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CPP: Chemische Physik und Polymerphysik

CPP 12: Crystallization in Polymers

CPP 12.3: Vortrag

Donnerstag, 5. April 2001, 16:25–16:45, 111

Two different mechanisms of recrystallization after melting found in comparative SAXS — •Mahmoud Al-Hussein and Gert Strobl — Fakultät für physik der Albert-Ludwigs-Universität, 79104 Freiburg, Germany

Several semicrystalline polymers show a recrystallization after melting during a heating scan. This results in thicker crystallites which then melt at a higher temperature. The extent of this process depends on the stability of the crystallites formed in the initial crystallization and on the heating rate of the experiment. Generally speaking recrystallization takes place in a partially disentangled melt in contrast with initial crystallization which takes place in an entangled melt or totally amorphous state. This stimulated us to study the mechanisms of such recrystallization process in order to draw some comparison between initial crystallization and recrystallization after melting mechanisms.

In this report we present the results of a SAXS study of the mechanisms of recrystallization after melting for two different polymers, namely syndotactic polypropylene (sPP) and isotactic polystyrene (iPS). The main findings of this study showed that these two polymers show different recrystallization mechanisms. In sPP case the recrystallization process is very much like the initial crystallization mechanism in a way that it follows a two-step route. For iPS, however, it proceeds as a direct growth from the melt without passing through any intermediate phases. This might indicate that the two-step route is the general route for polymers crystallize from an entangled melt or an amorphous state. As a special case, however, when crystallization sets in a partially disentangled melt, as it is the case for recrystallization after melting, the crystallization process proceeds as a direct growth from the melt.