Morphological studies of PE crystallized between iPP and PTFE oriented films

The crystallization behavior of polyethplene (PE) between oriented isotacti c polypropylene (iPP) and poly(tetrafluoroethylene) (PTFE) substrates in sa ndwich triple layered samples at various crystallization conditions was stu died by means of transmission electron microscopy and electron diffraction. It is well known that both iPP and PTFE oriented substrates are active nuc leation agents for PE, but result in different crystallization manners of P E. While the iPP substrate leads to an epitaxial crystallization of PE in a way, with the molecular chain directions of both polymers +/-50 degrees ap art, an oriented overgrowth of PE on the PTFE substrate with parallel chain s of both polymers is identified. By using sandwich samples with the PE in between the two different substrates, i.e. iPP and PTFE, the nucleation eff iciency of both polymers for PE can be compared. The results indicate that at high undercoolings, the iPP and PTFE oriented crystals have about the sa me nucleation ability onto PE, but at lower undercoolings, the PE crystalli zes all on the PTFE side. This indicates unambiguously that the nucleation of PE on the PTFE substrate starts at a higher temperature than that on the iPP oriented substrate. (C) 2000 Elsevier Science Ltd. All rights reserved .