MadSci Network: Chemistry
Query:

Re: When rubber and sulfuric acid are mixed...

Date: Thu Apr 12 14:20:23 2001
Posted By: Kip Sturgill, Ph.D., R&D Engineer
Area of science: Chemistry
ID: 986233678.Ch
Message:

Hi Laura,

The weight gain is indeed very interesting and is caused by a process 
known as vulcanization.  Charles Goodyear discovered that adding sulfur 
(in your case sulfuric acid) to rubber made a hard, yet resilient 
material.  As you may recognize from his name, this material eventually 
became tires (hence Goodyear tires, though not started by Charles 
Goodyear).  What is happening when you the mix the sulfuric acid to the 
rubber is that the sulfur is "adding" itself to the rubber.  Rubber is 
made up of lots of polymer chains.  The additon of sulfur ties these 
chains together by the formation of sulfur "bridges."  These sulfur 
bridges provide the additional weight you are measuring. The additon of 
sulfur bridges is a crosslinking technique which can render a material 
chemically resistant and thermally stable.  However, if you had added to 
much sulfuric acid, you would have crosslinked the rubber so much it would 
have became brittle.

For more details on crosslinking (i.e. vulcanization), check out the 
following: http://www.psrc.usm.edu/macrog/xlink.htm

I hope this helps.  Let me know if you need any clarification.

KIP


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