Why does gum get harder to chew after a while? My Sister asked me this:


  "Why is it that when we chew gum,  it is soft and mushy to begin with , but slowly gets firmer and firmer like after 20 mins of chewing?"


I think  it is because when we initially chew gum it has plenty  of sugar causing rapid salivation and hence mushiness and the rubber polymer is very flexible to begin with and slowly looses its elasticity hence becomes firmer.

Is this the reason?

What is the chemistry involved ?
I would be surprised if there was reticulation of the gum's polymers upon contact with your saliva. According to this manufacturer, plasticizers are used, and the plasticizers appear to be fats. This would mean that, upon chewing, the plasticizers would be removed from the gum, rendering it unpleasantly harder.

Plasticizers are used to render a polymer more pliable, more elastic, than it naturally is. This could get its own question, imo.