What Makes a Fibre "Regenerated Cellulosic"

Every regenerated cellulosic fibre begins as cellulose — the same long-chain polymer that gives cotton, flax and wood their strength. Rather than being harvested as a ready-made textile fibre, that cellulose is extracted from plant material, purified, dissolved and then extruded through fine holes to form brand-new filaments. The result sits somewhere between natural and synthetic: the raw chemistry is plant-based, but the manufacturing route is thoroughly industrial. The family includes viscose (still called rayon in some markets), modal, lyocell and, in smaller volumes, cupro.

The feedstock is usually wood pulp from fast-growing species such as eucalyptus, beech, birch or pine. Bamboo and cotton linters also appear on the list, though the finished fibre's behaviour depends far more on how the cellulose is processed than on which plant supplied it.

From Wood Pulp to Dissolving Pulp

Not just any pulp will do. Fibre production needs "dissolving pulp", a highly purified sheet in which cellulose content typically exceeds 90 per cent, with most of the lignin and hemicellulose removed. Wood chips are cooked, washed, bleached without chlorine and dried into thick sheets or rolls. From this point the routes diverge, and each one shapes the character of the fibre that eventually leaves the mill.

The Viscose Route, Step by Step

The classic viscose process is a careful sequence of chemical steps:

• Steeping: pulp sheets are soaked in sodium hydroxide, which opens up the cellulose structure and forms alkali cellulose.
• Pressing and shredding: surplus liquor is squeezed out and the sheets are torn into crumbs.
• Ageing: the crumbs rest so the cellulose chains shorten to a workable length.
• Xanthation: carbon disulphide is introduced, converting the cellulose into cellulose xanthate.
• Dissolving: the xanthate is dissolved in dilute sodium hydroxide to give a honey-coloured, syrupy liquid — the "viscose" that gives the fibre its name.
• Filtering and de-aerating: the solution is cleaned and left to settle so that no bubbles spoil the filament.
• Spinning: the viscose is forced through spinnerets into an acid bath, where the cellulose regenerates into solid filaments.
• After-treatment: the tow is stretched, washed, desulphurised, bleached and dried.

That stretching step is crucial. Drawing the filaments while they are still soft aligns the polymer chains and sets the fibre's strength, lustre and handle.

Modal and Lyocell: Two Different Departures

Modal is essentially a refined viscose, typically made from beech pulp. The spin bath and drawing conditions are adjusted so the fibre develops a higher wet modulus, meaning it holds its shape better when wet. The practical payoff is a fabric that resists stretching, shrinking and creasing through repeated washing, which is why modal is a mainstay of underwear, jersey and bed linen.

Lyocell takes a more radical approach. Instead of reacting the cellulose into a derivative, it dissolves the pulp directly in an amine oxide solvent mixed with water. The solution is spun through an air gap into a dilute solvent bath — a technique known as dry-jet wet spinning. The result is a highly crystalline fibre with excellent dry and wet strength. More than 99 per cent of the solvent is recovered and reused, and the route avoids carbon disulphide altogether.

Lyocell does have a quirk: under abrasion in the wet state, its surface can fibrillate, splitting into tiny hairs. Left uncontrolled, that causes pilling; controlled deliberately or treated with enzymes, it produces the soft peach-skin finish found in premium casualwear.

Where These Fibres Work Hardest

The choice between them usually comes down to cost, handle and performance:

• Viscose offers fluid drape, a silk-like sheen and excellent moisture absorption at a modest price. It appears in linings, dresses, blouses, lightweight jersey, nonwovens and medical dressings. Its weakness is low wet strength, so it needs gentle handling.
• Modal brings similar softness with better dimensional stability, making it ideal for underwear, t-shirts, towels and sheeting that must survive frequent laundering.
• Lyocell delivers strength, a crisp-to-soft handle and good moisture management, so it suits denim, outerwear, activewear and bedding. It blends beautifully with cotton, linen, wool and small amounts of elastane.

Practical Notes for Buyers and Makers

On the factory floor, these fibres are forgiving to dye but demand care in finishing. Viscose loses strength when wet, so tension must be kept low and drying controlled to avoid distortion. Lyocell benefits from controlled fibrillation during wet processing — a deliberate step rather than an accident. Blending with cotton or polyester improves stability and reduces cost, while a few per cent of elastane adds recovery.

For care labels, gentle cycles, low spin speeds and drying flat or on a line usually serve all three fibres well. Tumble drying at high heat is the commonest cause of shrinkage, especially in lyocell. If pressing, use a moderate iron on the reverse while the fabric is slightly damp.

Finally, sourcing matters. Look for pulp certified to recognised forest schemes, and ask suppliers about solvent recovery, chemical recovery rates and energy sources. Regenerated cellulosics are only as sustainable as the mill that makes them — and the questions buyers ask are steadily shaping how those mills operate.