Local structure mapping of gel-spun ultrahigh-molecular-weight polyethylene fibers

Mathias K Huss-Hansen,Erik G Hedlund,Anton Davydok,Marie Hansteen,Jildert Overdijk,Gert De Cremer,Maarten Roeffaers,Matti Knaapila,Luigi Balzano

doi:10.1016/j.polymer.2021.124420

Abstract

We report on < 2 μm spatial resolution investigations of structural and morphological uniformity of aligned high-performance gel-spun ultrahigh-molecular-weight polyethylene (UHMWPE) fibers (thicknesses ranging from 60 μm to 300 μm) whose processing includes draw and quench. The degree of orientation of PE crystallites were found to increase near the surface of the fiber filaments (skin-core structure) in all samples when considering the P2 orientation parameter calculated from wide-angle X-ray scattering (WAXS). The degree of orientation increases with drawn down ratio (keeping the quench temperature constant) and decreases with increasing quench temperature (keeping the draw down ratio constant). Orientation parameter values calculated from polarized Raman spectroscopy measurements of the symmetric C–C stretching (1130 cm−1) bond of PE showed clear skin-core structure in the samples with the highest overall orientation. We also employ small-angle X-ray scattering computed tomography (SAXS-CT) to show that the morphology (on the length scale of tens of nm) exhibit clear skin-core structure in two of the samples. The thickness of the skin region (~12-17 µm) was estimated from the real-space SAXS morphology and found to be similar in undrawn and drawn filaments.

Highlights

Man-made fibers are found in products ranging from textiles, ther mal insulation, and composite reinforcements to specialized applica tions in high-demand areas, including heavy-lifting, off-shore anchoring, ballistic protection, and bio-medical engineering.Out of the fiber families, fibers made from ultra-high molecular weight polyethylene (UHMWPE) have the highest specific modulus and strength
The filaments are mapped perpendicular to the fiber axis and detailed analysis is performed by looking at the azimuthal profile of the 110 Bragg peak
The Hermans’ orientation parameter represents the degree of crystalline orientation about the filament fiber axis, with values ranging from − 0.5 for complete perpendicular orientation to 1 for complete parallel orientation with a value of zero representing the isotropic case

Summary

Introduction

Man-made fibers are found in products ranging from textiles, ther mal insulation, and composite reinforcements to specialized applica tions in high-demand areas, including heavy-lifting, off-shore anchoring, ballistic protection, and bio-medical engineering.Out of the fiber families, fibers made from ultra-high molecular weight polyethylene (UHMWPE) have the highest specific modulus and strength. The ultra-high strength of UHMWPE fibers was achieved with the invention of the gel-spinning process by Smith and Lemstra in the late 1970s [1,2,3,4]. In this process, UHMWPE (Mw > 1 × 106 g/mol) is dissolved in a solvent, spun and subsequently hot drawn at tem peratures close to the melting point of the pure polymer. In order to achieve the highest mechanical properties, the process of spinning followed by drawing was established to preferen tially orient the UHMWPE molecules along the fiber axis

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