دو ماهنامه علوم و تکنولوژی پلیمر
سال سی‌ام شماره 5 (پیاپی 151، آذر و دی 1396)

Artworks and historical monuments are often subjected to various damages and deteriorations, according to their age. Damages on artworks or repaired artworks may be provoked by human (vandalism) or by environmental factors such as humidity and light (UV). Nanotechnology provides new methods and innovative ways for the preservation of historical monuments. One of these methods is the preparation of more efficient nanomaterials with smaller particle size, and applying a thin layer coating of materials by different processes such as sol-gel method. In the current study, coating by a variety of conventional polymers is discussed with respect to their protective characteristics of historical monuments in addition to different assessment methods on their protection mechanisms. This study is extended to the important role of organosilicons for preparation of silica nanoparticles and latter protection capacity on coating properties. Another important category of polymers which may provide protective coatings for historical artworks are acrylic polymers. By considering the increasing importance of organic-inorganic hybrids in protection mechanism, some discussions are focused on such hybrids as nanocomposite coatings. The hybrids can be coated on different substrates to impart different properties such as hydrophobicity and anti-graffiti properties. In addition to the use of nanomaterials in conventional polymer coatings for protection and restoration of historical monuments, this paper further explains the preparation of nanomaterials for their usefulness in consolidating wall paintings, removal of aged polymers from historical monuments and enhancing cellulosic paper stability against fungal growth.

Water shortage is one of the most important environmental problems in arid and semi-arid areas which cause complications in land vegetations. The use of superabsorbent hydrogel is one of the most vital methods, which helps to optimize agricultural irrigations. The purpose of this research is preparation and study on properties the superabsorbent hydrogels by copolymerization of acrylamide and acrylic acid monomers using zeolite as nanoclay particles (0, 0.05, 0.1, 0.15). The optimum amount of nanoparticles in relation to its effect on superabsorbent structure and properties, such as water absorbency, was investigated through designing experiments using FFD software. We used methylene bisacrylamide and ammonium persulfate as crosslinker and initiator, respectively. Thermogravimetric analysis (TGA), Fourier transform spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffractometry (XRD) test results showed that the addition of nanoclay up to 0.1g caused improvement in the physical and chemical properties of superabsorbent such as thermal resistance, porous structure and uniform network structure. The superabsorbent hydrogel could absorb 1100 (g/g) distilled water. The water absorption and water retention of superabsorbent were studied by loading it in 5 different soil texture classes which were 0:100, 25:75, 50:50, 75:25 and 100:0 mixture fractions of sand/loam soil. As a result, it was observed that in the first week after irrigation, the best retention of initial moisture belonged to the soil with 50% sand texture, and also the soil with sand texture returned to its initial weight after 53 days (i.e., 30 days later than the control sample).

Lignin is the second most abundant polymer in the world after cellulose. Therefore, characterization of the structure and functional groups of lignin in order to assess its potential applications in various technical fields has become a necessity. One of the major problems related to the characterization of lignin is the lack of well-defined protocols and standards. In this paper, systematic studies have been done to characterize the structure and functional groups of lignin quantitatively using different techniques such as elemental analysis, titration and 1H NMR and FTIR techniques. Lignin as a black liquor was obtained from Choka Paper Factory and it was purified before any test. The lignin was reacted with α-bromoisobutyryl bromide to calculate the number of hydroxyl and methoxyl moles. Using 1H NMR spectroscopic method on α-bromoisobutyrylated lignin (BiBL) in the presence of a given amount of N,N-dimethylformamide (DMF) as an internal standard, the number of moles of hydroxyl and methoxyl groups per gram of lignin was found to be 6.44 mmol/g and 6.64 mmol/g, respectively. Using aqueous titration, the number of moles of phenolic hydroxyl groups and carboxyl groups of the lignin were calculated as 3.13 mmol/g and 2.84 mmol/g, respectively. The findings obtained by 1H NMR and elemental analysis indicated to phenyl propane unit of the lignin with C9 structural formula as C9 HAl 3.84HAr2.19S0.2O0.8(OH)1.38(OCH3)1.42. Due to poor solubility of the lignin in tetrahydrofuran (THF), acetylated lignin was used in the GPC analysis, by which number-average molecular weight of the lignin was calculated as 992 g/mol.

A hydrogel was prepared with high swelling capacity and a stable three-dimensional structure under environmental conditions. The methodology in this study involved the design and construction of a three-dimensional network for a superabsorbent hydrogel using hydrolyzed sulfonated polyacrylamide as polymer and nonahydrate aluminum nitrate as crosslinker. Further methodology involved data analysis to achieve a hydrogel optimized by response surface methodology. The optimum hydrogel in terms of three responses (i.e., gelation time, syneresis and swelling) was identified by designing a series of experiments. The chemistry and morphology of optimal superabsorbent hydrogel was determined by bottle tests (swelling and syneresis), rheology, energy dispersive spectroscopy (EDS), and thermogravimetric analysis (TGA). The results of this study demonstrated its polymer concentration of 40,000 ppm and crosslinker concentration of 6 wt% for preparation of optimum hydrogel. The syneresis of the optimum hydrogel was more than 180 days and it swelled to 2800-times of its initial dry weight; its elastic modulus was 15240 Pa with thermal stability by 325°C. The highest swelling rate (4000-times of the dry weight) was observed for a hydrogel with a polyacrylamide concentration of 20000 ppm and a weight ratio of 6 wt% of crosslinker to polymer. An undesirable syneresis time of less than 10 days was obtained. Moreover, the main factor in controlling the gelation time and syneresis was the weight ratio of crosslinker to polymer, while for controlling the swelling capacity it was found to be polymer concentration.

Photoresponsive functionalized polymer nanoparticles were prepared as useful materials for preparation of smart papers. Such polymer nanoparticles have wide applications in several fields including papers, sensors, bioimaging and biomedicine. First, carbazole as a photosensitive compound was modified with 2-bromoethanol through substitution nucleation reaction to its hydroxyl derivative (N-(2-hydroxyethyl) carbazole, CzEtOH). The synthesis of 2-N-carbazolylethyl acrylate (CzEtA) monomer was carried out by modification reaction of CzEtOH with acryloyl chloride and the chemical structures of the products were characterized. Next, CzEtA, methyl methacrylate (MMA) and butyl acrylate were copolymerized to prepare photoresponsive functionalized polymer nanoparticles through mini-emulsion polymerization in order to form a hydrophobic core. This was followed by copolymerization of MMA and glycidyl methacrylate by seeded emulsion polymerization to give a functionalized outer layer on the latex particles. Absorption characteristics, size, size distribution (narrow size distribution) and morphology of the nanoparticles were studied by ultraviolet-visible (UV-Vis) spectroscopy, dynamic laser light scattering (DLS) analysis and scanning electron microscopy (SEM) micrographs, respectively. Finally, due to the importance of photoresponsive smart papers and their wide applications, cellulosic fibers were reacted with the prepared functionalized latex particles for preparation of smart papers. Morphology of the fibers was investigated with respect to the surface-immobilized polymers on the cellulosic paper and their smart behavior was evaluated by UV irradiation at 254 nm. The results revealed fast color changes and the obtained cellulosic papers became violet upon irradiation. This work shows some promising feature of these materials for preparation of anti-counterfeiting papers, where the safety becomes a major concern.

Dextrin-g-polypyrrole/graphene oxides (PDGP/GO) nanocomposite was synthesized using in-situ polymerization and direct blending of PDGP and graphene oxide nanoparticles. The products were named nanocomposite 1 and nanocomposite 2, respectively. The prepared nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy. Surface morphology and structure of nanocomposites were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The performance of the synthesized nanocomposites in removing Pb (II) and methylene blue dye from aqueous solutions was evaluated. The effect of pH, adsorbent dosage, contact time and contaminant concentration on Pb (II) and methylene blue uptake capacity was studied. On the other hand, the percentage removal of Pb (II) metal ion by nanocomposite 2 (96%) was higher than that of nanocomposite 1 (88%). The optimum condition for effective removal of methylene blue dye by nanocomposite 1 (94%) and nanocomposite 2 (98%) could be obtained at pH 8, nanocomposite dosage of 100 mg, contact time of 60 min and methylene blue concentration of 80 mg/L. Langmuir and Freundlich isotherm models, pseudo-first-order and pseudo-second-order kinetics equations and thermodynamic models were used to determine the mechanism of Pb (II) and methylene blue adsorption on the nanocomposite 2. The results showed that the Langmuir isotherm, pseudo-first-order kinetic and spontaneous adsorption were suitable models for Pb (II) sorption on nanocomposite 2, while the Freundlich isotherm, pseudo-second-order kinetic and spontaneous adsorption were suitable models for methylene blue dye removal. Therefore, the PDGP/GO nanocomposite prepared by direct blending could be considered as a promising adsorbent for Pb (II) and methylene blue removal from aqueous solutions.