Plasticizers

In most applications in which plasticizers are incorporated into plastics, their purpose is to convert an otherwise hard and rigid plastic to a flexible or semiflexible tough part. In some instances the same or similar conversions are obtainable by copolymerizing certain flexibility imparting monomers or by blending or grafting elastomers with those rigid plastics. Some of them are specifically made for use as polymeric-type plasticizers (Gaechter and Mueller, 1990)

The low-molecular-weight plastizers show the best plasticizing performance but have the disadvantage of bing more prone to migration when in contact with other plastics and of being some what more volatile. The plasticizing power is proportional to the viscosity of the plasticizer or mixture of plasticizers, with the lowest viscosity resulting in the best flexibility.

Evaporation loss of plasticizers render plastics less flexible in time. The plasticizer vapors may cause windshield fogging in automobiles because they condense on the interior glass surfaces.

The effectiveness of any plasticizer in regard to imparted mechanical properties is very much temperature dependent. That is why most plastics are not compounded with plasticizers. At elevated temperature they would become too soft and at the low temperature range they would be too hard and brittle. The cellulostics and polyvinyl chloride represent notable exceptions.