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Iranian Journal of Polymer Science and Technology (10163255) 36(5)pp. 487-508
Traditional anti-corrosion coatings only act as a passive barrier on the metal substrate and have no active protective function if the coating on the surface is damaged. Recent smart anti-corrosion coatings can greatly increase the lifespan of the coating. On the other hand, self-healing technology in polymer coatings is a preventive method to progress of corrosion process on the surface of metals. This technique has been developed in order to prevent the growth and propagation of cracks in the early stages and to repair the damage automatically without external intervention. The increasing trend of published scientific articles shows that the use of anti-corrosion smart polymer coatings with self-healing capability has received much attention. In this type of coatings, corrosion inhibitors and healing agents can be loaded together or separately in spherical or nanofiber micro-carriers. In the case of damage of the coating surface, the anti-corrosion as well as healing processes trigger simultaneously to prevent the corrosion progress of the metal surface. The purpose of this study is to review novel epoxy-based coatings with self-healing and anti-corrosion properties. For this purpose, the self-healing mechanisms, methods of implementation of self-healing materials and anticorrosion agents on the coating have been reviewed and categorized. The use of polymer microcapsules with core-shell structures in the form of spherical particles or electrospun nanofibers in self-healing coating has been described. Various nanofiber systems have been classified in terms of the location of restorative and anticorrosion materials, the type of polymer shell and core materials, the electrospinning methods of nanofibers, and the method of dispersing within the coatings, for simultaneous anti-corrosion and self-healing properties. Finally, the recent studies on the coatings containing conductive and/or green nanofibers have been reviewed.
Journal of Polymer Research (15728935) 32(3)
Polystyrene (PS) fibers were fabricated via one-step electrospinning process, using tetrahydrofuran (THF) and N, N-dimethylformamide (DMF) as mixed solvent. The properties and structure of fibers were characterized by XRD, FTIR, DSC, FESEM, BET, and tensile strength analyses. The effect of operating parameters on the fiber structure in the electrospinning process was evaluated using the Taguchi experimental design. The production of fibers with a uniform surface, dense nanopores, and bead-free morphology can be controlled by optimizing the electrospinning conditions. For this purpose, the effects of solvent composition, solution concentration, feeding rate, and applied voltage were studied. The performance of the fibers was evaluated through adsorption and selectivity tests. The adsorption capacity of the fibers was measured using three different oil sources: sunflower oil, motor oil, and crude oil. The selectivity performance of the fibers was assessed with dispersed and dissolved crude oil in water. The results revealed that the maximum oil adsorption capacities of PS fibers for sunflower oil, motor oil, and crude oil were 58.4, 68.5, and 61.1 g/g, respectively. Furthermore, the PS fibers demonstrated excellent oil–water selectivity in the treatment of oily water. Moreover, polyaniline (PANI) was incorporated as a conductive polymer to enhance the properties of electrospun fibers. The conductive fibers exhibited improved microstructural properties and performance compared to PS fibers. The motor oil adsorption capacity increased to 71.5 g/g with the conductive PS/PANI fibers. The results of this study demonstrate that the conductive and hydrophobic PS/PANI fibers, as selective adsorbents, possess a high capacity for the adsorption of various oils. © The Polymer Society, Taipei 2025.
Diamond and Related Materials (09259635) 144
Graphene is a widely used nanoparticle in different industries, especially in nanocomposite applications. Prediction of its properties is of great importance for engineers. Therefore, a comprehensive study is first performed in this study to investigate the effect of temperature, strain rate, number of layers, and dimensions on the tensile properties of graphene nanosheets including elastic modulus (E), yield strength (YS), and ultimate tensile strength (UTS) using molecular dynamics simulation. Then, E, YS, and UTS are simultaneously optimized via response surface methodology. To determine the simplest and the most accurate machine learning algorithm for the prediction of tensile properties, three algorithms of Decision Tree (DT), Random Forest (RF), and Gradient Boosted Tree (GBT) are compared and the GBT algorithm is introduced as the best one. Furthermore, the architecture of each algorithm was optimized via the Taguchi design of experiment method to enhance the prediction accuracy. The DT algorithm with a maximum depth of 8 was obtained as the most accurate one. © 2024 Elsevier B.V.
Journal of Environmental Sciences (China) (10010742) 141pp. 287-303
Graphitic carbon nitride with nanorod structure (Nr-GCN) was synthesized using melamine as a precursor without any other reagents by hydrothermal pretreatment method. XRD, FTIR, SEM, N2 adsorption-desorption from BET, UV–Vis DRS spectroscopy, and photoluminescence were used to characterize the prepared samples. Also, the photoelectrochemical behavior of nanoparticles was studied by photocurrent transient response and cyclic voltammetry analysis. Polystyrene (PS) fibrous mat was fabricated by electrospinning technique and used as a support for the stabilization of the nanoparticles. The performance of the synthesized nanoparticles and photocatalytic fibers (PS/Nr-GCN) was evaluated in oilfield-produced water treatment under visible light irradiation. During this process, oil contaminants were adsorbed by hydrophobic polystyrene fibers and simultaneously degraded by Nr-GCN. The removal efficiency of chemical oxygen demand (COD) has been obtained 96.6% and 98.4% by Nr-GCN and PS/Nr-GCN, respectively, at the optimum conditions of pH 4, photocatalyst dosage 0.5 g/L, COD initial concentration 550 mg/L, and illumination time 150 min. The gas chromatography-mass spectroscopy analysis results showed 99.3% removal of total petroleum hydrocarbons using photocatalytic fibers of PS/Nr-GCN. The results demonstrated that the GCN has outstanding features like controllable morphology, visible-light-driven, and showing high potential in oily wastewater remediation. Moreover, the synergistic effect of adsorption and photocatalytic degradation is an effective technique in oilfield-produced water treatment. © 2023
Dental Materials (01095641) 39(10)pp. 863-871
Objective: The main aim of the current work was to develop dental acrylic-based composites with protein-repellent and antibacterial properties by using surface-modified silica nanoparticles. The effects of surface modification of silica nanoparticles in protein-repellent and antibacterial activity and mechanical properties of dental composites including flexural strength, flexural modulus, and hardness were discussed. Methods: The surface of silica nanoparticles was first chemically treated with 3-methacryloxypropyltrimethoxysilane (MPS) as a coupling agent and then with poly(ethylene glycol) (PEG) bonded to MPS. Dental acrylic-based composites were prepared with mass fractions of 10, 15, 20, 30, and 40 % of PEG-modified MPS-silica nanoparticles (PMS). The chemical surface modification of silica nanoparticles with MPS and PEG was confirmed by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Results: The dental composite containing 20 wt% PMS nanoparticles could reduce the protein adsorption by 28 % as compared with a composite containing 20 wt% MPS-modified silica. The antibacterial test indicated that the PMS nanoparticles can significantly reduce the adhesion of Streptococcus mutans and the biofilm formation on the surface of dental composites. It was found that the flexural strength increased by increasing the PMS nanoparticles from 0 to 20 wt% and then decreased by the incorporation of higher percentages of these nanoparticles. Also, with increasing the weight percentage of PMS nanoparticles, the elastic and the flexural modulus and the hardness of resin nanocomposites were increased. Significance: In the current work, for the first time, dental resin composites containing PEG were prepared with excellent protein-repellent and antibacterial properties. © 2023 Elsevier Inc.
Process Safety and Environmental Protection (17443598) 176pp. 87-100
To take advantage of solar energy, BiVO4/ZIF-8/Cu2S/Ag2S quaternary photocatalyst with different amounts of ZIF-8 was synthesized. Composites were characterized by FTIR, XRD, TEM, HR-TEM, PL, EDX, DRS and BET. The photocatalytic performance was evaluated and composite with 77.5, 15, 5 and 2.5 wt% of BiVO4, Cu2S, Ag2S and ZIF-8 showed the best qualification with 83.5 % metronidazole removal efficiency. Photocatalytic nanoparticles were incorporated into ABS/MWCNT membranes and they were characterized by SEM, EDX, AFM, electrical conductivity and contact angle measurements. The membrane with 2 wt% MWCNT had conductivity 106 times higher than that of pristine ABS membrane. The contact angles were decreased and the membrane with a more hydrophilic surface resulted in the flux improvement to 200 kg/m2. h. The enhanced drug retention up to 81 % indicated that by using the proper amount of photocatalyst it was possible to increase both the flux and rejection parameters. The flux recovery after solar illumination was obtained as 95.6 % for membrane with 0.5 wt% photocatalytic composites, that result in appropriate anti-fouling capability. finally, high performance photocatalytic activity makes membrane with 0.5 wt% photocatalyst and 1 wt% MWCNT superior for long-life filtration (36 h). © 2023 The Institution of Chemical Engineers
Journal of Drug Delivery Science and Technology (17732247) 84
In this work, tetracycline hydrochloride (TCH) as an antibiotic drug is encapsulated in carboxymethyl chitosan (CMCS) microcapsules (MCs). CMCS was synthesized by reacting chitosan with monochloroacetic acid to improve its pH sensitivity. The MCs were prepared by the emulsion crosslinking method and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), field emission-SEM (FESEM) and transmission electron microscopy (TEM). The in vitro drug release behavior of TCH-loaded MCs was investigated in buffer media with different pHs (4, 7 and 9) at 37 °C. The drug release in alkaline medium was higher as compared to acidic and neutral media that is desirable for infection treatment in which pH is relatively high due to bacterial activities. The kinetics of drug release was verified with conventional models and it was found that the Korsmeyer–Peppas model could predict the reduction of drug release at longer times. The physical stability of the MCs/TCH in different pH conditions was investigated with SEM and FTIR. The MCs/TCH showed appropriate antibacterial effects against E. coli and S. aureus, showing these microcapsules as promising candidates for drug delivery systems specially in wound dressing application. © 2023 Elsevier B.V.
Journal of Applied Polymer Science (00218995) 139(4)
Two series of novel blend membranes based on poly(ether-block-amide) (PEBAX® 2533) and 5 and 10 wt% of two glassy polymers (Matrimid® and polystyrene [PS]) were prepared using a new mixed solvent with a low boiling point for CO2/N2 separation. Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, and X-ray diffraction analyses were used to characterize the samples. A decrease in membrane crystallinity was observed by the addition of glassy polymers. The gas permeability measurements were performed to obtain CO2/N2 permselectivity of membranes. The maximum performance was found for the membrane with 5 wt% Matrimid content, for which CO2 permeability and CO2/N2 selectivity increased by 21% and 76%, respectively. Three permeation models were used to predict the CO2 permeability of blend membranes. The Maxwell model showed acceptable coincidence with the experimental data at 5 wt% content of the glassy polymer. For 10 wt% content of glassy polymer, the Lewis-Neilson model showed the most accurate predictions for CO2 permeability. A method for quantitative comparison of membrane performance was also proposed by defining the geometric closeness to the Robson upper bound limit. Finally, it was found that an increase in the feed pressure improved the membrane performance at high pressures. © 2021 Wiley Periodicals LLC.
Journal of Applied Polymer Science (00218995) 139(1)
Herein the kinetics of network formation (cross-linking) and network degradation (thermal decomposition) in a complex system based on epoxy resin reinforced with hyperbranched amino polymer-functionalized nanoparticles (HAPF) were discussed. Five classes of nanoparticles, that is, nano-SiO2, halloysite nanotubes (HNTs), HNTs@nano-SiO2 core/shell, HAPF/nano-SiO2, HAPF/HNTs@nano-SiO2 core/shell were loaded at 0.5, 1.0, 2.0 (optimal loading among prepared samples), and 5 wt% were examined. Parameters of the cure kinetics and degradation were correlated, and the mechanical properties were interpreted in terms of microstructure and rheological analyses. The isothermal chemorheological cure kinetics study (60, 70, and 80°C) revealed a low activation energy for epoxy/HAPF/HNTs@nano-SiO2 core/shell nanocomposite (72.21 kJ/mol), compared with the blank epoxy (79.99 kJ/mol). Correspondingly, gel time of the system decreased from 1040 to 515 to 237 s upon isotherms of 60, 70, and 80°C, respectively. Tensile strength was also increased vividly (ca. 32%), possibly due to the strong interfacial adhesion, which reflected in an induced shear yielding. Nitrogen-mediated thermal decomposition kinetics suggested an average degradation activation energies of ca. 150 and 210 kJ/mol for the assigned nanocomposites and the blank epoxy, respectively. Overall, there was a complete agreement between the kinetics of network formation and network degradation in the studied epoxy nanocomposite. This work enables understanding of structure-properties-performance in complex epoxy nanocomposites. © 2021 Wiley Periodicals LLC.
Dental Materials (01095641) 38(5)pp. 858-873
Objective: The main aim of the current work was to develop the novel self-healing dental composites contained poly(methyl methacrylate) (PMMA) microcapsules. The effects of PMMA microcapsule content in self-healing performance and mechanical properties of dental composites including flexural strength, flexural modulus, and fracture toughness were discussed. The antibacterial activity and non-toxicity properties of optimum self-healing dental composites were also investigated. Methods: Novel acrylic microcapsules were prepared using triethylene glycol dimethacrylate (TEGDMA) as healing agent and PMMA as microcapsule shell via solvent evaporation method. The silica nanoparticles with the mean size of 15–20 nm were treated by 3-methacryloxypropyltrimethoxysilane (MPS) to enhance their adhesion and dispersion within the acrylic matrix of composite. Acrylic microcapsules with mass fractions of 0%, 5%, 10%, and 15% were added into a mixture of acrylic resins and MPS-grafted SiO2 nanoparticles. The strength and elastic modulus of dental composites were measured by the flexural test. The single edge V-notched beam (SEVNB) method was applied to investigate fracture toughness (KIC) and healing efficiency. The results were then statistically analyzed using one-way analysis of variance (ANOVA) at the confidence level of 0.95. Results: Acrylic microcapsules were synthesized with the mean size around 30 µm and the core content of about 15 wt%. The grafting percentage of MPS surface modifier onto SiO2 nanoparticles was measured 3.2%. The incorporation of PMMA microcapsules into the dental composites had no significant effect on flexural properties. The self-healing dental composites also indicated the high efficient healing performance in the range of 78–121%. The self-healing dental composites also exhibited impressive antibacterial activity against Streptococcus mutans (S. mutans). The MTT assay also revealed that the incorporation of acrylic microcapsules in dental composites has no cytotoxicity effects. Significance: In the current study, for the first time, the self-healing dental nanocomposites contained acrylic microcapsules were prepared with excellent healing performance and antibacterial properties. © 2022 Elsevier Inc.
Smart Structures and Systems (17381584) 27(6)pp. 1001-1010
In this study, the effect of agitation speed as a key process parameter on the morphology and particle size of epoxy-Poly (methyl methacrylate) (PMMA) microcapsules was investigated. Thus, a new interpretation is presented to relate between the microcapsule size to rotational speed so as to predict the particle size at different agitation speeds from the initial capsule size. The PMMA shell capsules containing EC 157 epoxy and hardener as healing materials were fabricated through the internal phase separation method. The process was performed at 600 and 1000 rpm mechanical mixing rates. Scanning electron microscopy (SEM) revealed the formation of spherical microcapsules with smooth surfaces. According to static light scattering (SLS) results, the average diameter size of the epoxy/PMMA capsules at two mixing rates were 7.49 and 5.11 µm for 600 and 1000 rpm, respectively, indicating that the mean size increased as the mixing rates of the process increased. The D50, D90 and mean particle size values were the lowest for hardener/PMMA microcapsules at 1000 rpm. Moreover, the Fourier transform infrared (FTIR) spectroscopy was conducted to describe the chemical structure of epoxy and hardener PMMA capsules. To investigate the reinforcing role of microcapsules, they embedded in EPL-1012 epoxy resin with various amounts of 1 and 2.5 wt.% epoxy/PMMA capsules. The investigation also involved the effect of microcapsules on mechanical behavior as well as the reinforcement of polymer composite material. Experimental results showed that the tensile strength of the self-healing polymer composite slightly increased by 1 wt.% PMMA microcapsules prepared at 1000 rpm and then reduced with an increase in the concentration and mean size diameter of PMMA microcapsules. In addition, a similar trend of Young’s modulus was seen for pristine epoxy matrix and microcapsule-loaded epoxy composite. Copyright © 2021 Techno-Press, Ltd.
Chemical Engineering and Processing - Process Intensification (02552701) 168
Immobilizing an ionic liquid (IL) on a metal-organic framework (MOF) is proposed as a novel selective and CO2 facilitated transport material to improve gas perm-selectivity and plasticization pressure of Matrimid-based mixed matrix membranes (MMM) for CO2/CH4 separation. NH2-MIL-101(Cr) was synthesized and then impregnated with 1-butyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][Tf2N]) to prepare IL@NH2-MIL-101(Cr). The particles were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) analysis, and scanning/transmission electron microscopy (SEM/TEM). The particles were then dispersed in Matrimid to prepare MMM with 3, 5, and 7 wt.% contents. The membranes microstructure was investigated by FTIR and XRD, and the uniformity of MOF distribution was examined by SEM. Differential scanning calorimetry (DSC) displayed an increase in glass transition temperature (Tg) for the MMM associated with the polymer chains rigidification in the polymer/filler interphase. Permeation experiments showed that maximum separation performance was found for the MMM containing 7 wt.% IL@NH2-MIL-101 with increased CO2 permeability (162%) and CO2/CH4 selectivity (224%) over pristine Matrimid. This MMM increased plasticization pressure of the Matrimid membrane from 12 to 25 bar. Tensile strength and Young's modulus of the optimum MMM were 25% and 37% higher than those of pristine Matrimid membrane, respectively. © 2021 Elsevier B.V.
Chemical Engineering and Processing - Process Intensification (02552701) 147
The aim of the present study is to optimize the process factors in the degradation and separation of amoxicillin (AMX) by simultaneous combination of Fenton and nanofiltration processes (NF/FT), as well as to investigate the fouling of membrane samples. For this purpose, the Fenton Fe-based catalysts, i.e., goethite (Goe) and maleate ferroxane (Mf), are incorporated in the structure of polyacrylonitrile (PAN) film. A Central Composite Design (CCD) in response surface methodology (RSM) was used to optimize AMX separation and degradation. The amounts of H2O2, Fe-based nanoparticles in PAN/Goe and PAN/Mf membranes and AMX concentration were the effective factors. The NF/FT process could provide an appropriate opportunity to reduce the fouling of membranes by permeated flux of about 23.45 and 20.01 kg/m2h for PAN/Mf and PAN/Goe membranes, respectively, at the optimum conditions. The results indicated that by increasing the pollutant (AMX) concentration, the antibiotic removal efficiency increased for PAN/Goe membrane. © 2019 Elsevier B.V.
Chemical Engineering Research and Design (17443563) 153pp. 187-200
In this study, nanofiltration (NF) membrane process was combined with Fenton reaction (FT) by incorporating Fe-based nanoparticles (NPs), i.e., goethite (Goe) and maleate ferroxane (Mf) in the structure of polyacrylonitrile (PAN) film to improve the antifouling property and filtration performance of the membrane for amoxicillin (AMX) removal. The relation between the microstructure of the resulted composite with the antifouling properties and membrane performance is extensively investigated. It was found that by NF/FT combined process, foulants could be degraded and the AMX separation efficiency enhanced by 92.3 and 86.3% for PAN/Mf and PAN/Goe membranes, respectively. The permeate fluxes were also increased to 1.4 and 1.2 times of NF membrane filtration alone, respectively. Due to degradation of foulants, the combined NF/FT process exhibited better antifouling properties including flux recovery ratio (FRR) of 97.3 and 96.2% for PAN/Mf and PAN/Goe, respectively. The ratio of irreversible fouling to reversible fouling for NF/FT was lower than individual membrane process. Furthermore, the four cycles of AMX rejection, indicated the good stability and reusability of Fe-based NPs in composite membranes with FT reaction. Consequently, this research proves the successful combination of FT and NF membrane processes. © 2019 Institution of Chemical Engineers
Journal of Vinyl and Additive Technology (15480585) 26(4)pp. 548-565
Properties of silicone thin films and coatings are strongly hooked on curing reaction. We discussed about cure process of silicone nanocomposites containing halloysite nanotube (HNT) at different loading levels (0.5, 1.0, and 2.0 phr), both qualitatively and quantitatively. Systems containing pristine and aminosilane-functionalized HNT were cured nonisothermally and heat buildup of the reaction was recorded by differential scanning calorimetry (DSC) in terms of the time and the temperature varying the heating rate. Integral and differential isoconversional methods suggested that apparent activation energy (Ea) was strongly affected by the loading level and surface treatment of HNT. The exponent of the autocatalytic reaction (m) was decreased by the introduction and increasing the amount of pristine, and more remarkably the functionalized HNT to the silicone, where the Friedman method suggested 0.249, 0.119, and 0.045 values of m for the neat silicone rubber, and the nanocomposites containing 1 phr of pristine and functionalized HNT, respectively. The logarithm of frequency factor, ln A was also increased due to the enhanced collisions between curing moieties in the presence of pristine and functionalized HNTs form 23.57 seconds for silicone rubber to 24.25 seconds and 25.19 seconds for silicone nanocomposite containing 2 phr of pristine and functionalized HNT, respectively. The theoretical rate of reaction was in agreement with experimental data. © 2020 Society of Plastics Engineers
Separation and Purification Technology (13835866) 235
The effect of addition of ammoniated PVDF (NH2-PVDF) and amine-functionalized metal organic framework (MOF) NH2-MIL-101(Cr) were investigated on the gas permselectivity and plasticization behavior of Matrimid-based membranes for CO2/CH4 separation. The NH2-PVDF was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The NH2-MIL-101(Cr) nano-sized particles were synthesized and investigated via XRD, field emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller (BET) and dynamic light scattering (DLS). Then, the particles were dispersed in Matrimid/NH2-PVDF blend to produce ternary mixed matrix membrane (MMM). The membrane microstructures were examined by FTIR and XRD, while the uniform particle dispersion was confirmed by FESEM. Differential scanning calorimetry (DSC) showed that the Matrimid/NH2-PVDF blend is miscible up to 3 wt% of NH2-PVDF and the glass transition temperature increased with MOF content. Single-gas permeability measurements revealed that the best separation performance was obtained for the blend membrane with 3 wt% of NH2-PVDF with increased CO2 permeability and CO2/CH4 ideal selectivity by 39% and 33% respectively, over the neat Matrimid values. Much higher improvements (125% and 136% respectively) were obtained when 5 wt% of NH2-MIL-101(Cr) was added. Also, the plasticization pressure was increased from 12 to 26 bar by adding 3 wt% of NH2-PVDF and 7 wt% of MOF in the neat Matrimid. © 2019 Elsevier B.V.
Iranian Polymer Journal (10261265) 29(6)pp. 479-491
Gas separation membranes with enhanced performance were developed by the introduction of nanosized palladium particles. In this study, gas separation performance of Matrimid membrane incorporated with palladium-zeolitic imidazolate framework-8 (Pd@ZIF-8) particles, prepared by solution casting method, has been investigated. ZIF-8 nanoparticles were first synthesized using rapid room-temperature method and Pd@ZIF-8 nanoparticles were prepared through an assembly approach. The synthesized nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffractometry (XRD), and Fourier transform infrared equipped with attenuated total reflection (FTIR-ATR). TEM images exhibited that the incorporated Pd nanoparticles are well confined within the ZIF-8 crystals. The prepared mixed matrix membranes (MMMs) with various Pd@ZIF-8 contents (0–30 wt%) were characterized by SEM and XRD. All the modified membranes exhibited enhanced gas separation performance for selected gas pairs compared to a neat Matrimid membrane. The highest performance was observed for nanocomposite membranes with incorporation of 30 wt% of Pd@ZIF-8 into Matrimid which resulted in 72% increase in H2 permeability. The separation factors of H2/CO2, H2/CH4 and H2/N2 were improved from 3.25, 126.13, 95.21 for Matrimid/ZIF-8 to 5.82, 228.2 and 169.1 for Matrimid/(Pd@ZIF-8) membranes, respectively. Finally, the increase in feed pressure significantly improved the separation performance quality in all the membranes. © 2020, Iran Polymer and Petrochemical Institute.
Advances in Colloid and Interface Science (00018686) 286
Nowadays, metal oxide nanoparticles (NPs) have been applied in various fields of nanotechnology including catalysis of chemical reactions, drug delivery, water treatment, textile industries, polymer composites, adhesives, and coatings. The greatest challenge in relation to metal oxide NPs is high tendency to aggregation. Chemical surface modification of metal oxide NPs has gained widely interest to control of dispersion and aggregation of NPs. Silane modifiers are one of the most important bifunctional modifiers that are frequently used for surface treatment of metal oxide NPs. In this review paper, we first focus on the synthesis, surface thermodynamic properties, surface modification techniques, and kinetic of silanization reaction of metal oxide NPs. Then, the recent development in using silane modifiers for treatment of metal oxide NPs in various applications were investigated. It was found that the unmodified NPs have high surface energy and are thermodynamically unstable. The thermodynamic properties of NPs including Gms, Hms, and Smsincrease with decreasing the particle size. Aggregation phenomena is the simple way to reduce the excess surface energy of NPs that leads to an increase in particle size. Therefore, the chemical surface modification of NPs using silane modifiers can be used as an effective method for the prevention of NPs agglomeration and improvement of NPs stability. © 2020 Elsevier B.V.
Jouyandeh, M. ,
Moini jazani, O. ,
Navarchian, A.H. ,
Shabanian, M. ,
Vahabi, H. ,
Saeb, M.R. Applied Surface Science (01694332) 479pp. 1148-1160
Hydroxyl-rich halloysite nanotube (HNT)/silica nanosphere (SiO 2 ) core/shell particles were functionalized with multi-arm hyperbranched polyethylenimine macromolecule to develop epoxy superadhesives for metal/polymer composite interfaces. A variety of techniques including FTIR, TGA, XRD, XPS, and TEM were employed to precisely monitor the surface and bulk chemistry of HNTs flecked with silica particles and subsequently with hyperbranched polymer. Amine groups of the functionalized core/shell nanoparticles were exchanged with imide ones through the reaction with pyromellitic acid dianhydride to make the system thermally stable. Incorporation of the developed reactive bushy-surface hybrid nanoparticles into epoxy resulted in a highly crosslinkable superadhesive with exceptional thermal and mechanical properties; so that addition of only 0.5 wt% of core/shell nanoparticles caused a rise of about 31 °C in glass transition temperature with respect to the blank epoxy, suggesting very high potential of particles to cure with epoxy. Cure of adhesives containing 2 wt% of bushy-surface hybrid nanoparticles via nonisothermal differential scanning calorimetry was indicative of facilitated crosslinking, as detected by a higher enthalpy of ca. 106 J/g at low heating rate of 5 °C min −1 in a narrower temperature interval of ca. 13 °C compared to blank epoxy, visualized by the Cure Index universal dimensionless criterion. From property standpoint, a rise of ca. 130% in lap shear strength was surprisingly observed for adhesives containing bushy-surface hybrid nanoparticles. © 2019 Elsevier B.V.
Polymer Testing (01429418) 73pp. 395-403
Self-healing composites based on epoxy resin containing poly(methyl methacrylate) (PMMA) microcapsules filled with healing agents were prepared. The effect of healing agents microcapsules on mechanical properties and self-healing behavior of epoxy composites were investigated in this work. Epoxy and mercaptan as curing agent were microencapsulated in PMMA shell as two-component healing agent through internal phase separation method, and then, epoxy composites containing 2.5, 5, 7.5 and 10 wt% of healing agent microcapsules were prepared. The fracture toughness and healing efficiency of these composites were measured using a tapered double cantilever beam (TDCB) specimen. The results indicated that about 80% healing efficiency was achieved with 10 wt% PMMA microcapsules at room temperature after 24 h. The tensile strength of the epoxy with 2.5 wt% PMMA microcapsules increased initially and then decreased gradually with increasing microcapsules content up to 10 wt% PMMA microcapsules. DSC results also indicated that this system has good potential for spontaneous self-healing performance at room temperature. © 2018 Elsevier Ltd
Reactive and Functional Polymers (13815148) 135pp. 77-93
In this study, polyacrylonitrile nanofiltration membranes containing two Fe-based nanoparticles were fabricated through phase inversion method by incorporation of goethite (Goe) and maleate ferroxane (Mf), separately in casting solutions. Goe and Mf nanoparticles were first synthesized and characterized by scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) spectrometer, and X-ray diffraction (XRD) analyses. The synthesized membranes were characterized by SEM, FTIR-attenuated total reflectance (FTIR-ATR), atomic force microscopy (AFM), water contact angle (CA), and porosity measurements. The nanofiltration performance of membranes was studied by investigation of dye removal. Composite membranes showed better dye retention as compared with pristine PAN due to the higher repulsive force between dye and nanocomposite membrane functional groups. The presence of nanoparticles in the PAN membranes decreased CA, increased permeated water flux (PWF), and bulk water affinity (BWA). The reason of these changes was improvement in the surface hydrophilicity and decreasing the surface roughness. The addition of nanoparticles resulted in reduction of fouling phenomenon. Composite membranes had higher reversible fouling and flux recovery ratio (FRR) than bare membranes. In addition, the results displayed that the 0.5 wt% Mf membrane had the best performance among other membranes. FTIR-ATR analysis demonstrated the stability of nanoparticles after three times of dye rejection. Also, the membranes retained the acceptable performance after four cycles of powder milk fouling tests. © 2018 Elsevier B.V.
Journal of Applied Polymer Science (00218995) 136(41)
Material encapsulation is a relatively new technique for coating a micro/nanosize particle or droplet with polymeric or inorganic shell. Encapsulation technology has many applications in various fields including drug delivery, cosmetic, agriculture, thermal energy storage, textile, and self-healing polymers. Poly(methyl methacrylate) (PMMA) is widely used as shell material in encapsulation due to its high chemical stability, biocompatibility, nontoxicity, and good mechanical properties. The main approach for micro/nanoencapsulation of materials using PMMA as shell comprises emulsion-based techniques such as emulsion polymerization and solvent evaporation from oil-in-water emulsion. In the present review, we first focus on the encapsulation techniques of liquid materials with PMMA shell by analyzing the effective processing parameters influencing the preparation of PMMA micro/nanocapsules. We then describe the morphology of PMMA capsules in emulsion systems according to thermodynamic relations. The techniques to investigation of mechanical properties of capsule shell and the release mechanisms of core material from PMMA capsules were also investigated. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48039. © 2019 Wiley Periodicals, Inc.
Macromolecular Research (15985032) 27(3)pp. 290-300
Poly(vinyl alcohol) hydrogel films containing (1-5% (w/w)) chitosan-modified montmorrilonite (CsMMT) were prepared through phase separation method for wound dressing application. The prepared nanocomposites were characterized by Fourier transform infra-red (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of organoclay content on gel fraction, water vapor permeability, water uptake and tensile/rheological properties of films were also investigated. The XRD patterns and TEM micrographs show intercalated/partially exfoliated morphology of nanocomposites. The strong interactions between the polymer matrix and silicate layers via the formation of hydrogen bonds increase the gel fraction and tensile strength of hydrogels. It was found that the equilibrium water absorption, water diffusion coefficient and water vapor permeability were strongly affected by crystallite size of PVA macromolecules and tortuous path originated from CsMMT. The most appropriate results for the examined properties were obtained for 3% CsMMT content (w/w). The rheological results indicated a dominant elastic property and strong network structure for the hydrogels. The wound dressing films were loaded with nitrofurazone (NFZ) and their drug release behavior was studied at simulated wound condition. The drug loading and the release rate of NFZ showed a dependency on the quantity of CsMMT in the membrane. The interaction between NFZ and CsMMT together with tortuosity due to the presence of silicate layers, controlled the duration of total drug release to over 6 days. A Fickian diffusion mechanism was found for the drug release from the nanocomposite membranes. © 2019, The Polymer Society of Korea and Springer.
Progress in Organic Coatings (03009440) 132pp. 288-297
In this study, poly(methyl methacrylate) (PMMA) microcapsules filled with linseed oil (LO) as healing agent were prepared by solvent evaporation method. The effect of mechanical mixing rate in the range of 300–1000 rpm on mean size and morphology of PMMA microcapsules was investigated. Optical microscopy (OM) and scanning electron microscopy (SEM) images indicated that spherical microcapsules were formed with the mean size in the range of 2.6–11.6 μm. In order to enhance the interfacial interaction between microcapsule shell and epoxy matrix of coating, the surface of PMMA microcapsules was modified by hexamethylene diamine (HDMA). The chemical structure of amine functionalized-PMMA microcapsules was characterized by Fourier-transform infrared (FTIR). The surface modification results indicated that the roughness parameters (Rq and Ra) were higher for modified microcapsule compared to unmodified ones as proved by atomic force microscopy (AFM). Self-healing performance of epoxy coatings containing 10 wt. % (modified and unmodified) PMMA/LO microcapsules was evaluated in 3.5 wt.% NaCl aqueous solution using electrochemical impedance spectroscopy (EIS). The results indicated that the chemical surface modification of PMMA/LO microcapsules improves the healing performance of epoxy coatings as compared with the epoxy coatings filled with unmodified microcapsules. This can be due to the higher interfacial adhesion between the HMDA on the microcapsule surface and the epoxy matrix. © 2019 Elsevier B.V.
Progress in Organic Coatings (03009440) 136
Rubber/clay nanocomposites (RCNs) have attracted an emerging interest from academia and industry alike due to their outstanding tunable properties. The present paper addresses the viscoelastic behavior of silicone/clay systems in order to get an understanding of physical interactions in the RCNs systems as well as making possible interpretation of the effect of nanoparticle shape and surface functionality on viscoelastic behavior of molten RCNs. Rheological behavior determination of silicone/clay composites provides insight into dependency of properties of resulting nanocomposite coatings on processing and preparation conditions. The effect of bare and (3-aminopropyl) triethoxysilane (APTES) functionalized platy and tubular clays on viscoelastic behavior of silicone rubber nanocomposites were investigated by rheometric mechanical spectrometer (RMS). The analysis was set to the strain and frequency sweep tests, where the linear viscoelastic zone of the uncured nanocomposites were determined by dynamic strain sweep and then frequency sweep to probe into the role of dispersion of nanoparticles in silicone matrix. Well-known Han, Cole-Cole and van Gurp-Palmen models were applied to peruse silicone/clay interaction and to find additional information on rheological properties of nanocomposites under the influence of the shape, surface chemistry and content of nanoparticles. The findings depicted the effective role of physical interactions on APTES-functionalized clay on appropriate dispersion of clays throughout silicone matrix. This effect was more obvious in the presence of platelet-like clays in view of improved intercalation and/or exfoliation. © 2019 Elsevier B.V.
Karami, Z. ,
Moini jazani, O. ,
Navarchian, A.H. ,
Karrabi, M. ,
Vahabi, H. ,
Saeb, M.R. Progress in Organic Coatings (03009440) 129pp. 357-365
Silicone elastomer coatings are known for their softness and high elongation properties, but not for faithful service over time because of their inadequate adhesion, thermal, and mechanical properties. Addition of nanofillers to silicone would be the solution to such long-standing shortcomings, but yet there is a little guarantee of success because of silicone crosslinking being significantly hindered by filler incorporation. In this work, well-cured 3D silicone networks are formed by peroxide curing in the presence of pristine and silane-functionalized halloysite nanotubes (HNTs). Nanofillers are incorporated into silicone at different loadings and the curing potential of the resulting nanocomposite coatings are evaluated by dimensionless indexes of T* and ΔH* calculated from nonisothermal differential scanning calorimetry. Regardless of the content and surface chemistry of the HNTs, silicone nanocomposite was outstandingly cured by peroxide thanks to reactive surface of nanofillers. Overall, ΔH* value of ≈ 2 was indicative of a two-fold rise in the amount of heat release in silicone nanocomposites whatever heating rate. Moreover, T* values obtained were slightly lower than 1, a signature of an unhindered curing. The excellence of facilitated crosslinking brought about by the use of HNTs was featured by an improved polymer-filler interaction, which seems promising for coating applications. © 2019 Elsevier B.V.
Radiation Physics and Chemistry (18790895) 152pp. 1-5
In the present research, polyvinyl butyral film was prepared and irradiated by gamma-ray at various doses up to 250 kGy. Then, the effects of irradiation on the PVB were studied through the tensile test, FTIR, 1H-NMR and AFM techniques. The results of tensile tests show the existence of ‘necking’ up to 100 kGy and an increase in the toughness up to 70 kGy. Structural study by spectroscopic techniques show the formation of new groups as a result of increased conjugated double bonds. At higher doses, however, the polymer began to decompose due to degradation of the main chains, which led to reduced mechanical strength. Finally, AFM examination of the samples revealed less rough surface by irradiation. © 2018 Elsevier Ltd
Journal of Polymers and the Environment (15662543) 26(4)pp. 1702-1714
Abstract: A composite of thermoplastic starch (TPS), low-density polyethylene (LDPE) and citric acid-modified montmorillonite (CMMT) was prepared in a twin screw extruder for packaging film application. Starch was first converted to the thermoplastic state by using sorbitol and water. Composite films were produced on a chill roll system and then were modified for printability by grafting of acrylonitrile onto the starch backbone. Antimicrobial property and printability of the films were studied from which the sample with the highest antimicrobial property and the best printability was selected. This optimal sample was then characterized by Fourier transform infrared, thermal gravimetric analysis, differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. The composite film showed a matrix/dispersed morphology in which LDPE formed a continuous phase and TPS/CMMT nanocomposite particles appeared as dispersed phase. Biodegradability, water absorption, oxygen permeability, tensile strength and transparency of optimal film were also studied. The results indicated very good properties of the produced composite film for packaging application. © 2017, Springer Science+Business Media, LLC.
Progress In Color, Colorants And Coatings (20082134) 11(2)pp. 103-112
Polysulfide is well known elastomer for use in aerospace applications due to providing flexible coating and chemically resistant sealants. In this work, the effects of carbon black content on curing behavior of polysulfide elastomer were investigated and rheological properties for samples with different filler content (15, 20 and 25 phr) were evaluated by rheometric mechanical spectrometer (RMS). According to RMS analysis, sample with 20 phr carbon black had minimum gel point temperature and loss factor and highest elasticity. Also, the time sweep test for the optimal sample resulted from temperature and frequency sweep at 90 °C was done and gel time obtained less than a few minutes. From the dynamic differential scanning calorimetry (DSC) diagram for polysulfide sample with 20 phr carbon black observed one exothermic peak in heat flow for uncured sample that corresponded to the formation of cross-linking network and curing of polysulfide elastomer. © Institute for Color Science and Technology.
Solid State Ionics (01672738) 320pp. 84-91
In this study, the effect of poly (vinylidene fluoride)/poly (vinyl acetate) (PVDF/PVAc) ratio in the cathode binder of the LiMn2O4 (LMO) electrode on the electrochemical performance of a rechargeable hybrid aqueous battery (ReHAB) is investigated. The miscibility of two polymers is confirmed by Furrier transform infrared (FTIR) and differential scanning calorimetry (DSC) measurements. The binary blends with different PVDF/PVAc ratios (100/0, 75/25, 50/50, 25/75 and 0/100) are used as binder for the LMO cathode preparation. It is found that incorporation of PVAc in the blend decreases the crystallinity of PVDF and increases the cathode hydrophilicity, leading to better wetting by the aqueous electrolyte. The morphology and electrochemical properties of the cathode are also studied. Electrochemical cyclic voltammogram, discharge capacity, capacity retention, electrochemical impedance and rate capability are investigated. It is concluded that the blend with a PVDF/PVAc ratio of 25/75 has the best cycle performance (80% capacity retention after 100 cycles at the rate of 1 °C), with 0.2 °C discharge capacity (110 mAh gr−1) and the best rate capability. © 2018 Elsevier B.V.
Progress In Color, Colorants And Coatings (20082134) 11(4)pp. 199-207
Epoxy coatings are usually reinforced by the use of nanofillers, but reactive nanofillers having physical tendency towards epoxide ring opening are preferable. In this work, nanosilica (SiO2) and halloysite nanotubes (HNTs) known for their hydroxyl-contained surface are used and their effects on the curing behavior of an epoxy/amine coating is compared. The spherical and tubular nanoparticles used in epoxy led to somewhat different crosslinking. Epoxy/amine systems containing equivalent amount of silica spherical and halloysite nanotube particles were compared for their cure characteristics, i.e. temperatures of starting and ending of curing reaction (TONSET and TENDSET), the exothermal peak temperature (Tp), the temperature range among which curing reaction was completed (ΔT= TENDSET - TONSET) and the total heat of curing reaction (ΔH). Fourier-transform infrared spectrophotometry and scanning electron microscopy analyses were used to assess formation of SiO2. Nonisothermal differential scanning calorimetry was performed at different heating rates and cure characteristics together with values of glass transition temperature of two kinds of systems containing SiO2 and HNTs were calculated, where both nanofillers revealed accelerating role in epoxy curing reaction. © Institute for Color Science and Technology.
Iranian Polymer Journal (10261265) 27(3)pp. 193-205
Poly(vinyl alcohol) (PVA) hydrogel membranes were prepared through three different preparation methods including freeze-thawing (FT), solution casting (SC) followed by thermal annealing, and phase separation (PS). The prepared hydrogels were characterized by Fourier transform-infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy. Nitrofurazone (NFZ) was then loaded in the hydrogels. FT and SC methods led to obtaining dense membranes, while PS method resulted in an asymmetric one. The effects of hydrogel preparation method on water absorption, gel fraction, water vapor and oxygen permeabilities, bacterial barrier, tensile properties, and drug release profiles were investigated. The water vapor permeability of the hydrogel prepared through PS method was about 1.5 times higher than those obtained through FT and SC methods. Gel formation in PS method is probably responsible for the highest degree of crystallinity, and consequently the maximum gel fraction for the corresponded membrane. The elongation-at-break for this membrane in wet state was 41% higher than that made by FT method and 18% greater than that of SC method. Membranes prepared by all three methods showed excellent barrier property against bacterial penetration during 1 week. The results showed that PS membrane could control the release of NFZ more effectively as compared with the other two samples. © 2018, Iran Polymer and Petrochemical Institute.
Chemical Engineering Science (00092509) 185pp. 92-104
In this work, the effect of addition of MIL-101(Cr) metal–organic framework (MOF) and poly(vinylidene fluoride) (PVDF) on physicochemical, morphological and CO2/CH4 separation properties of Matrimid was investigated. MIL-101(Cr) micron-sized particles were synthesized and dispersed as filler in Matrimid/PVDF blended matrix so that a mixed matrix membrane (MMM) was formed. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis were used to characterize the MIL-101(Cr) particles. The Matrimid/PVDF blend membranes were investigated by optical microscopy (OM), differential scanning calorimetry (DSC) and Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectrophotometry. SEM images were employed to characterize the morphology of membranes. Single-gas permeability measurements for prepared membranes were performed and the results showed improvement in gas permeability of fabricated membranes in comparison with the neat Matrimid membrane. The best performance of blend membrane was obtained with 3 wt% of PVDF, leading to increase 29% and 23% in CO2 permeability and CO2/CH4 selectivity, respectively, as compared to the pristine Matrimid. Furthermore, the gas permeability and CO2/CH4 selectivity were improved simultaneously for Matrimid/PVDF/MIL-101 membrane. The CO2 permeability in this membrane increased 102% and 58%, and the ideal selectivity increased 77% and 45% as compared to the neat Matrimid and Matrimid/PVDF(97/3) membranes, respectively. © 2018 Elsevier Ltd
Progress in Organic Coatings (03009440) 125pp. 222-233
Properties of a rubber/clay nanocomposite coating depend on rubber network formed in the presence of clay platelets. Not surprisingly, however, a few is known about the state of cure in silicone nanocomposites. In this work, nanoclay flakes are modified with trifunctional silane, fully characterized, and then added to silicone coatings. The resulting nanocomposites are underwent nonisothermal differential scanning calorimetry (DSC) varying heating regime. Fourier-transform infrared spectrophotometry, X-ray diffractometry, and thermogravimetric analysis (TGA) techniques were employed to quantify grafting reaction efficiency and thermal stability of modified nanoclay. Cure characteristics of nanocomposites (exothermal peak temperature as well as cure enthalpy) containing pristine and silane-modified nanoclays were discussed in terms of clay content under different DSC heating rates. The mysterious state of cure in silicone/clay nanocomposite coatings was unraveled and then explained by solving curing puzzle for silicone/clay systems through comparison between newly defined T* and ΔH* dimensionless indexes dedicated to the crosslinked nanocomposite networks with respect to blank silicone coating. The progressive/diffusional crosslinking and complete/partial/imperfect curing were respectively evaluated by analyzing fluctuations in T* and ΔH* values, where the effects of clay content and surface chemistry were satisfactorily quantified. © 2018
Jouyandeh, M. ,
Moini jazani, O. ,
Navarchian, A.H. ,
Shabanian, M. ,
Vahabi, H. ,
Saeb, M.R. Applied Surface Science (01694332) 447pp. 152-164
Curing behavior of epoxy-based nanocomposites depends on dispersion state of nanofillers and their physical and chemical interactions with the curing moieties. In this work, a systematic approach was introduced for chemical functionalization of nanoparticles with macromolecules in order to enrich crosslinking potential of epoxy/amine systems, particularly at late stages of cure where the curing is diffusion-controlled. Super-reactive hyperbranched polyethylenimine (PEI)-attached nanosilica was materialized in this work to facilitate epoxy-amine curing. Starting from coupling [3-(2,3-epoxypropoxy) propyl] trimethoxysilane (EPPTMS) with hyperbranched PEI, a super-reactive macromolecule was obtained and subsequently grafted onto the nanosilica surface. Eventually, a thermally-stable highly-curable nanocomposite was attained by replacement of amine and imine groups of the PEI with imide and amide groups through the reaction with pyromellitic acid dianhydride. Fourier-transform infrared spectrophotometry, X-ray diffractometry, X-ray photoelectron spectroscopy and transmission electron microscopy approved successful grafting of polymer chains onto the nanosilica surface. Thermogravimetric analyses approved a relatively high grafting ratio of ca. 21%. Curing potential of the developed super-reactive nanoparticle was uncovered through nonisothermal differential scanning calorimetry signifying an enthalpy rise of ca. 120 J/g by addition of 2 wt.% to epoxy at 5 °C/min heating rate. Even at low concentration of 0.5 wt.%, the glass transition temperature of epoxy increased from 128 to 156 °C, demonstrating prolonged crosslinking. © 2018 Elsevier B.V.
Journal of Polymers and the Environment (15662543) 25(3)pp. 628-639
Poly(acrylamide-co-maleic acid)/montmorillonite nanocomposites, were synthesized via in situ polymerization with different maleic acid and MMT content. The capability of the hydrogel for adsorption of crystal violet (CV) was investigated in aqueous solutions at different pH values and temperatures. The pseudo-second-order kinetics model could fit successfully the adsorption kinetic data. The effects of maleic acid to acrylamide molar ratio (MAR), weight percent of MMT (MMT%), the pH of medium and the solution temperature (T) on the CV adsorption capacity (qe) of adsorbents were studied by Taguchi experimental design approach. The results indicated that increasing the MMT% leads to a greater qe. The qe value of adsorbents increased also with increasing both MAR and pH, while reduced when the temperature of medium increased. The relatively optimum conditions to achieve a maximum CV adsorption capacity for P(AAm/MA)/MMT adsorbents were found as: 0.06 for MAR and 5 % of MMT%, medium pH = 7 and T = 20 °C. © 2016, Springer Science+Business Media New York.
Polymer Testing (01429418) 64pp. 330-336
Mechanical properties of microcapsule shell have great influence on microcapsule suitability as a mechanical trigger in a self-healing composite. The elastic modulus and hardness of polymethyl methacrylate (PMMA) microcapsules containing epoxy prepolymer (EC 157) and pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) as healing agents were investigated using nanoindentation technique. The influence of the PMMA average molecular weight (MW), the kind of core material, and the mechanical mixing rate on the mechanical properties of the microcapsule shell were studied using the Taguchi experimental design approach. The results indicated that the most important factors which affect the elastic modulus and the hardness of microcapsules shell are the Mw of PMMA and the kind of core material. The average elastic modulus of PMMA shell of epoxy and mercaptan-loaded microcapsules was found between 2.386 and 3.495 GPa. The hardness of PMMA shell of healing agent microcapsules was obtained in the range of 0.064–0.219 GPa. This constitutes essential knowledge in order to design capsules with tailored properties for self-healing materials. © 2017 Elsevier Ltd
Applied Surface Science (01694332) 399pp. 721-731
Polymethyl methacrylate (PMMA) microcapsules filled with epoxy prepolymer, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, and pentaerythritol tetrakis (3-mercaptopropionate) as healing agents have been prepared separately through internal phase separation method for self-healing purposes. PMMA with two different molecular weights (M¯ 1 = 36,000 g/mol and M¯ 2 = 550,000 g/mol) were used with two types of different emulsifiers (ionic and polymeric) to prepare microcapsules. The morphology of healing agent microcapsules was investigated using field emission scanning electron microscopy (FESEM). It was found that PMMA microcapsules separately filled with epoxy and amine had core-shell morphologies with smooth surfaces. The mercaptan/PMMA particles exhibited core-shell and acorn-shape morphologies. The surface morphology of mercaptan microcapsules changed from holed to plain in different emulsion systems. The spreading coefficient (S) of phases in the prepared emulsion systems were calculated from interfacial tension (σ) and contact angle (θ) measurements. The theoretical equilibrium morphology of PMMA microcapsules was predicted according to spreading coefficient values of phases in emulsion systems. It was also found that the surface morphology of PMMA microcapsules depended strongly on the nature of the core, molecular weight of PMMA, type and concentration of emulsifier. © 2016 Elsevier B.V.
IEEE Sensors Journal (1530437X) 17(10)pp. 2992-3000
In this paper, we present fabrication, characterization, and sensing performance of four sensor elements, including two conducting polymers (polypyrrole and polyaniline), and two polymer/carbon black (CB) composites consisting ethyl cellulose (EC) and poly(caprolactone) (PCL). The identifications of four different vapors (methanol, ethanol, acetone, and ammonia) by these four sensors have been successfully demonstrated by using the principal component analysis. The sensing mechanisms of the examined sensors were investigated and a discussion on the similarity of gas sensor responses and the creep behavior has also been given. It was found that the response/recovery behavior of gas sensors can be presented by the Kelvin-Voigt rheological model. The effect of CB content on polymer/carbon sensor performance was investigated in the range of 15-20 wt. %. The increase of CB wt. %, led to increase the sensor response. The morphology of the produced EC/CB and PCL/CB composite sensors has been characterized by scanning electron microscopy and atomic force microscopy. Polyaniline indicated the highest response to ammonia due to effect of p-phenylene resonance on deprotonation process. The PCL/CB sensor response was more pronounced as compared with EC/CB, due to its higher porous structure. © 2001-2012 IEEE.
Smart Materials and Structures (09641726) 25(9)
In this study, epoxy prepolymer (EC 157) and pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) as hardener were encapsulated separately in polymethyl methacrylate (PMMA) shells through an internal phase separation method. Chemical structures, morphologies, and thermal properties of healing agent micro/nanocapsules were characterized by Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), and thermal gravimetric analysis (TGA) respectively. The effects of encapsulation processing conditions such as mechanical mixing rate, ultrasonication, emulsifier type, and co-emulsifier concentration on encapsulation yield, capsule mean diameter and core content were studied using the Taguchi experimental design approach. The results indicated that the main significant factors affecting the yield of encapsulation are emulsifier type and ultrasonication. The most important factors which affect the mean diameter of capsules are emulsifier type and mechanical mixing rate. The core content was influenced by ultrasonication and mechanical mixing rate. The relative optimum condition of encapsulation was also determined using overall evaluation criteria. © 2016 IOP Publishing Ltd.
Journal of Reinforced Plastics and Composites (07316844) 35(23)pp. 1685-1695
Epoxy-based adhesives reinforced with silica and alumina fillers (20, 40, and 60 phr) were prepared and successfully applied for lap-joint bonding of carbon fiber composite with steel. The mechanical properties of adhesives were assessed as different cure temperatures to find optimum cure temperature. Morphology of the reinforced epoxy adhesives was observed by optical microscopy to disclose the interplay between composite properties and distribution fashion of the silica and alumina fillers within the epoxy matrix. Thermal stability and interfacial interaction situation were explored by thermogravimetric and Fourier transform infrared spectroscopy analyses, respectively. Rheological behavior of the composite samples was also studied. Lap shear test was an indication for a considerable improvement of about 12% and 20%, compared to unfilled epoxy/hardener systems, for composites containing 60 phr of alumina and silica, respectively. However, the presence and population of voids in case of samples cured at elevated temperature deteriorated lap shear strength. Of note, the storage and loss modulus of the latter adhesive have been increased by 797% and 472%, respectively. Thermal stability on the basis of initial degradation temperature and char yield (> 500.,) of the assigned adhesive under N2 and air have also been enhanced. Higher performance of silica-based adhesives was mechanistically and morphologically discussed on the bedrock of formation of a 3D inter-connected network of filler particles. © SAGE Publications.
Polymers for Advanced Technologies (10427147) 27(9)pp. 1228-1236
Mixed-matrix membranes (MMMs) of Matrimid® and polyaniline/clay (PC) are investigated for CO2/CH4 separation and CO2-induced plasticization. PC particles are synthesized through in-situ polymerization of aniline in the presence of organophilic clay and then incorporated into Matrimid by solution casting method. Chemical structure and morphology of PC powder and fabricated membranes are analyzed by Fourier transform infrared (FTIR), X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetric analysis (DSC/TGA) and scanning electron microscopy (SEM). The XRD spectra of PC particles show the exfoliation of silicate layers throughout the polyaniline (PAni) matrix, and SEM images indicate flower-petal morphology for PC particles. The permeability values of CO2 and CH4 increase 30–35% by incorporation of 10 wt% PC without any significant drop in selectivity. PC particles with flower-petal morphology plays an important role in increasing the gas permeability values of both gases while Matrimid is the only phase that controls CO2/CH4 selectivity. The plasticization pressure was increased to 30 bar by incorporation of 10 wt% PC in the Matrimid matrix. CO2 permeability and pplast improved 35% and 200%, respectively, resulting in 300% enhancement in the capacity of MMM in the purification of natural gas with a selectivity of about 40. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
Polymer Science - Series A (0965545X) 58(3)pp. 487-498
Barrier properties of pristine polyethylene (PE) and polyethylene/montmorillonite-clay (PE/MMT) nanocomposite films with different MMT layers configurations were studied using molecular dynamics simulation within NVT ensemble. The force field parameters were optimized for bond lengths, bond angles and torsion angles of the MMT structure. A special simulation box was designed to simulate the diffusion of oxygen, nitrogen and methane, through pristine PE and PE/MMT nanocomposite films. The diffusion coefficients of these gases and the tortuosity values were calculated and analyzed. Results showed that the configuration of clay nanoparticles has strong effect on the barrier properties of the nanocomposite films. The parallel configuration for layered silicates was predicted to have a low diffusion coefficient and a high tortuosity parameter for gas diffusive molecules. The simulation could also indicate that the diffusion coefficient of oxygen is higher than those of nitrogen and methane gases in the examined systems which can be attributed to the smaller kinetic diameter of oxygen. © 2016, Pleiades Publishing, Ltd.
IEEE Sensors Journal (1530437X) 15(3)pp. 1697-1704
This paper addresses the preparation of one-dimensional nanostructured polyaniline (PANI) and polypyrrole (PPy). The Fourier transform infrared spectroscopy was used to characterize the chemical structure of the samples. The morphology of the samples was investigated by scanning electron microscopy and transmission electron microscopy. A nanofibrillar morphology was observed for the synthesized PANI and a nanotubular structure was obtained in the case of PPy. The alcohol sensing behaviors of PANI and PPy nanostructures were investigated for methanol, ethanol, propanol, and butanol, and the sensing mechanism of these systems has been discussed in detail. Both PANI and PPy systems were capable of detecting very low alcohols concentration (as low as 3 ppm) and demonstrated a linear behavior with a fast response/recovery performance especially in the case of ethanol vapor. The PPy-based sensor showed a better cyclability in response as compared with PANI when exposed to ethanol atmosphere. The surface characteristics of the PANI and PPy sensitive layers were investigated via atomic force microscopy. Ultraviolet-visible spectroscopy was used to study the effect of alcohol exposure on the electronic transport properties of nanostructured PANI and PPy layers. © 2001-2012 IEEE.
Synthetic Metals (03796779) 210pp. 404-411
The nanocomposites based on polypyrrole (PPy) nanostructures containing tin dioxide (SnO2) or zinc oxide (ZnO) nanoparticles were prepared and studied via different methods such as Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The ammonia sensing performances of one-dimensional (1-D) nano-structured polypyrrole and its nanocomposites with metal oxides were investigated and the effect of nanofiller type on the sensors behaviour was studied. The PPy and its nanocomposites with metal oxides exhibited high selectivity for ammonia with respect to methanol and ethanol vapors. The response of the sensor based on PPy/ZnO nanocomposite was found to be much pronounced and more retainable than that of PPy and PPy/SnO2 when exposed to ammonia. The cyclability and linearity of the response for this sensor in presence of ammonia vapor has been investigated as well, suggesting a great potential in detection of ammonia for the prepared sensor. © 2015 Elsevier B.V. All rights reserved.
Journal of Plastic Film and Sheeting (87560879) 31(3)pp. 309-336
Starch/poly(vinyl alcohol)/montmorillonite (MMT) nanocomposites were prepared in a twin-screw extruder for food packaging film application. In order to obtain a better compatibility between starch and silicate layers, MMT modification was performed using citric acid. X-ray diffraction (XRD) analysis was used to characterize the expanded microstructure of citric acid-modified MMT (CMMT). The effects of some compositional and operational factors including poly(vinyl alcohol) content, CMMT content, screw speed, and temperature profile in the extruder, on the tensile strength parameter of resulted films were investigated by using Taguchi experimental design. It was found that PVA content, CMMT percentage and screw speed were the most important factors, respectively, affecting the tensile strength property; while the temperature profile was insignificant factor, in the range of examined levels. The best levels of examined factors that could lead to the maximum tensile strength were obtained. The optimum sample was further characterized by XRD, transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), water uptake, biodegradability, oxygen permeability, and overall migration test. © The Author(s) 2015.
Synthetic Metals (03796779) 199pp. 37-44
This work addresses the preparation of polypyrrole (PPy) nanostructures using a template based on methyl orange (MO) and iron(III) chloride (FeCl3). A mechanistic discussion is proposed to justify the effect of reactants molar ratios (Py:MO:FeCl3) on the final polymer morphology. Fourier transform infrared (FT-IR) spectroscopy, CHNS elemental analysis, and Ultraviolet-visible (UV-vis) spectroscopy were applied to prove the proposed hypothesis. The results indicated that utilization of relatively high amount of monomer possibly ensures the occurrence of template degradation process resulting in the formation of a hollow tubular structure; while the presence of low amount of pyrrole leads to a non-hollow fibrillar morphology. The relative molar ratio of MO:FeCl3 is supposed to be important for formation of template-based nanostructures. The effect of monomer addition method on the morphology of the final polypyrrole was also investigated, indicating that dropwise addition of pyrrole leads to the formation of PPy well-formed nanotubes, while the instantaneous addition manner results in formation of nanoparticles, as well. © 2014, Elsevier Ltd. All rights reserved.
Advances in Polymer Technology (07306679) 33(S1)
This paper addresses the preparation of polyaniline (PAni) and polypyrrole (PPy) nanostructures as humidity sensor elements. The semicrystalline microstructure and chemical structure of synthesized PAni and PPy were studied by X-ray diffraction and Fourier transform infrared spectroscopy, respectively. The morphology of these polymers was studied by scanning electron microscopy and transmission electron microscopy, indicating fibrillar and tubular nanostructures for PAni and PPy, respectively. The humidity sensing performances of sensors based on the prepared nanostructural PAni and PPy were investigated, and the sensing mechanisms of both systems have been discussed. The interesting reverse behaviors during humidity exposure of PAni- and PPy-based sensors in different water vapor concentrations have been comprehensively justified. The temperature dependency of the electrical conductivity for PAni and PPy samples was investigated. The UV-vis spectroscopy was used to study the effect of moisture on the electronic transport properties of PAni and PPy nanostructures. © 2014 Wiley Periodicals, Inc.
Advances in Polymer Technology (07306679) 33(4)
The pH-sensitive poly(acrylamide-co-maleic acid)/montmorillonite (P(AAm-MA)/MMT) nanocomposite hydrogels were synthesized through in situ polymerization. The chemical structure and morphology of nanocomposites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. The resulted disks were then loaded by caffeine, a moderately soluble model drug, using soaking method. The swelling and the drug release experiments were carried out in enzyme-free simulated gastric and intestinal fluids. The release experiments showed that with the addition of MMT, the burst effect is well controlled, and the barrier property of nanocomposite hydrogels is improved. The effects of some compositional parameters including maleic acid to acrylamide (MA/AAm) molar ratio (MA R), weight percent of MMT (MMT%), cross-linker/AAm molar ratio (CR), and also the influence of pH of medium on the equilibrium swelling ratio (Q) as well as caffeine release behavior of disks were studied by Taguchi method. The results indicated that shifting the pH value from 1.2 to 7.4 leads to a greater Q. The Q value and the release percentage (P%) increased with increasing the MAR in the structure of disks at pH 7.4. The amounts of P% and Q in both external media decreased with increasing both MMT% and CR. Mathematical behavior of release process was well represented by Peppas Power law model (at short times) and a two-dimensional Fickian mass transfer model (at long times). The caffeine release behavior in both media was corresponded to the non-Fickian transport mechanism. © 2014 Wiley Periodicals, Inc.
Progress in Organic Coatings (03009440) 77(2)pp. 347-353
In this study, polyaniline (PANI) and polyaniline/clay nanocomposites were prepared via in situ oxidative polymerization. The morphology of nanocomposites structures was investigated by X-ray diffraction (XRD). The chemical structures of PANI and PANI/clay nanocomposites were examined via Fourier transform infrared (FT-IR) spectroscopy. Polyaniline-based pigments were introduced into epoxy paint and applied on steel substrates. The effect of clay addition and the type of clay cation, including Na+ in natural clay (MMT) and alkyl ammonium ions in organo-modified montmorillonite (OMMT), on the anticorrosion performance of epoxy-based coatings was investigated through electrochemical Tafel test, electrochemical impedance spectroscopy and immersion measurements in NaCl solution. The stability of the adhesion of the neat and modified epoxy coatings to the steel surface was also examined. The results indicated that introduction of PANI/OMMT nanocomposite into epoxy paint results in improved anticorrosion properties in comparison with PANI/MMT and neat PANI. © 2013 Published by Elsevier B.V. All rights reserved.
Talaiekhozani, A. ,
Jorfi, S. ,
Fulazzaky, M.A. ,
Ponraj, M. ,
Abd majid m.z., ,
Navarchian, A.H. ,
Reza talaie, M. ,
Zare, S. Desalination and Water Treatment (19443994) 52(19-21)pp. 3585-3593
Propylene glycol (PG) is not a toxic matter. However, it can dramatically increase BOD of water resources and that is why removal of PG is important. Removal of PG in synthetic wastewater was studied in a continuous activated sludge pilot-scale reactor. The influence of various factors (pH, nitrogen source, COD and wastewater feed salinity (conductivity)) on micro-organism growth as a measure of removal was determined, and the optimum condition for maximizing this response was obtained using Taguchi experimental design method. Primary micro-organisms were obtained from the return sludge line of the Shahrak-Gharb wastewater treatment system located in the city of Tehran. The micro-organisms have been adapted to high organic loads during five stages in 119 days. The maximum PG removal efficiency was equal to 85%. In the selected range of levels, the best pH was equal to 8 and the influent COD was 1300 mg/L. The best nitrogen source was urea, and salinity was obtained equal to 8%. © 2013 © 2013 Balaban Desalination Publications.
Journal of Vinyl and Additive Technology (15480585) 19(4)pp. 276-284
Poly(vinyl alcohol) (PVA)/montmorillonite nanocomposites were prepared via solution polymerization. The nanocomposites were formed either by first hydrolyzing poly(vinyl acetate) (PVAc) to PVA and then preparing the PVA/clay, or by initially preparing PVAc/clay and then hydrolyzing the matrix to PVA. The morphology of the nanocomposites was examined by X-ray diffraction and transmission electron microscopy, which suggested the proper dispersion of silicate layers within the PVA matrix. The influences of some variables including method of preparation, clay content, and time and temperature of saponification on the tensile properties (elastic modulus, stress and elongation at break) of the nanocomposite samples were investigated by using the Taguchi experimental design approach. The results indicated that the tensile properties of the nanocomposites improved as clay content, and the temperature and time of saponification increased. Effect of each factor on the ultimate properties of as prepared nanocomposites are discussed in detail. The analysis of variance (ANOVA) showed that the method of preparation did not influence the ultimate tensile properties of the nanocomposite samples. Thermal degradation of the nanocomposites was studied by thermogravimetric analysis, which showed that their thermal stability was higher than that of virgin polymer. © 2013 Society of Plastics Engineers.
Journal of Polymers and the Environment (15662543) 21(1)pp. 233-244
In this study the biodegradability of starch-graft-acrylonitrile (St-g-AN) copolymer has been investigated using some microorganisms including Aspergillus niger. The fungus A. niger was isolated from the soil and from the wastewater of an acrylic fiber company. The effects of four factors including environment temperature, primary inoculum concentration, pH and weight of copolymer film, on the biomass generation as a measure of biodegradation rate of copolymer, were studied using Taguchi experimental design. The statistical analysis of the results showed that the primary inoculum concentration and temperature were the most important factors affecting the biodegradation of St-g-AN copolymer. The optimum levels of temperature, pH, inoculum concentration, and weight of films to attain the maximum biodegradation (as much as 8. 59 % by weight percentage during 28 days) were obtained as 30 °C, 4. 75, 108 spore/mL, and 1. 1 g, respectively. The changes in the structure and morphological properties of the copolymer before and after degradation were determined using transform infrared spectroscopy and scanning electron microscopy. © 2012 Springer Science+Business Media, LLC.
Advances in Polymer Technology (07306679) 32(3)
This paper addresses the preparation of polyaniline (PANI) via a rapid mixing method in which a nanosheet (nanoflake) structure was observed by scanning electron microscopy. The microstructures of acid- and ammonia-dedoped PANI samples were studied by Fourier transform infrared spectroscopy. The effects of polymerization conditions (time and temperature of reaction, monomer/oxidant ratio, and acid type) on the polymerization yield, electrical conductivity, and ammonia-sensing performance of PANI-based sensors were investigated using a Taguchi experimental design. It was found that acid type has the most significant effect on polymerization yield and ammonia-sensing property of PANI. The conductivity of PANI films was mostly influenced by reaction time, reaction temperature, and acid type, respectively. Some interesting behaviors were observed for influential factors that have been comprehensively justified. © 2013 Wiley Periodicals, Inc.
Chemical Engineering Science (00092509) 69(1)pp. 431-439
A detailed model was developed for emulsion polymerization of styrene in batch reactor to predict the evolution of the product particle size distribution. The effect of binary surfactant systems (ionic/non-ionic surfactants) with different compositions was studied. The zero-one kinetics was employed for the nucleation rate, with the model comprising a set of rigorously developed population balance equations. The modeling incorporated particle formation by both nucleation and coagulation phenomena. The partial differential equations describing the particle population were discretized using finite volume elements. Binary surfactant systems, comprising sodium dodecyl sulfate (SDS) as anionic, and a commercial polyether polyol (Brij35 ®) as non-ionic surfactants, were examined with different mass ratios. Increasing non-ionic surfactant mass fraction in binary surfactant system showed the decrease of particle number due to intensifying the coagulation between particles. Broader particle size distributions with greater average particle size were obtained with non-ionic surfactant comparing those obtained with anionic one. © 2011 Elsevier Ltd.
Progress in Organic Coatings (03009440) 72(3)pp. 486-491
In this paper the effects of structural and process variables on wear resistance of polyurethane/titanium dioxide coatings on aluminium surface is studied. The parameters were polyol molecular weight, diisocyanate type, surface pretreatment method, NCO/OH ratio and pigment volume concentration. The experiments were carried out based on the design of experiments using Taguchi method. The analysis of variance showed that among the parameters studied, polyol molecular weight and pigment volume concentration have the most significant effects on wear resistance. Coatings with higher molecular weight polyol represent more resistance due to higher elongation at break of polymer which consequently increase the wear resistance of coating. The pigment particles provide equivalent physical crosslinks, so it increases the wear resistance. The optimum sample was prepared according to the best levels of each factor, and its morphology was examined by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. © 2011 Elsevier B.V.
Polymers for Advanced Technologies (10427147) 22(12)pp. 2022-2031
In this paper, two polyurethane/clay nanocomposite systems with crosslinked structure were synthesized via in situ polymerization of a polyether- as well as a polyester-based prepolymer with methylene-bis-ortho-chloroanilline (MOCA). Two types of modified clays with different organic modifiers were used in order to see the effect of compatibility between polymer matrix and clays on elastic modulus of nanocomposites. The morphology and the dispersion of clay layers in polyurethanes have been characterized by X-ray diffraction (XRD) and microscopic techniques. The changes of elastic modulus of nanocomposites with clay content were examined and compared with those predicted by some conventional composite models. The results showed a reasonable fitting of experimental and theoretical values only at very low clay contents. As the clay content exceeds 1.5wt% in this system, a reduction in elastic modulus was experimentally observed due to insufficient dispersion degree of silicate layers throughout the crosslinked matrix. This behavior was not predicted with the conventional composite theories. A new model on the basis of Wu model was then developed in order to predict the reduction of elastic modulus at various clay contents in crosslinked PU matrix. This model fitted reasonably the experimental results. © 2010 John Wiley & Sons, Ltd.
Polymers for Advanced Technologies (10427147) 21(4)pp. 263-271
This paper addresses the effects of operating variables on mechanical properties of polyurethane/clay nanocomposites including tensile strength, abrasion resistance, and hardness. The variables were prepolymer type, clay cation, clay content, and prepolymer-clay mixing time. The experiments were carried out based on the design of experiments using Taguchi methods. The nanocomposites were synthesized via in situ polymerization starting from two different types of prepolymers (polyether- and polyester-types of polyol reacted with toluene diisocyanate), and methylene-bis-ortho-chloroanilline (MOCA) as a chain extender/hardener. Montmorillonite with three types of cation (NaR, alkyl ammonium ion, and MOCA) were examined. Among the parameters studied, prepolymer type and clay cation have the most significant effects on mechanical properties. Polyester nanocomposites showed larger improvements in mechanical properties compared to polyether materials due to higher shear forces exerted by polymer matrix on clay aggregates during polymer-clay mixing. The original MMT with Na+ cation results in weak improvements in mechanical properties compared to organoclays. It is observed that the stress and elongation at break, and abrasion resistance of the nanocomposite samples can be optimized with 1.5% of clay loading. The morphology and chemical structure of the optimum sample were examined by X-ray diffraction and FT-IR spectroscopy, respectively. © 2009 John Wiley & Sons, Ltd.
Carbohydrate Polymers (18791344) 79(3)pp. 547-554
Starch/clay nanocomposites were prepared via solution casting method and the effects of starch source, clay cation, glycerol content, and mixing mode on clay intercalation and Young's modulus of nanocomposites were investigated using a Taguchi experimental design approach. The clay intercalation was examined by X-ray diffraction (XRD) patterns. Nanocomposites prepared with montmorillonite (MMT) modified with citric acid demonstrated the highest Young's modulus compared to pristine MMT and organoclay. A combined mechanical and ultrasonic mixing mode led to an extensive dispersion of silicate layers and thus the highest Young modulus in nanocomposites. The effect of clay content on tensile properties was also investigated. It was observed that the maximum stress strength would be attained for nanocomposite films with 6% (by weight) of clay loading. The chemical structure and morphology of the optimum sample was probed by FT-IR spectroscopy and transmission electron microscopy (TEM). © 2009 Elsevier Ltd. All rights reserved.
Journal of Applied Polymer Science (00218995) 113(5)pp. 2739-2746
In this article, the influences of five operating variables on the molecular weight (or K-value), polydispersity index (PDI), as well as polymerization yield of emulsion poly (vinyl chloride) in batch reactor were investigated simultaneously using Taguchi experimental design approach. The variables were temperature (T), water to monomer weight ratio (r), concentrations of initiator ([I]) and emulsifier ([E]), and agitation speed (S). Statistical analysis of results revealed the significance order of factors affecting the product qualities and quantity. It was found that the reaction temperature is the principal operating factor to control the molecular weight, and this is attributed to promotion of chain transfer reactions to monomer in this system. The effect of this factor on PDI is also comprehensively discussed. The significance sequences of important factors on yield are: S > [E] > r. The polymerization yield increases with S and [E] but decreases as r is increased. The relative optimum condition for a typical paste application was also determined using overall evaluation criteria. © 2009 Wiley Periodicals, Inc.
Journal of Applied Polymer Science (00218995) 111(1)pp. 338-347
In this article, the influences of operating variables on the particle size (PS) and particle size distribution (PSD) of emulsion poly(vinyl chloride) in batch reactor were investigated using Taguchi experimental design approach. The variables were temperature (T), water to monomer weight ratio (R), concentrations of initiator ([I]) and emulsifier ([E]), and agitation speed (S). Scanning electron microscope was used, together with image analysis software to determine the PS and PSD. Statistical analysis of results revealed that the PS of emulsion poly(vinyl chloride) strongly depends on emulsifier and initiator concentrations, respectively, whereas the other factors have no significant effects in the range of levels investigated in this study. Except initiator concentration, all factors have important influence on the PSD (significance sequence: S > R > T > [E]). It is implied from the greater influence of agitation speed relative to temperature on PSD that the shear coagulation predominates the Brownian coagulation in this system. The relative optimum condition for a typical paste application was also determined using overall evaluation criteria. © 2008 Wiley Periodicals, Inc.
Journal of Applied Polymer Science (00218995) 114(1)pp. 531-542
Quantification of the layered silicates dispersion level is necessary to more accurately evaluate the performance in polymer/clay nanocomposites. In this article, a new approach is developed to quantify the degree of exfoliation, intercalation, and immiscibility of layered silicates in polymer matrix, based on bright-dark pixel measurement (BDPM) in transmission electron microscope (TEM) images. Several examples of exfoliated, intercalated, and immiscible composites with different polymer and clay systems were examined. The method is capable of estimating the percent contribution of all morphologies present in the image. Comparing with X-ray diffraction (XRD) evidences, it is indicated that as a rule of thumb, the exfoliated structure is dominant whenever the exfoliation percent calculated by BDPM methodology is over 65%, no matter what kind of clay or polymer matrix is used. The intercalated structure can be ascribed to the images with exfoliation level less than 65%, but with the intercalation degree over 28%. Application of this method can facilitate the modeling or correlation of various nanocomposite properties with respect to exfoliation degree. A quantified relation is also possible between XRD and TEM using this approach. © 2009 Wiley Periodicals, Inc.
Polymer Engineering and Science (15482634) 2005pp. 149-157
In this paper the rheokinetics of Polyurethane formation and the influence of shear rate on its kinetics have been studied. Two different linear polyurethane systems with 0% and 100% hard segments are examined in a cone and plate rheometer. The isothermal increase of viscosity during polyurethane formation has been measured at different shear rates and different temperatures and is modeled with an exponential function. The molecular weight vs. time curves and the reaction kinetic constants have been obtained for various shear rates and temperatures using gel permeation chromatography (GPC). It was concluded that kinetics of polyurethane formation is enhanced as the shear rate is increased. Phase separation is found to be responsible for irregularities in the viscosity build up due to formation of polyurethane with hard segments at high conversions.
Advances in Polymer Technology (07306679) 23(3)pp. 239-255
Reactive extrusion of poly(urethane-isocyanurate) (PUIR) was studied in an intermeshing corotating twin-screw extruder. Toluene diisocyanate (TDI) and polypropylene glycol (PPG) were used as initial materials with dibutyltin dilaurate (DBTDL) as catalyst. The reaction was first examined in a batch reactor as well as in an internal mixer in order to obtain the kinetics and temperature/torque evolution trends during the formation of PUIR, respectively. For the specified screw speed and temperature profile of the extruder, a working domain can be recommended for the reactive extrusion, in terms of NCO/OH ratio (r) and catalyst concentration (C), to reach a sufficient extent of reaction. The effects of screw speed and temperature profile on the residence time parameters of the reaction mixture were investigated. It is found that the axial mixing and the RTD behavior of the reaction mixture in the extruder can be well represented by the axial dispersion model. For the reaction condition of r = 3, C = 2%, and barrel temperature profiles of 75-150°C or 90-165°C, the optimum screw rotation speed for complete NCO conversion is 20 rpm. The structures, thermal stabilities, morphologies, and physical and dynamic mechanical properties of reactively extruded PUIRs were investigated. © 2004 Wiley Periodicals, Inc.
Journal of Applied Polymer Science (00218995) 90(4)pp. 963-972
Poly(urethane-isocyanurate)s were synthesized by reacting toluene diisocyanate and poly(propylene glycol) with various stochiometric ratios (1-3) in the presence of different concentrations of dibutyltin dilaurate (DBTDL) and ferric acetylacetonate (FeAA). The influence of the NCO/OH ratio and the catalyst type and concentration on the extent of urethane and isocyanurate formation were examined using Fourier transform IR spectroscopy. No trimer formation was observed in the presence of the FeAA catalyst. The percentage of the trimer group and the trimer/urethane content were found to be increased with increasing the stochiometric ratio or DBTDL concentration. The thermal decomposition of the copolyurethanes in an inert atmosphere was studied by means of thermogravimetry (TG). The TG curves showed three decomposition steps with the principal degradation temperature at about 355-385°C. The effects of the NCO/OH ratio, catalyst type and concentration, and heating rate on the thermal stability of the copolyurethanes were determined. The Flynn-Wall, Kissinger, and Ozawa methods were used to calculate the activation energies of thermal decomposition. The swelling behavior of solid copolyurethanes in toluene showed that, as the DBTDL concentration and/or NCO/OH ratio increased, the swelling ratio and average molecular weight between crosslinks were decreased whereas the crosslink density was increased. The sol fraction of solid copolyurethanes was examined and found to be reduced when the percentage of DBTDL or the stochiometric ratio was raised. © 2003 Wiley Periodicals, Inc.
Journal of Polymer Engineering (21910340) 23(4)pp. 225-240
A kinetic study of the catalyzed reaction between toluene diisocyanate (TDI) and polypropylene glycol (PPG) was carried out in the bulk state by using quantitative Fourier transform infrared (FTIR) spectroscopy. The polymerization was studied in the presence of the catalysts dibutyltin dilaurate (DBTDL) and ferric acetylacetonate (FeAA) at three different temperatures. The kinetics was shown to obey a second-order scheme and the rate plots showed a distinct break in continuity, due to diferent reactivities of NCO groups. It was concluded that the appearance of this break point is related to the use of catalyst as well as type of polyol. The rate constants (k1,k2) and the activation parameters Ea1Ea2, ΔS1#, ΔS2#) for the isocyanate groups in the para and ortho positions in TDI molecule were calculated. It was found that the reactivity of p-NCO is 5 to 8 fold higher than o-NCO. The temperature enhances the reactivity of o-NCO rather than the p-NCO. It was also concluded that the FeAA is more sensitive than DBTDL to temperature and is more selective to enhance the reactivity of the o-NCO. © 2011, by Walter de Gruyter GmbH & Co. All rights reserved.
