A comparison of the crystallization behavior of HDPE on oriented iPP and sPP substrates

The crystallization behavior of high-density polyethylene (HDPE) on highly oriented isotactic or/and syndiotactic polypropylene (iPP or/and sPP) subst rates at various conditions was studied by means of transmission electron m icroscopy and electron diffraction. The results indicate that HDPE crystals always grow epitaxially on the iPP substrates under the conditions perform ed, while on the oriented sPP substrate epitaxially grown HDPE can only be observed when quenching the HDPE-melt directly to room temperature. The rea son for this phenomenon results from the thinner lamellae of sPP compared t o iPP, and consequently smaller critical nucleus size of HDPE is required f or the occurrence of its epitaxial crystallization on the sPP substrate. It is further found that the melt-drawn oriented polymer films are ideal subs trates for conducting comparative studies of polymer hetero and graphoepita xy. By comparing the hetero and graphoepitaxies of HDPE-iPP and HDPE-sPP sy stems, it is concluded that the heteroepitaxial interaction between polymer s is stronger than their graphoepitaxial counterpart. Therefore, heteroepit axy of polymers takes place prior to their graphoepitaxy (C) 1999 Elsevier Science Ltd. All rights reserved.