Synthesis of Rayon - Fibers - Lu Le Laboratory

Rayon is a manufactured regenerated cellulose fiber. Because it is produced from naturally occurring polymers, it is neither a truly synthetic fiber nor a natural fiber; it is a semi-synthetic or artificial fiber. Rayon is known by the names viscose rayon and art silk in the textile industry. It usually has a high luster quality giving it a bright sheen. (Wikipedia)

In the experiment, cellulose in filter is dissolved and, upon acidification, precipitated and regenerated as rayon.

 

Reaction

Copper hydroxide is prepared by reacting copper(II) sulfate with aqueous ammonia:

Cu²⁺_(aq) + 2 OH^- → Cu(OH)_{2 (s)}

                                                                                                                          Blue-Green

    

     The copper hydroxide reacts with additional aqueous ammonia to form tetraammoniecopper(II) hydroxide, Cu(NH₃)₄(OH)₂ . The filter paper(cellulose) dissolves in this complex and is regenerated upon acidification as the polymer rayon. Rayon is insoluble in aqueous solution, so it precipitates when it is squirted in the aqueous acid solution.

Chemical

1.      Aqueous ammonia 28%: 100mL

2.      Copper sulfate

3.      Sulfuric acid

4.      Cellulose

 

Procedure

1.      Prepare this solution of copper(II) hydroxide prior to the demonstration:

a.       Place about 125mL of water in a 500mL beaker.

b.      Add copper sulfate and stir until the solution is saturated.

 

c.       With constant stirring, add concentrated aqueous ammonia drop by drop until a blue-green color appears and a precipitate forms. Do not add too much aqueous ammonia. If the solution becomes dark blue, start again. 

 Do not add too much aqueous ammonia or the solution would turn dark blue

 Copper(II) hydroxide is a cyan precipitate

 

2.      With 11-cm filter paper, filter the solution you have prepared to recover the copper(II) hydroxide. Wash it once and discard the filtrate.

 

3.      Place the filter paper and the filtrate in a second 125mL Erlenmeyer flask with a stopper. Shred two more pieces of filter paper and place these pieces in the flask also.

 

4.      Place the Erlenmeyer flask on a magnetic stirrer and add 100mL of concentrated aqueous ammonia. Continue stirring until the paper is all dissolved and the solution becomes thin enough to pour easily. This should take about 30 minutes. You may need to add a little more aqueous ammonia.

 After 1500rpm stirring, the solution become jelly

5.      Place 200mL of 0.5M sulfuric acid in a 400mL beaker.

 

6.      Carefully fill a dropper or syringe with the dark blue solution.

7.      Place the tip of the dropper beneath the surface of the acid in the beaker. Eject the  dark blue solution from the dropper.

 Rayon forms immediately

8.      Observe the rayon thread for a few minutes. Wash it several times. Dry it in room temperature. 

 The rayon appears blue at the first minutes

It becomes white after several minutes or stirring

After washing several times, it becomes white

It is the final product

 

References

1.      Lee R. Summerlin and James L. Ealy, Jr. (1988) Chemical Demonstrations A Source Book for Teachers Volume 1, Second Edition. Washington, DC: American Chemical Society.

2.      Wikipedia