Three-dimensional crystal structure evolution and micropore formation of β-iPP during biaxial stretching. (20th May 2020)

• Record Type: Journal Article
• Authors: Ding, Lei; Zhang, Daoxin; Wu, Tong; Yang, Feng; Lan, Fang; Cao, Ya; Xiang, Ming
• Is Part Of: Polymer. Volume 196(2020)
• Publication Date: 2020-05-20
• Subjects: β-iPP -- Biaxial deformation -- Molecular orientation; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2020.122471
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: In this article, the crystalline and microporous structure evolution of β-iPP during sequential biaxial stretching are analyzed from a three-dimensional view. The calculated orientation and scanning electron microscope images show that the hedrites has intense cavitation during longitudinal stretching, leading to the lower orientation degree along with three-dimensional directions. But abundant coarse fibrils form during longitudinal stretching due to the three-dimensional asymmetric lamellae stack mode of hedrites. Consequently, these coarse fibrils hinder the slip and deflection of lamellae during the following transverse stretching and thus result in the uneven pore size distribution. However, the better compression performance obtains due to the plenty of connections or support structure along the thickness direction. On the other hand, the radial-growth spherulites slip significantly during longitudinal stretching, resulting in a much higher orientation degree along with three-dimensional directions and finer fibrils due to uniform dispersion of lamellae. Therefore, a more uniform pore size distribution with larger pore size can be detected on the surface after biaxial stretching. But the connection along thickness direction is much poor, causing the weak compression property. Therefore, it is critical to control the crystalline structure of β-iPP cast film during the practical processing. Graphical abstract: Image 1 Highlights: Three-dimensional structure evolution of β-iPP during biaxial stretching researched. The uneven dispersion of lamellae was the reason for poor pore size distribution. Compression resistance had negative correlation with the pore size distribution. Adjusting the condensed structure within cast film could balance the two properties.