Enhanced Dispersion and Mechanical Behavior of Polypropylene Composites Compounded Using Extension-Dominated Extrusion

J of Applied Polymer Sci

Maia

2020

Extensional mixing elements (EMEs) were previously developed for twin-screw extruders (TSEs) to incorporate extensional flows through stationary singleplane or double-plane hyperbolic convergence-divergence channels. In Part 1 of this work, the EME concept is extended to single-screw extruders (SSEs), which are known for their good pumping characteristics but limited dispersive mixing capability, to enhance the latter. Flow simulations are performed to optimize the EME design for SSE. Experimental validations are performed on immiscible polymer blends (varying viscosity ratio) and nanocomposites. Morphological results show tremendous improvement in mixing capability of SSE when equipped with EME without significant throughput and pressure drop penalties. Rheological and crystallinity studies are observed to be in line with the morphological analysis. Morphological and mechanical results are benchmarked with TSE operations in Part 2 of this work.

Section: Introductionmentioning

confidence: 99%

Extension‐dominated improved dispersive mixing in single‐screw extrusion. Part 1: Computational and experimental validation

J of Applied Polymer Sci

Maia

2020

“…EMEs were also made aggressive by incorporating a vertical hyperbolic contraction, termed as biaxial EME, and were found computationally to impart even higher extension rates. 64 The optimized designs have also been tested experimentally for blend and nanocomposite systems and were found to yield higher dispersive mixing. EMEs have also been proven to generate phase changes when reactive extrusions were conducted on polyamide-6 dispersed in the polystyrene with styrene-maleic anhydride used as the compatibilizer.…”

Section: Introductionmentioning

confidence: 99%

“…Pressure drop was minimized by finding the optimized number of channels which will not compromise its dispersive mixing capability. EMEs were also made aggressive by incorporating a vertical hyperbolic contraction, termed as biaxial EME, and were found computationally to impart even higher extension rates 64 . The optimized designs have also been tested experimentally for blend and nanocomposite systems and were found to yield higher dispersive mixing.…”

Section: Introductionmentioning

confidence: 99%

Extension‐dominated improved dispersive mixing in single‐screw extrusion. Part 2: Comparative analysis with twin‐screw extruder

J of Applied Polymer Sci

Chen

et al. 2020

In Part 1 of this work, the possibility of improving single-screw extruders (SSE) better dispersive mixer was explored by harnessing extensional flows provided by the hyperbolic contracting-diverging channels of extensional mixing elements (EME). Addition of the EME to the pin screw generated enhanced breakup for polymer blends and nanocomposite systems without significant penalty in flow rate. In Part 2, experiments are performed on immiscible polymer blends (low-viscosity ratio and high-viscosity ratio) and nanocomposites on both SSE and twin-screw extruder (TSE) with the same rotation speed and throughput. Morphological results show tremendous improvement in dispersive mixing capability of SSE when equipped with EME that are mainly comparable to conventional TSE that is, with kneading blocks as mixing sections, although not as good as TSEs equipped with EMEs. Mechanical results also show enhanced modulus when EME is used in SSE operations.

“…[19] The idea of biaxial contraction, meaning hyperbolic contractions in both the horizontal vertical direction, was also introduced to make it more aggressive. [20] The number of channels in the EME design were optimized to lower the pressure drop without limiting the dispersive mixing capability. Carson et al, [18] Chen et al, [19,21] and Danda et al, [20] validated the EME dispersive mixing efficiency experimentally, for two types of systems: (a) Immiscible polymer blends, that is, fluid-fluid systems, and (b) Nanocomposites, that is, fluid/solid systems.…”

Section: Introductionmentioning

confidence: 99%

“…[20] The number of channels in the EME design were optimized to lower the pressure drop without limiting the dispersive mixing capability. Carson et al, [18] Chen et al, [19,21] and Danda et al, [20] validated the EME dispersive mixing efficiency experimentally, for two types of systems: (a) Immiscible polymer blends, that is, fluid-fluid systems, and (b) Nanocomposites, that is, fluid/solid systems. The EME has been shown to being effective in dispersing droplets up to very high viscosity ratios in the case of blends, and yielding significant smaller aggregates in the case of polymer nanocomposites than even the most aggressive KB-based geometries.…”

Section: Introductionmentioning

confidence: 99%

Comparative computational analysis of dispersive mixing in extension‐dominated mixers for single‐screw extruders

Polymer Engineering & Sci

Maia

2020

Enhanced dispersive mixing can be achieved by harnessing extensiondominated flows, because they are more efficient in agglomerate/droplet breakup than shear-dominated flows. Herein, we compare computationally the performance of two single-screw extrusion mixing sections with significant extensional flow components, the Chris Rauwendaal dispersive (CRD) mixer and the extensional mixing element (EME), recently proposed by the authors. Tapered slots in the CRD and hyperbolic contractions in the EME attempt to create extensional stresses through significant velocity gradients. Our studies confirm that EMEs are a better dispersive mixer than the CRD mixer, as they impose more intense and uniformly distributed extensional flow in a higher volume fraction of the material, and with less specific mechanical energy consumption. Overall, the EME design with a biaxial contraction was found to be the best dispersive mixer for single-screw extruders (SSE). The manuscript also summarizes all the existing dispersive mixers for SSE and ranks them relatively for their dispersive mixing capability.