# Spinline Cooling as a Determinant of Crystalline Structure and Mechanical Properties in Melt-Spun UHMWPE/HDPE Blend Fibers

## TL;DR

This study shows that rapidly cooling fibers during production improves their strength and structure by preserving a flexible state that enhances performance.

## Contribution

The study reveals that rapid quenching preserves a precursor state that enhances stress-induced crystallization and fiber performance.

## Key findings

- Rapid quenching (f5) preserves a low-crystallinity precursor state with enhanced chain mobility.
- Quenched fibers (f5) achieve peak tensile strength (1.33 GPa) and high crystal orientation (fc > 0.95).
- Slow cooling (f1) results in rigid structures with limited performance due to high initial crystallinity.

## Abstract

This study investigates the influence of cooling rates on the structural evolution and mechanical properties of ultra-high-molecular-weight polyethylene/high-density polyethylene fibers by systematically varying cooling media from ambient air (f1) to room-temperature water (f5). A significant structural inversion was observed between the as-spun and drawn fiber stages: while slow cooling (f1) promotes thermodynamic crystallization to form large, stable grains and maximum initial crystallinity (54%), rapid quenching (f5) effectively “freezes” the molecular chains in a low-crystallinity, highly orientable precursor state by suppressing thermal relaxation. During subsequent hot-drawing, the quenched samples (f5) exhibited a superior response to tensile stress, achieving the highest maximum draw ratio due to reduced crystalline obstacles and enhanced chain mobility. This enables efficient stress-induced crystallization, leading to near-perfect crystal orientation (fc > 0.95) and a dense microfibrillar framework. Consequently, the fiber performance trends reversed, with f5 achieving peak tensile strength (1.33 GPa) and modulus, whereas f1 remained limited by its rigid thermal history. These findings highlight that rapid quenching is essential for developing high-performance fibers by preserving a precursor structure that maximizes the potential of stress-induced crystallization.