Sharif Digital Repository

A thorough investigation on different controlled release systems were evaluated. The required devices were constructed simultaneously and the required experiments were performed. The polymeric network and membranes of poly vinyl alcohol with cross-linking agent glutaraldehyde for preparation of hyrogel system was effected. Paraquat, a type of herbicide was introduced as solute in the system. Glutaraldehyde was utilized as cross-linking agent at different concentration. Increase in the concentration of the cross-linking agent will cause a decrease in the extent of release out of the system. The effect of temperature on hydrogel adsorption demonstrates a higher adsorption at lower temperature.... 

A magnetic nanocomposite was prepared based on magnetic Fe3O4 nanoparticles entrapped into a cross-linked nitrogen rich polymer which has high loading capacity for immobilization of gold nanoparticles. The synthesized catalyst was characterized using various methods including Atomic absorption spectroscopy (AAS), Transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDX), Thermogravimetric analysis (TGA), scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET), VSM and X-ray diffraction (XRD) techniques. The catalyst was proven to be highly efficient for reduction of nitroarenes as well as Suzuki–Miyaura... 

Chitosan was crosslinked with different amount of glutaraldehyde to prepare appropriate hydrogels to be used as drug delivery system. The swelling behavior of freeze-dried hydrogels in aqueous media at different temperature and pHs has been examined. The swelling, porosity and biocompatibility behavior of samples were investigated to check effects of polymer/polymer and polymer/drug interactions on these system characteristics. Obtained experimental results illustrates that with increasing crosslinking agent from 0.068 to 0.30, swelling of the prepared samples degrees from 1200% to 600% and pore diameters change from 100 to 500 μm. To investigate systems biocompatibility in gastric... 

The current investigation was to present composite membranes with strong interfacial adhesion between top polymeric selective layer and the bottom micro-porous support layer with appropriate gas permeation behavior and practically suitable processing characteristics. To this end, a series of acrylate-terminated polyurethanes (APUs) based on poly (ethylene glycol) (PEG) with different molecular weights (Mn) of 600, 1000, 1500, 2000 and 4000 g/mol, toluene diisocyanate (TDI), and 2-hydroxyethyl methacrylate (HEMA) were synthesized. Composite membranes were prepared with UV-curable acrylate-terminated polyurethane/acrylate diluent (APUAs) as selective layer and polyester/polysulfone (PS/PSF) as... 

Cell-laden hydrogel microcapsules enable the high-throughput production of cell aggregates, which are relevant for three-dimensional tissue engineering and drug screening applications. However, current microcapsule production strategies are limited by their throughput, multistep protocols, and limited amount of compatible biomaterials. We here present a single-step process for the controlled microfluidic production of single-core microcapsules using enzymatic outside-in cross-linking of tyramine-conjugated polymers. It was hypothesized that a physically, instead of the conventionally explored biochemically, controlled enzymatic cross-linking process would improve the reproducibility,... 

A series of biopolymer-based superabsorbent hydrogels based on carboxymethyl cellulose has been prepared by free-radical graft copolymerization of acrylamide and 2-acrylamido-2-methylpropan sulfonic acid (AMPS) in aqueous solution using methylenebisacrylamide as a crosslinking agent and ammonium persulfate as an initiator. The effect of variables on the swelling capacity such as: acrylamide/AMPS weight ratio, reaction temperature, and concentration of the initiator and crosslinker were systematically optimized. The results indicated that with increasing the amount of AMPS, the swelling capacity is increased. FT-IR spectroscopy and scanning electron microscope analysis were used to confirm... 

In this research work, different devices made of glutaraldehyde cross-linked chitosan hydrogels loaded by amoxicillin, have been prepared using freeze-drying method. Effects of system parameters such as cross-linker concentration, pH, and gel structure on the morphology and release behavior of devices have been investigated using standard methods. Morphological studies were performed using SEM instrument and controlled releases are followed via spectrophotometeric method. Reaction of glutaraldehyde with chitosan has been studied using FTIR instrument. SEM micrographs have shown that with increasing cross-linker percentage in hydrogel, pore sizes increased where pore size distribution... 

In this paper, attention is paid to synthesis and swelling behavior of a superabsorbent hydrogel based carboxymethylcellulose (CMC) and polyacrylonitrile (PAN). The physical mixture of CMC and PAN was hydrolyzed in NaOH solution to yield hydrogel, CMC-poly(NaAA-co-AAm). During alkaline hydrolysis, the nitrile groups of PAN were completely converted to a mixture of hydrophilic carboxamide and carboxylate groups followed by in situ crosslinking of the grafted PAN chains. A proposed mechanism for hydrogel formation was suggested and the structure of the product was established using FTIR spectroscopy. The reaction variables affecting the swelling capacity of the hydrogel were systematically... 

The Taguchi method, a robust experimental design, was used for optimization of synthesis of a novel biopolymer-based superabsorbent hydrogel, kappa-carrageenan (K-C)-g-acrylic acid (AA)-co-2-acrylamido-2- methylpropanesulfonic acid (AMPS). The Taguchi method was applied for the experimental and standard 18 orthogonal arrays (OA) with seven factors and three levels for each factor. In the synthesis of the superabsorbent, N,N'-methylene bisacrylamide (MBA) as crosslinker, ammonium persulfate (APS) as initiator, monomer ratio (AA/AMPS), K-C concentration, Total Monomer, neutralization percent (NU), and reaction temperature were used as important factors. After analyzing with analysis of... 

A novel biopolymer-based superabsorbent hydrogel was synthesized through chemical crosslinking by graft copolymerization of partially neutralized acrylic acid onto the hydrolyzed collagen, in the presence of a crosslinking agent and a free radical initiator. The Taguchi method, a robust experimental design, was employed for the optimization of the synthesis reaction based on the swelling capacity of the hydrogels. This method was applied for the experiments and standard L16 orthogonal array with three factors and four levels were chosen. The critical parameters that have been selected for this study are crosslinker (N,N′-methylene bisacrylamide), initiator (potassium persulfate), and monomer... 

The insulation lifetime of power cables is determined by several factors. One of the more important of these is the occurrence of partial discharge (PD) at the dielectric. The ability to detect and locate a PD source is limited by attenuation of the high frequency PD pulses as they propagate through the cable. Therefore it is necessary to understand the high frequency response of such cables. Further, to enable reconstruction of PD signals as emitted a viable high frequency model for simulation is needed. This paper presents results of measurements of PD calibration pulse and high frequency sinusoid propagation in HV XLPE cables. In addition to the tests a cable model was developed using the... 

Thermal cracking is the prevalent type of distress experienced by asphalt pavements in cold regions. It is widely assumed that when thermal stresses induced in the pavement exceed the tensile strength of the asphalt surface layer, cracking occurs; however, the role of thermal fatigue should not be ignored. To better describe the low-temperature (LT) performance properties of modified asphalt binders, a new parameter, normalised tensile stress (NTS), was defined in this research. NTS values were compared with bending beam rheometer (BBR), direct tension (DT) and semi-circular bending (SCB) fracture test results. The m-value parameter of the BBR test specifies the type of asphalt binder. This... 

Thermal cracking is the prevalent type of distress experienced by asphalt pavements in cold regions. It is widely assumed that when thermal stresses induced in the pavement exceed the tensile strength of the asphalt surface layer, cracking occurs; however, the role of thermal fatigue should not be ignored. To better describe the low-temperature (LT) performance properties of modified asphalt binders, a new parameter, normalised tensile stress (NTS), was defined in this research. NTS values were compared with bending beam rheometer (BBR), direct tension (DT) and semi-circular bending (SCB) fracture test results. The m-value parameter of the BBR test specifies the type of asphalt binder. This... 

Enzymatic removal of Bisphenol A (BPA), acknowledged as an environmentally friendly approach, is a promising method to deal with hard degradable contaminants. However, the application of “enzymatic treatment” has been limited due to lower operational stability and practical difficulties associated with recovery and recycling. Enzyme immobilization is an innovative approach which circumvents these drawbacks. In this study, laccase from Trametes hirsuta was used for BPA removal. Amino-functionalized magnetic Fe3O4 nanoparticles were synthesized via the co-precipitation method followed by surface modification with (3-aminopropyl)trimethoxysilane (APTMS). The as-prepared nanoparticles were... 

In this article, we report the first multiwalled carbon nanotube-polyelectrolyte gel containing vinylimidazolium-typed ionic liquid monomer as an absorbent of less-polar or nonpolar organic solvents. To prepare such MWCNT-polyelectrolyte gel, the modified MWCNTs with polymerizable vinyl groups on their surfaces were prepared and then underwent copolymerizations with dodecyl methacrylate and vinylimidazolium in the presence of AIBN as initiator, yielding a cross-linked polyelectrolyte. In order to estimate the compatibility between the solvents and the polymers, a series of vinylimidazolium-typed ionic liquid monomers ([Cnvim][X]) with different alkyl tail length (C6, C10 and C12) and counter... 

Very fine alumina nanoparticles were loaded in novolac type phenolic resin (PF) using solution mixing method. The concentration of nanoalumina in PF was varied between 2.5 to 20 wt%. All the compounds were compression molded and then subjected to scanning electron microscopy (SEM), tensile, flexural, and dynamic mechanical analysis (DMA) tests. SEM analysis showed that the nanoalumina were dispersed uniformly at low concentrations, however, at high concentrations, dispersion was suppressed leading to agglomerates in the composites. Mechanical testing revealed that the nanoalumina had a great influence on the strength and stiffness of PF resin particularly at concentrations below 5 wt%.... 

PVDF/nanoclay nanocomposites were prepared via melt mixing method. The intercalated dispersion of the nanoclay in PVDF matrix was confirmed by XRD. According to FTIR, DSC and XRD results, the presence of nanoclay facilitated transition from α-to-β crystalline phase. Electron beam irradiation decreased the melting point of the nanocomposites. The decrease in melting point of the nanocomposites was about 11 C at 500 kGy. The crystallinity of nanocomposites increased at an irradiation dose of 100 kGy and decreased at higher irradiation doses. The extent of crosslinking of the nanocomposites increased significantly with irradiation up to 300 kGy. The nanoclay intensified the increase in yield... 

Low structure carbon black (CBN330), conductive high structure carbon black (CBXE2B) and carboxylated multiwalled carbon nanotube (MWCNT) were loaded into the blend of natural rubber (NR) and styrene butadiene rubber (SBR) at different contents up to 10 phr. Kraus plots showed that all the reinforcements interact with NR/SBR blend appropriately. However, the CBXE2B whose interfacial area is the highest showed greatest value of Kraus interaction parameter. Flory-Rhener model and effective torque value revealed that all of the reinforcements enhanced the crosslink density, among them CBXE2B showed the highest impact and MWCNT placed in the second rank. It was also shown that the cure kinetic... 

A simple method for synthesis of novel organogels based on multiwalled carbon nanotubes (MWCNTs) is reported. Three classes of organogels were synthesized by crosslinking polymerization of dodecyl methacrylate with various weight percentages of 1,4-butanediol dimethacrylate, vinyl-group-modified MWCNTs or pristine MWCNTs in the presence of 2,2-azoisobutyronitrile as initiator. In this reaction, the carbon nanotubes (CNTs) served simultaneously as an adsorbent, a comonomer and a crosslinking agent. The oil-absorbent containing CNTs showed much higher swelling capacity in oil and organic solvents compared with that without CNTs. Therefore, CNT-based organogels can be introduced as a promising... 

The present work focused on the characterization of mechanical properties of novolac phenolic resin (PF) filled with two types of clays, including modified and unmodified ones, and multiwalled carbon nanotube (MWCNT). It was found that the solution mixing method is able to disperse the nanoparticles within the PF resin appropriately. It was also shown that the unmodified clay (Closite Na+) has the highest influence on the mechanical properties possibly due to the good level of dispersion as well as the good interfacial interaction. Theoretical analysis based on the rubber elasticity theory showed that the nanoparticles influence the evolution of crosslinking density and network structure