can't explain an observation with material properties

samedi 30 août 2014

I beg forgiveness if this should be in chemistry; to me it seems more of a physics problem.

This summer I had two Polyethylene terephthalate (PETE) spice bottles deform due to the sun shining on the clear plastic tub, Polypropylene(PP) in which they were stored.

The first time the big tub was on a picnic table in the desert and it was about 105F and in direct sun.

The second was inside my camper but with the sun shining through a window onto the clear plastic tub.

OK, that should be expected during the summer on a California desert. I unintentionally made a solar oven.

What is not understandable is that these two bottles were not alone and had PP bottles next to them in the same environment but they did not deform.

I looked up the heat-deflection for both and found: PP 100C, PETE 115C



Why would the plastic with the lower heat-deflection point not deform?



One difference it that the PETE bottles are clear and the PP are milky.

These are the McKormick spice bottles.



Happy Trails





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