The Degree Of Crystallization:Crystal Growth

Crystal growth is achieved by the further addition of folded polymer chain segments and only occurs for temperatures between the melting temperature Tm and the glass transition temperature Tg Higher the temperatures destroy the molecular arrangement and below the glass transition temperature, the movement of molecular chains is frozen.

The growth of the crystalline regions preferably occurs in the direction of the largest temperature gradient" and is suppressed at the top and bottom of the lamellae"by the amorphous folded parts at those surfaces. In case of strong gradient, the growth has a unidirectional, dendritic character. However, if temperature distribution is isotropic and static then lamellac grow radially and form larger quasi-spherical aggregates called spherulites. Spherulites have a size between about I and 100 micrometers, which often include the "maltese cross"pattern and other polarization phenomena caused by molecular alignment within the individual lamellae of a spherulite.