دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و پنجم شماره 2 (پیاپی 178، خرداد و تیر 1401)

Hypothesis: The goal of the study was to focus on improving the acoustic and mechanical properties of polyurethane foams doped with rock wool fibers, at different percentages (rock wool fiber) (0-1.2% by wt), that were synthesized using the polymerization process.

In order to fabricate acoustic composites, the relationship between non-acoustical parameters (airflow resistivity, porosity, density, and percentage of reinforcing fibers) and microstructure with sound absorption coefficient (SAC) was investigated. SAC was measured using a two-microphone impedance tube in the frequency range of 63-6400 Hz according to the ISIRI 9803 standard without an air gap behind the sample. Physical structure morphology and tensile strength were investigated using field emission scanning electron microscopy (FE-SEM) and tensile strength test, respectively. Non-acoustic measurements including porosity and air flow resistance (AFR) were performed using porosimetry test (BET) test, and Archimedes method. 

The results showed that increasing the RF amount in the polyurethane foam increased the hardness of the foam surface, and the SAC increased in all frequency range on all the studied samples. The highest SAC was shown by fiber-polyurethane composite foam (2% by wt) sample in the frequency range of 2000-4000 Hz. This increase in the sound absorption coefficient is probably related to the reduction in pore size with the increase in the amount of fibers in polyurethane foam, as shown by the morphological results. The mechanical properties (tensile strength) of foams were investigated by changing the amount of reinforcing fibers. The results showed that the tensile strength of composite foams significantly improved by adding fibers. Eventually, regression analysis was performed to investigate the relationship between non-acoustic parameters (airflow resistivity, porosity, density, and percentage of reinforcing fibers) and SAC. A relatively good fit between the experimental and statistical data was obtained. The data and results of this study showed that composite foams can be used to reduce noise.

Hypothesis: Nanofibrous yarns produced from twisted strings of electrospun polymers like nylon showed acceptable mechanical properties as sutures. Using biopolymers such as lignin with interesting properties like biocompatibility, antioxidant, anti-bacterial, and drug delivery ability in the form of nanofibrous yarns could improve suture yarn properties. Nanofibrous yarns containing lignin could be used as biocompatible drug delivery suture yarn when having an acceptable strength.

Nylon nanofibrous yarn, nylon-lignin-polyethylene oxide (N/L/P) hybrid nanofibrous yarn and its drug-loaded form were produced using the electrospinning method. The electrospinning conditions were optimized and the mechanical properties of the produced yarn were compared to a nanofibrous nylon yarn. The strength of knotted hybrid yarn (square knot and surgeon knot) with three different twist levels was examined and compared with each other. The presence of lignin and drug in N/L/P nanoyarn was proved using FTIR spectroscopy. The morphology of the produced yarn, its rupture mechanism, and degradation are studied by FESEM microscopy. The degradation rate of yarn was examined in a phosphate buffer medium. Drug delivery properties and drug release mechanisms are also investigated by loading a drug in N/L/P nanoyarn.   

Statistical comparison between N/L/P and nylon nanofibrous yarn showed that there is no significant difference in their strength. The rupture test showed that the hybrid nanoyarn has a two-stage rapture compared to the single-stage rapture of nylon nanoyarn. The hybrid yarn showed a degradation percentage of 46.13% in 60 min, while the drug release from the drug-loaded yarn was about 97% after 4 h. In conclusion, the results showed that the N/L/P nanofibrous yarn can be used as a drug delivery suture with good mechanical strength and a proper drug release profile for a short period of time.

The physical properties of electrospun nanofibrous mats have a significant effect on the behavior of electrospun mat in interaction with other surfaces, as well as on its efficiency in various applications. Therefore, determining and predicting these structural properties using controllable factors in the electrospinning process are of particular importance. On this basis, in the present research each of the structural properties of nanofibrous mat, including mat porosity, diameter and porosity of fiber, were estimated using mathematical relationships. Also, the prediction and optimization of input factors and the porosity of the mat and fibers were performed using the response surface methodology (RSM).

Poly(lactic-glycolic-acid) was used to produce nanofibrous mats. After the determination and optimization of the electrospinning process factors, which influence the structural properties of nanofibrous mats, 18 types of mats were prepared. Considering the combined effect of three electrospinning factors, including solution concentration, humidity and collector linear speed, RSM and regression methods were used to optimize and model the relationship between variables and mat properties, respectively.

Based on the mathematical relationships between the input factors and the structural characteristics of the mat, it can be revealed that the concentration is the most effective factor on the fiber diameter and mat porosity, and the collection speed is the most effective factor on the fiber porosity. According to the RSM models, the optimized values for the initial factors of concentration, humidity and collection speed based on the model designed for fiber porosity are 2% (w/v), 45% and 0.4 m/s, and based on the model designed for mat porosity are 3% (w/v), 45% and 2.4 m/s, respectively. The predicted optimized values of fiber porosity and mat porosity are 0.342% and 0.989%, respectively, which are not much different from the experimental values obtained from these points. The nanofibrous mat introduced by each of these models has created the most porosity.

Hypothesis: Medicinal compounds, pharmaceutical substances and their metabolites enter the environment through hospital, domestic and pharmaceutical industries. Conventional technologies are not able to treat such wastewaters fully and therefore they are abundantly found in water. So far, various chemical, physical and biological methods have been used to remove medicinal compounds from aqueous solutions. In this research, PVDF/g-C3N4/Chitosan as a new and powerful membrane was prepared and removal of cefixime from aqueous solutions was investigated using response surface methodology (RSM).

PVDF/g-C3N4/Chitosan membrane was prepared by immersing the PVDF/g-C3N4 membrane in a solution containing different percentages of chitosan. To evaluate the efficiency of the PVDF/g-C3N4/chitosan membrane in removing cefixime, the response surface methodology was used based on the central composition design and four parameters, i.e., chitosan percentage, g-C3N4 value, pH of solution and cefixime concentration were selected as dependent variables. The quadratic model was used to calculate the four dependent variables.

The results showed that among the studied parameters, chitosan had a major effect on the structural properties of the PVDF/g-C3N4/chitosan membrane due to the conversion of polyvinylidene fluoride membrane to hydrophilic ones. According to the results, the maximum cefixime removal by the PVDF/g-C3N4/chitosan membrane was about 81.34% at a solution pH of 4.42, 3.19% chitosan, 0.11 g g-C3N4 and cefixime concentration of 42.51 mg/L. The numerical optimization results showed a slight difference between the predicted number (81.34%) and the experimentally obtained number (78.21%). Also, the high correlation coefficient (99.41%) showed that the response surface methodology has a high potential for predicting and optimizing the cefixime removal process by PVDF/g-C3N4/chitosan membrane with a small number of experiments.

Today, the lack of access to fresh water has become a serious problem for people around the world. Finding an appropriate method to solve this problem has attracted the attention of many researchers. In recent years, the well-known electrospinning technique has been used as a conventional method to prepare nanofibrous membranes.

A hydrophobic and oleophobic (omniphobic) nanofibrous membrane made of poly(vinylidene fluoride) (PVDF) was prepared by electrospinning. The surface of the nanofibrous membrane was modified using low-pressure plasma polymerization. First, the membrane surface was activated using argon gas plasma to generate free radicals on the polymer chain. Then, perfluorodecyl acrylate monomer was polymerized on the surface of nanofibers in a low-pressure plasma medium. The long-term performance of the prepared omniphobic nanofibrous membrane was evaluated in an air gap membrane distillation (AGMD) module. For this purpose, a saline solution (3.5% by wt) containing 0.2 mM of sodium dodecyl sulfate was used as the feed solution.

To prove the membrane omniphobic characteristic, the contact angle for isopropanol, engine oil, kerosene and water droplets was measured as 120°, 126°, 127°, 140°, respectively. In the AGMD module, the unmodified membrane became wet and unusable after 25 min, whereas the modified membrane maintained a flux of 4.2 L/ (m2.h) and salt rejection of 98% for a time period as long as 300 min. To be more precise, in comparison to the unmodified membrane, the long-term performance and wetting resistance of the modified membrane enhanced more than 12 times. In this research, an efficient and relatively simple technique was provided to modify the surface of electrospun PVDF fibers by low-pressure plasma polymerization of perfluorodecyl acrylate monomer. The modified membrane can be considered for water desalination using AGMD technique.

Butene-1 is in excess in the polyolefin plants of Iran. Considering the properties of isotactic polybutene-1, including high creep and environmental stress cracking resistances, excellent elastic reversibility and good chemical abrasion resistance, there is a need to localize it in Iran.

Polybutene-1 was synthesized with an industrial Ziegler-Natta catalyst. To do this, polybutene-1 was synthesized by coordination polymerization of butene-1 with the help of triethylaluminium (TEAL) cocatalyst in n-hexane. By changing the monomer pressure from 1 to 1.7 bar and hydrogen amount from 0.01 to 0.13 L a wide range of polybutene-1s with different properties was obtained.

The highest values of activity and isotacticity for 0.06 L hydrogen and 1.4 bar monomer pressure were 24.76 kgPB-1/gTi.barB-1 and 97%, respectively. An increase in hydrogen led to a decrease in weight average molecular weight. Using cyclohexylmethyl dimthoxysilane as external electron donor, samples with weight average molecular weight from 149500 to 913000 g/mol, polydispersity index from 2.49 to 4.29, MFR from 0.19 to higher than 100 g/10 min, density from 0.876 to 0.911 g/cm3 for crystalline form I, and isotacticity from 81% to 97% were synthesized. The highest polydispersity index was obtained for the sample synthesized under 1.4 bar monomer pressure and 0.01 L hydrogen. The lowest isotacticity index was related to the sample synthesized under 1 bar monomer pressure and 0.13 L hydrogen. This catalyst has the ability to produce polybutene-1 with a narrower molecular weight distribution compared to those reported in other works. Comparison of mechanical properties with those reported by other researchers showed an increase in elongation-at-break for the sample. With the expansion of operational conditions, variety of products and their commercialization will be possible.