Can traveling to ghana or china make me ineligible to donate plasma?

Yes for 1 year: Traveling to countries where malaria exists will make you ineligible to donate blood products for at least one year. This is true even if you travel to parts of a country which don't have malaria--the rules are designed to keep blood products safe. More importantly you will need to see your local travel doctor (istm.Org) to get proper protection from malaria and other health hazzards.

Red Cross guidelines: Red cross states in regards to international travel, "wait 12 months after travel in an area where malaria is found. Wait 3 years after living in a country or countries where malaria is found. Persons who were born in or who lived in certain countries in western africa, or who have had close contact with persons who were born in or who lived in certain west african countries are not eligible.".