Orientation of Poly(ε-caprolactone) in Its Poly(vinyl chloride) Blends Crystallized under Strain: The Role of Strain Rate.

Ruru Wan,Shouke Yan,Xiaoli Sun,Huihui Li,Zhongjie Ren

doi:10.3390/ma13245655

Abstract

The blends of high and low molecular weights poly(ε-caprolactone) (PCL) with poly(vinyl chloride (PVC) were prepared. The samples before and after the crystallization of PCL were uniaxially stretched to different draw ratios. The orientation features of PCL in a stretched crystalline PCL/PVC blend and crystallized from the amorphous PCL/PVC blends under varied strains were studied by wide-angle X-ray diffraction (WAXD). It was found that a uniaxial stretching of crystalline PCL/PVC blend with high molecular weight PCL results in the c-axis orientation along the stretching direction, as is usually done for the PCL bulk sample. For the stretched amorphous PCL/PVC blend samples, the crystallization of high molecular weight PCL in the blends under a draw ratio of λ = 3 with a strain rate of 6 mm/min leads to a ring-fiber orientation. In the samples with draw ratios of λ = 4 and 5, the uniaxial orientation of a-, b-, and c-axes along the strain direction coexist after crystallization of high molecular weight PCL. With a draw ratio of λ = 6, mainly the b-axis orientation of high molecular weight PCL is identified. For the low molecular weight PCL, on the contrary, the ring-fiber and a-axis orientations coexist under a draw ratio of λ = 3. The a-axis orientation decreases with the increase of draw ratio. When the λ reaches 5, only a poorly oriented ring-fiber pattern has been recognized. These results are different from the similar samples stretched at a higher strain rate as reported in the literatures and demonstrate the important role of strain rate on the crystallization behavior of PCL in its blend with PVC under strain.

Highlights

The multiscale structure control of crystalline polymers is of great importance for regulating their macroscale properties and developing high-performance polymeric materials
When stretching the blend films at a strain rate of 20 mm/min immediately after cooling down to room temperature, the ring-fiber orientation is obtained at low draw ratios and/or low poly(vinyl chloride) (PVC) contents, while an a-axis orientation along the stretching direction together with the dominated ring-fiber orientation are observed with the increasing draw ratio and PVC content [51]
We found on the contrary that the ring-fiber and a-axis orientations for the L-PCL/PVC blend coexist only at draw ratios less than λ = 5 and the a-axis orientation decreases with the increasing draw ratio

Summary

Introduction

The multiscale structure control of crystalline polymers is of great importance for regulating their macroscale properties and developing high-performance polymeric materials. Similar results have been obtained through the melt recrystallization of highly oriented iPP fibers by controlled melting status, reflecting the different chain orientation in the melt caused by varied chain relaxation [6,7,8,9,10] This stimulates the extensive studies of crystallization from oriented (amorphous) chains for different polymeric materials, including individual polymers and polymer blends. When stretching the blend films at a strain rate of 20 mm/min immediately after cooling down to room temperature, the ring-fiber orientation is obtained at low draw ratios and/or low PVC contents, while an a-axis orientation along the stretching direction together with the dominated ring-fiber orientation are observed with the increasing draw ratio and PVC content [51] In both cases, the c-axis of PCL crystals is characterized by a perpendicular alignment with respect to the stretching direction.

Materials

Sample

Structure

Crystallization

Discussion

Conclusions