insulators have no free electrons.How they are getting charged by friction?

I;m rele sorry that noone has answered this question since 5 days but herz the answer.

 

When u apply friction, the heat generated will provide enery to the atoms to excite the electrons to such a level that it will be a free electron without the influence  a  fixed nucleus. Hence they acquire a charge

 

 

yes ….there is a logic....but...I think electric force between nucleus and electron is much stronger due to small distance between them...is heat energy overcome this......