Page 555 - Carrahers_Polymer_Chemistry,_Eighth_Edition

518 Carraher’s Polymer Chemistry

15.15 SUMMARY

1. Most polymers contain materials added to modify some chemical and/or chemical property that
allows them to better fulfill their intended use. These added materials are called additives.

2. Plasticizers allow polymer chains to move past one another allowing wholesale fl exibility.

They can enhance flexibility above and below the glass transition temperature of a polymer.
Plasticization can occur through addition of an external chemical agent or may be incorporated
within the polymer itself.
3. Antioxidants retard oxidative degradation.
4. Heat stabilizers allow some protection to heat-induced decomposition.
5. UV stabilizers act to quench UV radiation. UV radiation is strong enough to break chemical
bonds, and thus cause polymer chains to break either increasing the amount of cross-linking
through subsequent formation of bonds or can result in a decreased chain length. Either of these
result in a decreased overall strength of the polymeric material.
6. Flame retardants impart to the polymers some ability to resist ready combustion. Since fuel,
oxygen, and high temperature are essential for the combustion of polymers, the removal of any
of these prerequisites retards combustion. Flame retardants act through a variety of mecha-
nisms, including char formation, combination with free radical species that promote further
combustion, through release of water, and so on.
7. A variety of inorganic and organic compounds are used to color polymers.
8. The rate of cross-linking of polymers, such as natural rubber, is increased through the use of
accelerators, often misnamed as catalysts.
9. Antistats reduce the electrostatic charge on the surface of polymers.
10. Gas-producing additives are essential for the formation of cellular products such as foam
cushions.
11. Biocides are used to prevent or retard attack on polymers by microorganisms.
12. Lubricants server as processing aids that discourage the sticking of polymers to metal surfaces
during processing.
13. Other important additives are coloring agents, curing agents, antistatic agents, chemical blow-
ing agents, and microorganism inhibitors.
14. Each of these additives performs a critical role in allowing polymers to be processed and uti-
lized giving the variety of useful products we have today.

GLOSSARY

Accelerator: Catalyst for the vulcanization of rubber.
Acicular: Needle shaped.
Antioxidant: Additive that retards polymer degradation by oxidative modes.
Antiplasticization: Hardening and stiffening effect observed when small amounts of a plasti-
cizer are added to a polymer.
Antistat: Additive that reduces static charges on polymers.
Aspect radio: Ratio of length to diameter.
Biocide: Additive that retards attack by microorganisms.

Blocking: Sticking of sheets of film to one another.
Bulk molding compound (BMC): Resin-impregnated bundles of fi bers.
Bound rubber: Rubber adsorbed on carbon black and that is insoluble in benzene.
Carbon black: Finely divided carbon made by the incomplete combustion of hydrocarbons.
Cellular polymers: Foams.
Chemical blowing agent: Volatile liquids and gasses that expand and/or volatilize during pro-
cessing of a material creating pockets leading to lighter weight materials.
Comminuted: Finely divided.

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