دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و پنجم شماره 1 (پیاپی 177، فروردین و اردیبهشت 1401)

Today, the prevalence of bacterial infections and their resulting human and financial losses has led scientists constantly to seek solutions to develop knowledge in controlling these pathogenic microorganisms. Bacterial adhesion and their growth on different surfaces cause the accumulation of these microorganisms and the formation of biofilms. These developed microcolonies can grow and detach from the surface and spread infections. Therefore, the best way to prevent spreading the infections and diseases is to prevent the formation of biofilms using antimicrobial surfaces. In this regard, one of the most important tools introduced is the use of antibacterial polymer coatings. Polyurethanes have received much attention due to their unique properties such as biocompatibility, the possibility of using various raw materials, and controllable properties. In recent years, waterborne polyurethanes have been extensively studied due to less frequent use of volatile organic compounds (VOCs) in their preparations, easy fabrication, low viscosity, the possibility of spraying, high adhesion to different surfaces, high abrasion resistance, ability to disperse a variety of additives, and rapid film formation in biomedical fields such as antibacterial coatings, wound dressings, and biological products. In this review article, first, the various methods of preparing antibacterial polymer coatings are described. These methods include the use of nanostructures, combined with antibacterial polymers, and the use of antibacterial monomers. As a result, polyurethanes and waterborne polyurethanes have been developed. The following is a review of studies on the preparation of antibacterial waterborne polyurethanes using different strategies such as the addition of nanostructures, blending with antibacterial polymers, drug loading, the use of antibacterial monomers, and polymer surface modification. The products developed during these studies have been proposed for a variety of applications such as medical equipment coating, wound dressings and packaging industry.

Hypothesis:

Ultrafiltration (UF) membranes play a vital role in chemical processes through the separation of high molecular weight compounds, but suffer from a fouling phenomenon in which materials precipitate or adhere on the membrane surface; since the UF membrane feed is susceptible to the growth of microorganisms, biofouling can occur more often, which reduces the membrane performance. Some methods have been suggested to overcome the biofouling phenomenon which one of the best methods is the application of nanoparticles in the membrane.

ZnO and CuO nanoparticles and ZnO/CuO nanocomposite at three different concentrations (1, 3 and 5% by weights) were used to improve the antibacterial properties of PVC membrane. First, nanoparticles were synthesized through co-precipitation method and characterized by XRD and FTIR analyses. Then, the mixed matrix membranes were prepared and their properties were investigated in terms of permeation flux, porosity and contact angle. 

To study the antibacterial properties of the fabricated membranes, the disk diffusion method using Escherichia coli as gram-negative model was applied. The membrane containing 5% (by weight) ZnO with clear zone diameter equal to 9 mm and the membranes containing 3% (by weight) ZnO and 5% (by weight) CuO with clear zone diameter equal to 8.1 mm showed the best antibacterial activities. The results showed that the synthesized nanoparticles can improve the characteristics of the PVC membranes such as hydrophilicity (reducing contact angle from 86.28° to 67.55°) and impart antibacterial activities in the membranes. This method can be utilized to reduce the biofouling of membranes in the separation processes.

Hypothesis:

The presence of dyes in water sources has posed challenges for environmental scientists due to their high thermal and chemical stability against degradation by light, heat, and natural oxidants. The presence of dyes in water sources has not only reduced the penetration of sunlight into the water but also endangered the health of humans and living organisms. In this regard, hydrogels are effective adsorbents for the removal of dyes. In this study, carbon black nanoparticles were used to improve the removal performance of fuchsin dye by carboxymethyl cellulose grafted acrylic acid and itaconic acid copolymers hydrogel (carboxymethyl cellulose-g-poly(acrylic acid-co-itaconic acid)/carbon black nanocomposite).

Copolymer and nanocomposite hydrogels were synthesized by free radical polymerization method. The performance of their adsorption in different operating conditions was investigated in batch mode. Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and scanning electron microscopy equipped X-ray energy dispersive (SEM-EDS) were used to identify synthesized adsorbents.

The maximum removal efficiency of nanocomposite containing 5% (by weight) of nanoparticles in operating conditions of pH 7, adsorbent dose 1 g/L, initial concentration 10 mg/L and contact time 60 min was 98.76%. Kinetic analysis showed that the experimental data followed a pseudo-second-order model. Examination of the equilibrium data showed that the Langmuir model is the most suitable model for fitting the data. The maximum adsorption capacity for copolymer and nanocomposite hydrogels was 31.6036 and 33.75247 mg/g, respectively, showing the effectiveness of the addition of nanoparticles in improving the performance of the hydrogel for the removal of fuchsin dye. Finally, it can be concluded that the synthesized adsorbents have a high potential for the remediation of fuchsin dye.

Hypothesis:

Hemodialysis is a procedure in which a dialyzer is used to clean the blood from waste products such as urea. Man-made membranes are often used to make hemodialysis dialyzers. Most of the employed polymers are not well compatible with blood. Coating method with hydrophilic polymers is a very simple and effective method that is used to improve the hydrophilic and biocompatible properties of produced membranes. Polydopamine is one of the hydrophilic polymers that has been considered for its high hydrophilic properties and good adhesion to cover membranes.

The coating of the inner surface of hollow fiber membranes was applied for the first time. The polysulfone membrane was coated with polydopamine solution, injected at specified time and pressure. The structural and permeability properties of the membrane treated by this technique were compared with the untreated membrane and the membrane whose outer surface was coated with polydopamine solution.

 No statistically significant change in hydraulic permeability and pore size of hollow fiber membranes was observed after treatment at 95% confidence level. Also, studies were performed by scanning electron microscopy and X-ray energy diffraction spectroscopy techniques on the cross-sectional area of hollow fibers before and after treatments. The results of X-ray energy diffraction spectroscopy technique showed that the amount of elemental oxygen on the inner surface of hollow fibers that were internally coated with polydopamine has significantly increased. The mechanical properties of hollow fiber membranes were also evaluated. The statistical analysis of the treated and untreated membranes showed that the strength of the membrane treated by injection technique in comparison with untreated and external surface treated membranes has significantly increased at 95% confidence level.

Hypothesis:

The aim of this study was to propose a modified model for the prediction of a stress softening behavior (Mullins effect) in carbon black filled rubber compounds. A new equation was suggested for the calculation of the damage variable in the classical Ogden-Roxburgh model based on a previously developed kinetic equation. The parameters of the new model were assumed dependent on the first principal strain. The developed model was verified by comparison of the model predictions with experimental data

Four rubber compounds based on S-SBR and E-SBR reinforced by 40 and 60 phr carbon blacks were prepared and cured into rubber sheets. The rubber test specimens (ASTM D412 C) were cut and subjected to cyclic tensile tests at an extension rate of 500 mm/min. In order to show the stress softening behavior, three cycles were selected in a way that the maximum stretch at each cycle was increased consecutively. The volumetric tests were also carried out to determine the bulk modulus and Poisson's ratio. The finite element models of the mentioned tests were created for Abaqus code. The new model was implemented into Abaqus through a user-defined subroutine developed specifically for this research. An optimization algorithm developed in Isight code was employed to determine the parameters of themodel for the prepared compounds

Comparing the predicted force versus time and force versus displacement with their corresponding experimentally measured data and goodness of fitting for new model and classical Ogden-Roxburgh model revealed that the developed model has higher capability and accuracy in prediction of the mechanical behavior of the rubber compounds. Comparing the ratio of the computed errors between two models showed that the new model has higher accuracy with an average of 38%. Moreover it is found that there are good correlations between variation of the model parameters with rubber grades and filler contents.

Hypothesis:

Polymeric foams have fascinating specific properties due to their cellular and porous structure and these properties have attracted much attention in industrial and scientific societies nowadays. The variations in cellular structure of polymeric foams including expansion ratio, cell density, and cell size may affect their final properties. For this reason, it seems necessary to study the effect of process parameters on the cellular structure of polymeric foams. On the other hand, the rotational molding method is developing rapidly compared to other processing methods due to its ability to fabricate large complex hollow parts Different process parameters can affect the structural properties of polymeric foams Utilizing nucleation agents as a material parameter improves the structural properties of polymeric foams significantly in different processing methods.

The effect of adding two types of nucleating agents including talc microparticles and clay nanoparticles in different sizes on the structural properties of polyethylene foams made by rotational molding process was investigated Azodicarbonamide was used as the chemical blowing agent. Talc microparticles (1% by weight) and clay nanoparticles were added to polyethylene and foamed using rotational molding process. Cell density, cell size, and expansion ratio were investigated as structural properties.

The findings revealed that the effect of talc microparticles on increasing cell density and decreasing cell size was more significant than the effect of clay nanoparticles. Cell density of polyethylene foam was improved by 96% and 89% by adding 1% (by weight) of talc microparticles and clay nanoparticles, respectively. A 20% and 17.5% decrease in the cell size of polyethylene foam was also observed with the addition of 1% (by weight) of talc microparticles and clay nanoparticles respectively.