On Sep 24, 8:05*pm, Christopher Tidy
wrote:
Ed Huntress wrote:
I wonder what process causes the change in the properties of the plastic.
Anyone know?

They often used excessive amounts of plasticizer back in the '50s and '60s,
to keep the plastic flexible. But the plasticizers were volatile. When they
dried out, the plastic shrunk (you've probably seen this on old plastic
parts of mechanisms) and became weak and brittle.

Do you know the names of any of those plastics and plasticisers? I'd be
interested to know.

Best wishes,

Chris

http://msds.chem.ox.ac.uk/DI/dibutyl_phthalate.html