TABLE OF CONTENTS Crystallinity is a state of molecular structure referring to a long-range periodic geometric pattern of atomic spacings. In semi-crystalline polymers, such as polyethylene (PE), the degree of crystallinity (% crystallinity) influences the degree of stiffness, hardness, and heat resistance.
In semi-crystalline polymers, some of the macromolecules are arranged in crystalline regions, known as crystallites, while the matrix is amorphous. The greater the concentration of these crystallites, i.e., the greater the crystallinity, the more rigid the polymer. Morphology denotes the internal structure of a material (separate polymer phases, crystalline regions, amorphous orientation, and so on). Amorphous is a term generally used to describe polymers totally lacking in long-range spatial order (crystallinity). It is also used to denote non-crystalline regions within partially crystalline polymers.
An understanding of the degree of crystallinity for a polymer is important since crystallinity affects physical properties such as storage modulus, permeability, density, and melting point. While most of these manifestations of crystallinity can be measured, a direct measure of the degree of crystallinity provides a fundamental property from which these other physical properties can be predicted.
Differential scanning calorimetry (DSC) is a technique that measures heat flow into or out of a material as a function of time or temperature. Polymer crystallinity can only be determined by DSC by quantifying the heat associated with the melting (fusion) of the polymer. The heat is reported as % crystallinity by ratioing against the heat of fusion for 100% crystalline samples of...
