How does the Plasma do that?

The plasma creates reactive molecules, electrons, ions and UV light. These interact in various ways with a surface. Organic contamination, in the form of long chain hydrocarbons, can be broken down by the plasma and removed from the surface, leaving an ultra-clean surface. On polymers, the plasma also breaks surface bonds, and then terminates these bonds with oxygen containing polar molecules, greatly improving the adhesion characteristics of the material by improving its wettability.
The 4 major effects of plasma are;

  1.  Surface cleaning: removal of hydrocarbons which impede adhesion
  2.  Micro-sandblasting: which increases the surface area and therefore wettability
  3. Cross-linking or branching of surface molecules: which impedes the migration of waxy additives from the bulk material to the surface
  4. Modification of surface chemical structure: to increase the surface energy and render a surface wettable and also to impart other specific functionality such as liquid repellency