On-Line Optical Monitoring of the Mixing Performance in Co-Rotating Twin-Screw Extruders

Abstract

The use of real-time techniques to evaluate the global mixing performance of co-rotating twin-screw extruders is well consolidated, but much less is reported on the specific contribution of individual screw zones. This work uses on-line flow turbidity and birefringence to ascertain the mixing performance of kneading blocks with different geometries. For this purpose, one of the barrel segments of the extruder was modified in order to incorporate four sampling devices and slit dies containing optical windows were attached to them. The experiments consisted in reaching steady extrusion and then adding a small amount of tracer. Upon opening each sampling device, material was laterally detoured from the local screw channel, and its turbidity and birefringence were measured by the optical detector. Residence time distribution curves (RTD) were obtained at various axial positions along three different kneading blocks and under a range of screw speeds. It is hypothesized that K, a parameter related to the area under each RTD curve, is a good indicator of dispersive mixing, whereas variance can be used to assess distributive mixing. The experimental data confirmed that these mixing indices are sensitive to changes in processing conditions, and that they translate the expected behavior of each kneading block geometry.

Residence Time Distribution in an Asymmetrical Twin-Screw Extruder

“…Hence, residence time distribution (RTD) is a key parameter which characterizes the flow behavior of a fluid in them, their self-cleaning performance, and axial mixing capacity. − Indeed, extensive studies focus on various aspects of RTD, including the characteristics of tracers and the corresponding measurement methods, − theoretical development, − and computational fluid dynamics simulations. − A tracer is a substance of which the flow behavior should be identical or at least similar to that of the fluid of interest, while its concentration is accurately measurable. In practice, the choice of a tracer is mainly based on its detectability by analytical instruments or visual tools, − whereas most of the time its match with the fluid in terms of flow behavior is a secondary issue. Exceptions are macro-tracers for polymers and compatibilizer tracers for polymer blends. − …”

A study of the mechanical performance of nanocomposites of polyethylene containing exfoliated boron nitride nanoplatelets

“…Recently, a lot of attention [16][17][18][19][20][21][22][23][24][25][26][27] has been also paid to the exfoliation and dispersion characteristics of oneand/or two-dimensional materials, formed in polymer melts, through continuous melt-mixing processes, such as via twin-screw extrusion. For example, Cho and Paul [17] prepared polymer organoclay nanocomposites through melt compounding, using a typical co-rotating twin screw extruder.…”

“…This in turn resulted in an enhancement of the physical properties the polymeric materials. Follow-on studies by Villmow et al, [18] Mayoral et al, [20,21,27] and Bernardo et al [22,23] were centered on the influences of processing profiles, such as rotation speed, throughput, and screw configuration and so forth, during the melting processing on the dispersion of multiwall carbon nanotubes (MWCNT) and graphenes in the polymer matrices. They showed that the continuous melt mixing processes through a twin-screw extrusion procedure could improve the exfoliation and dispersion of fillers in the polymer matrix.…”