Polymer Technology

simple homopolymers, as made pure. Only a few of these are finally sold as “pure” polymers, such as polystyrene drinking cups and polyethylene films. Much more often, polymers are
sold with various additives. That the student may better recognize the polymers,
the most important additives are briefly discussed.
On heating, linear polymers flow and are termed thermoplastics.To prevent
flow, polymers are sometimes cross-linked (•):

THE MACROMOLECULAR HYPOTHESIS

The cross-linking of rubber with sulfur is called vulcanization. Cross-linking
bonds the chains together to form a network. The resulting product is called
a thermoset, because it does not flow on heating.
Plasticizers are small molecules added to soften a polymer by lowering
its glass transition temperature or reducing its crystallinity or melting temperature.
The most widely plasticized polymer is poly(vinyl chloride). The
distinctive odor of new “vinyl” shower curtains is caused by the plasticizer,
for example.
Fillers may be of two types, reinforcing and nonreinforcing. Common reinforcing
fillers are the silicas and carbon blacks.The latter are most widely used
in automotive tires to improve wear characteristics such as abrasion resistance.
Nonreinforcing fillers, such as calcium carbonate, may provide color or opacity
or may merely lower the price of the final product.