Use this demonstration to produce rayon fibres in the classroom using cotton wool or filter paper

In this experiment, students observe as cellulose – in the form of cotton wool or filter paper – is dissolved in a solution containing tetra-amine-copper(II) ions. This produces a viscous blue liquid, which can then be injected into sulfuric acid with a syringe to form rayon fibres.

The demonstration takes up to one and a half hours, much of which is taken up by dissolving the cellulose. The time can be shortened to about 15 minutes if the cellulose solution is prepared beforehand.

Equipment

  • Eye protection (goggles)
  • Beakers, 250 cm3, x2
  • Beaker, 1 dm3
  • Glass stirring rod
  • Plastic syringe, 10 cm3 or 20 cm3, fitted with a hypodermic needle (see note 6 below)
  • Access to a fume cupboard
  • Access to a magnetic stirrer (optional)
  • Cotton wool (about 2 cotton balls), 2 g (see note 7)

Chemicals

  • Basic copper carbonate (HARMFUL), 10 g
  • Concentrated 880 ammonia solution (CORROSIVE, DANGEROUS FOR THE ENVIRONMENT), 100 cm3
  • Sulfuric acid, about 1 M (IRRITANT), 500 cm3

Health, safety and technical notes

  • Read our standard health and safety guidance.
  • Wear eye protection (goggles) throughout and work in a fume cupboard.
  • Basic copper carbonate, CuCO3.Cu(OH)2(s), (HARMFUL) – see CLEAPSS Hazcard HC026.
  • Concentrated 880 ammonia solution, NH3(aq), (CORROSIVE, DANGEROUS FOR THE ENVIRONMENT). Ammonia gas, NH3(g) (TOXIC), will diffuse from the solution. Work in a fume cupboard. See CLEAPSS Hazcards HC006 and HC005.
  • Sulfuric acid, H2SO4(aq), (IRRITANT) – see CLEAPSS Hazcard HC098a and CLEAPSS Recipe Book RB098.
  • If a hypodermic needle is to be used, this must be kept well supervised eg in a locked cupboard, until needed and after use. Alternatively, a hypodermic needle need not be used, however the fibre produced will be less fine.
  • It is important that the cotton wool is pure cotton and does not contain any synthetic fibres. Two grams of filter paper, or even newspaper, can be used as an alternative. However, the best results are obtained with cotton wool.
  • Glassware can be cleaned with dilute ammonia solution.

Procedure

Before the demonstration

Note: you can prepare a solution of cellulose before the demonstration to save time.

  1. Weigh 10 g of basic copper carbonate into one of the 250 cm3 beakers, and, working in a fume cupboard, add 100 cm3 of 880 ammonia solution.
  2. Stir (with a magnetic stirrer, if available) for two minutes, allow to settle and then decant the resulting deep blue solution – which contains tetra-amine-copper(II) ions – into the second 250 cm3 beaker.
  3. Add bits of the finely shredded cotton wool, slowly and with stirring, until the solution has the consistency of shower gel. This uses about 1–1.5 g of the wool.
  4. Stir until there are no lumps, but avoid trapping any air bubbles in the liquid. Complete dissolution may take up to an hour.

The demonstration

  1. Withdraw a few cm3 of this viscous solution – which is called ‘viscose’ – into the plastic syringe, avoiding taking up any remaining lumps.
  2. Fit a hypodermic needle to the syringe and inject a stream of viscose under the surface of about 500 cm3 of the sulfuric acid in the 1 dm3 beaker.
  3. A thin blue rayon fibre will forms. This slowly turns white as the acid neutralises the alkaline tetra-amine-copper(II) solution, and destroys the complex.
  4. After a few minutes, remove the rayon fibre carefully and wash under a stream of tap water and leave to dry on a filter paper. The fibre is likely to be relatively weak.

Teaching notes

You may not only prefer to make the viscose solution beforehand, but also form some rayon fibres using the syringe to have these in reserve in case the demonstration does not go according to plan.

Rayon is a so-called ‘regenerated fibre’ which was once called artificial silk. The polymer contains about 270 glucose units per molecule compared with cotton, which contains between 2,000 and 10,000.

The first step in the demonstration is a reaction of basic copper carbonate with aqueous ammonia to form tetra-amine-copper(II) ions:

CuCO3.Cu(OH)2.H2O(s) + 4NH3(aq) → CuCO3(s) + [Cu(NH3)4]2+(aq) + 2OH–(aq) + H2O(l)

When the insoluble cellulose is added to this solution it is converted to a soluble complex compound. This in turn is converted into insoluble rayon once the pH is reduced to the acidic value found in molar sulfuric acid. Accordingly, rayon precipitates out when extruded into the acid. The blue colour quickly fades away after the copper(II) ions diffuse into the solution.

On an industrial level, the blue solution is passed through spinnerets and regenerated in a hardening bath that neutralises the product and removes the copper and ammonia.

‘Cuprammonium rayon’ is usually made in fine filaments that are used in blouses, lightweight summer dresses and in combination with cotton for textured fabrics.

The ‘cuprammonium process’ duplicated in this activity is one of the earliest methods used for producing rayon, but is less cost-effective now than some other more modern methods.

Rayon is used to manufacture carpets, tyre cords and surgical materials as well as clothing.

Additional information

This is a resource from the Practical Chemistry project, developed by the Nuffield Foundation and the Royal Society of Chemistry.

Practical Chemistry activities accompany Practical Physics and Practical Biology.

© Nuffield Foundation and the Royal Society of Chemistry