  Melt-mixing in twin-screw extruders is a key process in the development of
polymer composites. Quantifying the mixing performance of kneading elements
based on their internal physical processes is a challenging problem. We discuss
melt-mixing by novel kneading elements called "pitched-tip kneading disk
(ptKD)". The disk-stagger angle and tip angle are the main geometric parameters
of the ptKDs. We investigated four typical arrangements of the ptKDs, which are
forward and backward disk-staggers combined with forward and backward tips.
Numerical simulations under a certain feed rate and screw revolution speed were
performed, and the mixing process was investigated using Lagrangian statistics.
It was found that the four types had different mixing characteristics, and
their mixing processes were explained by the coupling effect of drag flow with
the disk staggering and pitched-tip and pressure flows, which are controlled by
operational conditions. The use of a pitched-tip effectively to controls the
balance of the pressurization and mixing ability.
