Radial gradients in PET monofilaments: A Raman mapping and SAXS tomography study

E Perret,K Chen,O Braun,R Muff,R Hufenus

doi:10.1016/j.polymer.2021.124422

Abstract

Surface properties of monofilaments can be tailored with radial structural gradients, which is of specific interest for technical textile applications. Radial gradients in fine (≤ 40 μm thick) poly(ethylene terephthalate) monofilaments have been studied with high-resolution Raman mapping and one-dimensional microbeam small-angle x-ray scattering tomography. Filaments have been melt-spun by using online and offline drawing techniques. Radial structural gradients are strongly affected by the drawing method. Raman mapping revealed that offline drawn filaments have a higher crystallinity in the core than in the surface region, whereas the opposite is the case for online drawn filaments. The molecular alignment was the highest in the core for all filaments. Microbeam SAXS tomography revealed that the long-spacing between crystals, in the direction of the fiber axis, increases towards the fiber surface. Fibers that have been drawn to a larger extent, resulting in improved tensile strength, have been found to have a larger long-spacing.

Highlights

Poly(ethylene terephthalate) is the most used polymer for melt-spun fibers in the textile industry due to its excellent physical properties and low price
We have investigated the effect of the drawing method on the radial structural gradient of fine PET filament cross-sections with 2D Raman mapping and 1D small-angle x-ray scattering (SAXS) tomography
The momentum transfers, s12 and s3, are calculated using the following equations, where x12 denotes the horizontal distance of the pixel centers to the direct beam position, x3 denotes the vertical distance of the pixel centers to the direct beam position, λ = 1.1 Å is the wavelength of the x-rays, and F = 2.152 m is the sample to detector distance

Summary

Introduction

Poly(ethylene terephthalate) is the most used polymer for melt-spun fibers in the textile industry due to its excellent physical properties and low price. Other methods to obtain one-dimensional gradients are for example polarized light microscopy [7] and conventional Raman spec troscopy [8]. The disadvantage of the latter techniques is that the signal is averaged over the depth of the measured filament region, resulting in a smeared 1D profile. The confocal 2D Raman mapping has been shown to be an ideal laboratory tool to study the radial structure (crystallinity, molecular alignment) in PET fiber cross-sections [9]. We have investigated the effect of the drawing method on the radial structural gradient of fine PET filament cross-sections with 2D Raman mapping and 1D SAXS tomography. 5.2 mapping analysis of the crystallinity and molecular alignment in fine (≤ 40 μm) PET filament cross-sections is presented. 1D SAXS tomography was used to extract complementary information about e.g. long-spacings between crystals and crystal tilts

Materials

Characterization

Raman mapping

Microbeam SAXS tomography

Perret

Conclusion