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