In-Line Rheo-Optical Investigation of the Dispersion of Organoclay in a Polymer Matrix during Twin-Screw Compounding

Abstract

The dispersion mechanisms in a clay-based polymer nanocomposite (CPNC) during twin-screw extrusion are studied by in-situ rheo-optical techniques, which relate the CPNC morphology with its viscosity. This methodology avoids the problems associated with post extrusion structural rearrangement. The polydimethylsiloxane (PDMS) matrix, which can be processed at ambient and low temperatures, is used to bypass any issues associated with thermal degradation. Local heating in the first part of the extruder allows testing of the usefulness of low matrix viscosity to enhance polymer intercalation before applying larger stresses for clay dispersion. The comparison of clay particle sizes measured in line with models for the kinetics of particle dispersion indicates that larger screw speeds promote the break-up of clay particles, whereas smaller screw speeds favor the erosion of the clay tactoids. Thus, different levels of clay dispersion are generated, which do not simply relate to a progressively better PDMS intercalation and higher clay exfoliation as screw speed is increased. Reducing the PDMS viscosity in the first mixing zone of the screw facilitates dispersion at lower screw speeds, but a complex interplay between stresses and residence times at larger screw speeds is observed. More importantly, the results underline that the use of larger stresses is inefficient per se in dispersing clay if sufficient time is not given for PDMS to intercalate the clay galleries and thus facilitate tactoid disruption or erosion.

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

“…Therefore, the results indicate that for the material, geometry of the kneading blocks, and operating conditions used in the experiments, residence time is the predominant effect. Similar results have been recently reported for polymer/clay nanocomposites [ 59 ]. Therefore, and as anticipated, KB90-6 is the most efficient configuration for dispersion, as it is associated to higher residence times.…”

Can Biomass Mastication Assist the Downstreaming of Polyhydroxyalkanoates Produced from Mixed Microbial Cultures?

“…A possible explanation for the overestimation of W is given in Figure 1 c. At shear rates corresponding to those taking place in the squeezing chamber of the masticating unit, the slurry with 50 wt% dried biomass actually did not flow as predicted by Equation (1). Instead, strain localization and nonhomogeneous flow, which are ubiquitous in the rheology of dense suspensions, took place as suggested by the stress plateau at larger shear rates in Figure 1 c. Thus, a stress value on the order of 1 to 10 kPa should be considered to compute the mechanical work, which would then reach values between 7.5 and 126 kJ·kg −1 and compare to mechanical works computed for the melt mixing of, for example, polymer composites [ 40 ].…”

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

“…Furthermore, it was established that for higher degrees of exfoliation and dispersion, by melt processing, often required an adequate residence time in the extruder and an appropriate shear profile. These results suggested that melt processing technique, using a continuous melt mixing procedure in a twin‐screw extruder, can result in comparatively higher levels of exfoliation and dispersion of fillers in polymer nanocomposites, such as those containing, clay, [ 22 ] carbon nanotubes, [ 24 ] and graphite, [ 25 ] without chemical modifications, or by using compatibilizers. However in this context, so far no report(s) on the exfoliation and dispersion of h‐BN in the polymeric matrices via melt‐processing using continuous melt‐mixing processes in a twin‐screw extruder can be found in the literature.…”

“…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.…”