HumanJHawkins

I have a Papermate "Titanium" mechanical pencil. It's about a $4 pencil with a white eraser if that helps guess the chemistry. It is roughly 15-18 years old and has been used in various temperatures and also sat for long periods in a drawer during it's time since purchase. I probably have not used the eraser in maybe 2 years, but I definitely used it, including erasing, 2 years (or so) ago. I went to erase something yesterday and it was kind of sticking to the paper. On looking at it, getting curious, and squeezing it, I found that the eraser had become like a thick bubble gum. It actually has the consistency of a kneaded (charcoal art) eraser, but not the functionality. This is an eraser that worked like a good wooden pencil eraser... Never was too squishy before. Obviously this is a curiosity question... I can drop in a new eraser or just buy a new mechanical pencil. But what about the chemistry of erasers would cause one to work well for 13+/- years, and then turn into a gummy putty over the course of two more?