MadSci Network: Chemistry
Query:

Re: Does a chemical reaction occur when a polymer is physically severed?

Date: Wed May 24 12:12:31 2000
Posted By: Enrico Uva, Secondary School Teacher Chemistry, Physical Science
Area of science: Chemistry
ID: 959132088.Ch
Message:

The answer to your imaginative question is no! Severing a material is a 
physical reaction: only the bonds between the molecules are broken, not 
the ones within the polymeric molecule. Take polyethylene as an example: 
each polymer contains about 10000 -CH2CH2-units. That means that there are 
a total of 2*10000= 20 000 atoms of carbon and 40000 atoms of hydrogen per 
polymeric molecule. Although that's a monstrous molecule with a molar mass 
of 10000* (24 + 4) = 28000g/mole, a single molecule is only a miniscule 
portion of a mole: 1/6.02 X 10^23 and its mass is only that fraction of 
28000 g = 4.65 X 10^-20. So it certainly doesn't run across the length of 
the paper. 

Another thing to keep in mind is that natural materials like starch and 
diamonds are also polymers. Cutting them in no way alters their taste, 
hardness or appearance, again suggesting that no chemical reaction has 
taken place. Also, if cutting plastic produced free radicals since these 
are reactive, it would make the material biodegrade pretty quickly. 
Plastic, however, as you know, is not biodegradable.

Enrico Uva



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