نشریه پژوهش های کاربردی مهندسی شیمی - پلیمر
سال چهارم شماره 3 (پیاپی 13، پاییز 1399)

Research subject:

 The sensitivity of electrical conductivity of rubber/conductive filler composites against swelling strains is a phenomenon that can lead to the creation of sensors to detect the type or leakage of hydrocarbon liquids. In the swollen conductive composites, the variation of filler network structure reduces the Statistical frequency of the tunneling and interconnection of conductive particles. This behavior can be a sign for a solvent or hydrocarbon fuel detector system in a flexible sensors.

Research approach:

 In this study, nitrile rubber/graphite composite samples with several concentrations (20, 30, 40, 50, 60, 70 and 80phr) of graphite particles were prepared and their electrical characteristics were measured. The changes in the electrical resistance of nitrile rubber /graphite samples were investigated based on increasing the content of graphite particles, immerse to toluene, and repeating the period of the swelling/recovery process for each sample.

The sensitivity of composites with higher concentrations than the percolation threshold (53.5phr of graphite particles) to the conductivity changes due to the swelling phenomenon is appropriate for use in the sensor. Also, incremental changes in the electrical resistance of the samples immersed in the toluene solvent were measured and it was observed that all the samples were eventually converted to electrical insulation. In order to study the repeatability performance of sensor, samples with 60, 70 and 80phr of filler were swelled and recovered for three periods, which is less than the conductivity of the sample before the second and third swelling process compared to the conductivity before the first one. This difference is very small in the sample containing 80phr of graphite particles. The trend of change in electrical resistance is significantly different in the second swelling process compared to the primary swelling. But there is little difference between the third swelling process and the second one. This phenomenon has occurred for all three samples, which can be observed to be similar to Mullins effect.

Research Subject:

 Poly(dimethylsiloxane) (PDMS) is a silicone polymer that nowadays despite unique characteristics and high application potential of its microparticles, their preparation via bulk emulsification methods is a main challenge due to the limitations in mixing process, high viscosity and low surface energy of PDMS that make impossible accurate  control of final obtained particles. In the present work, size-controlled PDMS microparticles were prepared from a high-viscosity material.

Research Approach: 

PDMS microparticles were obtained by using glass capillary co-flow microfluidic device. The designed microfluidic device is facile, inexpensive and reusable and facilitated preparation of the high-viscosity PDMS microdroplets. Stabilizing the oil-in-water emulsion was obtained by optimizing the bath components and curing process that resulted in monodisperse and spherical PDMS microparicles. Effect of the some important adjustable parameters such as microchannel diameter and flow rate on the flow regimes and microparticles polydispersity were investigated by means of optical microscopy and scanning electron microscopy.

Results showed a dripping regime for producing monodisperse microparticles at low flow rates of the continuous phase and monodisperse microparticles from it. On the contrary, microparticles obtained from jetting regime are more polydisperse and smaller in comparison with dripping regime. By reducing the diameter of inner microchannel, microparticles with a diameter of 1.83 µm were obtained. Using the designed technology, uniform nanocomposite PDMS/ZnO microparticles 318 µm in diameter containing 15% ZnO were obtained from an oil phase viscosity of 7550 mPa.s. Therefore by an optimized and facile method, size-controllable uniform microparticles can be prepared that are proposed for various applications including drug delivery, bioengineering and electronic industry.

Metformin enhances insulinchr('39')s effect and increases cells’ sensitivity to insulin. In this paper, nanocomposite was designed and used in the metformin release system, which was able to release the required drug in a controlled manner. In this research, nanoparticles of zinc oxide (ZnO) were prepared via the sol-gel method. The experimental design central composite response surface method was applied for the optimization of the nanoparticles based on varied variables such as the weight of zinc acetate (gr) (X 1) and the volume of triethanolamine (ml) (X2). The particle size of the optimized nanoparticle was reported to be 28 ± 21.27 nm; zeta potential and PdI were 25.54 ± 1.64 mV, 0.168 ± 0.05 respectively. The chitosan polymer was used to improve environmental compatibility and increase drug release control; finally, metformin was loaded on the optimized nanocomposite. Structural properties were analyzed using scanning electron microscopy (SEM) X-Ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and Dynamic Light Scattering (DLS). The SEM images showed that the average nanocomposite size was 40 nm. The results of XRD patterns and SEM images were also consistent with each other and the average particle size was the same. Infrared spectrophotometry showed the presence of chitosan used to coat nanoparticles on their surfaces and confirmed the loading of metformin. An in-vitro metformin release from the nanocomposite was conducted in PBS (pH=7.4) and analyzed by a spectrophotometer at 233 nm. Metformin has a high solubility in water, and since it is difficult to prepare a slow release form of high-solubility drugs, the aim of this study was to design a slow-release formulation of metformin with a suitable profile that could control release without explosive release for up to 120 hours.

Research Subject: 

The conversion of anthropogenous CO2 gas into value-add chemicals known as solar fuel technology attracted much consideration from the beginning of the 21st century owing to the potential of this technology in solving the climate change and energy shortage issues.

Research Approach:

 In the current study, Bismuth and copper modified TiO2 were prepared using sol-gel and wet impregnation method in order to investigate as a catalyst for photocatalytic conversion of carbon dioxide into renewable methane.  

The results of X-ray diffraction analysis, Field emission scanning microscope images and Transmission electron microscope images demonstrated that titanium dioxide nanoparticles with 20 nm in size were synthesized that after the addition of bismuth, the size of particles became smaller. Also, using energy dispersive x-ray analysis and elemental mapping technique, it was determined that the bismuth and copper were uniformly inserted in the prepared nanoparticles. Diffuse reflectance spectroscopy showed that the bandgap became smaller in bismuth and copper-containing samples, which resulted in visible light absorption. In addition, photoluminescence spectroscopy showed an impressive decrease in the rate of electron-hole separation in the prepared nanocomposite. The result of CO2 photoreduction experiments revealed that the incorporation of 3 wt% Bismuth and 1.5 wt% copper into the structure of TiO2 would increase the amount of methane production to 7.6 times greater than bare TiO2. This superior activity for methane generation could be related to the ability of bismuth compounds in adsorption and activation of carbon dioxide molecules and also the efficient separation of charge carriers given by copper. Additionally, the smaller particle size and increase in the surface area had also a positive effect on the CO2 reduction enhancement.

Research subject:

 It is not an easy task to get a suitable model of polymerization due to complex mechanism and kinetic of such processes. Polymerization temperature, as an intermediate variable between determining final polymer properties, is a good selection to be controlled. Fuzzy logic has ability to be applied to processes with unknown or less informed dynamics.

Research approach:

 In this research, control of semi batch poly(ethylene terephthalate) reactor temperature was studied. To do so, error and error variation were calculated using measured reactor temperature. Error and error variation were fuzzified using triangular membership functions. Five and three fuzzy sets were introduced to fuzzify error and error variation, respectively. Hence, fifteen rules were defined. Five fuzzy sets were defined to quantify these fifteen rules. Weight average defuzzification method was applied to calculate necessary heat to the reactor. Poly(ethylene terephthalate) was synthesized in a semi batch reactor based on a two steps method. It is possible to monitor temperature, pressure, rotation speed and mixing torque in this set up.

Produced water during esterification determines reaction advancement. In polycondensation step, mixing torque determines end of the process. Linguistic based fuzzy rules were applied to both steps. Reference temperatures were 230oC and 260oC, respectively. Reactor temperature was controlled with 1-2oC precision. Control logic was applied using C#.net real time programming.

Research subject: 

The rice husk is the coating on a rice grain and a by-product of the rice milling process. In this study, the extraction of amorphous silica from this agricultural residue by thermal as well as acid/thermal treatment method was studied.

Research approach:

 The process was designed as follows: after burning the paddy in the open field, the obtained ash was washed with acid followed by drying. Finally, the amorphous silica was obtained by placing the prepared powder in an electric furnace (acid/thermal treatment). Also, a sample of silica was produced by eliminating the acid treatment step (thermal treatment). Afterward, the obtained silica powder was employed in a conventional passenger radial tire belt formula instead of commercial precipitated one, and whole the physical-mechanical properties, including rubber-to-wire adhesion force, were studied under normal and aging conditions.

The results of the XRD demonstrated that the silica produced in both methods were amorphous. The XRF analysis also showed that the purity of amorphous silica were 98.6% and 93.9% for the sample produced by acid/heat treatment and the heat treatment, respectively. The results of the tire test showed that the rubber-to-wire adhesion decreased slightly under normal conditions in the presence of new silica samples, but the same property under the timed conditions for the new silica samples was better than commercial precipitated silica. Other properties of the rubber compound did not change significantly in the presence of new silica grades. As a result, it can be said that rice husk has a potential to produce suitable silica for use in blend of radial tire belt.

Research subject: 

Superabsorbents are hydrophilic hydrogels that can accommodate large amounts of water in their three-dimensional structures and have wide applications in various sciences such as pharmaceuticals, medicine, and agriculture. These materials are hydrophilic polymers that are physically or chemically cross-linked. Conversion and swelling ratio of synthesized hydrogels are two counter effects. Therefore, determining the appropriate conditions for polymerization to achieve optimal properties and swelling rate of hydrogels is a challenge for researchers.

Research approach:

 In this study, optimizing the synthesis conditions of semi-interpenetrating poly (acrylic acid)/xanthan hydrogels, the response surface methodology (RSM) was used by Box-Behnken design (BBD). The variables of this method were the molar ratio of the cross-linking agent (X1), the weight percentage of xanthan gum (X2) as the reaction medium, and the amount of initiator (X3), each of which was considered at three levels. The evaluated responses in RSM were the rate of polymerization conversion (Y1) and the rate of swelling (Y2) of the hydrogels in the water.

Based on the 17 experiments proposed by RSM (BBD), the cross-linker, xanthan gum, and initiator were combined and radical polymerization was performed into silicone molds at 65 ° C. The results of ANOVA analysis showed that the data error of this study was small and the coefficient of determination (R2) of both proposed models for the responses Y1 and Y2 was higher than 0.9. The 46 experiments proposed for the optimal point by RSM (BBD) with the desirability of more than 50% indicate the synthesis of hydrogels that have both a good conversion rate and an optimal amount of swelling. For example, by 13% of cross-linking agent, 0.043 g of initiator and 1% wt. the solution of xanthan, hydrogels with a 95% conversion rate, and 102% water uptake were prepared. These hydrogels can be used in a variety of fields, including the treatment of colored wastes in factories, agriculture, pharmaceutical systems, medical attractions, and more.

Research subject: 

Magnesium ethoxide is a metal alkoxide used as a support for preparation of Ziegler-Natta catalyst. This important material which is used in HDPE production plants is not produced in Iran. It forms a complex with the catalyst that results in increase of the number of the reacting transition metal atoms inside it. Therefore the catalyst activity increases. The chemical reaction between magnesium and ethanol, in presence of iodine, results in magnesium ethoxide production.

Research approach: 

In this work, by performing analyses such as thermal gravimetric analysis (TGA), BET and scanning electron microscopy (SEM), the effects of reaction conditions such as iodine/magnesium, ethanol/magnesium, temperature and mixer speed on morphology and characteristics of magnesium ethoxide were investigated.

By using Iodine, proper morphology of product was obtained. The mixer rotation speed didnchr('39')t affect the reaction time. The particle size of the product was dependent on the magnesium amount and particle size and mixer speed. Increasing the rotation speed of the mixer at high amount of magnesium (low ethanol/magnesium) led to more collision of the particles and therefore finer product particles. Reaction at temperatures as low as 60 ₒC led to formation of fine particles with undesirable flake-like morphology. Magnesium with two average particle sizes (420 and 840μm) was used. It was shown that synthesis with magnesium of 840 μm(FW40) led to a sample similar to the commercial one with appropriate specific surface area. Lowering the temperature from 110 to 100 ₒC and reflux of ethanol at boiling point resulted in higher specific surface area.