Abstract: The crystallization behavior of isotactic polypropylene （iPP）/multi-walled carbon nanotubes （MWCNTs） composites at different pressurization rates and temperatures was studied by using wide angle X-ray diffractometer （WAXD） and differential scanning calorimetry （DSC）. The results indicated that a lower temperature was advantageous to the formation of α-iPP under the condition of low pressurization rate （1 MPa/s）， but a higher temperature was more conducive to γ-iPP. MWCNTs could induce the crystallization of iPP. The formed γ-iPP has a stable structure and cannot recrystallize during the heating process. Pure γ-iPP could be prepared at a lower pressurization temperature under the condition of a high pressurization rate （200 MPa/s）. However， the presence of MWCNTs resulted in an increase in the viscosity of iPP melt and hindered the movement of its molecular chains， which was disadvantageous to crystal growth. The γ-iPP crystal was formed in a poor structural perfection， and it was unstable and tended to recrystallize during the heating process. Therefore， the metastable mesophase iPP can be prepared at a higher pressurization temperature. The crystalline structure of iPP was determined by the synergistic effect of pressurization rate and melt memory effectiveness. At a low pressurization rate， melt memory effect generated a greater impact on the crystallization structure of the composite， and this effect weakened with an increase in the pressurization rate.

Key words: isotactic polypropylene, multi-walled carbon nanotube, pressurization rate, melt memory effect, crystalline structure