Chemical Engineering, Department of
http://hdl.handle.net/1974/769
2017-09-24T21:00:06ZNormal Stress Differences from Oldroyd 8-Constant Framework: Exact Analytical Solution for Large-Amplitude Oscillatory Shear Flow
http://hdl.handle.net/1974/22607
Normal Stress Differences from Oldroyd 8-Constant Framework: Exact Analytical Solution for Large-Amplitude Oscillatory Shear Flow
Saengow, Chaimongkol; Giacomin, A. Jeffrey
The Oldroyd 8-constant framework for continuum constitutive theory contains a rich diversity of popular special cases for polymeric liquids. In this paper, we use part of our exact solution for shear stress to arrive at unique exact analytical solutions for the normal stress difference responses to large amplitude oscillatory shear flow (LAOS). The nonlinearity of the polymeric liquids, triggered by LAOS, causes these responses at even multiples of the test frequency. We call responses at frequency higher than twice the test frequency higher harmonics. We find the new exact analytical solutions to be compact and intrinsically beautiful. These solutions reduce to those of our previous work on the special case of the corotational Maxwell fluid. Our solutions also agree with our new truncated Goddard integral expansion for the special case of the corotational Jeffreys fluid. The limiting behaviors of our exact solutions for the Oldroyd 8-constant framework yield new explicit expressions for the normal stress difference responses in small-amplitude amplitude oscillatory shear flow (SAOS). Finally, we use our exact solutions to see how η∞ affects the normal stress differences in LAOS.
2017-03-01T00:00:00ZExact Analytical Solution for Large-Amplitude Oscillatory Shear Flow from Oldroyd 8-Constant Framework: Shear Stress
http://hdl.handle.net/1974/22606
Exact Analytical Solution for Large-Amplitude Oscillatory Shear Flow from Oldroyd 8-Constant Framework: Shear Stress
Saengow, Chaimongkol; Giacomin, A. Jeffrey; Kolitawong, Chanyut
The Oldroyd 8-constant model is a continuum framework containing, as special cases, many important constitutive equations for elastic liquids. When polymeric liquids undergo large-amplitude oscillatory shear flow, the shear stress responds as a Fourier series, the higher harmonics of which are caused by the fluid nonlinearity. We choose this framework for its rich diversity of special cases (we tabulate 14 of these). Deepening our understanding of this Oldroyd 8-constant framework thus at once deepens our understanding of every one of these special cases. Previously [Macromol Theor Simul, 24, 352 (2015)], we arrived at an exact analytical solution for the corotational Maxwell model. Here, we derive the exact analytical expression for the Oldroyd 8-constant framework for the shear stress response in large-amplitude oscillatory
shear flow. Our exact solution reduces to our previous solution for the special case of the corotational Maxwell model, as it should. Our worked example uses the special case of the corotational Jeffreys model to explore the role of η∞ on the higher harmonics.
2017-01-01T00:00:00ZRadical Polymerization of Bio-Renewable Butyrolactone Monomers
http://hdl.handle.net/1974/22035
Radical Polymerization of Bio-Renewable Butyrolactone Monomers
Luk, Sharmaine
In this study, a bio-derived monomer, -methyl--methylene--butyrolactone (MeMBL) was saponified with sodium hydroxide (NaOH) to make the water-soluble monomer sodium 4-hydroxy-4-methyl-2-methylene butanoate (SHMeMB), that was copolymerized via radical polymerization in aqueous solution with acrylamide (AM) and crosslinker to synthesize superabsorbent hydrogels. Absorbency of these hydrogels was shown to be much higher than sodium acrylate hydrogels, with mechanical properties varying with molar composition and crosslinking content. Reactivity ratio of SHMeMB:AM at 50C and 15 wt% were estimated using low conversion data (rSHMeMB=0.12 and rAM=1.10), and the integrated Mayo-Lewis equation (rSHMeMB=0.17 and rAM=0.95). However, in-situ NMR results showed that SHMeMB:AM copolymerizations proceed at a slower rate than of a similar system of AM copolymerized with sodium 4-hydroxy-2-methylene butanoate (SHMB), a similar monomer produced by ring-opening of -methylene--butyrolactone (MBL). Pulsed-laser polymerization coupled with size exclusion chromatography (PLP-SEC) studies were done for both systems at 60°C and 10 wt% monomer concentration. Homopolymerization kp values were estimated to be 25 and 165 L/mols for SHMeMB and SHMB, respectively, confirming that SHMeMB is less reactive than SHMB.
Further kinetic studies of SHMeMB:AM copolymerization and homopolymerization of SHMeMB were conducted at elevated temperatures. SHMeMB conversions achieved a limiting value which decreased at higher temperatures, suggesting that polymerization rate was limited by depropagation. Comonomer composition drift also increased with temperature, with more AM incorporated into the polymer while SHMeMB underwent depropagation. Homopolymerization of SHMeMB with added sodium chloride (NaCl) showed a decrease in polymerization rate explained by an increase in propagation rate coefficient (kp) but an even greater increase in termination rate coefficient (kt) as supported by parameter estimation done using PREDICI. Even with added salt, however, depropagation was the dominant mechanism at higher temperatures. Lastly, the kinetic parameters estimated were implemented in a copolymerization model used to estimate the variation of kt with composition in SHMeMB:AM copolymerizations. It was found that the overall termination rate coefficient was dominated by the presence of SHMeMB, with as the estimate for kt,SHMeMB of the same order of magnitude as kt of another ionized water-soluble monomer, sodium methacrylic acid.
Polymer Processing Partitioning Approach: Extruding Plastic Pipe
http://hdl.handle.net/1974/22017
Polymer Processing Partitioning Approach: Extruding Plastic Pipe
Saengow, Chaimongkol
The proposed thesis research aims at deepening our understanding of the flow of polymer melts through eccentric plastic pipe extrusion dies. Specifically, the proposed thesis research will explore how viscoelasticity affects the (1) velocity profile, (2) extrudate shape, (3) residual stresses, (4) axial and lateral forces on the eccentric mandrel, and on (5) knuckle formation (knuckling). Since pipe is only as strong as its thinnest part, a non-uniform extrudate shape wastes material. Pipe manufacture is thus preoccupied with perfecting extrudate shape.
2016-01-01T00:00:00Z