Accession Number : AD0810498

Title :   SURFACE MELTING AND CRYSTALLIZATION OF POLYETHYLENE.

Descriptive Note : Technical rept.,

Corporate Author : RENSSELAER POLYTECHNIC INST TROY NY DEPT OF CHEMISTRY

Personal Author(s) : Wunderlich, Bernhard ; Melillo, Louis ; Cormier, C. M. ; Davidson, T. ; Snyder, Gordon

Report Date : 30 DEC 1966

Pagination or Media Count : 43

Abstract : Extended chain polyethylene crystals yield on fracturing a striated surface. By statistical analysis it is shown that the striations are random and no compelling reason for assumption of interior grain boundaries. The rough fracture surface starts melting at 100 C or lower, 40 deg below the equilibrium melting point. The interior is unaffected by this annealing process. Measurements on micron-thin slices of extended chain crystals were carried out and showed less superheating before melting than large crystals and a decreased heat of fusion in the high temperature region. This supports a melting mechanism which calls for melting starting from chain ends or folds. The surface reorganization process is shown to be a two step process, melting followed by recrystallization into folded chain lamellae. The epitaxial lamellae thus grown are analyzed with respect to frequency of occurrence and fold length. From the instability of the rough surface it is concluded that under normal crystallization conditions, extended chain nuclei would be unstable.

Descriptors :   (*POLYETHYLENE PLASTICS, MELTING), (*CRYSTALLIZATION, POLYETHYLENE PLASTICS), CRACKS, SURFACES, HEAT OF FUSION, MICROSTRUCTURE, GRAIN BOUNDARIES, FRACTURE(MECHANICS), NUCLEATION, EPITAXIAL GROWTH, BRITTLENESS, ELECTRON MICROSCOPY.

Subject Categories : Polymer Chemistry
      Crystallography

Distribution Statement : APPROVED FOR PUBLIC RELEASE