A New Extensional Mixing Element for Improved Dispersive Mixing in Twin‐Screw Extrusion, Part 1: Design and Computational Validation

Polymer Engineering & Sci

Zhu

Maia

2020

Control of the crystalline phase transition of polymers is critical to improve mechanical properties and to achieve good levels of thermal properties in polymer engineering. Current methods control the transition process by using thermal methods that is, annealing above the glass transition temperature (T g ) to get the targeting crystalline phase. It requires precise control of the temperature and process time and is limited to a small scale. In contrast, a novel processing-based method developed in our group by combining the use of reactive processing technique and extensional mixing elements (EME) allows different sizes of minor phase droplets in immiscible polymer blends to be achieved by controlling the degree of aggressiveness of the EME. The use of EME can confine polyamide crystalline structure into the γ-phase from the α-phase. The reactive processing benefits in stabilizing these droplets and in freezing the corresponding crystalline morphologies in droplets. Crystalline phase transition of the minor phase in these droplets is therefore observed as the size of droplet decreases from micro to submicron. Furthermore, phase transition can be precisely controlled by tuning additives and EME blocks. FIG. 7. Curves of the first cooling cycle of DSC measurements for various pellet-shaped samples with a cooling rate of 10 C/min.

Section: Resultssupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Phase Control of Polyamide 6 via Extension‐Dominated Polymer Blend Reactive Extrusion

Polymer Engineering & Sci

Zhu

Maia

2020

J of Applied Polymer Sci

“…Finally, the element should interface with a conventional TSE without interrupting its normal function or adding extra equipment systems or controls. 45 The first designed EME prototype, which was designed to F I G U R E 1 Grace plot for Newtonian-Newtonian emulsions/ blends (adapted from Carson et al 46 ) impart relatively mild extension on the melt, showed tremendous improvement in the mixing of nanocomposites and immiscible polymer blends by comparison with standard KB-configured screw configurations. 46 EME designs for TSE were made aggressive by increasing the contraction ratio to the limit such that recirculation could be avoided.…”

Section: Introductionmentioning

confidence: 99%

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

Pandey

Maia

2020

Self Cite

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.

“…The tip clearance and wedge‐like region were primarily respond for dispersive mixing, and the interaction window could help improving the distributive mixing. Specially, the relative minor elongational flow component would exist near the entrance of rotor wing tip, and could have major effect on the dispersive mixing …”

Section: Introductionmentioning

confidence: 99%

Mixing ability examination of three different rotor cross sections and rotor geometry quantification with pressurization coefficient

Hao

J of Applied Polymer Sci

et al. 2018

The geometry of rotor cross section would affect the velocity profile of circumferential flow in continues mixer, which further dominated the mixing ability of rotor. To reveal the relationship between the geometry and mixing ability of rotor cross section, three rotor cross sections with different geometries were chosen, and the POLYFLOW simulations were applied to analyze the velocity profile and the flow stretching. The distribution for three rotors was evaluated both numerically and experimentally with the particle tracking technology. Then, the rotor geometry was quantified with pressurization coefficient S, which is a geometric parameter considering the wedge angle a, width of wing tip e, tip clearance h and the maximum clearance H 0 between rotor and chamber wall. The results showed that the mixing ability and S for three rotor cross-sections would vary with the rotor geometry changing, furthermore, the rotor cross-section with larger S would have stronger mixing ability. Decreasing a or e, as well as increasing the H 0 , would induce the increase of S, and further resulting in the improvement of the mixing ability. Rotor geometry quantification with S would intuitionally reveal the relationship between rotor geometry and the mixing ability, and would contribute to the rotor cross-section design and optimization.