quite large volumes of air are recycled by, you guessed it, recirculation fans, on many RPT type aircraft
Recirculated is different to recycled.
If the cabin was completely sealed, we would not need a pressurisation system
Now as the cabin is not completely sealed, a constant supply of outside fresh air is required to maintain pressurisation.
If you are willing, turn the bleed air valves off and see how long you maintain pressurisation.