Environmental Engineering Reference
In-Depth Information
Figure 3.7
The change in elastic modulus
E
of a semicrystalline and
amorphous polymers with the temperature.
Extending a plastic material in one direction (anisotropically) results in
forcing the chains into aligning themselves in that direction. As the chains
get closer to each other, further crystallization is encouraged. At very high
extensions,theplasticbecomesahighlycrystalline,anisotropicfibersuchas
those used in textiles.
3.2.4 Chain Branching and Cross-Linking
In conventional organic compounds, any branching is characteristic of the
molecular structure and is reflected in its IUPAC name. For instance, the
alkanemolecule3-ethylhexanehasabranchinthestructure,anethylgroup
onthethirdcarbon. WithapolymersuchasPE,short,medium length,long,
or even complex branches can be present on a small fraction repeat units on
the chain, but still,
all
these molecules are identified as “polyethylene.”
