Static Charge polarity

Q: What materials can build up static charge?

In theory, any materials can build up static charges, as static charges are just a result of re-distribution of electrons. Electrons are present in all objects.

It is only that whether the static charges, once produced, could be maintained long enough because of leakage or some other means.
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Q: What is the Static Charge polarity in Plastic? +ve or -ve
It depends what other materials are used to rub plastic. But plastic is more prone to be negatively charged because of its position in the electrostatic series.
If fur , wool or silk is used to rub plastic, then plastic will become negatively charged.