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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 ?

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  • $\begingroup$ @CHM what are plasticizers used for BTW $\endgroup$ – The-Ever-Kid May 14 '12 at 14:00
  • $\begingroup$ Also something I've noticed is that when I have a pack of gum sitting in my pocket for days at a time it becomes really soft and mushy, almost to the point where you can't chew it, but then after chewing it for a while it seems to stiffen up. I was curious as to if this is due to the moisture, heat, or something different $\endgroup$ – Sean Sep 10 '12 at 6:30
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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.

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