“Artificial silk” experiment

It’s be­come fash­ion­able to say that we eat noth­ing but chem­i­cals nowa­days. But we also wear “chem­i­cals”, as it hap­pens! In this in­ter­est­ing ex­per­i­ment you’ll find out how to make ar­ti­fi­cial silk.

Safe­ty pre­cau­tions

Wear pro­tec­tive gloves and glass­es and work in a well-ven­ti­lat­ed room.

Reagents and equip­ment:

• 20 g of cop­per hy­drox­y­car­bon­ate;
• 50 ml of 25% am­mo­ni­um;
• beaker;
• sy­ringe;
• 2M so­lu­tion of sul­fu­ric acid;
• rod;
• cot­ton wool (cel­lu­lose).

Step-by-step in­struc­tions

In the beaker, dis­solve cop­per hy­drox­y­car­bon­ate in am­mo­ni­um. Then pour the mix­ture into an­oth­er beaker, to re­move the re­mains on the undis­solved salt. Place the cot­ton wool in the re­sult­ing bright blue so­lu­tion and ob­serve it dis­solve. Draw the so­lu­tion into the sy­ringe and squeeze the con­tents into the so­lu­tion of sul­fu­ric acid. Blue threads form which turn white over time.

Pro­cess­es de­scrip­tion

When a so­lu­tion of cop­per salts re­acts with am­mo­ni­um, cop­per am­mine forms, which has a very in­ter­est­ing prop­er­ty–it can dis­solve cel­lu­lose, with the for­ma­tion of a com­plex com­pound of cop­per, am­mo­ni­um and cel­lu­lose. If this com­plex is squeezed into a so­lu­tion of sul­fu­ric acid through a sy­ringe or straw, the com­plex breaks down, and vis­cose is formed in thin threads, from which the ar­ti­fi­cial fab­ric cupro or ar­ti­fi­cial silk is made.