دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و چهارم شماره 3 (پیاپی 173، امرداد و شهریور 1400)

In recent years, hydrogels have been considered as one of the most promising materials due to their unique properties. Hydrogels are cross-linked hydrophilic polymer structures that are able to absorb and holding water or biological fluid. Thus, the hydrogel networks can extensively swell in water media without dissolution. In the last few decades, hydrogels been used in various industries such as food, packaging, pharmaceuticals and drug delivery systems, agriculture, biomedical and bioengineering applications, manufacturing of technical and electronic devices, and as adsorbents for the removal of pollutants in environmental applications. Superabsorbent polymer (SAP) hydrogels are a type of hydrogel that, due to the hydrophilic nature of polymer chains can absorb and retain extraordinary large amounts of water or aqueous solution up to hundreds of times their weight. In recent years, , new superabsorbent hydrogels have been developed for different applications. High demand for these substances, especially in personal hygiene, has led to an increase in their production (now over three million tons per year). Because the main components of commercial and widely used SAPs in industry are based on raw materials derived from fossil resources (oil, gas and coal), the widespread use of SAPs and their increasing production, on the one hand, have contributed to environmental concerns by contributing to water, soil and air pollution, and, on the other hand, have threatened global price fluctuations and the degradability of fossil resources. Therefore, the replacement of at least some components of SAPs with natural, biobased or renewable raw materials (such as lactic acid, succinic acid and itaconic acid) and the production of SAPs with hybrid structures have been considered. The purpose of this paper is to review the hybrid SAPs based on some biobased compounds that are used in three structural parts of the polymer network including crosslinker, surface modifier and monomer.

The porosity of silica-based chromium catalysts is one of the important issues in the petrochemical industry due to the high catalytic activity attracted by university and industrial researchers. One of the most important parameters that strengthens the structure of the hydrogel is the aging process that is considered in this study. By performing the aging operation on the primary silica hydrogel, the size of the initial particles increases and the surface area decreases. By doing the drying process, the pore volume of silica is reduced due to the capillary force. With changing the solvent from water to alcohols and ethyl acetate, the pore volume of the silica supported also increases. This is due to the reduction in surface tension between the silica wall and the water in the cavities.

The formation of supported silica using sol-gel method and the parameters affecting it have been investigated. Also, in the drying step by azeotropic distillation method, five solvents such as water, 1-propanol, 2-propanol, 1-butanol and ethyl acetate were used. FTIR, SEM and BET analyses were used to identify silica supported.

The effect of organic solvents on pore volume was investigated; so that all hydrogels were synthesized under the same conditions, while different solvents were used in the drying step by azeotropic distillation method. The use of different organic solvents did not show significant changes in the specific surface area of the supported silica but caused significant changes in the its pore volume. The results showed that the morphology of the silica support was improved by solvent replacement using organic solvents and the best morphology and crack-free structure of the ethyl acetate solvent were reported. The highest catalytic activity of 80 kgPE/gCr.h was obtained for slurry polymerization with silica support dried by ethyl acetate solvent.

Design and fabrication of hydrogel scaffolds with the required characteristics are the major issues of their development in tissue engineering. A wide variety of physicochemical, mechanical, and morphological properties of hydrogel scaffolds has provided new opportunities to overcome various challenges in tissue engineering.

A series of nanocomposite hydrogels comprised of dextran (Dex) and sol-gel derived bioactive glass (BG) nanoparticles were prepared as scaffolds for bone tissue engineering. The swelling behaviour and mechanical strength of the obtained hydrogel scaffolds by different contents and chain molecular weights of dextran were evaluated.

Fourier transforms infrared spectroscopy study provides information on intermolecular interaction between the dextran chain and the bioactive glass nanoparticles through influence on hydrogen bond strength. The influence of the given parameters on the morphology of scaffolds was probed using field emission scanning electron microscopy (FE-SEM). The results of FE-SEM showed that Dex/BG scaffolds consisted of a porous 3D microstructure with a pore size range of 102-156 μm. The effects of hydrogen bonding and chain entanglements showed significant differences in pore morphologies of the prepared hydrogels. According to the obtained apparent density and equilibrium swelling, the increase in the dextran content showed that the change in the gel porosity results in reduced free water of the network. Meanwhile, the amount of equilibrium swelling dropped while the compressive modulus increased due to the effective interaction between the dextran chains and bioactive glass nanoparticles. Furthermore, the results obtained by thermogravimetric analysis indicated an increase in thermal stability of dextran nanocomposites hydrogel, which could be due to the effective interaction between dextran chains and bioactive glass nanoparticles.

Methylene blue and crystal violet dyes are the most widely used dyes in some industries such as textiles, silk, and wood. Accumulation of cationic dyes in water resources is harmful to humans, animals, and the environment, so their removal from the effluents of the dyeing industry is essential. Among all the treatment methods, adsorption is one of the most attractive routes for the treatment of polluted water due to its low cost and simplicity of design. According to the studies, it can be seen that zeolites modified with iron nanoparticles show a high adsorption capacity in the removal of dyes. However, the use of adsorbents in the form of fine powders is still difficult and their use in continuous systems is limited due to the cracking and the pressure drop.

To solve the problems of adsorbents in powder form, the ionic gelation method was used to prepare a granular adsorbent based on natural zeolite clinoptilolite modified with Fe3O4 nanoparticles. In order to prepare granules with suitable appearance and high adsorption percentage, the effect of various parameters such as initial pH of the solution, type and concentration of the crosslinking solution and initial ratio of alginate to nanocomposite was investigated. The synthesized granules were investigated by XRD, SEM-EDX and BET analysis.

The results showed that the pH was ineffective and the iron (III) chloride solution was optimal with a concentration of (2 w/v%) and an initial ratio of 1:4 alginate to nanocomposite. The maximum adsorption capacity of the prepared granules towards methylene blue and crystal violet adsorption was determined as 12.484 mg/g and 11.904 mg/g by Langmuir isotherm, respectively, which indicated to a high ability of the prepared granules to remove these cationic dyes.

Unsaturated polyester resin has many applications in composite industry. In thick part items made with this resin, a lot of heat is released in a short time during curing, on the other hand, the low heat transfer coefficient of this resin increases the temperature in the center of the part to 200°C. In thick parts, the large temperature difference between the center and walls of the sample causes internal stresses, so the addition of particles with high thermal conductivity can help to eliminate this defect. Therefore, in this research, graphene oxide particles have been used to improve the properties of unsaturated polyester resin.

In this study, graphene oxide and modified graphene oxide were used to improve the thermal conductivity and dynamic properties of unsaturated polyester resin. The effect of adding graphene oxide and modified graphene oxide particles on thermal conductivity and dynamic properties of the resin by amounts of 0.05 and 0.3% (wt) of the particles was studied by a thermal conductivity measuring device for solids and DMA test.

The results showed that silane modifier can cause strong covalent bonds between the particles and resin and change the thermal conductivity coefficient and dynamic properties. Addition of 0.05% by weight of graphene oxide to the resin increased the storage modulus in the glass region by 10%. Adding the same amount of modified graphene oxide increased the storage modulus by 36%. Silane modifier improved the dispersion of graphene oxide particles in the resin, and created stronger interactions between the particles and the resin network, so significantly increased the resin storage modulus. Better particle dispersion in the resin can increase the surface heat resistance of the particles. Therefore, the thermal conductivity is reduced compared to the thermal conductivity of unmodified graphene oxide.

Spills of oil and its products into the open-waters of the world and the creation of oil slicks have become a global concern due to severe environmental and economic problems. Therefore, achieving an effective technology in cleaning up spilled oil is very important for environmental protection. One of the effective methods in separating oil stains is the use of adsorbents based on nanocomposite aerogels. The current study was carried out on the preparation of polyacrylonitrile aerogels for oil adsorption and separation of water from oil effluents, to improve the mechanical properties of aerogels due to the presence of polyacrylonitrile fibers in the aerogel structure, while extending the study on the effect of various parameters on morphology, and the porosity and percentage of aerogel oil adsorption.

Aerogels were characterized by conventional methods such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), optical microscopy (OM), BET, thermogravimetric analysis (TGA) and their density and adsorption rate were measured. Parameters such as fiber percentage, fiber length, and PVA percentage are effective on the adsorption rate, however the percentage of PVA is the most effective parameter on the adsorption rate.

The results showed that a chemical bond was formed between fibers and poly(vinyl alcohol) (PVA) and a network structure was obtained. Optimal conditions were determined as 3% by weight of polyacrylonitrile fibers, 5 mm length of polyacrylonitrile fibers and 1% by weight of PVA, in which the adsorbent was able to absorb about 1294% of oil. In addition, the specific surface area of the optimal sample was determined at 100.35 m2/g, which indicated that the prepared adsorbent could be suitable for oil adsorption.