viscose fiber manufacturing process

Email address for business inquiries: [email protected] #textilesolutionbyenglablu The manufacturing process of viscose fiber (also known as rayon) involves converting natural cellulose (mainly from wood pulp or cotton linters) into regenerated cellulose fiber through chemical treatment. It is a semi-synthetic fiber widely used in textiles due to its silk-like feel, good drape, and dyeing properties. Here’s a step-by-step outline of the viscose fiber manufacturing process: 1. Preparation of Cellulose Raw material: Wood pulp (from beech, pine, or eucalyptus) or cotton linters. The cellulose content should be around 90–98% pure. Sheets of cellulose pulp are sliced into small pieces for easier chemical penetration. 2. Steeping The cellulose chips are steeped in 18–20% caustic soda (NaOH) solution at about 50 °C for 1–2 hours. This process produces alkali cellulose and removes unwanted impurities such as hemicellulose, wax, and lignin. 3. Pressing The excess NaOH solution is squeezed out using hydraulic presses. Alkali cellulose is left with about 30% NaOH concentration and mercerized cellulose structure. 4. Shredding The pressed alkali cellulose is shredded into fine crumbs/fluffy particles to increase surface area. These crumbs are more reactive for the next process. 5. Aging (Controlled Oxidation) The crumbs are stored in metal containers at 20–30 °C for about 48 hours. During aging, controlled oxidation and depolymerization occur, reducing the cellulose chain length (degree of polymerization) to a spinnable range. 6. Xanthation The aged alkali cellulose is treated with carbon disulfide (CS₂) under controlled conditions. This produces cellulose xanthate, an orange-colored compound. Cell–OH (alkali cellulose) + CS₂ → Cell–O–CSSNa (cellulose xanthate) Cell–OH (alkali cellulose) + CS₂ → Cell–O–CSSNa (cellulose xanthate) 7. Dissolving The cellulose xanthate is dissolved in dilute caustic soda solution (2–5% NaOH). This forms a thick, honey-like viscose solution. The viscose is filtered and deaerated to remove bubbles and undissolved particles. 8. Ripening (Maturation) The viscose solution is stored for several hours to days at controlled temperature. During this stage, the solution attains the right viscosity and spinnability. 9. Spinning (Fiber Formation) The viscose solution is extruded through spinnerets (fine holes) into a coagulation bath containing sulfuric acid (H₂SO₄), sodium sulfate (Na₂SO₄), and zinc sulfate (ZnSO₄). Chemical reactions occur: Cellulose xanthate is decomposed. Regenerated cellulose filaments are formed. Cell–O–CSSNa + H₂SO₄ → Cell–OH (cellulose) + CS₂ + NaHSO₄ Cell–O–CSSNa + H₂SO₄ → Cell–OH (cellulose) + CS₂ + NaHSO₄ 10. Drawing & Stretching The filaments are stretched (2–3 times) to: Orient the cellulose molecules. Increase strength. Improve luster and uniformity. 11. Washing The regenerated viscose filaments are washed thoroughly to remove: Acid Salts Sulfur compounds 12. Finishing Fibers are bleached (to improve whiteness). Lubricants or softeners are added. The fiber is dried and cut into desired staple lengths or wound as filament yarn.