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Volume 42 (2014)
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- Issue 4 Pages 219-
- Issue 3 Pages 161-
- Issue 2 Pages 77-
- Issue 1 Pages 1-
Volume 42, Issue 1
Displaying 1-11 of 11 articles from this issue
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ORIGINAL ARTICLES
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Mohammad-Ali Ranjbar, Mohammad Jalalisendi, Kayvan Sadeghy2014 Volume 42 Issue 1 Pages 1-8
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSIn the present work, the effect of a fluid's thixotropic behavior is investigated numerically on the frequency response of an encapsulated gas microbubble. Relying on Moore's model to represent the thixotropicity of the surrounding liquid and the Kelvin-Voigt model to represent the viscoelasticity of the enclosing shell, the modified integro-differential Rayleigh-Plesset equation is solved numerically using Gauss-Laguerre Quadrature (GLQ) method. It is shown that by an increase in the breakdown-to-buildup ratio new harmonics are generated. Also, the resonance frequency of the bubble is predicted to shift to lower values by an increase in this ratio with the effect being more evident for the harmonics. An increase in the viscosity ratio in the Moore's model is predicted to lower the resonance frequency of the bubble with the effect being most significant for the main frequency.View full abstractDownload PDF (1671K) -
Alireza Kalantari, Alireza Riasi, Kayvan Sadeghy2014 Volume 42 Issue 1 Pages 9-17
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSPeristaltic flow of a viscoelastic fluid is numerically studied in a plane channel. The fluid is assumed to obey the Giesekus model as its constitutive equation, and the flow is assumed to be occurring under incompressible, laminar, and two-dimensional conditions. To simplify the equations of motion, use is made of the long-wavelength assumption together with the creeping-flow assumption. It is shown that for this particular fluid model, the governing equations are reduced to a system of coupled nonlinear ODEs, which are solved numerically using finite difference method. Numerical results show that the elastic behavior of a fluid can significantly decrease the pressure rise of peristaltic pumps. On the other hand, a radially-imposed magnetic field is shown to increase the pressure rise of the pump when the flow rate is less than a certain value. The results are interpreted in terms of the extensional-flow behavior of the fluid as represented by the fluid's mobility (or, extensional) factor.View full abstractDownload PDF (1262K) -
Hideo Kobayashi, Osamu Urakawa, Fumitoshi Kaneko, Tadashi Inoue2014 Volume 42 Issue 1 Pages 19-23
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSThe δ-cocrystal of syndiotactic polystyrene (sPS) can capsulate various small guest molecules in the cavity of the crystalline region. We examined the rotational motion of isolated polar guest molecule, benzonitrile (BN), caged in the crystalline cavities by dielectric spectroscopy and the results were compared with the previously reported data of sPS / methyl ethyl ketone (MEK) system. The relaxation of BN in the crystalline region was specified from the comparison with the dielectric data of atactic-PS / BN system in which only the amorphous phase exists. The rotational relaxation time of BN in the crystalline cavity was 6 orders of magnitude longer, and the activation energy of BN was twice larger than those of MEK. These results suggest that spatial restriction due to the small cavity size strongly retards the rotational dynamics of the larger guest molecule, BN. Two-site model could successfully describe the temperature dependence of the dielectric intensity for sPS / BN system, revealing that there exist two stable states of BN molecules with energy difference of 7.42 kJmol-1 in the crystalline cavity.View full abstractDownload PDF (738K) -
Takaaki Hattori, Masataka Sugimoto, Kiyohito Koyama2014 Volume 42 Issue 1 Pages 25-31
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSModifications of rheological and mechanical properties by various kneading methods and histories were studied for high density polyethylene (HDPE) polymerized by a standard Phillips Cr/silica catalyst. The HDPE exhibits long-time relaxation in linear viscoelasticity and apparent strain-hardening in elongational viscosity due to long chain branches. These rheological features were depressed by single-screw extrusion. This phenomenon is known as “shear modification”. However, we found that the depressed property could be recovered quickly and easily by two-roll milling. This probably means that different modification being contrary to shear modification exists. The sample processed by an internal batch mixer with a low fill factor showed similar properties to the one kneaded by the two-roll mill, however, another sample processed with a high fill factor was close to the one prepared by the single-screw extruder. It is likely that the ratio influences the balance of convergent flow and shear flow which are generated between two counter-rotating blades and between each blade and the casing, respectively. Since convergent flow contains elongational flow, the modification which should be distinguished from shear modification may be called “elongational modification”. Furthermore, stress crack resistance changed as well as rheological properties in spite of no change of Charpy and tensile impact strength.View full abstractDownload PDF (673K) -
Akihiko Takada, Koji Saeki, Shoichi Murata, Yukihiro Motoyama, Atsushi ...2014 Volume 42 Issue 1 Pages 33-38
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSSolid-like and liquid-like viscoelastic behaviors at low and high temperature, T, respectively, observed for carboxyl-terminated telechelic poly(ethyrene-butylene) (CTPEB) neutralized with octadecylamine ODA prepared by melt mixing are studied in relation with the structure examined by XRD, FT-IR, DSC and small angle neutron scattering. When the mole ratio of -NH2 and -COOH, NH2/COOH in CTPEB/ODA is 1.4 or higher, CTPEB/ODA was solid-like at 298K, while it was liquid-like having almost the same viscosity as CTPEB at 343K. The network structure formed at low T was easily fractured by small strain and cannot be reformed at low T. However, when the sample is annealed at 353K, cooled and kept for a few hours at T < 300K, the solid-like behavior is reproduced. It was concluded that the network formation at low T and its disappearance at high T for CTPEB/ODA is caused by non-crystalline association/dissociation of C18 residues in ODA connected to CTPEB by ionic bond (NH3+COO-). Due to the small Mw of CTPEB, only longer chains (∼ 1/3 of total chains) connected to ODA aggregates form network structure and sustain the constant G'in this system at low T.View full abstractDownload PDF (582K) -
Eiichi Takatori, Toshitaka Shimura, Shigeru Yao, Yoshio Shindoh2014 Volume 42 Issue 1 Pages 39-43
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSWe studied the dependencies of material properties on several types of average molecular weight for a recycled high density polyethylene that was obtained from PET-bottle caps. We discussed the correlations of the average molecular weights with the density, melt index, high load melt index, yield stress, and elongation at break. We concluded that these material properties of the recycled HDPE are similar to those of the virgin HDPE with the identical average molecular weight.View full abstractDownload PDF (907K) -
Eiichi Takatori, Toshitaka Shimura, Takayuki Adachi, Shigeru Yao, Yosh ...2014 Volume 42 Issue 1 Pages 45-49
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSWe studied tensile properties and rheological properties of a recycled HDPE that was obtained from PET bottle caps and a virgin high density polyethylene (HDPE) which was the molding grade for PET bottle. In the previous study we concluded this recycled HDPE had the same dependency of the material properties on the averaged molecular weight as the virgin HDPE. However, a 1mm - thick sheet and 0.1 mm - thick film of the recycled HDPE was brittle compared to a sheet and a film from the virgin HDPE. We also found that the dependence of the tensile fracture energy on the duration of UV irradiation was essentially the same in these samples. In the case of the HDPE samples we could validate the theoretical equation that the authors proposed for the recycled polypropylene. Then we observed their morphology using TEM. Images were seen in Figures 5 and 6. At last we found the recycled HDPE melt had thermo-rheological complexity like LDPE. After UV irradiation the virgin HDPE had thermo-rheological complexity, too.View full abstractDownload PDF (1050K) -
Abdessamade Rafiki, Ahmed Hifdi, Mohamed Ouazzani Touhami, Seyed Moham ...2014 Volume 42 Issue 1 Pages 51-60
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSThe linear stability of a plane Poiseuille flow of an electrically conducting viscoelastic fluid in the presence of a transverse magnetic field is investigated numerically. The fourth-order modified Orr-Sommerfeld equation governing the stability analysis is solved by a spectral method with expansions in Lagrange polynomials, based on collocation points of Gauss-Lobatto. The combined effects of a magnetic field and fluid's elasticity on the stability picture of the plane Poiseuille flow are investigated in two regards. Firstly, the critical values of a Reynolds number and a wavenumber, indicating the onset of instabilities, are computed for several values of a magnetic Hartman number, M, and at different values of an elasticity number, K. Secondly, the structure of the eigenspectrum of the second-order and second-grade models in the Poiseuille flow is studied. In accordance to previous studies, the magnetic field is predicted to have a stabilizing effect on the Poiseuille flow of viscoelastic fluids. Hence, for second-order (SO) fluids for which the elasticity number K is negative, the critical Reynolds number Rec increases with increasing the Hartman number M, for various values of the elasticity number K. However, for second-grade (SG) fluids (K > 0), the critical Reynolds number Rec increases with increasing the Hartman number only for certain values of the elasticity number K, while decreases for the others.View full abstractDownload PDF (896K)
NOTE
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Shigeru Yao, Aya Tominaga, Hiroshi Sekiguchi, Eiichi Takatori2014 Volume 42 Issue 1 Pages 61-64
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSWe previously reported that the inner structures of thick (>3 mm) injection-molded test pieces of virgin polypropylene and recycled pre-consumer polypropylene were very different, even though their molecular and mechanical properties were almost the same. This difference was thought to be caused by the molding history of pre-consumer polypropylene. Due to this difference in their internal structures, thin films (<100 μm) of recycled pre-consumer polypropylene were very brittle. By examining the degradation properties of these thin films in response to UV irradiation, we found that the toughness of these samples decreased exponentially in a UV irradiation time-dependent manner. This dependence was almost the same in virgin and recycled samples, and we could superimpose of the results. We also found that the UV irradiation time-dependence was associated with the number of molecules that connected domains within the samples. In this study, we investigated the mechanical and UV irradiation time-dependent properties of thick samples composed of a blend of virgin and recycled pre-consumer materials. We found that the mechanical properties of these non-irradiated samples were almost the same. However, the mechanical properties of irradiated samples were significantly different. We also found that this difference linearly depends on the blend ratio. These results suggest that specimens containing recycled polymers can exhibit very poor durability even though there are no differences in their non-irradiated mechanical properties.View full abstractDownload PDF (1628K) -
Osami Kamigaito2014 Volume 42 Issue 1 Pages 65-67
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSA crack in an elastic material propagates, giving phenomenally viscoelastic behavior, in some stress intensity factor range. The upper limit of the range, KIC, is expressed in terms of the nearest atomic distance, d0, and Young's modulus, E, as KIC = 0.9d01/2E. The lower limit of the range, K0, is not expressed in the similar form as KIC, which causes some difficulty in the estimation of the safe factor for the stress, under which no crack propagates. The expression for K0 was studied on a less empirical basis, using the expression for KIC as well as the theoretical one for surface tension, γT. The following results were given: K0 ∼ 0.5 KIC, γT ∼ (1/11) d0E, the theoretical strain limit, εf ∼ 0.3, for any material whose KIC follows the expression, KIC = 0.9d01/2E. The “surface bond energy: γb”, the origin of KIC expressed as KIC = (2γbE)”1/2, is related to γT as γb = 4γT. The estimated value of K0 is in good agreement with literature values.View full abstractDownload PDF (517K)
BOOK REVIEW
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Yuichi Masubuchi2014 Volume 42 Issue 1 Pages 69
Published: March 15, 2014
Released on J-STAGE: March 10, 2014
JOURNAL FREE ACCESSDownload PDF (165K)
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