Comparison of the Structural Evolution of β Polypropylene during the Sequential and Simultaneous Biaxial Stretching Process

• Published in: Chinese journal of polymer science Vol. 39; no. 5; pp. 620 - 631
• Main Authors: Zhang, Dao-Xin, Ding, Lei, Yang, Feng, Lan, Fang, Cao, Ya, Xiang, Ming
• Format: Journal Article
• Language: English
• Published: Beijing Chinese Chemical Society and Institute of Chemistry, CAS 01.05.2021; Springer Nature B.V
• Subjects: Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Deformation; Evolution; Fibers; Industrial Chemistry/Chemical Engineering; Mechanical properties; Polymer Sciences; Polypropylene; Stretching; Simultaneous biaxial stretching; Sequential biaxial stretching; Structure evolution; Polypropylene
• ISSN: 0256-7679; 1439-6203
• DOI: 10.1007/s10118-021-2534-y

In this work, the lamellar structural evolution and microvoids variations of β polypropylene ( β -PP) during the processing of two different stretching methods, sequential biaxial stretching and simultaneous biaxial stretching, were investigated in detail. It was found that different stretching methods led to significantly different lamellae deformation modes, and the microporous membranes obtained from the simultaneous biaxial stretching exhibited better mechanical properties. For the sequential biaxial stretching, abundant coarse fibers originated from the tight accumulation of the lamellae parallel to the longitudinal stretching direction, whereas the lamellae perpendicular to the stretching direction were easily deformed and separated. Those coarse fibers were difficult to be separated to form micropores during the subsequent transverse stretching process, resulting in a poor micropores distribution. However, for the simultaneous biaxial stretching, the β crystal had the same deformation mode, that is, the lamellae distributed in different directions were all destroyed, forming abundant microvoids and little coarse fibers.