دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و یکم شماره 6 (پیاپی 158، بهمن و اسفند 1397)

Heavy metal ions (e.g., Cd2+, Pb2+, Cu2+, Mg2+) and organic pollutants (like dyes) present in industrial wastewaters are one of the major causes of pollution of groundwater sources. These pollutants are toxic to humans, plants and aquatic life and should be removed from wastewater before disposal. Various treatment technologies have been reported to treat pollutants from aqueous media, such as coagulation and flocculation, oxidation, membrane filtration, and adsorption. Most of these methods are associated with some shortcomings and challenges in terms of applicability, efficiency, and cost. Based on economical aspect, flexibility and simplicity of design, and availability of wide range of adsorbents, adsorption is recommended as an effective method for removal of organic/inorganic pollutants from aqueous media. Hydrogels are three-dimensional flexible polymeric networks with extensive applications in the biomedical, pharmaceutical, agriculture, biotechnology and separation processes fields. Due to the unique physical and chemical characteristics of hydrogels, such as hydrophilicity, swelling ability, high adsorption capacity, the presence of various specific functional groups and modifiability, an increasing research interest in the development and application of novel hydrogels in water and wastewater treatment has emerged. Hydrogels have exhibited superior performance in the adsorptive removal of a wide range of aqueous pollutants including heavy metals and toxic dyes. Due to the lack of an overview on applications of hydrogels in adsorption of pollutants, this review investigates the different steps involved in the hydrogel-based treatment systems, the influencing factors and mechanisms of pollutants removal. Major challenges about adsorption kinetics, operational pH range, interference, and hydrogel recovery are discussed. Finally, important considerations like stability, reusability of hydrogels and resource recovery are discussed for economic and sustainability concerns.

Hypothesis: Due to the outstanding properties of polyurethanes (PUs) and their widespread uses in various industries such as coatings, adhesives, and on the other hand, increasing the environmental concern to reduce VOC during production or application of  products, waterborne PUs have attracted much attention. In this study, a group of self-colored-PUs based-on isophorone and hexamethylene diisocyanate, PEG-400 and an azo-diol were synthetized. Dimethylol propionic-acid (DMPA) and N-methyl-diethanolamine (NMDA) were used as internal ionic groups, and then converted to the corresponding anionomer or cationomer using triethylamine or iodomethane, and finally dispersed in water by addition of water (PUDs). The effect of the anionizing group type and location (inner block (C) or outer block (T)), degree of neutralization and solid content of PUDs was studied on their dispersion viscosity and stability, color and particle size. The thermal properties, morphology, scratch resistance, and color migration of polymer films were studied. These studies were performed by rotational viscometry, DLS, FTIR and NMR spectroscopy, XRD, DMTA, TGA and DSC techniques.   The results indicate that anionomers are orange to reddish-fire-brick, and show increased viscosity and reduced particle size by increasing solid content. They showed decreased viscosity and increased particle size by reducing the degree of neutralization. Polymers with DMPA-T block, in higher solids content, have higher dispersion stability and smaller particle size than polymers with DMPA-C block. The cationomers are reddish-brown to dark-magenta. Cationomers with NMDA-C block exhibited smaller particle size and thermal stability than polymers with NMDA-T block. Generally, anionomers exhibited greater dispersion stability, lower particle size, and higher water absorption, scratch resistance and thermal stability than cationomers. T5% of PUD-DMPA-T and PUD-DMPA-C were 27°C and 250°C; respectively.

Hypothesis: In this work, hyaluronic acid-aloevera (HA-AV) nanoparticles were prepared by nanoprecipitation method. Both HA and AV have shown great biocompatibility potential as antibacterial agents. Also chemical crosslinking of these two materials by esterification reaction could change stability and biodegradability. Doxycycline was selected as a drug model and encapsulated by HA-AV nanoparticles. Aloevera powder was prepared from the plant leaf and characterized by FTIR and NMR. The synthesis of HA-AV was carried out through esterification reaction. Size and shape of nanoparticles were measured by dynamic light scattering (DLS) and scanning electron microscopy (SEM). Anti-bacterial test was obtained against Staphylococcus aureus and Escherichia coli bacteria and also minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were measured. Average size of each particle before and after drug loading was about 118 nm and 171 nm, respectively. Doxycycline with an optimum concentration of 200 µg/mL was loaded, and drug loading content of 5.43% and drug loading efficiency of 40.14% were obtained. The sustained release profile showed 93.4% release during 16 days in PBS buffer solution. The results showed that the nanocarriers affected on both bacteria but the growth inhibitory loop was greater in Staphylococcus aureus. The cell viability test of nanocarriers was performed on NIH3T3 cell line by MTT assay method and nanoparticles containing 10 μg/mL of drug were selected as an appropriate concentration. Overall, this study has demonstrated that HA-AV nanocarriers can potentially be suitable for controlled release of doxycycline as a therapeutic agent for treatment of infectious diseases.

Hypothesis: Despite the wide application of nanofiltration (NF) membranes in aqueous solutions, their potential usage in the treatment of organic solution has been considered. However, it is still a challenge to develop polymeric solvent resistant nanofiltration membranes (SRNF) that can be applied in a broad range of organic solvents. There are many polymers with high resistance to solvents such as polyimide (PI) and polybenzimidazole (PBI) which used for making ultrafiltration membrane for SRNF. Poly(2,5-benzimidazole) (ABPBI) is a sort of polymer with similar or even better chemical structure than PBI. At first, a high-purity poly(2,5-benzimidazole) (ABPBI) polymer was synthesized. In the next step, ABPBI and polyvinylidene fluoride (PVDF) membranes were synthesized. TFC polyamine membranes were prepared by the interfacial polymerization (IP) of polyethylenimine and cyanuric chloride. Finally, the physical and chemical structure as well as chemical stability and membrane performance of UF and TFC membranes obtained by ABPBI polymer were evaluated and compared with those of PVDF membrane. Chemical stability tests including solubility, gel content and swelling degree indicated much higher stability of ABPBI membrane. The swelling degree in ethanol, methanol and n-hexane for ABPBI and PVDF membranes were 0.0132, 0.175, 0.01 and 0.9, 0.808, 0.34, respectively. The water fluxes for ABPBI-PA and PVDF-PA membranes were 20 and 26 kg/m2.h and the rejection for 10 ppm aqueous solution of crystal violet (CV, 408 g/mol) was 85 and 81, respectively.

Hypothesis: Among nanostructures, nanofibers and nanoparticles have a tremendous efficiency in tissue engineering and controlled release of drugs due to their high specific surface area and excellent biocompatibility. The production of nanofibrous scaffolds from polylactic acid (PLA), gelatin (Gel) and graphene (G) has been conducted in order to investigate their application in bone tissue engineering. The use of a combination of natural and synthetic polymers resulted in simultaneous use of the appropriate mechanical stability of PLA and the unique biological properties of Gel. The loading of graphene in the Gel/PLA structure caused the formation of nanofibrous mat with great resemblance to bone tissue. For the production of scaffolds from two mentioned polymers, the dual electrospinning method was applied. Gelatin solution was injected from a syringe and PLA or PLA-G solutions from another syringe. The morphological properties of the produced scaffolds showed that the addition of graphene to PLA solution reduced the diameter of the fabricated fibers, significantly. The addition of Gel to PLA and graphene to Gel/PLA decreased the contact angle of the samples. Gel/PLA-G hybrid nanofibers revealed good biocompatibility in the presence of human osteosarcoma cells, and no trace of cellular toxicity was observed. The cells grown on the scaffolds exhibited a spindle-like and broad morphology and almost uniformly covered the entire mat structure. The fabricated nanofibers due to smooth and nanofibrous morphology, good cellular behavior and higher hydrophilicity can be a good candidate for use in bone tissue.

Hypothesis: The pyrolysis process of bioplastics, prepared from a mixture of two animal proteins and whole potato flour, was studied and their kinetics and thermodynamic behavior during pyrolysis was investigated. The proteins used in this study included whey protein and bovine gelatin, which were extracted from the wastes of animal breeding and processing industries. To study kinetics of thermal decomposition, various isoconversional methods including Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink were used and the kinetic parameters of thermal decomposition were calculated for bioplastic samples consisting of bovine gelatin-whole potato flour (BG), whey protein-whole wheat flour (Wh) and whole potato flour (P) as control. The results showed that the variation in activation energy calculated by the Friedman method for BG, Wh and control (P) bioplastic samples was 60.15-214.65 kJ/mol, 59.16-264.07 kJ/mol and 50.38-216.68 kJ/mol, respectively. Prediction of reaction model using Criado’s method in the conversion ranges of 0.1-0.4, and 0.1-0.9, in order to cover the behavior of the bioplastics in two modes of processing and producing renewable energy, respectively, showed that in all investigated bioplastics, Valensi model (D2) in processing mode and Jander model (D3) in the second mode had the best linearity coefficient (R2) between theoretical master plots and experimental reduced rates. Thermodynamic analysis showed that the maximum enthalpy change for BG was observed in the conversion of 0.5 and was equal to ~210 kJ/mol and for the control and Wh bioplastics were observed in the conversion of 0.6 and were equal to ~259 kJ/mol and ~212 kJ/mol, respectively. The results of this study not only determined the thermal behavior of potato-based bioplastics at different temperatures and the thermal decomposition process, but also helped to generate renewable energy from bioplastic wastes.