IRANIAN POLYMER JOURNAL
Year:2020 | Volume:29 | Issue:7|Papers Count:8

The encapsulation of phase change materials (PCMs) as thermal energy storage materials is a big issue. PCM is usually encapsulated to avoid spillage, flammability and its reaction with the surrounding environment to improve its application. In the last decade, various methods have been employed and all kinds of microencapsulated PCM are produced. In this paper, we present a facile route to produce an encapsulated PCM with an organic and inorganic shell. The encapsulated phase change material (PCM) was prepared using a coaxial micro-fluidic system combined with an ionic cross-linking process. The alginate was used as the basic shell and a range of capsules was obtained by modifying the original shell using two inorganic components such as sodium carbonate and sodium silicate. Various samples, each with a different surrounding layer, were prepared by combining alginate calcium (Alg–, Ca) as an organic shell with an inorganic component such as alginate calcium carbonate (Alg–, CaCO3) and alginate calcium silicate (Alg–, CaSiO3). In these experimental works, we have investigated the compatibility and the stability of capsules modified with the inorganic component. The scanning electron microscopy (SEM) technique and optical microscopy were utilized to study the capsule morphology. The chemical composition of the shell was evaluated by Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetry analysis and SEM coupled with the EDX analysis, and the capsule stability was estimated under an accelerated thermal cycling.

The disposal of recycled tires is a problem that has gained considerable importance since it has involved the environmental as well as various disciplines and points of view. Currently, the burning and outdoor storage of disposed tires are forbidden practices because of their polluting effect, damage to health and the fact that they contribute to the spread of diseases due to vectors such as insects. Therefore, it is important to research alternative methods that provide added value. In this work, waste ground tire rubber was treated by applying a combination of oxidation with potassium permanganate/hydrogen peroxide, followed by microwave exposure in the presence of a devulcanizing agent. Devulcanized tire rubber was analyzed by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, cross-link density and sol fraction. Styrene butadiene rubber composites were prepared using devulcanized tire rubber and sulfur cure system. The blends were mixed in a two roll mill laboratory. The vulcanized specimens were obtained by compression molding. Curing properties, tensile and tear strength, elongation at break, hardness (Shore A units), abrasion resistance (mm3), and compression set of these rubber composites were evaluated and the morphology of the fractured surfaces from tensile specimens were analyzed with scanning electron microscopy. The results showed that microwave exposure with devulcanizing agent reduced the cross-link density and increased the soluble fraction of rubber tire. Improved flow through viscosity reduction (low torque) and higher mechanical strength were obtained by compounding styrene butadiene rubber with ground rubber tire (thermo-oxidized followed by microwave exposure with devulcanizing agent), whose market values were similar to those obtained for virgin styrene butadiene rubber/silica composite.

Quadruple shape memory hydrogels were prepared by one-pot in situ copolymerization using acrylamide, acrylic acid, agar, and poly(vinyl alcohol). The hydrogels have multiple reversible shape memory based on the coordination bonds of poly(acrylic acid) with Fe3+, borate bonds based on poly(vinyl alcohol), and hydrogen bonds of agar and poly(vinyl alcohol). The hydrogel demonstrated tunable mechanical properties when the hydrogels immersed in different solutions for various lengths of time. After immersion in the ferric chloride solution, tensile stress and elastic moduli of the hydrogels were enhanced with increasing soaking time. After immersion in the borax solution, tensile stress first increased and then decreased with increasing soaking time. Due to the reversible effect of the borate bond, the hydrogel achieved ultra-fast self-healing. The hydrogel after immersion in borax solution could begin healing in 24 h and healed at 44 h. The tensile stress and tensile strain of the self-healing hydrogel increased when soaking time increased from 48 to 96 h, and tensile stress at healing times of 96 h was nearly as the same as that of the original hydrogel when compared with it. The combination of tunable mechanical properties, efficient recoverability and self-healing abilities coupled with facile preparation endowed the developed hydrogel a high potential for use in biomedical applications.

Polylactic acid (PLA) is a well-known renewable and biodegradable polymer but is still limited by its low heat distortion temperature and brittleness. In this study, a PLA/flax composite containing flax fiber strands (5 wt%) was prepared through melt-compounding process followed by gamma irradiation at doses ranging from 0 to 20 kGy in the presence of a small amount of triallyl isocyanurate (TAIC) as cross-linking agent. The gel fraction of the composite was tested, and the datum showed that the gel fraction sharply increased first, and then slightly decreased with increasing irradiation dose. Gamma irradiation induced cross-linking of the polymer to form a three-dimensional network in the PLA/flax composite system. Irradiated composite could only swell instead of dissolving completely in chloroform, and the swollen morphology correlated with irradiation dose. The thermal stability of the PLA/flax composite was characterized using thermogravimetric analysis (TGA) temperature, and dimensional stability. Overall, irradiation modification improved the thermal resistance and dimensional stability of PLA composites. The mechanical property tests of the irradiated composites revealed increased tensile and impact strengths, reduced elongation-at-break, and unchanged tensile modulus. The analysis of water absorption of the composite demonstrated that the irradiation cross-linking induced no obvious effect on water absorption. Irradiation cross-linking modification cannot change the hydrophilicity or hydrophobicity of PLA composites. Overall, these findings look promising for future use in reinforcement and improvement of the thermal resistance of PLA/flax composites.

The chemically prepared pristine and graphene-doped polyaniline (PANI) samples are utilized for the fabrication of room temperature methanol sensors. For the fabrication of PANI/graphene-based sensing devices, four samples of PANI/graphene composites were prepared with four different concentrations of graphene (2, 4, 6 and 8 wt%). The surface morphology of the prepared composites was analyzed under field emission scanning electron microscopy (FE-SEM), which revealed the agglomerated structures of PANI/graphene composites. X-Ray diffraction studies carried out on these samples revealed the semi-crystalline nature of the samples, whereas, Raman studies confirmed the growth of PANI with the presence of all fundamental bands of PANI in the pristine as well as in its doped state. The prepared PANI/graphene composites devices were tested for alcohol detection at two different concentrations (50 and 100 ppm) of methanol. The change in electric current with the change in environment has been recorded as a sensing parameter and is employed to determine other sensor parameters such as percentage response, response time and recovery time. The sensing response of the prepared samples is found to increase with graphene doping concentration as well as methanol ppm level. The PANI/graphene composite with 8 wt% doping of graphene has shown the highest response (~ , 61. 5% at 100 ppm) and the lowest response time (55 s). The mechanism of gas sensing has also been discussed in details with the possible theoretical analogy with the adsorption and desorption of gas molecules in accordance with Langmuir kinetic theory.

Preparation of single-walled carbon nanotubes (SWCNTs) with carboxylic (–, COOH) acid was executed by functionalization with amine functional groups (–, NH2). The obtained functionalized SWCNTs were supported by macroporous resin (amberlite XAD-7HP). The synthesized nanocomposite has been characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) methods. FTIR analysis indicates that functionalized SWCNTs supported onto the amberlite resin were synthesized successfully. The surface morphology of the nanomaterial was also successfully embedded into the amberlite of the functionalized SWCNTs. Huge solid residues of onions are produced as agricultural and food wastes each year. The related biowaste includes biologically active phenolic compounds which have positive effects with strong antioxidant properties on human health when properly isolated and concentrated. In the present research, functionalized SWCNTs have been utilized for the separation of bioactive phenolics from onion waste extracts. Equilibrium (Langmuir, Freundlich and Toth) and kinetic (pseudo-first order, pseudo-second order, intraparticular diffusion and Elovich) models have been applied for analysis and representation of data. Pseudo-second-order model is in good agreement with the experimental data. On the other hand, the equilibrium findings were represented best with Freundlich isotherm model. Additionally, thermodynamic indicators have also demonstrated that the current system is a spontaneous and exothermic chemisorption process.

In our recent work, we have reported on hydrogels devoid of cross-linkers. After observing the successful swelling and water retention properties, we have introduced β,-cyclodextrin in acrylamide-co–, N-(hydroxymethyl)-acrylamide hydrogel to introduce hydrophobic cores. In this work, we have focussed to improve the sustainable drug release and toxic dye removal performance of hydrogel by introducing β,-cyclodextrin (β,-CD). Four different grades of β,-cyclodextrin grafted acrylamide-co–, N-(hydroxymethyl)-acrylamide have been synthesized through free radical polymerization technique at room temperature. Different proportions of β,-CD and fixed amount of acrylamide (AM), N-(hydroxymethyl)-acrylamide (NHMA) and 2, 2′,-azobis-[2-(2-imidazolin-2-yl)-propane] dihydrochloride (AIPD as an initiator) have been used. The synthesized grades were characterized using FTIR, SEM, TGA, UV–, visible and powder XRD. Hydrogels have shown high swelling capacity, i. e. 3000 times higher than dry weight. The diffusion studies of drug loaded hydrogels have been performed which have followed quasi-Fickian drug release behavior. Cumulative drug release studies of diclofenac sodium has been investigated in buffer solution at pH 7. 4 for 66 h. The toxic cationic dye (methylene blue) removal studies have been carried out in highly concentrated dye contaminated aqueous solution at neutral pH. Hydrogel resulted in complete removal of MB dye with lesser dose and in short span of time. β,-Cyclodextrin grafted acrylamide-co–, N-(hydroxymethyl)-acrylamide-2 and β,-cyclodextrin grafted acrylamide-co–, N-(hydroxymethyl)-acrylamide-3 showed highest 77% drug release and almost 100% dye removal from solution, respectively.

Natural fiber-based composites are applied in many structural engineered products from civil constructions to automobile manufacturing due to the properties such as low density, high aspect ratio, biodegradability and ease to work. During the past decades such composites have been thoroughly studied for their mechanical properties and failure behavior and their properties compared with those of synthetic fiber-based composites. Other properties, such as the thermal behavior of natural fibers and composites, have also been studied because they determine the performance of their products possible. It deals with the effect of temperature on adhesive curing, effect of high temperature and fire damage during fabrication. Further, the thermal properties have equal importance in structural applications such as temperature transfer from end to end, load capacity at specific temperature, material behavior and dimensional stability at high temperature. In this respect the isothermal and non-isothermal thermogravimatric analyses are discussed and the improtance of glass transition temperature is studied during prepapration of composites to ensure their ultimate properties. Although there are several works that have been done on thermal behavior, especially thermogravimetric analysis of natural fibers and their composites, there is no review article available specially focused on natural fiber-based composites, hybrid composites, and nanocomposites. The aim of this review was to focus on the advances in the comprehension of thermogravimetric behavior of natural fibers and compare the effect of natural fibers as reinforced materials in polymer composites.