Comparison Between Lyocell and Viscose Fibre Manufacturing Processes

Parameter	Lyocell Process	Viscose Process
Dissolution method	Direct dissolution using NMMO	NaOH and CS₂ treatment
Dissolution type	Physical dissolution	Chemical dissolution
Chemical reaction	No chemical reaction	Mercerization and xanthation reactions
Spinning method	Dry-jet wet spinning	Wet spinning
Dope viscosity	Highly viscous spinning solution	Relatively low-viscosity spinning solution
Fiber formation	Extruded through spinneret into an air gap and then into coagulation bath	Extruded directly into an aqueous coagulation bath
Fiber structure	More ordered molecular arrangement with crystallite formation	Relatively amorphous structure
Fiber properties	Generally higher tenacity	Generally lower tenacity
Stretching	Molecular orientation develops during air-gap spinning and drawing	Stretching is performed after regeneration
Solvent recovery	More than 99% NMMO recovery	Approximately 25–30% CS₂ may not be recovered
Environmental impact	More environmentally friendly	Higher environmental load
Water consumption	Solvent recycling requires considerable energy	High water consumption

1. Lyocell Manufacturing Process

1. Cellulose is dissolved directly in NMMO solvent.
2. A highly viscous spinning solution (dope) is formed.
3. The dope is extruded through a spinneret.
4. Filaments pass through an air gap.
5. Filaments enter a coagulation bath, where cellulose regenerates.
6. Fibres are washed, dried and finished.

Important: Lyocell uses physical dissolution without converting cellulose into a chemical derivative.

2. Viscose Manufacturing Process

1. Cellulose is treated with sodium hydroxide (NaOH).
2. Mercerized cellulose is produced.
3. Cellulose reacts with carbon disulfide (CS₂) during xanthation.
4. Cellulose xanthate is dissolved in dilute NaOH to form viscose dope.
5. The dope is extruded through a spinneret into an acidic coagulation bath.
6. Cellulose is regenerated, followed by stretching, washing and finishing.

Important: Viscose involves chemical reactions to convert cellulose into soluble cellulose xanthate before regeneration.

3. Key Difference to Remember for Examination

Lyocell: Physical dissolution → Dry-jet wet spinning → Higher tenacity

NMMO solvent, no cellulose derivatization, high solvent recovery.

Viscose: Chemical conversion → Wet spinning → Relatively lower tenacity

NaOH + CS₂, mercerization and xanthation, higher environmental load.

Exam tip: The most important distinction is that Lyocell dissolves cellulose directly using NMMO, whereas viscose converts cellulose into cellulose xanthate using CS₂ before dissolving and spinning.