دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و یکم شماره 1 (پیاپی 153، فروردین و اردیبهشت 1397)

Hypothesis: The separation of carbon dioxide from methane is an important process in chemical industry and gas refineries from both economic and environmental perspectives. The conventional method for natural gas sweetening involves physical absorption by amines, but it has high operational cost. In this study, dual-layer mixed-matrix membranes based on poly(ether-b-amide), with trade name Pebax, containing zeolitic imidazolate frameworks-8 (ZIF-8) nanoparticles were synthesized and dispersed within the polymer matrix for separation of carbon dioxide/methane gas mixtures
To improve the distribution and compatibility of the nanoparticles in the polymeric matrix, the particles were modified by (3-aminopropyl) triethoxysilane (APTES). The modified nanoparticles were characterized and examined using XRD, FTIR, and BET. The supporting polyether sulphone (PES) sublayer was synthesized by solution casting and wet phase separation methods. The optimum thickness of this layer in the casting solution stage was found to be 200 μm. The selective Pebax/ZIF-8 layer was subsequently formed by dry phase separation method. To compare and evaluate the effect of nanoparticles on gas separation performance, some mixed matrix membranes were synthesized with different nanoparticles loadings. The permeability test was performed toward carbon dioxide and methane gases.
Findings: The mobility of polymer chain increased with the presence of ZIF-8 particle. With increasing ZIF-8 loading in the mixed matrix up to 40 wt%, the selectivity and gas permeability changed to 10.6 and 169 Barrer, respectively. APTES-modified particles showed the best performance. The bond between silane agent and the particle surface led to higher compatibility of particles in the polymeric matrix. The presence of APTES-modified particles also increased the selectivity and permeability at the same time. At 40% wt loading, the permeability and selectivity of carbon dioxide significantly increased to 925 Barrer and 16, respectively. Also, the selectivity reduction was about 34% in a 1:1 molar mixture of carbon dioxide and methane.

Hypothesis: In the past decades, the increasing resistance to antibiotics among some nosocomial infection pathogens has been one of the largest challenges of human health. One of the ways to reduce antibiotic resistance in bacteria is the combination use of cationic polymers with antibiotics. Poly(styrene-alt-maleic-anhydride) (PSMA) is an alternative biodegradable copolymer which can react with bioactive agents such as alkyl amines through a ring-opening reaction. In this study, for the first time, the antibacterial activity of poly(styrene-alt-maleic-anhydride) (PSMA) conjugated with spermine (Spm-PSMA) and its influence on resistance of Enterococcus faecalis to ceftazidime and ciprofloxacin antibiotics have been investigated.
Spm-PSMA was synthesized by reaction of PSMA with spermine in the presence of triethylamine catalyst under argon atmosphere at room temperature and characterized by FTIR and DSC. The antibacterial activity of Spm-PSMA was evaluated against two nosocomial infective bacteria, Enterococcus faecalis (E. faecalis) and Acinetobacter baumannii (A. baumannii) by two-fold microdilution method. Its ability to reduce the resistance of E. faecalis to the ciprofloxacin (CP) and ceftazidime (CAZ) antibiotics, active oxygen species (ROS) levels and morphological changes in acidic conditions was evaluated.
Findings: The glass transition temperature of Spm-PSMA (197°C) is higher than that of PSMA (164°C) due to intermolecular hydrogen bonding. Spm-PSMA reduces the growth of Gram-positive E. faecalis in a dose-independent manner, whereas it has no significant antibacterial activity against Gram-negative A. baumannii in acidic condition. E. faecalis susceptibility to ceftazidime and ciprofloxacin antibiotics is increased in the presence of Spm-PSMA at pH 5.5. The SEM results show that Spm-PSMA alone and in combination with antibiotics causes the transformation of E. faecalis cells from coccoid to coccobacilli shape. The results of this study show that Spm-PSMA is a biocompatible polymer with antibacterial activity and antibiotic sensitivity against E. faecalis bacteria.

Hypothesis: The removal of dyes using polymers with different functional groups is of great concern in environmental applications. Polymeric adsorbents, particularly hydrogels, through formation of polymer complexes by electrostatic attraction and hydrogen bonding have the ability to remove dyes. The hydrogels of polyacrylic acid (PAA), polyacrylamide (PAM) and poly(acrylic acid-co-acrylamide) (poly(AA-co-AM)) were used as adsorbents for basic red 46 (BR 46) dye removal from wastewater.
All three hydrogels were prepared through radical polymerization mechanism by N'-N-methylene-bis(acrylamide) in water. Hydrogel adsorbents were investigated using SEM, FTIR spectroscopy, and TGA-DTG analysis. In order to study the bleaching characteristics of adsorbent, the factors affecting bleaching process such as pH, adsorbent dosage, dye concentration, and contact time were investigated.
Findings: The results showed that pH increase, adsorbent dosage, and contact time had direct impact on bleaching and the concentration of dye had a reverse relationship with it. In addition, the physical and chemical properties in removal of cationic dye of BR46 conformed well to Langmuir isotherm model and the experimental data followed the pseudo-second-order kinetic model well. In evaluation of the reusability of the adsorbent it was shown that after 5 cycles of the absorption/desorption test, the hydrogel absorption capacity decreased from 94.4% to 63.3%. The swelling test of poly(AA-co-AM) hydrogel and its dependence on pH changes revealed its highest percentage of swelling in alkaline environment at pH value of 8.

Hypothesis: Polymer nanocomposites have found enormous applications owing to superior physical and mechanical properties such as modulus, strength and barrier behaviour, etc. Contrary to polymer microcomposites, polymer nanocomposites benefit from lower density and being less problematic in processing. In this study, nanocomposites of polyolefin elastomer (POE)/nanosilicon carbide (SiC) and polyolefin elastomer/nanoclay with different percentages of nanoparticles were prepared using melt mixing method in the presence of vinyltriethoxy silane as interfacial modifier.
Nanocomposite samples were prepared in a Brabender internal mixer using a roller mixing equipment. The fill factor was selected as 0.75. The mixing was carried out at a speed of 60 rpm at 120°C. The resulting nanocomposites were then subjected to various tests to investigate their physical, mechanical and rheological properties.
Findings: Sheet-like nanoclay particles have higher aspect ratio compared to spherical nanoSiC particles. Nevertheless, the results indicated that POE/SiC nanocomposites had higher tensile strength and elongation-at-break compared to nanoclay-reinforced composites. This was attributed to higher interactive efficiency between SiC nanoparticles and POE matrix. The moduli of nanocomposites at similar content of nanoparticles showed the same values regardless of the type of nanoparticles. Higher rheological properties were observed for nanoclay nanocomposites, though; the amount of increase was lower than those reported in literature. Morphology investigations of SiC and clay nanocomposites exhibited a comparable degree of dispersion of nanoparticles for both types of nanocomposites at similar compositions. Thermal properties of nanocomposites were studied by thermogravimetric analysis and differential scanning calorimetry. The results showed that the melting temperature and degree of crystallinity of both types of nanocomposites decreased with increasing nanoparticles content; however, the observed decrement was higher for POE/SiC nanocomposites. Thermal stability of POE/clay nanocomposites was higher, which could be attributed to the nanoparticle geometry.

Hypothesis: Shape memory polymers (SMPs) are intelligent materials that can be set into temporary shape and return to their permanent (original) shape when an external stimulus is applied. Poly(vinyl acetate) (PVAc) is a low cost biopolymer. However, its use in biomedical applications, especially as an SMP, is limited due to its low modulus and strength. On the other hand, poly(lactic acid) (PLA) is a biodegradable polymer with robust structure. Hence, blending of these two polymers can improve mechanical properties as well as shape memory behavior of PVAc.
a series of shape memory materials were prepared through blending of PVAc and PLA through solution mixing method using chloroform as solvent.
Findings: Microstructure of the prepared samples studied by X-ray diffraction spectroscopy (XRD) and atomic force microscopy (AFM), indicated that the components of the blends were favorably compatible. Moreover, dynamic mechanical thermal analysis (DMTA) and tensile test showed that the blending of these compatible biopolymers led to improvement in tensile strength and modulus of PVAc. Finally, the shape memory experiments revealed that the PVAc/PLA blends exhibited improved shape memory behavior as compared with their parent polymers. For instance, by incorporation of 30 wt% PLA into PVAc, the shape recovery increased from 75.4 to 91.5%. The improvement in the shape recovery was assigned to higher stored elastic energy in the blends as compared with that in neat polymers, which provided a larger driving force for corresponding quick and almost complete shape recovery. This procedure may open an avenue to fabricate SMPs through a simple blending method to be applied in different biomedical areas.

Hypothesis: Biodegradable polymer blends in comparison to petroleum-based polymers consume less energy in the production process, and do not produce environmental pollution due to their renewable sources. One of these biodegradable blends is polyolefin elastomer/starch (POE/S) blend. In this study, the effect of composition ratio of polyolefin elastomer/starch on properties such as mechanical, morphology, rheology and biodegradability properties of the blend were investigated. Because of non-polar microstructures of POE and polar starch, a polyolefin elastomer/maleic anhydride copolymer (POE-g-MAH) was used to improve their compatibility.
Blends of polyolefin elastomer and starch were prepared in presence of POE-g-MAH as synthetic compatibilizer with a Brabender internal mixer. The concentration of POE-g-MAH was fixed at 10 wt% and the content of starch in both binary and ternary blends was varied between 0 wt% and 55 wt%.
Findings: The results showed changes in the tensile, hardness, SEM micrographs, and void increasing after exposing the blends to fungi for three months at room temperature. To examine the compatibility of the blends, Fourier transform infrared spectroscopy (FTIR) was used. The observations of the scanning electron micrographs of polymer blends showed that by increasing the amount of starch from 15 to 55 wt%, the size of the dispersion phase increased; though it was reduced by adding 10 wt% of POE-g-MAH in the polymer blends. The rheology tests were carried out using rheometrics mechanical spectrometry (RMS) and the results indicated an increase in the complex viscosity, loss modulus and storage modulus after the addition of the compatibilizer into the blend. By adding starch to POE in the blend, the tensile strength and elongation-at-break decreased. The comparison between the blends with and without compatibilizer showed higher tensile strength and elongation-at-break for the blends with compatibilizer. The biodegradation experiments for the blend with 15 wt% of starch showed that the degradation of blend composition was negligible, but with higher starch content, the degradation rate increased and the blend with compatibilizer showed less degradation than the blend without compatibilizer.

Hypothesis: Currently, the dyes/heavy metal ions contamination of wastewater is the most important environmental problem throughout the world. Up to now, many techniques such as ion exchange, precipitation, adsorption, and membrane processes have been employed to remove dyes/heavy metal ions from water. Among them, adsorption is a simple and inexpensive technique for the removal of dye contaminations. The aim of the current work is the development of a low cost material based on hydrolyzed poly(N-vinylpyrrolidone-co- maleic anhydride) and rice husk as an effective adsorbent for Rhodamine B (RB) removal. The adsorption studies on the synthesized nanocomposite were carried out under different conditions, including, pH of solution, contact time, nanocomposite dosages and initial dye concentrations. Furthermore, the kinetic and thermodynamic studies of the adsorption data were examined.
Hydrolyzed poly(N-vinylpyrrolidone-co-maleic anhydride)/rice husk nanocomposite was prepared by a two-step method. In the first step, the poly (N- vinylpyrrolidone-co-maleic anhydride)/rice husk nanocomposite was synthesized through in-situ radical polymerization technique using benzoyl peroxide as initiator. In the second step, the hydrolyzed poly(N-vinylpyrrolidone-co-maleic anhydride) /rice husk nanocomposite was prepared through hydrolysis using sodium hydroxide solution (2 N).
Findings: The prepared nanocomposite was characterized by FTIR, XRD, SEM and TGA. The SEM images showed that the nanocomposite had a particle size between 50-100 nm and the XRD patterns revealed an amorphous structure. The results demonstrated that more than 88% of RB was removed by a nanocomposite synthesized under the conditions of pH 8, 70 mg adsorbent, 40 mg/L dye concentration and 180 min contact time. Furthermore, the experimental data showed a good agreement with Freundlich isotherm and pseudo-second order kinetic models.