Iranian Polymer Journal / Volume 7 Number 2 (1998) 73–78 ISSN: 1026-1265/1998
Chemical Engineering Department, Isfahan University of Technology, Isfahan 84156, I.R.Iran
A capillary rheometer was designed and constructed to carry out studies on the flow behaviour of viscous non-Newtonian fluids. Two capillary tubes were attached to the pressure chamber which increase the accuracy of the rheological measurements (power law index as well as consistency index). By employing two capillary tubes, the power law index can be calculated directly from the measuring values and the accuracy of consistency index increases as well. Capillary tubes with different diameters and various lengths can be used and a wide range of shear rates can be covered by using different tubes. Tests were conducted with solutions of sodium carboxymethyl cellulose (CMC) of different concentrations and various temperatures. The CMC solutions exhibited characteristics typical of power law model of non-Newtonian fluids. The measurements illustrated that the consistency index varies significantly with both concentration and temperature. Increasing concentration enhances consistency index while promoting temperature has a reverse effect. Also concentration has noticeable effect on power law index. As concentration increases the power law index decreases. The effect of temperature on power law index is negligible.
Iranian Polymer Journal / Volume 7 Number 2 (1998) 79–82 ISSN: 1026-1265/1998
Electrical Conductivity of Nickel-Poly(acrylate divinylbenzene)
Sh.M. Yousaf1, Sh. Taj1, Z. Ahmad1, and F.A. Khawaja2
(1) Department of Chemistry, Quaid-I-Azam University, Islamabad, Pakistan
(2) Material Research Laboratory, Department of Physics, Quaid-I-Azam University, Islamabad, Pakistan
The electrical conductivity of nickel-poly(acrylate divinylbenzene) has been studied over a wide range of temperatures. Poly(acrylic acid-divinylbenzene) was doped with nickel acetate to prepare samples containing 5.35, 9.73 and 25.0% (w/w) nickel and current-voltage relationship was studied as a function of concentration and temperature. There is a linear variation of electric current with applied voltage. The slopes of ln (I) vs ln (V) plots being equal to one which suggests the ohmic behaviour of charge carriers. The conductivity has a strong concentration and temperature dependence and is non-monotonic. The conductivity is considered to be due to thermal hopping motion of localized charge carriers which are believed to be polarons.
Iranian Polymer Journal / Volume 7 Number 2 (1998) 83–93 ISSN: 1026-1265/1998
A Semi-Empirical Correlation for Free Coating of
Viscoelastic Fluids onto a Vertical Surface
S. Savarmand1, M.R. Golcar Narenji1, and W.L. Wilkinson2
(1) Faculty of Chemical Engineering, Amir Kabir University of Technology, Tehran, I.R.Iran.
(2) Bureau of Nuclear Fuel Ltd., Warrington, U.K.
The coating of viscoelastic fluids onto a vertical surface continuously withdrawn from a liquid bath is considered. A theoretical treatment is presented based on a one-dimensional approach neglecting the inertia of the fluid and assuming that the rheological behaviour of the fluid can be described by upper convected Maxwell models. Film thickness measurements have been carried out using the same apparatus as that of Spiers et al. . A capacitance technique is used to measure the fluid film thickness. This method is accurate and convenient. In order to take into account the elasticity and fading memory of the fluids, two dimensionless groups, i.e. Weissenberg number and Deborah number are included in the analysis obtained from steady shear experiments and elongational rheometry, respectively. Steady shear experiments consist of measurements of shear stress and first normal stress difference in terms of shear rate using a coaxial-cylinder viscometer, Haake RV1, and a cone-and-plate Weissenberg rheogoniometer, R-18, to obtain the desired low and medium shear-rate ranges. Elongational rheometry consists of the determination of the relaxation times of the fluid from the tubeless siphon data. The results of this analysis, with the previous work of Spiers et al. , yield a semi-empirical correlation that is in good agreement with experimental data.
Iranian Polymer Journal / Volume 7 Number 2 (1998) 95–101 ISSN: 1026-1265/1998
Effect of Electrochemical Cell Overcharge on Electrical and
Electrochemical Properties of Polymer
Composite Electrodes (I)
V. Haddadi-Asl1 and M.S. Rabbani2
(1) Department of Polymer Engineering, Amir Kabir University of Technology, Tehran, I.R. Iran
(2) Faculty of Science, Tehran University, Tehran, I.R. Iran
The effect of overcharge on the performance of the vanadium redox cell that employs conductive carbon-polymer composite/graphic felt electrodes is examined. The electrical, electrochemical and surface properties of the electrodes are investigated in order to determine the effect of each deterioration mechanism to the loss in cell performance during overcharge. The electrical resistivity of the electrode and the cell resistance show a dramatic increase after overcharge. The effect of overcharge on the electrical resistivity and surface chemistry of the graphite felt was also investigated.
Iranian Polymer Journal / Volume 7 Number 2 (1998) 103–111 ISSN: 1026-1265/1998
Morphology of High-Density/Linear Low-Density
Polyethylene Drawn Tapes
S.H. Jafari1, P. Kar2, and S.K. Rana1
(1) Centre for Polymer Science and Engineering, Indian Institute of Technology, New Delhi-110016, India
(2) Department of Textile Technology, Indian Institute of Technology, New Delhi-110016, India
The drawn tapes of high-density polyethylene(HDPE) and blends of high-density/linear low-density polyethylene(LLDPE) were made in the composition range of 0-15% LLDPE by melt extrusion and drawing on hot plate. The morphologies of the drawn tapes were investigated through differential scanning calorimetry and scanning electron microscopy after etching with chlorosulphoric acid. The HDPE drawn tape shows a tenacity as high as 650 MPa which rapidly drops to 450 MPa on the incorporation of 10% LLDPE and an improvement of 15% in tenacity thereafter. The elongation-at-break increases linearly throughout the composition range with increase in LLDPE content from 23.5 to 25% . The superiority in tenacity of HDPE drawn tape is due to the greater long folded-chain crystallites (LFCC) and fine diameter, less imperfect, and less branched fibrils. The addition of LLDPE increases the population of short folded-chain crystallites (SFCC). It also transforms a part of LFCC to SFCC. The dimension and imperfection of the fibrils increased as the LLDPE content increased in the drawn tapes. The circular fibrils of HDPE modified to non-circular fibrils on incorporation of LLDPE. It is seen that the fineness of the fibrils improves the tenacity, whereas, the severity in branching reduces it.
Iranian Polymer Journal / Volume 7 Number 2 (1998) 113–119 ISSN: 1026-1265/1998
Polysiloxanes: Synthesis and Purification of Silicon
Obtained from Iran’s Domestic Micronized Sand
A. Rahimi1, A. Aiazi2, and M. Barikani1
(1) Iran Polymer Institute, Tehran, I.R.Iran
(2) North Division of Islamic Azad University, Tehran, I.R.Iran
Polysiloxanes are prime examples of inorganic polymers with unique combination of high temperature stability and excellent low temperature elastomeric properties. These materials have alternating silicon and oxygen atoms with organic groups linked to silicon atoms. There are two major routes to polysiloxanes: Kipping-Grignard and the catalytic reaction. The first step of both routes involves the reductive conversion of sand into silicon. In this paper, the main features and industrial routes of preparing polysiloxane are discussed and the results of preparation and purification of silicon using domestic micronized sand are reported. Silicon is a starting material for preparing dichlorodimethylsiloxane which is used extensively in manufacturing of silicones of numerous applications, such as silicone rubber.
Iranian Polymer Journal / Volume 7 Number 2 (1998) 121–128 ISSN: 1026-1265/1998
Polymerization of 1-Methyl-2,5-bis[1-(4-phenylurazolyl)]
Pyrrole with Alkyl Diacid Chlorides
Sh.E. Mallakpour and B. Sheikholeslami
Organic Polymer Chemistry Research Laboratory, College of Chemistry, Isfahan University of Technology
Isfahan, 84156, I.R. Iran
1-Methyl-2,5-bis[1-phenylurazolyl)] pyrrole (3) from the reaction of 4-phenyl-1,2,4-triazoline-3,5-diones (1) with N-methylpyrrole (2) was reacted with excess acetyl chloride. Acylation reaction occurred at room temperature and led to the formation of diacetylated adduct in quantitative yield. This product was characterized with IR, 1H NMR, and elemental analysis. Polymerization of monomer (3) with suberoyl chloride and adipoyl chloride was performed in N,N-dimethylacetamide, chloroform and dimethylsulphoxide in the absence and presence of pyridine or triethylamine and lead to the formation of novel polymers. Some structural characterization and physical properties of these novel polymers are reported.
Iranian Polymer Journal / Volume 7 Number 2 (1998) 129–135 ISSN: 1026-1265/1998
Study on Vibromixing for Polymer Solutions
C. Ibănescu1, M. Lungu1, G. Lungu2, and A. Sachelarie2
(1) Faculty of Chemical Engineering, Department of Macromolecules, Technical University “Gh. Asachi”
Bd. Copou 11A, 6600-Jassy, Romania
(2) Faculty of Mechanical Engineering, Department of Machine-Tools, Technical University “Gh. Asachi”
Bd. D. Mangeron 65, 6600-Jassy, Romania
Vibromixing studies were performed by using a laboratory installation equipped with stirring disks of different diameters. They had different frequencies and amplitudes of oscillation and were used for stirring some polymer solutions. Temperature differences rising due to the dissipation of the movement energy of the vibromixing process were measured and these data allowed us to calculate the consumed power. The manner in which this power varied with the frequency and amplitude of oscillations was also established. We also investigated the dependence of the power consumption on the flow regime and the characteristic equation of Kn=C.Re-m type for this process was derived.