcium carbonate (chalk = craie)

• Natural fibres

• Glass fibres

• Wood dust (poussière de bois)

• Talc

How are the filler’s fibres oriented?

What does it do?

Random orientation → reinforcement in all directions

What’s the typical length of a filler’s fibre?

~ 0.5mm

What happens to the material as the fibre content of the filler increases?

The material becomes more brittle (less ductile) because fibres restrict the movement of polymer chains (stiffer, less able to deform before breaking)

What’s the usual limit of fibre content?

And for glass fibres?

Up to 60%, 40 to 50% for glass fibres