دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و سوم شماره 5 (پیاپی 169، آذر و دی 1399)

Nowadays, polymer nanocomposites have attracted much attention in research activities due to their high mechanical strength, high thermal stability, low-cost, with possibility for their applications in many areas. Polyurethanes (PUs), as a main group of polymers, show a diverse and controllable range of physical and mechanical properties due to their tailored properties depending on the nature of precursors like polyols and isocyanates. This diversity and controllability of their properties make different types of PUs (elastomers, fibers, foams, hydrogels, and coatings) preferred candidates for a variety of uses, including transportation, clothing, furniture, and biomaterials. Many studies have been performed on polyurethane nanocomposites using different types of nanostructures such as graphene-like nanosheets, carbon nanotubes, metal oxides, and so on. Layered double hydroxides (LDHs) are eco-friendly layered mineral nanostructures with positively charged layers and anion-exchange capability. Depending on the types of anions and structure of layers, the LDHs nanostructures can be used broadly for the applications such as catalysts, drug delivery, separation technology, and also as a UV absorbent, corrosion, and a flame inhibitor for polymers. Recently, LDHs nanostructures are used in the fabrication of polyurethane nanocomposites to improve their mechanical, thermal, and flame properties. In this review, in addition to the description of LDH nanostructures, polyurethanes and their applications, LDH-based polyurethane nanocomposites are discussed in detail.

Mixed matrix polyether sulfone (PES)-based membranes, containing cobalt-ferrite nanoparticles, were prepared by polymer solution casting technique through phase inversion method in water bath.

The concentration effect of CoFe2O4 nanoparticles, synthesized in polymeric solution, on the morphology and separation performance was studied. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), porosity measurement, water contact angle, water flux, Na2SO4 rejection as well as membrane antifouling ability were used to characterize the membrane.

The SEM images showed the movement of NPs toward water-membrane interface to reduce surface energy during the fabrication process. The SEM images also showed an asymmetric structure with a dense active layer and a porous sub-layer with finger-like channels for the prepared membranes. The use of cobalt ferrite nanoparticles in the membrane matrix decreased the water contact angle from 71° to 48°. The results of AFM images also showed a smoother surface for the prepared mixed matrix membranes compared to the bare ones, which improved the membrane antifouling property in BSA rejection. Pure water flux (PWF) was initially enhanced by incorporation of cobalt ferrite NPs and then decreased by up to 1 wt% NPs due to NPs agglomeration. Moreover, Na2SO4 salt rejection increased from 60% for the neat membrane to 80% for the modified ones with 1.0 wt% cobalt-ferrite nanoparticles. The mixed matrix membrane containing 1.0 wt% cobalt-ferrite nanoparticles showed better performance compared to others.

Chemical modification of commercial and industrial copolymers and polymers such as polypropylene (PP) is one of the challenges of polymer chemistry. In this research work, a polypropylene nanocomposite modified with polystyrene (PSt) and carbon nanotube was synthesized by new methods, including living free radical polymerization (LFRP).

Maleic anhydride was grafted onto polypropylene (PP) followed by opening of the anhydride ring with ethanolamine to produce hydroxylated polypropylene (PP-OH). Hydroxyl groups were esterified using α-phenyl chloroacetyl chloride to obtain PP-Cl. Then 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) was immobilized onto the PP backbone using a nucleophilic substitution reaction to produce PP-TEMPO macroinitiator. Afterward, the monomer (St) was grafted onto the backbone (PP) through “grafting onto” technique to afford (PP-TEMPO)-g-PSt. The chloride-end-caped PP-g-PSt copolymer was then attached to the oxidized MWCNTs in the presence of DMF as solvent to produce the MWCNTs-g-(PP-g-PSt) nanocomposite by solution intercalation method. Also, the present study confirmed that PP-g-MA was efficient to promote the dispersion of MWCNTs in the PP matrix, which solved the problem of CNTs aggregation and limited compatibility between nanotubes and polymer matrices. In another study nanotubes-polypropylene nanocomposities were prepared through esterification process.

The chemical structures of all samples were identified using Fourier transform infrared spectroscopy. Chemical bonding (PP-TEMPO)-g-PSt to MWCNTs was confirmed by thermogravimetric analysis and differential scanning calorimetry results. In addition, morphology studies were investigated using TEM and SEM images. A synthesized MWCNTs-g-(PP-g-PSt) nanocomposite can be used as a reinforcement for polymer (nano-) composites due to the superior features of MWCNTs as well as their compatibility with polymer materials after functionalization processes.

Vascular tissue engineering offers innovative solutions to the vascular replacement problems, especially low diameter grafts. Electrospinning is a cost-effective and versatile method for producing tissue engineering scaffolds. Although this method is relatively simple, but at theoretical level the interactions between process parameters and their influence on fiber morphology are not yet fully understood. In this paper, the aim was to find the optimal electrospinning parameters to obtain the smallest fiber diameter by Taguchi’s methodology for vascular tissue engineering applications.

The scaffolds were produced by electrospinning of a polyurethane solution in dimethylformamide. Polymer concentration and process parameters were considered as effective factors. Taguchi’s L9 orthogonal design was applied to the experiential design. Optimal conditions were determined using the signal-to-noise (S/N) ratio with Minitab 17 software. The morphology of the nanofibers was studied by an SEM. Then, human umbilical vein endothelial cells (HUVECs) were cultured on the optimal scaffolds to investigate cellular toxicity of the scaffolds and cell adhesion.

The analysis of experiments showed that polyurethane concentration was the most significant parameter. An optimum combination to reach the smallest diameters was obtained at 12 wt% polymer concentration, 16 kV of the supply voltage, 0.1 mL/h feed rate and 15 cm tip-to-distance. The average diameter of the nanofibers was predicted in the range of 242.10 to 257.92 nm at a confidence level of 95%. The optimum diameter of the nanofibers was experimentally 258±30 nm, which is in good agreement with the estimated value of the Taguchi’s methodology. Cell viability was also reported to be 88.59% and the cells showed good adhesion to the scaffold. These scaffolds can show promising results in mimicking the extracellular matrix and thus in vascular tissue engineering.

Chemical recycling of poly(ethylene terephthalate) bottle waste and production of value-added materials are the most appropriate ways in accordance with the principles of sustainable development and environmental protection. To design and build industrial-scale recycling plants, kinetic data and the relationship between reaction rate and material concentration and temperature and, most importantly, the degradation reaction constant are required.

Chemical recycling of poly(ethylene terephthalate) was performed using more than five times the stoichiometric amount of monoethanolamine and without any catalyst. The product was characterized using the conventional polymer characterization methods such as Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric (TGA), and the elemental analysis. The aminolysis reaction was carried out at three temperatures of 120, 140, and 160°C and the kinetics of the aminolysis reaction and its relationship with temperature were determined by sampling and weighing the residual or unreacted amount of PET at consecutive times.

Complete chemical degradation or aminolysis of poly(ethylene terephthalate) and its conversion to bis(hydroxyethyl) terephthalamide (BHETA) were performed in the presence of an excessive amount of monoethanolamine. The assumption of the first-order degree kinetics regime was used and its accuracy was confirmed by calculation error values. Experiments were performed at three temperatures to determine the rate of PET aminolysis reaction with respect to reaction temperature. Degradation of aminolysis under heating conditions using a jacket system for the reactor showed less activation energy than heating conditions with microwave radiation.

Design and synthesis of self-curable solutions containing polyethylene glycol (PEG) and polyhedral oligomeric silsesquioxane (POSS) is a simple and economical method to enhance the physical and mechanical properties of biodegradable PEG.

First POSS nanoparticles were treated with acryloyl chloride (AC) to obtain POSS-AC nano-powder. In another reaction, PEG was copolymerized with fumaryl chloride to prepare polyethylene glycol fumarate (PEGF). POSS-AC was subsequently dispersed in PEGF matrix in 1 and 2% (wt) in the presence and absence of N-vinyl pyrrolidone as a reactive diluent. The obtained slurries were photocured by blue light irradiation using camphorquinone as photoinitiator. The crystal structure, dispersion quality, crosslink ability, mechanical, thermal and thermomechanical characteristics of the prepared nanocomposites as well as crosslinked neat PEGF were studied by XRD, TEM, equilibrium swelling, tensile, TGA and DMTA tests, respectively.

The XRD pattern of nanocomposites did not show any sharp peak related to the aggregation and agglomeration of the nanoparticles. TEM pictures revealed good dispersion of POAA-AC nanoparticles with mean diameter within 10-50 nm range. Furthermore, the presence of POSS-AC and reactive diluent led to an increase in the Tg of cured PEGF (as a blank system) from -16°C to a value in the range of -13 to -3°C, gel content from 45% to 62-84%, storage modulus from 1.6 GPa to 2.2-3.3 GPa, maximum decomposition temperature from 395 °C to 408-432°C, and Young's modulus from 0.46 MPa to 1.2-1.6 MPa. As a result, the nanocomposites designed in this study exhibited good mechanical properties and fast curing which would be considered as potential candidates for tissue engineering and biomedical applications.