Search for: molecular-weight
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    Rheological measurement of molecular weight distribution of polymers

    , Article e-Polymers ; Volume 13, Issue 1 , 2013 , Pages 217–228 ; 16187229 (ISSN) Khak, M ; Ahmad Ramazani, S.A ; Sharif University of Technology
    This paper has described a method to obtain the molecular weight distribution (MWD) of polymeric materials from their rheological data. The method has been developed for linear polymers with log normal molecular weight distribution. The rheological data required to obtain the molecular weight distribution are the shear storage modulus,G' (ω), and shear loss modulus,G' (ω) , extending from the terminal zone to the plateau region. For determining the molecular weight average, the method uses the relationship between stress moduli and relaxation spectrums, with the equation that connects dynamic rheological data with molecular weight distribution, and so it is not necessary to achieve the... 

    Correlation between rheological and mechanical properties of black PE100 compounds - effect of carbon black masterbatch

    , Article Express Polymer Letters ; Volume 11, Issue 8 , 2017 , Pages 622-634 ; 1788618X (ISSN) Pircheraghi, G ; Sarafpour, A ; Rashedi, R ; Afzali, K ; Adibfar, M ; Sharif University of Technology
    BME-PT and GTE  2017
    Black PE100 compounds were prepared using a co-rotating twin screw extruder by addition of carbon black masterbatches containing 35-40 wt% carbon black and different polymer carriers to a pipe grade PE100 material with bimodal molecular weight distribution. Different properties of carbon black masterbatches and PE100 black compounds were evaluated using thermal, rheological and mechanical tests. Rheological results indicated an inverse correlation between melt flow index (MFI) of masterbatch samples and storage modulus, complex viscosity and shear viscosity of black compounds, while flow instabilities of compounds were also postponed to higher shear rates. TGA indicated that masterbatch with... 

    Role of Molecular Weight and Molecular Weight Distribution on Weldability and Joint Strength of Polypropylene by Hot Plate Welding

    , M.Sc. Thesis Sharif University of Technology Azhdari, Moein (Author) ; Kokabi, Amir Hossein (Supervisor) ; Bagheri, Reza (Supervisor)
    In this study, role of molecular weight and Molecular Weight Distribution (MWD) on joint strength of polypropylene was investigated by hot plate welding. Standard tensile specimens of three different co-polypropylene with low, medium and high Melt Flow Index (MFI) values (MR230C, 440L and 548R respectively) were injected and welded after cutting. Hot plate welding device was used to join specimens. Melt Flow Index and dynamic rheology tests were employed in order to study the rheological behavior of polymers melt. Furthermore tensile test was done to investigate joint strength of specimens at 150, 175 and 200 ͦ C. It was observed that in constant temperature, increasing viscosity (typically... 

    Fabrication of sintered porous polymeric materials: effect of chain interdiffusion time on mechanical properties

    , Article Polymer International ; Volume 67, Issue 4 , 2018 , Pages 422-430 ; 09598103 (ISSN) Salari, M ; Pircheraghi, G ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    In this study, sintered porous polymeric materials made of high density polyethylene (HDPE) were fabricated through controlling the chain interdiffusion time at the transition temperature of semicrystalline and melt states. At this intermediate state, where both crystalline and amorphous phases coexist, the interfacial welding of HDPE particles is facilitated thanks to interdiffusion caused by chain relaxation phenomena. Then, by assuming a spherical shape and a cubic packing configuration of particles, a geometrical model was developed to predict porosity variations as sintering progresses. Moreover, the HDPE used, as a broad molecular weight distributed polymer, has different family chains... 

    Molecular weight control of a batch suspension polymerization reactor

    , Article Iranian Polymer Journal (English Edition) ; Volume 11, Issue 6 , 2002 , Pages 403-411 ; 10261265 (ISSN) Shahrokhi, M ; Fanaei, M. A ; Sharif University of Technology
    This paper concerns molecular weight control of a batch polymerization reactor where suspension polymerization of methyl methacrylate(MMA) takes place. For this purpose, a cascade control structure with two control loops has been selected. The slave loop is used for temperature control using on-line temperature measurements, and the master loop controls the average molecular weights based on its estimated values. Two different control algorithms namely proportional-integral(PI) controller and globally linearizing controller (GLC) have been used for temperature control. An estimator, which has the structure of an extended Kalman filter (EKF), is used for estimating monomer conversion and... 

    A new model for estimation of the critical properties of alkanes

    , Article Theoretical Foundations of Chemical Engineering ; Volume 39, Issue 1 , 2005 , Pages 78-80 ; 00405795 (ISSN) Pazuki, G. R ; Mokhatab, S ; Jahanshahi, V ; Sharif University of Technology
    A simple model is proposed to estimate the critical properties of alkanes-temperature, pressure, and volume. This model is dependent on normal boiling and molecular weight of hydrocarbons. The model has been expanded based on a Taylor series in the form of a polynomial function of normal boiling. Because methane has the simplest structure among hydrocarbons, this model has been calculated around methane. The coefficients of this model were assumed in the form of a linear function of molecular weight. These parameters can be obtained from regression between experimental results and results from this model. By a comparison of this model and previous models, it is shown that this model is... 

    SiO 2 -covered graphene oxide nanohybrids for in situ preparation of UHMWPE/GO(SiO 2 ) nanocomposites with superior mechanical and tribological properties

    , Article Journal of Applied Polymer Science ; Volume 136, Issue 31 , 2019 ; 00218995 (ISSN) Haddadi, S. A ; Saadatabadi, A. R ; Kheradmand, A ; Amini, M ; Ramezanzadeh, M ; Sharif University of Technology
    John Wiley and Sons Inc  2019
    The modified Hummer technique was used in the preparation of graphene oxide (GO) nanosheets, and then SiO 2 decorated GO [GO(SiO 2 )] nanosheets were synthesized via the sol–gel method. Then, ultrahigh-molecular-weight polyethylene (UHMWPE) nanocomposites loaded with 0.5, 1, 1.5, and 2 wt % of GO(SiO 2 ) were prepared using magnesium ethoxide/GO(SiO 2 )-supported Ziegler–Natta catalysts via the in situ polymerization. Morphological study of the prepared polymer powders was assessed using field-emission scanning electron microscopy, which showed that GO(SiO 2 ) nanohybrids have been uniformly dispersed and distributed into the UHMWPE matrix. Also, the neat UHMWPE and its nanocomposites were... 

    Characterization of basic properties for pure substances and petroleum fractions by neural network

    , Article Fluid Phase Equilibria ; Volume 231, Issue 2 , 2005 , Pages 188-196 ; 03783812 (ISSN) Boozarjomehry, R. B ; Abdolahi, F ; Moosavian, M. A ; Sharif University of Technology
    A set of conventional feedforward multilayer neural networks have been proposed to predict basic properties (e.g., critical temperature (T c), critical pressure (Pc), critical volume (V c), acentric factor (ω) and molecular weight (MW)) of pure compounds and petroleum fractions based on their normal boiling point (T b) and liquid density at 293 K. The accuracy of the method is evaluated by its application for basic property estimation of various components not used in the development of the method. Furthermore, the performance of the method is compared against the performance of the other alternatives reported as the most accurate and general methods for basic property prediction. Results of... 

    Effects of nano graphene oxide as support on the product properties and performance of Ziegler-Natta catalyst in production of UHMWPE

    , Article Polymers for Advanced Technologies ; Volume 26, Issue 4 , 2015 , Pages 315-321 ; 10427147 (ISSN) Kheradmand, A ; Ramazani, S. A ; Khorasheh, F ; Baghalha, M ; Bahrami, H ; Sharif University of Technology
    John Wiley and Sons Ltd  2015
    The synthesis of mono- and bi-supported Ziegler-Natta catalysts using magnesium etoxide Mg(OEt)2 and graphene oxide (GO) as catalyst support for production of Ultra High Molecular Weight Polyethylene (UHMWPE) is reported in this investigation. Nano-graphene oxide was prepared by the modified Hummer's method and its structure was analyzed by XRD and FTIR indicating the presence of hydroxyl groups on graphene oxide and the formation of an exfoliated structure. The activity of TiCl4/Mg(OEt)2, TiCl4/Mg(OEt)2-GO, and TiCl4/GO catalysts in terms of grams of PE produced per mmol of Ti per hour was experimentally obtained for catalysts with different ratios of co-catalyst (triisobutylaluminium) to... 

    Layer-by-layer self assembly deposition and characterization of TiO 2 nanoparticles by using a short chain polycation

    , Article EPJ Applied Physics ; Volume 48, Issue 1 , 2009 , Pages 10602p1-10602p7 ; 12860042 (ISSN) Rahman, M ; Taghavinia, N ; Sharif University of Technology
    Using low molecular weight polyethylenimine (PEI), transparent thin films of TiO2 nanoparticles were prepared by layer-by-layer self assembly method. UV-visible spectrophotometry was employed in a quantitative manner to monitor the adsorbed mass of TiO2 and PEI after each dip cycle. The adsorption of both TiO2 and PEI showed a saturation dip time of 10 min. The effect of dip time on the growth mode and surface morphology was investigated by scanning electron microscopy (SEM) and non-contact atomic force microscopy (AFM). It was found that growth proceeds in the form of laterally broad islands in case of short dip times, and taller but laterally smaller islands in case of longer dip times. A... 

    Cobalt -mediated radical polymerization of vinyl acetate in a packed column system: simultaneous effective control of molecular weight, separation, and purification

    , Article Journal of Polymer Research ; Volume 29, Issue 12 , 2022 ; 10229760 (ISSN) Sabzevari, A ; Dadkhah, A. S ; Kohestanian, M ; Mahdieh, A ; Semsarzadeh, M. A ; Sharif University of Technology
    Springer Science and Business Media B.V  2022
    The simultaneous control of the molecular weight, separation, and purification of polyvinyl acetate was achieved using a cobalt-mediated radical polymerization (CMRP) in a packed column with silica gel particles (PC-CMRP). The controlled radical polymerization of VAc in the packed columns was evaluated from the linear time dependence of Ln[M]0/[M], linear increase of molecular weight with the increase in conversion, and narrow molecular weight distribution. PC-CMRP method was used to produce high-purity polymers with controlled molecular weight and narrow molecular weight distribution without requiring additional purification steps. The high ability of silica gel particles to adsorb free... 

    Synthesis and Characterization of High Molecular Weight Polyacrylamide and Cationic Polyacrylamide

    , M.Sc. Thesis Sharif University of Technology Abdollahi Banouei, Zohreh (Author) ; Frounchi, Masoud (Supervisor) ; Dadbin, Susan (Supervisor)
    In many industrial processes there is an urgent need for flocculation of suspensions that can’t flocculate easily through the time so flocculants are wildly used in these industries. Polymeric flocculants because of less needed dose are economically used. Polymeric flocculants divided to three categories: nonionic, anionic and cationic those are almost from polyacrylamide group. Studying mechanisms of flocculation, one of the main factors that enhance flocculation is molecular weight of polymer. Hence one of the goals of this work is to improve molecular weights of synthesized polymers as much as possible that is followed by viscometery, NMR, DSC and FTIR studies and ended with jar test.... 

    Optimization of uhmwpe/graphene nanocomposite processing using ziegler-natta catalytic system viaresponse surface methodology

    , Article Polymer - Plastics Technology and Engineering ; Vol. 53, Issue. 9 , June , 2014 , pp. 969-974 ; ISSN: 03602559 Shafiee, M ; Ramazani, S. A. A ; Sharif University of Technology
    Optimization of operational conditions for the preparation of Ultrahigh-molecular-weight polyethylene (UHMWPE)/Graphene nanocomposites with Ziegler-Natta catalyst was carried out via response surface methodology (RSM). This study deals with the optimization of process variables to optimize the productivity and molecular weight. A three-factor, three-level Box-Behnken design with temperature (X1), monomer pressure (X2), and [Al]/[Ti] molar ratio (X3) as the independent variables were selected for the study. The dependent variables were productivity and molecular weights of the final nanocomposites. It was developed by using the three parameters at three levels including 50, 60, and 70°C for... 

    Thermal degradation behavior and kinetic analysis of ultra high molecular weight polyethylene based multi-walled carbon nanotube nanocomposites prepared via in-situ polymerization

    , Article Journal of Macromolecular Science, Part A: Pure and Applied Chemistry ; Volume 49, Issue 9 , 2012 , Pages 749-757 ; 10601325 (ISSN) Shariati, J ; Saadatabadi, A. R ; Khorasheh, F ; Sharif University of Technology
    T&F  2012
    Thermal degradation behavior of multi-wall carbon nanotubes (MWCNTs)/ultra high molecular weight polyethylene (UHMWPE) nanocomposites, with different nanotubes contents (0.5, 1.5 and 3.5 wt%) prepared via in-situ polymerization technique have been investigated using thermal gravimetric analysis (TGA). TGA spectra revealed that these nanocomposites had enhanced thermal stability and no significant mass loss (<0.4 wt%) occurred up to 350°C. Thermal degradation of these UHMWPE/MWCNT nanocomposites was investigated in terms of parameters such as the onset temperature of degradation (T 10), the decomposition temperature at 50% wt loss (T 50), the degradation temperature of maximum rate of the... 

    High performance Dyneema® fiber laminate for impact resistance/macro structural composites

    , Article Journal of Thermoplastic Composite Materials ; Volume 25, Issue 4 , 2012 , Pages 403-414 ; 08927057 (ISSN) Karbalaie, M ; Yazdanirad, M ; Mirhabibi, A ; Sharif University of Technology
    UHMWPE composite materials are increasingly used in armors design due to their high strength-to-weight ratios and energy absorption capacities. In this study the effect of production parameters upon the terminal ballistic properties of UHMWPE composite were examined under different conditionings. The composite armor plate laminates were produced by hot pressing with three different pressing times from 10-30 minutes and the laminates conditioned at +115, +125, and +135°C. The molding temperature of SK66 fiber composite has the main direct effect on the ballistic absorption energy, so the relation of molding temperature with the adhesive bonding force between layers, the thickness of the... 

    Experimental investigation of asp flooding in fractured heavy oil five-spot systems

    , Article 74th European Association of Geoscientists and Engineers Conference and Exhibition 2012 Incorporating SPE EUROPEC 2012: Responsibly Securing Natural Resources, 4 June 2012 through 7 June 2012 ; 2012 , Pages 3924-3928 ; 9781629937908 (ISBN) Sedaghat, M. H ; Ghazanfari, M. H ; Masihi, M ; Rashtchian, D ; Sharif University of Technology
    European Association of Geoscientists and Engineers, EAGE  2012
    Although alkaline-surfactant-polymer flooding is proved to be efficient for oil recovery from heavy oil reservoirs, the displacements mechanism/efficiency of this process in fractured systems needs to more discussion, especially in five-spot patterns. In this work, several ASP flooding test were performed on fractured micromodels which were initially saturated with heavy oil at constant flow rate and different fracture geometrical characteristics conditions. The ASP solutions are constituted from 5 polymers i.e. four synthetic polymers include three hydrolyzed polyacrylamide with different molecular weight as well as a non-hydrolyzed polyacrylamide and a biopolymer, 2 surfactants i.e. a... 

    Amine-functionalized magnetic nanocomposite particles for efficient immobilization of lipase: effects of functional molecule size on properties of the immobilized lipase

    , Article RSC Advances ; Volume 5, Issue 42 , Apr , 2015 , Pages 33313-33327 ; 20462069 (ISSN) Esmaeilnejad Ahranjani, P ; Kazemeini, M ; Singh, G ; Arpanaei, A ; Sharif University of Technology
    Royal Society of Chemistry  2015
    A cost-effective design of reusable enzyme-functionalized particles with better catalytic activity is of great scientific interest due to their applications in a wide range of catalytic reactions in several industrial processes. In this work, a systematic approach for preparing amine-functionalized magnetic nanocomposite particles through the surface modification of core/shell type Fe3O4 cluster@SiO2 particles by the small molecules of 3-(2-aminoethyl)aminopropyltrimethoxysilane (AAS) or the large molecules of polyethyleneimine (PEI) with two different molecular weights, as the support materials for enzyme immobilization, has been demonstrated. The functional... 

    Partitioning of l-lysine monohydrochloride in aqueous two-phase systems of poly(ethylene glycol) and dipotassium hydrogen phosphate or trisodium citrate 5-hydrate

    , Article Journal of Chemical and Engineering Data ; Volume 55, Issue 9 , 2010 , Pages 3005-3009 ; 00219568 (ISSN) Mirsiaghi, M ; Pazuki, G ; Vossoughi, M ; Alemzadeh, I ; Sharif University of Technology
    The partition constants of l-lysine HCl were measured in polymer-salt aqueous two-phase systems. These systems contain poly(ethylene glycol) with a nominal molecular weight of 4000 or 10000 and two different salts (dipotassium hydrogen phosphate or trisodium citrate 5-hydrate). The experimental data were obtained at temperatures of (293.15, 298.15, and 303.15) K. The effects of temperature, pH, polymer and salt concentrations, polymer molecular weight, and salt type on the partitioning of l-lysine HCl were also studied. The results showed that salt concentration has a significant effect on the partition constant while temperature has less effect. The Diamond and Hsu model was used to... 

    A study on plant polymer: pectin production and modification

    , Article International Journal of Engineering, Transactions B: Applications ; Volume 23, Issue 2 , 2010 , Pages 107-114 ; 1728-144X (ISSN) Alemzadeh, I ; Sharif University of Technology
    Pectin from two different plant sources: apple and sugar beet was studied. Apple pectin was modified by chemical treatments such as: acid, alkali and ammonia, so as to obtain an ester level equal to or less than 50 %, which is described as low methoxyl (LM) pectin. LM pectin form gels with significant characteristic. In this study, de-esterification of apple pectin with acid treatment resulted in gel specification with higher molecular weight and viscosity. Acid treatment resulted in pectin with average molecular weight of 32000 Dalton. Pectin was extracted from sugar beet pulp by acid and alkali treatments. The quality of gel formation and water uptake was improved using sugar source... 

    Preparation and investigation of tribological properties of ultra-high molecular weight polyethylene (UHMWPE)/graphene oxide

    , Article Polymers for Advanced Technologies ; Volume 27, Issue 9 , 2016 , Pages 1172-1178 ; 10427147 (ISSN) Bahrami, H ; Ramazani S. A., A ; Shafiee, M ; Kherad Mand, A ; Sharif University of Technology
    John Wiley and Sons Ltd 
    This article has been devoted to investigation of the tribological properties of ultra-high molecular polyethylene/graphene oxide nanocomposite. The nanocomposite of ultra-high molecular polyethylene/graphene oxide was prepared with 0.5, 1.5, and 2.5 wt% of graphene oxide and with a molecular weight of 3.7 × 106 by in-situ polymerization using Ziegler–Natta catalyst. In this method, graphene oxide was used along with magnesium ethoxide as a novel bi-support of the Ziegler–Natta catalyst. Analyzing the pin-on-disk test, the tribological properties of the nanocomposite, such as wear rate and mean friction coefficient, were investigated under the mentioned contents of graphene oxide. The...