دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و چهارم شماره 2 (پیاپی 172، خرداد و تیر 1400)

Nowadays, the use of renewable energy resources has been considered as one of the imminent issues in human life. By converting solar energy into electricity, solar cells can meet most of the needs of communities for domestic and industrial use. Meanwhile, polymer solar cells have received much attention in recent years for their acceptable performance and easy manufacturing method. Nevertheless, researchers are trying to simultaneously decrease the cost of preparation and increase efficiency. In addition to the high efficacy of polymer solar cells, their stability in the manufacturing process is a challenge. For decades, rapid advances in photovoltaic cells have strongly linked the world of polymers and photovoltaic energies. Stable solar cells can be used in a variety of applications, such as space station equipment, solar vehicles, sensors, traffic lights, clocks and watches and more. Due to their high sensitivity to environmental factors, degradability and susceptibility to oxidation, polymer solar cells are very important in performance and stability. Polymer solar cells with high sensitivity to environmental factors and configuration containing of degradable and oxidizing materials have attached much attention in the discussion of stability and performance. In the present study, effective properties in reducing the stability of polymer solar cells, including semi-stable morphology, oxygen, heat, stress, etc., will be discussed. Moreover, outstanding methods for increasing stability such as architectural manipulation and morphology of the active layer, reverse configuration, optimization of buffer layers, stable electrodes, molecular restructuring of polymers and other components, etc. are reviewed and in each section, the principal researches are briefly discussed.

Hypothesis:

 Proper dispersion of silica nanoparticles in epoxy resin leads to promising improvements in mechanical and thermal properties of nanocomposite. A comparative study of dispersion between GPOSS-modified silica nanoparticles and neat silica nanoparticles shows a measure of GPOSS efficiency in dispersion of silica nanoparticles.

Nanoparticle dispersion was investigated through polymer cumulative behavior such as rheological parameters and viscosity measurement. Using the ultrasonic technique, a pre-dispersed compound containing 20 %wt silica nanoparticles and GPOSS was first prepared. The pre-dispersed compound was then diluted to a final percentage of silica nanoparticles of 2, 5 and 10 %wt. An atomic force microscope (AFM) was also used to further investigate the dispersion of silica nanoparticles in the pre-dispersed compound.

According to the rheometry test results, all samples with pre-dispersed compound showed lower viscosity than their corresponding counterparts. It seems that the GPOSS is able to lower the composition viscosity through minimizing interfacial interactions between silica nanoparticles as well as possible interactions between epoxy chains and silica nanoparticles. In comparison with the sample prepared without pre-dispersed compound, the viscosity of the composition containing 10% (wt) silica nanoparticles was drastically reduced, i.e. from 246000 cP to 39000 cP. AFM surface images of the pre-dispersed compound represent the presence of particles with a statistical accuracy of 95% in the range of 12 nm to 20 nm, proving that the silica nanoparticles are well dispersed in GPOSS. The interesting finding of this study was that a pre-dispersed compound of GPOSS and silica nanoparticles not only improves the dispersion of silica nanoparticles and hence the final mechanical properties, but also improves the easy use through reducing the viscosity of the epoxy-based composition.

Hypothesis: 

In recent years, much attention has been paid to the use of BaFe12O19 barium ferrite magnetic material in the manufacture of polymer composite magnets. Hence, nitrile butadiene rubber-polyvinyl chloride (NBR-PVC) polymer composite magnets containing barium ferrite alloy powder BaFe12O19 with particles less than 5 microns were made with optimal properties

The effect of different amounts of barium ferrite magnetic powder in the polymer substrate on the magnetic, morphological and mechanical properties of barium ferrite polymer magnets was investigated using SEM images and VSM diagrams and tensile test.

NBR-PVC/ BaFe12O19 composite magnets containing 70 %wt NBR and 30 %wt PVC with 100 units of base rubber (phr) including 2 units of sulfur as baking agent, 4 units of zinc oxide as activator, 3 units of stearic acid as lubricant, 2 units of tetramethyl thioram disulfide (TMTD) and 2 units of mercapto-benzythiazyl disulfide (MBTS) as accelerator and barium ferrite powder BaFe12O19 were fabricated with a particle size of less than 5 microns and a combination of different percentages as a magnetic agent. Among the samples made, N-P/F80 composite magnets with a ratio of 20:80 (powder:polymer) had the highest saturation magnetism of Ms and the residual magnetization of Mr and the lowest intrinsic coercivity of Hc. As expected, the best sample in terms of tensile strength was N-P/F20 with a powder:polymer ratio of 80:20, and finally, according to all the results related to the magnetic, morphological and mechanical properties of the samples, the most suitable one in terms of good particle dispersion in the polymer substrate and suitable tensile strength and appropriate magnetic properties of N-P/F50 with 50:50 (powder:polymer) ratio was selected.

Hypothesis:

 Today, with the development of different indus tries and the disposal of untreated was tewaters, environmental pollution and pollution of water resources are increasing very rapidly. Membrane technology is an advanced and hopeful way to treat water and was tewater. Nanofiltration technology is widely used in water treatment and desalination of seawater.

The performance of thin film polyamide membranes containing unmodified and modified manganese dioxide nanotubes was inves tigated. After hydrothermal synthesis of manganese dioxide nanotubes, the inner surface of the nanotubes was modified with polydopamine, and then, their performance in thin film polyamide membranes (in terms of monovalent/divalent ions rejection and permeation flux) was inves tigated.

Unmodified and modified nanotubes were characterized by Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and X-ray diffraction analysis (XRD). In addition, the morphology and s tructure of the thin film membranes were inves tigated by FESEM tes t and the performance of the membranes was s tudied in terms of permeation flux, contact angle and rejection of sodium and copper ions. The maximum pure water flux, 18.6 L/m2h, was obtained for the membrane containing 0.10 %wt modified nanotube; an increase of 21.88% compared to the neat membrane. Creation of tiny pores on the surface of the membranes through hydrophilic nanotubes resulted in higher flux while there are extra routes through the nanotubes for water permeation. The maximum rejection of sodium ion (97.02%) for the membrane containing 0.2 %wt modified nanotubes could be related to the s tacking of the nanotubes and more spatial hindrance, reduction in the diameter of the nanotube due to the coating and permeation of water through the nanotubes.

Hypothesis: 

Nowadays, the use of mixtures of natural and synthetic polymers in the production of biological scaffolds has been considered by researchers because of their ability to achieve the desired properties.

Nanofibers from polylactic acid (PLA) and nanofibrillated chitosan/zinc oxide nanoparticles (CS/ZnO) with three different blend ratios of 1:1, 2:1 and 1:0 were fabricated by electrospinning method. In order to reduce the number of experiments and thus reduce the cost of materials and time, nine different experiments were performed using Taguchi test design method with three factors: PLA concentration (PLA 7, 9 and 11% by wt), CS/ZnO concentration (5, 10 and 20% by wt) and three different CS/ZnO ratios of 1:1, 2:1 and 1:0. The contact angle and morphology of the produced scaffolds were evaluated using scanning electron microscopy (SEM).

The results of scanning electron microscopy showed that with increasing PLA concentration, the beads and spindle-like morphologies are lost and the fibers are almost smooth and uniform. The results showed that by increasing the CS/ZnO concentration from 5% to 20%, the diameter of nanofibers first decreased and then slightly increased. The contact angle of fabricated samples decreased with increasing CS/ZnO concentration from 5% to 10%. Also from the samples obtained by Taguchi method, nanofiber sample containing PLA (7%, CS/ZnO 2: 1) with CS/ZnO concentration of 10%, due to having a smaller diameter (345±30 nm), very thin structure and lower contact angle (101°) was reported as the optimal sample. The contact angle, morphology and surface roughness for the optimum sample were examined and the surface roughness for the optimal sample was about 178 nm. Cell culture studies on the optimal sample was successfully performed.

Hypothesis: 

b-Nucleation in synergy to rubbery phase of impact polypropylene copolymer (b-IPC) leads to enhanced impact strength at low temperature. The extent of crystallinity is a major factor affecting the mechanical performance and impact strength. An important step to develop the application of this polymer on industrial scale is to study its crystallization kinetics especially in non-isothermal mode which is more closely related to industrial processes. For this purpose, the effect of beta nucleating agent concentration on the non-isothermal crystallization kinetics of µ-IPC has been investigated in this article by theoretical models.

Non-isothermal melt crystallization kinetics of b-IPC samples with two different amounts of calcium pimelate as the beta nucleating agent, prepared in solution blending method, was investigated at various heating rates of 1, 10 and
25°C/min using differential scanning calorimetry.

The results showed that the total crystallinity improved by increasing the content of b-nucleating agent (b-NA). Also, increasing the cooling rate and increasing the concentration of the nucleating agent were in favor of beta crystal formation. On the other hand, the results of calculating the half-time for crystallization, changes in conversion rate with relative crystallization, Mo's analysis and the evaluated activation energy based on Kissinger method showed that the higher the share of beta crystal and the lower the share of alpha, the crystallization kinetics of b-IPC slowed down. Therefore, increasing the concentration of beta nucleating agent reduces the rate of crystallization of b-IPC. The Ozawa model was not accurate enough due to the presence of secondary crystallization, while the Mo's analysis was well able to elucidate the effect of the concentration of the nucleating agent on the crystallization kinetics.