Page 85 - Carrahers_Polymer_Chemistry,_Eighth_Edition

48 Carraher’s Polymer Chemistry

FIGURE 2.23 Idealized structure illustrating crystalline (ordered) and amorphous (nonordered) regions of
lightly branched polyethylene chains for a prestressed and stressed orientation.

100

Hard
Crystallinity (%) 50

Waxy Soft

Liquid

Molecular weight
FIGURE 2.24 General physical states of materials as a function of crystallinity and molecular weight.

and flexibility. The fi nal properties of a material are then dependent on the molecular structure of

that material.

Through the use of specific treatment(s) the crystalline/amorphous regions can vary from being
largely random to being preferentially oriented in one direction with a greater degree of “crystal-
line-type” structures when unidirectional stress is applied (Figure 2.23). Here the amount of free
space or volume is less with the overall order greater and properties associated with these changes
also changed. The material will be stronger, and have a greater ability to resist attack by acids,
bases, oils, and other external agents, and the diffusion of gases and other agents through it is less.

Polymers can be oriented (such as the pulling of fibers or films) in one or two directions. This pref-

erential orientation results in the fiber or film material with anisotropic properties, with the material

showing greater strength along the axis of pull.

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