Subject: Why did my balloon create less static the more I rubbed it on a wool fabric

My 4th grade son is doing a science fair project using a balloon and wool 
fabric to demonstrate how the balloon will pick up negative ions from the wool 
and then picks up positive ions from paper confetti pieces.  The results are 
that the more the balloon is rubbed on the wool the less confetti pieces it 
will pick up.  We used a new balloon each time but the same wool blanket.  Did 
the blanket give up all of it's negative ions eventually or do the atoms get 
so hyper that they neutralize themselves rubbing on the blanket?  We did the 
experiment 2 times, once rubbing the balloon on the wool blanket 10-100 times 
increasing by increments of 10. The second experiment was rubbing the balloon 
on the wool 1-15 times.  The results were the same, the more the blanket was 
rubbed the fewer the confetti it picked up.  Can you help us with a conclusion?

Re: Why did my balloon create less static the more I rubbed it on a wool fabric