Submitted by Athousandlipsticks t3_10bvhgz in askscience
PD_31 t1_j4d2i98 wrote
Usually polymers go through a glass transition at a certain temperature (called, surprise, surprise, the glass transition temperature). Below that they are hard and rigid (like glass), above that they become rubbery. Smaller molecules, called plasticisers, can be added which will artificially decrease the glass transition temperature (e.g. PVC tubing compared to uPVC used in windows and doors). Since these are small molecules they are more volatile and once gone, the polymer will become glassy (those PVC tubes stiffening with age). So my guess would be that the plasticisers in the bag have evaporated, causing the polymer to transition from rubber to glass despite the increase in temperature.
Athousandlipsticks OP t1_j4d5dtx wrote
Thank you! So if I understand correctly, once it is at this glass state, it can become rubber if heat is continuously applied or is this glass state permanent? Hopefully I’m understanding this process correctly
PD_31 t1_j4dkuc6 wrote
Yes, while it is above the glass transition temperature it will be rubbery and become glassy again when it cools.
Athousandlipsticks OP t1_j4f8mor wrote
Thank you so much :)
[deleted] t1_j4gc2ew wrote
[removed]
Coomb t1_j4hlulq wrote
Standard lightweight plastic grocery bags are generally low density polyethylene, which has a glass transition temperature well below room temperature without plasticizers. What's more likely to be happening is some combination of crystallization and thermal breakdown of the polymer.
Viewing a single comment thread. View all comments