Fibre Migration — A Vortex Mystery In Our Mill
We had been supplying blended yarns for years. Cotton/polyester, cotton/modal, cotton/viscose — you name it.
But we had never asked the question our Japanese buyer asked one fine morning.
We were discussing the possibility of supplying cotton–viscose blended yarn from our Vortex machine when Takamori suddenly leaned forward and asked: “In a blended yarn, which fibre will dominate the surface — cotton or viscose?”
We froze. Not because the question was difficult. But because we had never thought about it at all.
We always spoke proudly about blend ratios — 50/50, 60/40, 70/30 — as if that alone defined the yarn. But surface dominance? That was a new angle.
Seeing our silence, Takamori‑san assumed we didn’t understand. He stood up, drew a yarn cross‑section on a paper, and repeated the question.
I cleared my throat and said: “Takamori‑san… we understood your question the first time. But we don’t have the answer.” That was the truth.
At that time, our quality in‑charge jumped in. “I have studied somewhere that the viscose fibre, being a long one, would align with the vortex and become a wrapper fibre, and so it will be at the outer surface of the yarn!”
The production in‑charge immediately disagreed. “As the cotton fibres are coarse and are shorter also, they are easily thrown away from the vortex due to centrifugal force, and so cotton will be dominant in the outer surface”
And just like that, the debate exploded. Two confident men. Two opposite theories. Zero evidence.
We needed a conclusion — not a debate. So we decided to produce a 50/50 cotton–viscose yarn on the Vortex machine and send it to a certified lab for fibre‑distribution analysis.
I understood that the lab followed the following procedure for testing the fibres.
- Embedding the yarn
The lab placed a 10–20 mm yarn piece inside a mould and poured epoxy resin over it. After curing for 24 hours, the yarn was trapped inside a solid block — so fibres wouldn’t shift during cutting.
- Microtome slicing
A microtome sliced ultra‑thin sections (5–20 µm) from the block. These slices reveal the yarn’s cross‑section perfectly.
- SEM imaging
The slices were examined under a Scanning Electron Microscope (SEM) at around 1000× magnification. SEM clearly shows fibre boundaries.
- Identifying fibres
Under SEM: Cotton shows convolutions, Viscose appears smooth and cylindrical. This makes fibre mapping easy.
The Result Day
All technical staff gathered in the meeting hall. The VP walked in with the lab report in his hand — like a judge entering a courtroom. He looked at us, cleared his throat, and announced:
“Cotton fibres dominate the yarn surface. Viscose fibres dominate the core.”
The quality in‑charge gasped. “Impossible! I thought cotton would be inside!”
The VP smiled like a professor who had solved a mystery. “I confirmed with the machinery manufacturer also. Cotton will be on the surface.”
I asked him: “Sir, did they explain why?” He nodded and began his lecture.
The VP’s Explanation:
Based on Fibre Length:
Cotton is shorter and stiffer → pushed outward by swirling air → becomes wrapper fibres → stays on the surface.
Viscose is longer, flexible, cohesive → follows the centre airflow → stays in the core.
Based on Fibre Fineness:
Coarser fibres → migrate outward
Finer fibres → follow airflow inward
Cotton fineness: 1.3–1.7 dtex
Viscose fineness: 0.9–1.5 dtex
Unless viscose is extremely coarse (≈2 dtex), viscose stays inside and cotton stays outside.
After the above explanation, the VP looked proud — as if he had just solved Einstein’s unsolved equations. “Is this theory applicable for different blend ratios, sir? For example, cotton/ viscose at 70/30 and 30/70 ratios?” asked the production in-charge.
The VP replied: “Yes. Cotton will still tend to be on the surface — but less dominant as its proportion decreases.”
I also raised my doubt. “Sir, if fibres migrate, will the blend ratio change along the yarn?”
The VP laughed. “Do you think I didn’t ask that? Let me explain with an analogy.”
He continued: “Imagine a bowl with 50 red balls (viscose) and 50 blue balls (cotton). If you shake the bowl, red balls may move to the top and blue balls to the bottom. But the total number of red and blue balls remains the same. Migration changes position, not quantity.”
We all thanked him for the clear and confident explanation.
Later, at the BharatTex exhibition, I discussed the same matter with the machinery manufacturer.
They told me something surprising: “In the latest machine, fibre migration is almost eliminated.”
The reason? The swirl intensity is lower. The outer vortex layer is weaker. Short fibres are less likely to be thrown outward. Wrapper fibres — the main cause of visible migration — drop dramatically. In short, the vortex chamber has been redesigned so that radial separation is minimal.
While returning from the exhibition, a new doubt crept into my mind. “What about ring spinning and OE rotor spinning? Do they also have fibre migration?”
I realised I had opened a bigger topic — one that goes beyond Vortex.
I need to dig deeper, speak to experts, and understand the migration behaviour in ring and OE systems as well.
