Sharif Digital Repository

In this study, injectable PEG-based hydrogels containing Laponite particles with mechanical and structural properties close to the natural articular cartilage are introduced. The nanocomposites are fabricated by imide ring opening reactions utilizing synthesized copolymers containing PEG blocks and nanoclay through a two-step thermal poly-(amic acid) process. Butane diamine is used as nucleophilic reagent and hydrogels with interconnected pores with sizes in the range of 100–250 µm are prepared. Improved viscoelastic properties compared with the conventional PEG hydrogels are shown. Evaluation of cell viability utilizing human mesenchymal stem cells determines cytocompatibility of the... 

Polymer quality control in an industrial scale polyethylene fluidized bed reactor has been addressed. Since online measurements of polymer properties (melt index and density) are not available, they must be controlled indirectly via other available measurements. In the present paper, two algebraic equations correlating polyethylene melt index and density with the measureable concentrations of chemical components are obtained. Having the desired polyethylene properties and using these correlations, desired concentrations of chemical components are calculated and used via corresponding control loops. By using the infrequently available polyethylene property measurements, the correlation... 

Superparamagnetic iron oxide nanoparticles with proper surface coatings are increasingly being evaluated for clinical applications such as hyperthermia, drug delivery, magnetic resonance imaging, transfection, and cell/protein separation. To enhance the applicability of magnetic nanoparticles, two main problems must be overcome. First, as the drug coats the particle surface, a significant portion of it is quickly released upon injection (burst effect). Therefore, only small amounts of the drug reach the specific site after, for example, magnetic drug targeting. Second, once the surface-derivatized nanoparticles are inside the cells, the coating is likely digested, leaving the bare particles... 

In present paper, dynamic behavior and control of a fluidized bed reactor for polyethylene production has been considered. A double active sites model for Ziegler-Natta catalysts is used for simulation of polymerization reaction. Hydrodynamic behavior of the bed is modeled using a two phase model including bubble and emulsion phases in which bubble phase has plug flow pattern with differentially variable velocity and size through the bed and emulsion phase has the CSTR flow pattern. The reactor model is validated using industrial data. Conventional PID controllers with anti-windup are considered for control purposes. It has been shown that the control system has satisfactory performances... 

Ceramic suspensions were prepared from an alumino-silicate powder, polyethylene wax (PE-wax) as binder with additions of stearic acid (SA). The ceramic powder consisted of mullite, corundum and tridymite phases. The organic binders contained 3 to 8 wt.% ethylene-vinyl acetate (EVA) and were filled with various volume fractions of ceramic powder. The yield stresses of suspensions were estimated using shear stress-shear rate data measured at 90-120 °C. The addition level of EVA was shown to have a considerable effect on the yield stress of suspensions. The effect of EVA on the flow parameters was also investigated over the temperature range of 90 to 120 °C. It was shown that the addition of 5... 

Ultrahigh-molecular-weight polyethylene (UHMWPE)/graphene nanocomposites with molecular weights as high as 3 × 106 g/mol were prepared via in situ polymerization using a bi-supported Ziegler-Natta catalytic system. Effects of [Al]/[Ti] molar ratio, temperature, monomer pressure, and polymerization time on productivity of the catalyst have been investigated. Increasing [Al]/[Ti] molar ratio from 128 to 320, increased productivity from 1667 g PE/mmol Ti.h to maximum value which was 2420 g PE/mmol Ti.h. Further [Al]/[Ti] ratio decreased the productivity. Reaction temperature effect investigation reveals that the optimal activity was obtained at 60°C. the polymerization productivity increases... 

The biodegradability rates of two different kinds of polyethylene bonded with corn and potato starch are studied in this paper. While it is usual to use soil as the environment for biodegradation, an aerated sludge tank was used in this studywhich offers a richermicrobialmediumand increases the rate of biodegradation. The biodegradability is determined by two ways: first, comparing differences in the weight change of two samples, one placed inside distilled water and the other placed in aerated sludge tank. Second test for biodegradation is by examination of FTIR spectroscopy. Through FTIR spectroscopy, the biodegradability rate and reduction in some of the existing bonds in polymer before... 

A ternary dielectric is made of high density polyethylene (HDPE) and organoclay (OC) nanocomposites, through mixing granuls of ethylene vinyl acetate (EVA). The morphological properties of nanocomposites are examined using X-ray diffraction (XRD) spectra and transmission electron microscopy (TEM) which intercalate/exfoliate morphology of clay particles. It is shown that the electrical and mechanical properties of HDPE/EVA binary blend will be enhanced significantly when OC was treated with EVA compound. The insulation material which is developed in this work can be employed to insulate the adjacent core steel sheets of a high voltage transformer  

The radical chlorination of polyethylene was carried out in perchloroethylene solvent using chlorine gas and ultraviolet photoradiation to investigate a reaction kinetics model. The recurrent structure of chloromethylene (-CHCl-) and methylene (-CH 2 -) groups and the percentage of substituted chlorine were determined using hydrogen-nuclear magnetic resonance (H-NMR) (500 MHz) spectra. A kinetics model has been proposed for this reaction in which the conversion of methylene (-CH 2 -) units to chloromethylene (-CHCl-) units was considered to be the main reaction step. The simplified version of the obtained kinetics model indicates that the reaction is first order with respect to the chlorine... 

Polyolefin blends have attracted great attention for years because of their improved physical and mechanical properties; especially when micro/nanofillers are present in the compound. Previous investigations have proven that incorporation of small amounts of nanoclay can enhance physical and mechanical properties of the polymer. This research has focused on the role of clay distribution on morphology and mechanical properties of ternary nanocomposites containing a rubbery phase. High-density polyethylene/ethylene vinyl acetate/clay (HDPE/EVA/clay) is opted as a typical model for this purpose. EVA is selected to act as both compatibilizer, because of having polar vinyl groups, and... 

A series of water-soluble ABA triblock copolymers consisting of a polyethylene glycol central block joined to two blocks of six different homopolymers have been synthesized via simple solvent-free and ecofriendly routes and characterized by FTIR and 1HNMR spectroscopy. Dispersing and slump-retaining abilities of the copolymers in cement slurries were evaluated by mini-slump spread method. Rheological measurements of samples with the best performance were carried out using a rate-controlled coaxial cylinder viscometer. The test results indicate that the dispersing power of the copolymers in cement pastes is strongly affected by the structure and degree of polymerization of the monomers  

Doxorubicin-loaded nanocarriers were produced employing folate-modified polyethylene glycol (PEG)-functionalized gold nanoparticles for targeted delivery to positive folate-receptor cancer cells. Doxorubicin and folate were, respectively, conjugated to activated-folate and activated-PEG. The conjugates formed doxorubicin nanocarrier with an average size of 12 nm in diameter. The drug release response of functionalized gold nanoparticles was characterized by an initial rapid drug release followed by a controlled release. The doxorubicin nanocarriers showed higher cytotoxic effect on folate-receptor-positive cells (KB cells) than folatereceptor-negative cells (A549 cells). Cell viability in... 

In this work, the partition coefficients of Cephalexin in aqueous two-phase systems containing PEG [poly(ethylene glycol)] 4000, 10000 and K 2HPO4, Na3Citrate (C6H 5Na3O7 5, 5H2O) have been measured. The experimental data were obtained in a wide range of temperatures, (28.2 to 37.2) °C. The effects of temperature, pH, polymer concentration, polymer molecular weight, and salt concentration on the partitioning of Cephalexin were also studied. The results showed that salt concentration has a large effect on the partition coefficient, and temperature has an almost negligible effect. The Chen-NRTL Gibbs energy model was used to correlate the experimental results. © 2009 American Chemical Society  

This study addresses the issue of using recycled materials to obtain low-cost structural products for practical applications. Through the use and re-extrusion of virgin high-density polyethylene (HDPE), the effects of the degradation level of HDPE as a matrix phase on its mechanical properties and the mechanical performance of composites produced with the degraded polyethylene have been examined. The degradation level of HDPE caused by reextrusion has been evaluated by the measurement of the melt flow index and mechanical properties of virgin and degraded HDPEs. The results indicate that the modulus and strength of HDPE significantly increase with the addition of polypropylene filled with 30... 

In this study, water activities for the ternary systems of PEG6000 + sodium citrate (Na3Cit) + H2O and PEG6000 + potassium citrate (K3Cit) + H2O have been measured using an improved isopiestic method over the entire homogeneous mixing range at 298.15 K. From these measurements, values of the vapor pressure of solutions were also determined. The experimental data for the activity of water, collected in this work, were accurately correlated with local composition based models of the NRTL, modified NRTL, Wilson and modified Wilson. The results showed that these models can accurately correlate the water activity data generated in this work. © 2007 Elsevier B.V. All rights reserved