Solid‐state shear pulverization (SSSP) is a continuous polymer processing methodology based on a modified twin‐screw extruder. The unique application of low barrel temperatures and mechanochemistry has contributed to the development of an extensive range of polymer‐based materials, from environmentally responsible polymer blends to nanocomposites, for more than 30 years. The complex processing‐structure‐processing relationships in SSSP can be elucidated by way of integrated, measured covariants that capture the interplay between numerous processing parameters. Residence time distribution and specific mechanical energy are evaluated in a base case polypropylene (PP) study under a full factorial experiment involving screw design, screw speed, and throughput parameters. These factors are in turn correlated to dispersion morphology and thermal property results from a parallel study based on a model PP/carbon black composite. This investigation highlights the tunability of SSSP processing parameters for tailored output with desired purposes and applications. In particular, enhanced residence distribution can be achieved with low screw speed and high throughput settings, leading to high levels of material mixing and shear. POLYM. ENG. SCI., 60:503–511, 2020. © 2019 Society of Plastics Engineers
Measurement and Analysis of Pressure Profile Within Big Area Additive Manufacturing Single Screw Extruder.
Pressure distributions within a single screw extruder are dependent on several factors, namely, processing parameters and flow geometry. The Big Area Additive Manufacturing (BAAM) system involves a complex flow geometry with multiple flow zones following the screw extruder. This study utilized experimental data and a one-dimensional (1-D) analytical model to
compare pressures at specific areas of interest in the BAAM system. Initial results show a need for further two-dimensional (2-D) and three-dimensional (3-D) simulation and modeling of the BAAM extruder with more accurate underlying assumptions. The results of this work will allow for further study of BAAM input parameters for optimal print quality, material properties, and
print head geometric design.
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- Award ID(s):
- 1841507
- NSF-PAR ID:
- 10200739
- Date Published:
- Journal Name:
- Solid Freeform Fabrication Symposium proceedings
- ISSN:
- 1053-2153
- Page Range / eLocation ID:
- 1242-1250
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Additive manufacturing promises to revolutionize manufacturing industries. However, 3D printing of novel build materials is currently limited by constraints inherent to printer designs. In this work, a bench-top powder melt extrusion (PME) 3D printer head was designed and fabricated to print parts directly from powder-based materials rather than filament. The final design of the PME printer head evolved from the Rich Rap Universal Pellet Extruder (RRUPE) design and was realized through an iterative approach. The PME printer was made possible by modifications to the funnel shape, pressure applied to the extrudate by the auger, and hot end structure. Through comparison of parts printed with the PME printer with those from a commercially available fused filament fabrication (FFF) 3D printer using common thermoplastics poly(lactide) (PLA), high impact poly(styrene) (HIPS), and acrylonitrile butadiene styrene (ABS) powders (< 1 mm in diameter), evaluation of the printer performance was performed. For each build material, the PME printed objects show comparable viscoelastic properties by dynamic mechanical analysis (DMA) to those of the FFF objects. However, due to a significant difference in printer resolution between PME (X–Y resolution of 0.8 mm and a Z-layer height calibrated to 0.1 mm) and FFF (X–Y resolution of 0.4 mm and a Z-layer height of 0.18 mm), as well as, an inherently more inconsistent feed of build material for PME than FFF, the resulting print quality, determined by a dimensional analysis and surface roughness comparisons, of the PME printed objects was lower than that of the FFF printed parts based on the print layer uniformity and structure. Further, due to the poorer print resolution and inherent inconsistent build material feed of the PME, the bulk tensile strength and Young’s moduli of the objects printed by PME were lower and more inconsistent (49.2 ± 10.7 MPa and 1620 ± 375 MPa, respectively) than those of FFF printed objects (57.7 ± 2.31 MPa and 2160 ± 179 MPa, respectively). Nevertheless, PME print methods promise an opportunity to provide a platform on which it is possible to rapidly prototype a myriad of thermoplastic materials for 3D printing.more » « less
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Abstract Polymer films are widely used in various industries, and incorporation of nanofillers into polymer films can give much more versatility in their applications. Polymer/carbon nanotubes (CNTs) composite films with good electrical conductivity can easily find applications in anti‐static or electrostatic discharge (ESD) protection. In the present study, efforts were devoted to investigate novel ultrasound‐assisted twin‐screw extrusion technology on improving the dispersion and distribution of single‐walled carbon nanotubes (SWNTs) in polycarbonate (PC) composites films via extrusion process. As a key processing parameter, effect of screw configuration on the performance of the composite films were systematically studied. Electrical, rheological, morphological and mechanical properties were characterized to illustrate the processing‐structure–property relationship during continuous film casting of PC/SWNTs composites with ultrasound‐assisted twin‐screw extruder. Results indicated that the screw configuration containing more kneading blocks led to better SWNTs dispersion and distribution, while the effect of ultrasound was more prominent in screw design with less kneading blocks.
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Gas-dynamic virtual nozzles (GDVNs) play a vital role in delivering biomolecular samples during diffraction measurements at X-ray free-electron laser facilities. Recently, submicrometer resolution capabilities of two-photon polymerization 3D printing techniques opened the possibility to quickly fabricate gas-dynamic virtual nozzles with practically any geometry. In our previous work, we exploited this capability to print asymmetric gas-dynamic virtual nozzles that outperformed conventional symmetric designs, which naturally leads to the question of how to identify the optimal gas-dynamic virtual nozzle geometry. In this work, we develop a 3D computational fluid dynamics pipeline to investigate how the characteristics of microjets are affected by gas-dynamic virtual nozzle geometry, which will allow for further geometry optimizations and explorations. We used open-source software (OpenFOAM) and an efficient geometric volume-of-fluid method ( isoAdvector ) to affordably and accurately predict jet properties for different nozzle geometries. Computational resources were minimized by utilizing adaptive mesh refinement. The numerical simulation results showed acceptable agreement with the experimental data, with a relative error of about 10% for our test cases that compared bell- and cone-shaped sheath-gas cavities. In these test cases, we used a relatively low sheath gas flow rate (6 mg/min), but future work including the implementation of compressible flows will enable the investigation of higher flow rates and the study of asymmetric drip-to-jet transitions.more » « less
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