(i) F*illers*

Fillers are used for a wide variety of reasons. They can extend resin, increase stiffness and strength, improve impact performance, and shorten cycle times. They prevent hang-up in dies and neutralize the products of degradation. Fillers can also be used to add color, opacity, and conductivity to a compound. Unique property combinations can be achieved through the use of fillers.

Traditionally, a filler was a low-cost material of relatively large particle size that lowered a formulation’s cost simply because it was less expensive than the other ingredients in the formulation but nowadays it’s a true performance additive. Advances in compounding technology allow the use of much finer fillers that could not be used in the past. Today’s filler products are tailored for specific applications and designed to deliver value in new and interesting ways.

(ii) Plasticizers

A plasticizer is a material, generally gaseous or liquid, which is compatible with the polymer and can be absorbed into its interstices - the space around the polymer chains. Effectively, a solvent is a plasticizer, but generally with low permanence, i.e., a solvent is generally volatile and evaporates from the polymer fairly rapidly.  A plasticizer, therefore, may be considered as a solvent with low volatility.

Plasticizers, due to their compatibility with the polymer, are able to permeate into the free volume around the polymer chains. This interaction results in a few things.  First, it reduces the effects of secondary bonding forces which tend to keep the polymer “stuck” together. Secondly, it increases intermolecular distance which results in some swelling and increased free volume. Finally, as a result of the increased free volume and decreased secondary bonding forces, the plasticizer acts as a lubricant which enhances chain mobility - the polymer molecules are more easily able to move and slip past each other in response to an applied load.