|MadSci Network: Chemistry|
Hi Kevin, Before you asked this question, I believed Saran wrap (or Glad wrap, as it's known here in Australia) was made of polyethylene. But after a little research on the Web, I can now tell you that it is a co-polymer. That is, it is made of two different types of plastics mixed together. The names of these plastics are Polyvinylidene Chloride, abbreviated to PVDC (87%), and Polyvinyl Chloride, PVC (13%). PVC is also used a lot for things such as drainage pipes and electrical insulation. Now, the second part of your question - why does it stick to itself? This is caused by electrostatic attraction. Have your ever done a static electricty experiment, such as rubbing a balloon against your hair and causing your hair to be attracted towards the balloon (if not, try it - it's fun!) The same principle applies to Saran wrap. It is electrostatically charged, in other words, parts of it have a positive charge, and other parts have a negative charge. The postively charged bits attract the negatively charged bits, causing it to stick together when it touches itself. Pretty clever, huh! You can check out these references if you want to know a bit more:
http://www.britannica.com (search for 'polymers')
http://inventors.about.com (search for 'saran wrap')
http://www.dow.com/saran I hope this answer has satisfied your curiosity! Jonathan Feldman University of Technology, Sydney firstname.lastname@example.org
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