Rayon is made by dissolving plant-derived cellulose in chemicals, then extruding the resulting solution through tiny holes into a bath that re-solidifies it as fine filaments. The raw material is almost always wood pulp, and the dominant manufacturing route, known as the viscose process, uses sodium hydroxide and carbon disulfide to break cellulose down into a syrupy liquid before regenerating it as fiber. The chemistry is over a century old, but the basic sequence of dissolve, extrude, and regenerate still defines how most rayon reaches your closet.
From Trees to Pure Cellulose
All rayon begins with cellulose, the structural polymer that makes plant cell walls rigid. In theory, any cellulose source could work, but the textile industry overwhelmingly relies on wood. Eucalyptus, beech, spruce, and pine are common feedstocks, chosen because they grow relatively fast and yield high-quality pulp. The logs are chipped, then chemically cooked to strip away lignin, hemicellulose, and other non-cellulose components. What comes out of this pulping step is called dissolving-grade pulp, a highly purified form of cellulose that serves as the starting point for both the viscose process and its alternatives.1SpringerLink. Dissolving-grade pulp: a sustainable source for fiber production
Dissolving-grade pulp differs from the kraft pulp used to make cardboard or copy paper. Its cellulose content is much higher, typically above 90%, while kraft pulp retains more hemicellulose and lignin residues. That purity matters because leftover impurities would create weak spots in the finished fiber and gum up the spinning equipment. Once the dissolving pulp arrives at a rayon factory, it usually looks like thick white sheets, similar to heavy blotting paper. Those sheets are the last recognizably “woody” thing you will see in the process.
Steeping in Alkali
The viscose process starts by soaking those cellulose sheets in a concentrated sodium hydroxide solution, commonly called caustic soda. This step is known as steeping or mercerization, and its job is to swell the cellulose chains and make them chemically reactive. The concentration of sodium hydroxide matters: studies have found that a range of roughly 10 to 18 percent by weight is used, with higher concentrations driving a more complete transformation of the cellulose crystal structure from its native form into a more reactive arrangement.2Cellulose. Influence of pulp characteristics on the properties of alkali cellulose
After steeping for a controlled period, the swollen cellulose is pressed to squeeze out excess liquid, then shredded into fluffy white crumbs. At this stage the material is called alkali cellulose. It is left to age in air for a day or so, during which oxygen slowly trims the long cellulose chains to a shorter, more manageable length. That aging step is crucial for controlling the viscosity of the solution that comes next. If the chains are too long, the liquid will be too thick to push through a spinneret; too short, and the resulting fiber will be weak.
Xanthation and Dissolving
The aged alkali cellulose crumbs are tumbled in a rotating drum with carbon disulfide, a volatile and toxic liquid. Carbon disulfide reacts with the cellulose to form cellulose xanthate, a bright orange compound that, unlike raw cellulose, will dissolve in dilute sodium hydroxide. The crumbs turn from white to a deep pumpkin color as the reaction proceeds over a couple of hours.
Once xanthation is complete, the orange crumbs are dissolved in a dilute caustic soda solution to produce a thick, honey-like liquid called viscose. The name “viscose” comes from its sticky, viscous consistency. This solution is filtered to remove any undissolved specks and any air bubbles, then left to ripen for additional hours. During ripening, the xanthate groups slowly break down, which fine-tunes the solution’s behavior when it hits the spinning bath. Getting the ripening time right is one of the trickiest parts of the process: too little and the fiber structure will be uneven, too much and the cellulose starts to precipitate out of solution prematurely.
Spinning and Regeneration
The viscose solution is forced under pressure through a device called a spinneret, a metal plate drilled with thousands of tiny holes, each about the diameter of a human hair. The jets of viscose emerge directly into an acidified salt bath containing sulfuric acid, sodium sulfate, and often zinc sulfate. The acid neutralizes the sodium hydroxide and strips away the xanthate groups, which regenerates the cellulose in solid form. Simultaneously, the salt pulls water out of the emerging filaments, helping them coagulate into sturdy strands.
Zinc ions play a particular role here. Research on industrial yarn production has shown that as zinc diffuses into the coagulating gel, it slows the regeneration of the outer layer of each filament, giving the interior time to solidify more evenly. Without zinc, the skin of the filament hardens too fast while the core is still liquid, producing a weaker, less uniform fiber.3Journal of Applied Polymer Science. Studies on the mechanism of fine‐structure development during industrial cellulose yarn production
The freshly spun filaments are stretched as they travel through the bath and over a series of rollers. This stretching aligns the cellulose chains along the fiber’s length, increasing its tensile strength. After spinning, the filaments are washed to remove residual acid and salts, sometimes bleached, and then dried. The result is rayon fiber, ready to be cut into staple lengths and spun into yarn or left as continuous filament for different textile applications.
Beyond Viscose: The Lyocell Process
The viscose route dominates global rayon production, but it is not the only way to dissolve cellulose and spin it into fiber. The most commercially significant alternative is the lyocell process, marketed most famously under the brand name Tencel. Instead of the multistep chemical derivatization that viscose requires, lyocell dissolves cellulose directly in a solvent called N-methylmorpholine N-oxide, usually abbreviated NMMO.4Progress in Polymer Science. The chemistry of side reactions and byproduct formation in the system NMMO/cellulose (Lyocell process)
NMMO is a powerful organic solvent that can break apart the hydrogen bonds holding cellulose chains together, producing a spinnable solution without forming any intermediate chemical derivative. The dissolved cellulose is extruded through a spinneret into a water or water-alcohol bath, where the NMMO is washed away and the cellulose solidifies. Because no carbon disulfide is involved and upwards of 99 percent of the NMMO can be recovered and recycled, the lyocell process is widely regarded as the most environmentally friendly commercial route to man-made cellulosic fiber.5Cellulose. The chemistry of the lyocell process: a critical review of recent developments
Lyocell fibers also differ structurally from standard viscose rayon. They tend to have longer cellulose chains, higher crystallinity, and fibrils that are more tightly aligned along the fiber axis. This gives lyocell noticeably better wet strength and a slightly different drape and hand feel compared to viscose.6Journal of Bioresources and Bioproducts. A review on raw materials, commercial production and properties of lyocell fiber On the downside, lyocell fibers are prone to fibrillation, meaning tiny surface fibrils can peel away during washing and give the fabric a fuzzy or frosted appearance. Manufacturers deal with this through enzyme treatments or chemical crosslinking during finishing.
The economics of lyocell plants also look different from viscose. The solvent recovery system is the single largest cost driver, and its efficiency depends heavily on how the plant handles evaporation and recycling of the NMMO-water mixture.7BioResources. Lyocell fibre production using NMMO – A simulation-based techno-economic analysis Capital costs are higher than for a viscose plant of equivalent capacity, which is one reason viscose still accounts for the majority of regenerated cellulose fiber worldwide despite its environmental drawbacks.
Cuprammonium Rayon
A third and much older route is the cuprammonium process. Here, cellulose is dissolved in a solution of copper salts and ammonia, then extruded into an acid bath that strips away the copper and regenerates the cellulose. The resulting fiber, sometimes called cupro, is extremely fine and silky, which made it popular for linings and lightweight fabrics. Production volumes have shrunk dramatically because the process generates copper-laden wastewater that is expensive to treat. Recent research has explored whether wastepaper could serve as a cellulose feedstock for cuprammonium rayon, which would at least address the raw-material side of the sustainability equation.8PubMed Central. Wastepaper-Based Cuprammonium Rayon Regenerated Using Novel Gaseous-Ammoniation Injection Process
The Carbon Disulfide Problem
The viscose process has a well-known Achilles heel: carbon disulfide. This chemical is essential to the xanthation step but is volatile, flammable, and toxic. During production, a significant fraction of the carbon disulfide escapes into the air along with hydrogen sulfide, a foul-smelling byproduct of the regeneration step. Measurements at an Indian viscose plant estimated that producing one metric ton of viscose staple fiber released roughly 100 kilograms of carbon disulfide and 33 kilograms of hydrogen sulfide into the atmosphere. For filament yarn production, the carbon disulfide emissions were even higher, around 284 kilograms per metric ton.9Atmospheric Environment: X. Carbon disulphide and hydrogen sulphide emissions from viscose fibre manufacturing industry: A case study in India
Scaled to the global level, the numbers are striking. The same study estimated that worldwide viscose production in 2017 released roughly 578,000 metric tons of carbon disulfide and 192,000 metric tons of hydrogen sulfide, with China and India accounting for the largest shares. These gases contribute to air quality problems near factories and can travel considerable distances downwind.
For workers inside the plants, carbon disulfide exposure is more than an air-quality issue. It is a recognized occupational hazard linked to damage of both the central and peripheral nervous systems.10PubMed. Carbon disulfide exposure assessment in a Chinese viscose filament plant A clinical study of workers with long-term exposure to carbon disulfide in a viscose factory found that roughly half showed neurological abnormalities, and brain imaging revealed cerebral atrophy in a substantial number. The researchers concluded that even relatively moderate long-term exposure, punctuated by occasional high peaks, carried a real risk of developing neurotoxic disease.11PubMed. Carbon disulfide exposure and neurotoxic sequelae among viscose rayon workers
Modern viscose plants in Europe and North America use enclosed systems, carbon disulfide recovery units, and improved ventilation to reduce both emissions and worker exposure. Standards have tightened considerably since the mid-twentieth century, when exposure levels in some factories were many times what would now be permitted. Still, much of the world’s viscose production takes place in countries where enforcement varies, which is why sustainability certifications like those from the Changing Markets Foundation and Canopy have become important market signals for brands that want to source cleaner viscose.
Rayon’s Biodegradability Edge
Once rayon leaves the factory and eventually reaches a landfill or the ocean, its story diverges sharply from that of synthetic fibers. Because rayon is regenerated cellulose, microorganisms recognize it as food and break it down. Controlled biodegradation experiments have shown that cotton and rayon microfibers degrade readily in natural aquatic environments, while polyester microfibers persist for extremely long periods.12PubMed. Microfibers generated from the laundering of cotton, rayon and polyester based fabrics and their aquatic biodegradation Marine biodegradation studies confirm the same pattern: viscose rayon degrades quickly in seawater, whereas polyester, nylon, and polypropylene show virtually no breakdown.13Water, Air, & Soil Pollution. Marine Biodegradation Behavior of Wool and Other Textile Fibers
This biodegradability has caught the attention of industries beyond fashion. Researchers have tested rayon fiber ropes as replacements for synthetic ropes used at sea, where lost or discarded gear is a major source of marine plastic pollution. In biotic conditions, rayon yarns lost about 90 percent of their strength in just two weeks, and small rayon ropes degraded substantially within six months. Under sterile, abiotic conditions, the same ropes remained relatively stable, confirming that living organisms are doing the work.14PubMed. Rayon fibre rope: A biodegradable alternative for marine use? Rope construction also mattered: tighter braids slowed microbial access to the fiber core, suggesting that engineers could tune durability for specific applications while still offering an end-of-life advantage over nylon or polypropylene lines.
Biodegradability does not make rayon environmentally harmless, of course. The production-phase emissions described earlier are a separate problem that biodegradability at end of life cannot offset. But when the conversation turns specifically to microfiber pollution, the fact that rayon breaks down instead of accumulating is a genuine advantage.
Why Rayon Gets Weak When Wet
If you have ever pulled a rayon garment from the washing machine and felt how limp and fragile it became, you have encountered one of the fiber’s most distinctive quirks. Rayon loses a significant fraction of its tensile strength when wet, typically around 30 to 50 percent depending on the type. The reason traces back to the fiber’s internal structure. Compared to cotton, whose cellulose chains have had millions of years of evolutionary optimization to hold together in water, rayon’s regenerated cellulose has a more amorphous, less tightly packed arrangement. Water molecules easily penetrate the disordered regions between crystallites, swelling the fiber and disrupting the weak hydrogen bonds that give it shape and strength.
This is why care labels on rayon garments often recommend gentle washing or dry cleaning. Aggressive agitation while the fiber is swollen and weak encourages permanent distortion, shrinkage, and pilling. Some rayon fabrics are treated with chemical crosslinkers that create covalent bridges between cellulose chains, mimicking what happens in wrinkle-resistant cotton treatments. These finishes improve wet strength and dimensional stability, but they can also make the fabric feel stiffer and may reduce its ability to absorb dye evenly.15Journal of the Society of Dyers and Colourists. Self–smoothing Cellulosic Fabrics
Lyocell handles moisture somewhat better than standard viscose. Its higher crystallinity and better-aligned fibrils mean that water penetrates less deeply, so it retains more of its dry strength when laundered. Modal, another variant of regenerated cellulose made with a modified viscose process, falls somewhere in between. If wet strength is a priority and you prefer a cellulose-based fiber, lyocell is usually the better pick.
Emerging Research on Stronger Rayon
The century-old viscose process works, but its environmental baggage and the inherent weakness of standard rayon have pushed researchers to look for cleaner chemistries and better-performing fibers. One recent line of work combines dry-jet wet spinning with a deep eutectic solvent system based on zinc chloride, formic acid, and water. Rather than dissolving cellulose through the xanthate detour, this system dissolves it directly and then uses a combination of gravity-assisted stretching, calcium-ion crosslinking, and an ethanol-water coagulation bath to lock cellulose chains into highly aligned, crystalline filaments. The resulting fibers have shown crystallinity above 60 percent and orientation factors above 0.8, numbers that translate to mechanical properties far superior to conventional viscose.16PubMed. Super-Robust Cellulose Rayon Filaments Engineered via Molecular Orientation-Cross-linking Assembly
These experimental fibers are still a long way from factory floors, but they illustrate a broader trend. The field is moving toward direct dissolution solvents that avoid carbon disulfide altogether, combined with more sophisticated spinning techniques that give engineers finer control over the fiber’s internal architecture. If the economics can be made to work at scale, the next generation of rayon could be both greener to produce and tougher to wear than anything available today.
Ionic liquids are another active area. These are room-temperature molten salts that dissolve cellulose efficiently and can, in principle, be recycled like NMMO in the lyocell process. The catch is cost: most ionic liquids are expensive to synthesize, and some have toxicity or stability problems of their own. Deep eutectic solvents, which are cheaper and easier to prepare, are increasingly seen as a more practical middle ground between traditional viscose chemistry and the still-maturing ionic-liquid approach.
How Different Rayon Types Compare in Practice
Walk into a fabric store and you will see rayon sold under several names. Regular viscose rayon is the most common, offering a soft drape and good dye uptake at a low price. It wrinkles easily, weakens when wet, and can shrink unpredictably if not pre-treated. Modal is a higher-wet-modulus variant made from beech wood pulp using a modified viscose process; it holds its shape better through repeated washing and feels silkier against the skin, which is why it shows up so often in underwear and bed sheets. Lyocell is the premium option: strong wet and dry, smooth surface, a slight cool-to-the-touch feel, and the cleanest production footprint of the three. Cuprammonium rayon, where you can still find it, is prized for its extreme fineness and luster but is rarely offered outside specialty applications.
All four are classified as regenerated cellulose fibers, and all share the basic property of biodegrading in natural environments. They differ mainly in wet strength, luster, tendency to fibrillate, and the environmental cost of their manufacture. When brands market a garment as “eco-friendly rayon,” what they almost always mean is lyocell produced in a closed-loop solvent system. Standard viscose labeled “sustainable” usually refers to sourcing the wood from certified forests, not to eliminating the carbon disulfide from the chemical process itself. Reading past the marketing language and checking which specific fiber type a garment is made from tells you a lot more about both performance and environmental impact than any eco-label on its own.