Rayon

File:CelluloseHydroxyls.png

Cellulose, C₆H₇O₂(OH)₃, with the hydroxyl groups underlined

Rayon is any fiber made from dissolved cellulose. The cellulose may be chemically modified to become soluble, or solvents produced which can dissolve cellulose, or combinations thereof. Eventually the dissolved cellulose compound is extruded through a spinneret into an environment which causes the cellulose to solidify. The solidified cellulosic fibers are rayon.

Uses

Primary

• Artificial fiber sourced from wood waste

Natural occurrence

• None

Hazards

• Flammable unless treated specially

Production

The input material is cellulose, an insoluble polymer of glucose. Below it is written C₆H₇O₂(OH)₃ to emphasize the hydroxyl substitutions.

Cuperammonium

Schweizer's reagent can dissolve cellulose directly, which separates it from the remainder of the methods below.

1. Dissolve cellulose in a minimum of Schweizer's reagent
2. Extrude the concentrated solution through a spinneret into 10% sulfuric acid solution, breaking down the solvent into copper sulfate and ammonium hydroxide, and solidifying the cellulose.

   Cu(NH₃)₄(OH)₂(H₂O)₂ + H₂SO₄ → CuSO₄ + 4 NH₄(OH)

3. Distil the ammonia, recycle
4. Recycle copper sulfate

Producing Schweizer's reagent

This chemical tetraaminecopper dihydroxide dihydrate (Cu(NH₃)₄(OH)₂(H₂O)₂) dissolves cellulose in a way that it can be reconstituted by reaction with sulfuric acid, producing water and copper sulfate

from copper sulfate

This is the recycling path, since copper sulfate is the chemical produced when the dissolved cellulose is acidified with sulfuric acid.

• Combine copper sulfate, sodium hydroxide producing copper hydroxide (metathesis)

  CuSO₄(aq) + 2 NaOH(aq) → Cu(OH)₂(s) + NaSO₄(aq)

• Combine copper hydroxide and ammonia, producing the reagent

  Cu(OH)₂ + 4 NH₃ + 2 H₂O → Cu(NH₃)₄(OH)₂(H₂O)₂

from malachite

Malachite has the fortunate composition of copper hydroxide and copper carbonate, which eliminates the need for sodium hydroxide above

• Ammonia and malachite are combined directly, producing the reagent and carbon dioxide

  Cu₂CO₃(OH)₂ + 8 NH₃ + 5 H₂O → 2 Cu(NH₃)₄(OH)₂(H₂O)₂ + CO₂

Cellulose acetate

1. Combine acetic anhydride and cellulose, replacing one two or three of the hydroxide moieties with acetate producing cellulose acetate

   C₆H₇O₂(OH)₃ + (CH₃COO)₂O → C₆H₇O₂[(OH)_x(CH₃COO)_3 -x] (x:0..2)

2. Dissolve the cellulose acetate in a minimum of propanone
3. Extrude the concentrated solution through a spinnerette into warm dry air, allowing the solvent to evaporate (condensed and reused)

Viscose

In this case the cellulose is modified (to sodium cellulose xanthate) but reconstituted completely.

1. React wood pulp with aqueous sodium hydroxide, substituting a sodium for a hydrogen, yielding alkali cellulose

   C₆H₇O₂(OH)₃ + NaOH → C₆H₇O₂(OH)₂ONa + H₂O

2. React the alkali cellulose with carbon disulfide giving sodium cellulose xanthate.

   C₆H₇O₂(OH)₂ONa + CS₂ → C₆H₇O₂(OH)₂CS₂ONa

3. Concentrate ("ripen") the solution allowing its viscosity to get to the "right level"
4. Expose the ripened solution to dilute sulfuric acid, producing rayon or cellophane. The carbon disulfide may be recyclable.

   2 C₆H₇O₂(OH)₂CS₂ONa + H₂SO₄ → C₆H₇O₂(OH)₃ + 2 CS₂ + Na₂SO₄