PFI:AIR - TT: Extensional Mixing Elements for Improved Dispersive Mixing in Extrusion Operations

Case Western Reserve University, Cleveland OH

Investigators

Abstract

This PFI: AIR Technology Translation project focuses on translating a technology, extensional mixing elements (EMEs), that improves polymer extrusion by improving the blending and compounding ability of both single- and twin-screw extruders. The application of this technology spans existing plastic compounding as well as providing the ability to produce new polymers that require more complex mixing. The application of EMEs will improve the extrusion process and will allow new classes of polymers to be designed and brought to market leading to new, better performing, functional, lightweight products. The project will result in prototype EMEs optimized for both twin- and single-screw extruders. These are unique in that they provide much improved dispersive mixing due to the extension-dominated flow through stationary hyperbolically contracting channels. Preliminary results have shown significant improvement in the mixing of nanocomposites and immiscible polymer blends by comparison with standard kneading block-configured extruders. This project addresses a critical technology gap(s) as it translates from research discovery toward commercial application. Intermeshing co-rotating twin-screw extruders (co-TSE) are the equipment of choice for compounding of filled polymer systems and masterbatches, polymer melt homogenization, modification and blending mainly because of their good distributive and dispersive mixing capabilities. The mixing action in co-TSEs is usually imparted via sets of kneading blocks, which impart intensive shear on the material and some, but less, extension. Since shear flows are energetically inefficient for dispersive mixing by comparison with extensional flows, there is much room for optimization. Similarly, single-screw extruders are the most widespread type of extruder worldwide because even though they are typically poor mixing devices, they also allow for large throughputs. Again, it is highly desired to develop single-screw extruders with improved compounding ability, while maintaining their good pump characteristics. In the case of twin-screw extruders, the EME concept will be optimized by defining the minimum and maximum geometrical configurations admissible, e.g., contraction ration and length, which lead to improved mixing without an undue penalty in pressure drop and machine wear and tear. This will allow a better understanding of the design rules of the EMEs and perform upscaling to industrial-sized machines. In the second phase of this project, we propose to expand the EME concept to SSEs and thus improve significantly their mixing ability, while maintaining their excellent melt pump characteristics. This ability to achieve much finer and controlled structures and morphologies in polymer blends and composites TSEs and the transformation of SSEs into efficient compounders while maintaining their excellent pump characteristics will be transformational for the practice. The project will involve one graduate student who will develop first-hand knowledge of how to interact with top-level manufacturing companies. Besides preparing the technical documents, the student will participate in phone conversations/meetings with the potential customers, pre-meetings and post meeting debriefs, thus imparting him/her with first-hand familiarity with industry-directed research with deliverables, product development, project management and the ability to navigate high pressure situations. In addition, the student will have a tailored plan of studies, which will include courses from the CWRU Masters in Engineering Management, thus furthering his/her ability to develop these competencies.