During the manufacturing process of syringe barrels, oleic acid amide, a slip agent, is integrated within the polypropylene resin and is used to mold the syringe barrel.
This medium is incorporated into the plastic pellets by the resin manufacturer and is necessary to provide a smooth gliding force between the syringe barrel and plunger.
This “slip agent” is present on all surfaces of the syringe barrel and is typically not observable to an unaided eye. At times there may be a sufficient concentration that results in an appearance of flakes or threads that form as the plunger is moved within the syringe barrel. Typically, this particulate only forms behind the sealing surface of the plunger and the barrel, unless the plunger is moved back and forth multiple times, is removed from the barrel and reinserted, or there are excessive pressures or vacuum involved that can “pull” the flakes past the plunger sealing surface.
Although these flakes are benign in nature, visible particulates may raise concern with those unfamiliar with these characteristics of 2 part syringes but this compound is inert and used in medical devices so it is not harmful.