|The image to the right illustrates a melting CD, which is made of the polymer polycarbonate (movie). Notice that, although the polymer is melting, it does not sustain a flame and burn even while heating with a propane torch.|
Other polymers such as polyaramids do not melt in addition to not burning. These polymers are excellent for materials that require high heat and flame resistance such as protective clothing for firefighters.
What makes these polymers different?
|Melting Point:||Some polymers have a high degree of crystallinity and have relatively high melting temperatures, Tm. In addition, strong intermolecular bonds can further increase the Tm. Polyaramids (aromatic amides) have reasonably high melting points making them ideal for heat resistant materials. But melting point is not the only criteria.|
|Decomposition Temperature:||Polymers do not vaporize (become a gas) after melting, they break down or depolymerize into smaller molecules (fragments) at high enough temperatures. Polymers that have strong intramolecular bonds will tend to withstand high temperatures before decomposing. If the material does not depolymerize or decompose into smaller gaseous fragments, it will not readily burn even if it melts. The polymers that are heat and flame resistant will have relatively high decomposition temperatures as well as high melting points.|
|Chemical Composition:||Other polymers are inherently resistant to burn since they contain elements like chlorine as in PVC. These polymers release chemicals that interfere with the free radical mechanism. Combine high melting point, high degredation temperatures, and appropriate chemical composition and you have polymers that do not burn.|