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Polymeric materials offer an intrinsic advantage for
property enhancement by incorporation of fillers and
reinforcements at nano, micro and macro scales.
Apart from imparting the desired mechanical, thermal,
electrical and magnetic properties, there is a direct
impact on cost and performance. Increasing the filler
concentration especially in polypropylene increases
both stiffness and impact strength, a highly desired
Talc is a well-known mineral filler and is frequently
used for compounding. The primary reasons for using
talc include improvements in mechanical properties in
addition to heat-deflection temperature (HDT),
rigidity, creep resistance and miscellaneous benefits in
processing such as lower shrinkage.
The co-rotating twin-screw extruder was born as a ‘twin-screw kneader’ (ZSK). Among the
three kneading machines, the dispersive kneader (also referred to as Banbury Mixers, Farrel
Continuous mixers), the co-kneader and the twin-screw kneader, it was the twin-screw
kneader that had extrusion ability enabling the formation of pellets directly from the mixing
equipment. Therefore, it qualified to be called an extruder rather than being a mere kneader.
However, the primary function of the co-rotating twin-screw extruder is that of a mixing
vessel - a vessel that can continuously process viscous materials along with other
ingredients so that all materials can fuse together into a homogenous mass. A chemical
reaction or volatile extraction can be handled in addition to tasks such as dispersion of
pigments or distribution of fiber or the kneading of fillers. The kind of work that can be
carried out inside the Extruder Process Zone (EPZ) of the co-rotating twin-screw extruder
involves application of forces that cause shearing or smearing, elongation, bending, torsion
and compression – a cocktail of forces generally referred to as kneading (or dispersion) in
the industry.
If the EPZ of the co-rotating twin-screw extruder is set-up to deliver the right kind and
amount of work, (as a result of the application of the right forces) it is possible to prepare
materials with unique properties. During the past 50 years, substantial progress was made
in the field with the time required for mixing being reduced by half its original value every ten
years. However, the inability to control shear peaks and narrow the residence time
distribution resulted in the stagnation of the field over the last several years. As a result of a
better visualization of the movement inside the extruder, it is now possible to understand the
physical nature of the system even better. This has helped create game-changing
technological progress in the EPZ of the co-rotating twin-screw extruder.
Breaking barriers during melt compounding
co-rotating twin-screw extrusion
Compounding in an extruder with fine talc has been a
difficult task due to the tendency of the powder
material to get fluidized. This calls for special
geometry screw elements to efficiently convey at
high speeds followed by the ability to mix and knead
in a very short time.
In other words, can the extruder be transformed into
a mixing vessel with the compounder having
supreme ability to control the work carried out and
the time spent? This paper provides details of the
screw geometry and characteristics of such a high
performance extruder that not only enhances end
product quality and performance but also has
considerable impact on energy efficiency – meeting
the expectation of such a “game-changing
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