Apparatus for injection of fluid into an extruder is provided, including a static mixer section with a pipe assembly coupled with the static mixer outlet and leading to the extruder barrel； the pipe assembly outlet and barrel injection opening have diameters less than the maximum internal diameter of the static mixer casing. The invention greatly simplifies the fluid injection apparatus used with extruders, while giving more efficient absorption of thermal energy with a minimum of environmental contamination, and the ability to inject multiple streams into the extruder.
