Environmental aging of cold‐cured epoxy‐silica hybrids prepared by sol−gel process

The article investigates the effects of long term environmental aging on thermal and mechanical properties of epoxy‐silica hybrids. These nanostructured materials, prepared by non‐aqueous sol‐gel process and in situ generation of nanosilica during epoxy curing at room temperature, present the potential to be used as cold‐cured adhesives for civil engineering and Cultural Heritage applications. A specifically developed conditioning procedure for these cold‐cured nanostructured materials was applied before moisture/water absorption tests. The work evidenced the superior durability of the studied epoxy‐silica hybrid, which kept its performances in severe, but realistic, environmental conditions with respect to traditional epoxy adhesives. The reduction in the glass transition temperature and mechanical properties of the studied epoxy‐silica hybrid, observed in the first weeks of environmental aging, was followed by a significant recovery. This was attributed to two concomitant phenomena: the reactivation of the incomplete curing reactions in the epoxy domains and the continuation of the condensation reactions in the siloxane domains activated by the absorbed water. Finally, the Fickian behavior, presented by the studied epoxy‐silica hybrid, was used as an indirect indication of the homogeneity of achieved microstructure, with well dispersed silica nanostructures in the epoxy network. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40093.     

Stimuli‐sensitive nanostructured poly(sodium 4‐styrene sulfonate): Synthesis,characterization, and study of metal ion retention properties

Stimuli‐sensitive polymers are a type of smart polymers having the capability to change their configuration or properties under adequate stimuli as heat, pH, magnetic field, mechanical strength, among other. The aim of this work was to synthesize nanostructured polymers with antibacterial properties capable to change their retention properties of divalent metal ions by external stimuli (pH and ionic strength). For that, a polymerizable nanostructured crosslinker (PNC) based on silver nanoparticles (AgNPs) and acrylic acid was synthesized. Later, NPSS was synthesized by free‐radical polymerization, characterized by different analytical techniques and its retention properties of divalent ions (Cu²⁺, Fe²⁺, Mn²⁺, and Zn²⁺) were studied at different pHs and ionic strengths (5.0, 7.0, and 9.0; and 0.0, 0.5, and 1.5% NaCl, respectively). It was evidenced that AgNPs can be synthesized using acrylic acid as stabilizing agent, and later, be used for synthesis of NPSS by free‐radical polymerization. For NPSS, metal ion retention decreases as pH is increased; in addition, results suggest that the electrostatic interaction is not the only determining factor in the retention of ions. Other possible factors which would be affecting the retention are: water flow by swelling capacity and water flow by osmotic stress resulting of high salt concentration. NPSS showed antimicrobial activity against Escherichia coli and Staphylococcus aureus which was enhanced by incorporation of PNC based on AgNPs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46001.     

High‐Tg,heat resistant epoxy–silica hybrids with a low content of silica generated by nonaqueous sol–gel process

The epoxy‐silica hybrids showing high T_g and thermal stability are prepared by the non‐aqueous sol–gel process initiated with borontriflouride monoethylamine. Tetramethoxysilane (TMOS) is used as a precursor of silica and 3‐glycidyloxypropyl trimethoxysilane as a coupling agent to strengthen the interphase interaction with an epoxy matrix. The basic factors governing the nonaqueous sol–gel process are studied in order to reveal the formation–structure–properties relationships and to optimize the hybrid composition as well as conditions of the nonaqueous synthesis. The formation of the hybrid, its structure, thermomechanical properties and thermal stability are followed by chemorheology experiments, NMR, DMA and TGA. The most efficient reinforcement of the epoxy network is achieved by the combination of both alkoxysilanes, showing synergy effects. The hybrids with a low content (～10 wt %) of the in situ generated silica exhibit dramatic increase in T_g and the high modulus, 335 MPa, up to the temperature 300°C. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40899.     

Effects of cooling temperature and aging treatment on the morphology of nano‐ and micro‐porous poly(ethylene‐co‐vinyl alcohol) membranes by thermal induced phase separation method

Poly(ethylene‐co‐vinyl alcohol) (EVOH 32) / 1,3‐propanediol mixtures are processed by thermally induced phase separation for the formation of porous membranes. The crystallization line was determined both by the cloud‐point and DSC methods. Two precursor solution compositions, four quench temperatures and various aging times were explored. It is found possible to generate both polymer‐crystallization controlled morphologies (for high quenches and/or sufficiently aged dopes), especially globular microporous ones, and novel nano‐scale porous morphologies dominated by intra‐binodal phase separation (for low quenches and limited or no precursor solution aging). Structural characterization of the membranes was accomplished via application of scanning electron microscopy and wide angle X‐ray diffraction. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40374.     

Nano‐dimensional self assembly of regioregular poly (3‐hexylthiophene) in toluene: Structural,optical, and morphological properties

This article presents the optimization and systematic analysis of the growth kinetics of fiber formation of the regio‐regular poly (3‐hexylthiophene), rr‐P3HT. In addition to it a comparative study of as‐prepared fiber with fresh, quenched (at ?7°C) and commercial rr‐P3HT formed in toluene solvent. The rr‐P3HT (M_w ≈ 5340; polydispersity ≈ 1.22) is synthesized using a well known Grignard metathesis reaction and characterized by ¹HNMR and FTIR techniques. The films obtained by the ageing of rr‐P3HT solution for 20 days contain nanostructured fiber with 6–10 nm thickness. However, it acquires a nanostructured globular shape when same concentration of solution is sudden quenched at ?7°C. A saturation point for the growth of nano fiber is observed under UV–visible study and it is found that 10 days are sufficient for fiber growth. The concentration dependent free exciton band width of fiber growth is studied by Frank–Condon principle and correlated with AFM morphological studies. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40931.     

Flame‐retarding mechanism of organically modified montmorillonite and phosphorous‐Nitrogen flame retardants for the preparation of a halogen‐free,flame‐retarding thermoplastic poly(ester ether) elastomer

In this study, thermoplastic poly(ester ether) elastomer (TPEE) nanocomposites with phosphorus–nitrogen (P–N) flame retardants and montmorillonite (MMT) were prepared by melt blending. The fire resistance of the nanocomposites was analyzed by limiting oxygen index (LOI) and vertical burning (UL 94) tests. The results show that the addition of the P–N flame retardants increased the LOI of the material from 17.3 to 27%. However, TPEE containing P–N flame retardants only obtained a UL 94 V‐2 ranking; this resulted in a flame dripping phenomenon. On the other hand, TPEE containing the P–N flame retardant and organically modified montmorillonite (o‐MMT) achieved better thermal stability and good flame retardancy; this was ascribed to its partially intercalated structure. The synergistic effect and synergism were investigated by Fourier transform infrared spectroscopy and thermogravimetry. The introduction of o‐MMT decreased the inhibition action of the P–N flame retardant and increased the amount of residues. The catalytic decomposition effect of MMT and the barrier effect of the layer silicates are discussed in this article. The residues after heating in the muffle furnace were analyzed by scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and laser Raman spectroscopy. It was shown that the intercalated layer silicate structure facilitated the crosslinking interaction and promoted the formation of additional carbonaceous char residues in the formation of the compact, dense, folded‐structure surface char. The combination of the P–N flame retardant and o‐MMT in TPEE resulted in a better thermal stability and fire resistance because of the synergistic effect of the mixture. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41094.     

Transparency and water vapor barrier properties of polybenzoxazine‐silica nanocomposites provided with perhydropolysilazane

Poly[6,6′‐(1‐methylethylidene)bis(3,4‐dihydro‐3‐2H‐1,3‐hexylbenzoxazine)] (PB‐hda)‐silica nanocomposites were synthesized with perhydropolysilazane (PHPS) and PB‐hda by ring opening polymerization in one step. Both high transparency and good water vapor barrier property (WVP) are required to be improved in the field of packing and electronic materials, such as OLED, solar cell, and electronic paper. PB‐hda has shown high toughness and high thermal stability. However, it became dark brown and showed a reduction of WVP with increasing curing temperature, which make it difficult to be applied to packing and electronic materials. In this study, we aim to improve transparency and WVP by addition of PHPS into PB‐hda matrix. It was found that nanocomposites showed the improvement of WVP and transparency owing to Si? O? C linkages between PB‐hda and PHPS. In particular, a nanocomposite with 1 wt % of silica showed the most significant improvement in terms of transparency and the WVP. These properties were found to be influenced by the thickness of the combined polymer‐silica layers that formed around the silica particles; these layers were thickest in the 1 wt % sample. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44238.     

Graphene‐based molecularly imprinted polymer for separation and pre‐concentration of trace polycyclic aromatic hydrocarbons in environmental water samples

A composite of reduced graphene oxide and pyrene‐imprinted polymer was synthesized and employed as a solid phase for extraction of five selected polycyclic aromatic hydrocarbons (PAHs) from water samples. Gas chromatography‐time of flight/mass spectrometry was employed in the analysis of the extracts. The composite was prepared by a free radical polymerization of methacrylic acid and 4‐vinylpyridine as monomers and ethylene glycol dimethacrylate as a crosslinker. The adsorption studies were carried out through batch binding studies. The binding capacity for the imprinted and non‐imprinted composite was 101.83 and 68.21 µg g^?1, respectively. The adsorption followed the pseudo 2nd order and well fitted the Langmuir isotherm. Mean recoveries ranging from 73% to 105.4% for both spiked deionized water and environmental water samples were obtained when the imprinted composites were employed in solid phase extraction of the PAHs. The composites could be re‐used for five times without a significant loss in recoveries. The proposed method was employed for the analysis of spiked environmental water samples and did not show significant changes in the recoveries showing there were no matrix interferences. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45300.     

Fabrication of PFO‐DBT:OXCBA nanostructured composite via hard template

Poly[2,7‐(9,9‐dioctylfluorene)‐alt−4,7‐bis(thiophen‐2‐yl)benzo‐2,1,3‐thiadiazole] (PFO‐DBT) and o‐xylenyl‐C₆₀‐bisadduct (OXCBA) nanostructured composite has been fabricated via the hard porous alumina template‐directed method. Spin‐coating technique at the spin rate of 1000 rpm is used to assist the infiltration of polymer solution into porous template. PFO‐DBT nanotube is fabricated by replicating the porous alumina template before the formation of PFO‐DBT:OXCBA nanostructured composite. Formation of nanostructured composite is completed once the infiltration of OXCBA solution into PFO‐DBT nanotubes is achieved. Detailed results of morphological, structural, and optical properties of PFO‐DBT nanostructures (nanorods and nanotubes) of different solution concentrations are reported. By tuning the optical properties of PFO‐DBT nanostructures, the effect of solution concentration on the optical properties can be realized. The promising PFO‐DBT nanotubes are chosen for the further fabrication of OXCBA:PFO‐DBT nanostructured composite that acts as a core and shell, respectively. Although the nanostructured composite of PFO‐DBT:OXCBA yield low light absorption intensity, the absorption spans the whole visible region and produce low optical energy gap. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44228.     

Thermoelectric performance of electrodeposited nanostructured polyaniline doped with sulfo‐salicylic acid

Conducting polymers, in present days, are considered to be potential thermoelectric (TE) materials. Among them polyaniline (PANI) is a promising candidate. Nanostructured polyaniline doped with organic dopant is electrodeposited and structurally characterized. Its transport properties are investigated for thermoelectric applications. The analysis of transmission electron microscopy image reveals that the sample is rod like nanostructure. This study shows that the type (inorganic/organic) of dopants plays an important role to influence the dimension of nanostructure and the electrical transport properties of PANI. In this study, organic dopant sulfosalicylic acid is proposed for enhancement of figure of merit through an increase in thermoelectric power and decrease in thermal conductivity. Compared to our earlier work the figure of merit evaluated is two orders higher than that of the inorganic dopant bismuth nitrate doped PANI. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39920.     

Nanocomposites of poly(3‐hydroxybutyrate)/organomodified montmorillonite: Effect of the nanofiller on the polymer's biodegradation

Poly(3‐hydroxybutyrate) (PHB) is a biopolymer that can be degraded by extracellular PHB depolymerase. This enzyme is secreted by various microorganisms, but bacterial PHB depolymerases are the most widely studied. The biodegradability rate depends on various factors. By controlling them, the biodegradability rate can change and be customized, and thus, the applications of the polymer can increase and become more diverse. In this work, the role of organomodified montmorillonite (OMMT) on PHB biodegradation was investigated. Using the melt‐mixing method, nanocomposites of PHB and OMMT as the nanofiller were prepared. The enzyme was isolated from the fungus Penicillium pinophilum and the enzymatic degradation was studied for both pure polymer and its nanocomposites. It was found that, after 25 days of enzymatic degradation, the mass loss was very low, while the polymer's average molecular weight as measured by gel permeation chromatography was significantly reduced (more than 50%). Additional peaks corresponding to PHB oligomers (from pentamers to nonamers) appeared after biodegradation. This behavior was observed for pure PHB and the hybrid materials. Scanning electron microscopy imaging of the biodegraded surfaces and analysis of these images showed that the higher amount of nanoclay (10 wt %) resulted in larger biodegraded area of the specimens. The results presented here demonstrate that the presence of the nanoclays enhances the biodegradation rate of pure PHB polymer and provide quantitative data for the biodegradation of PHB/organoclay hybrid materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41656.     

Mechanism of action of different d‐spacings clays on the intumescent fire retardance of polymers

A series of sodic and organophilic clays with different d‐spacings was added to a polymeric matrix of poly (ethylene‐co‐butyl acrylate) EBA‐30, containing an intumescent formulation of ammonium polyphosphate (APP) and pentaerythritol (PER), in order to investigate the influence of the d‐spacings of the clays on their synergistic effects with the intumescent formulation. A series of samples was evaluated through cone calorimetry, SEM, TG‐FTIR, FTIR, and XRD of burned residues. The results revealed that the addition of clays with smaller d‐spacings led to a synergistic interaction with the intumescent formulation, and consequently to an improvement in the flame retardance of the materials. This effect was not observed with the addition of clays with d‐spacings larger than 30 Å. For these materials, the formation of a less homogeneous and structured intumescent layer, and a delay in the formation of the phosphocarbonaceous species which act as char precursors was observed. This delay could be responsible for the loss of synergy and also for the type of char morphology formed when larger d‐spacings clays were used. XRD analyses results indicated that the presence of clays in the materials promoted changes in the crystalline phase of the char when the samples were submitted to higher temperatures. Those changes probably allowed for the maintenance of the structures at high temperatures. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1759–1771, 2013     

Optimal designing of polyurethane‐based nanocomposite system for aerostat envelope

This article reports an optimal designing of thermoplastic polyurethane (TPU) nanocomposite formulation, particularly targeting aerostat envelope for enhanced weathering and gas barrier properties. The synergistic effect of conventional UV protective additive with advanced nano materials (i.e. nanoclay and graphene) on TPU‐based formulations was explored. A series of formulations were prepared in accordance with a mixture design for three components additives (UV stabilizer, nanoclay, and graphene) and coated on to a woven polyester (PET) fabric. The coated systems were evaluated for resistance to UV radiation, resistance to helium gas permeability, and loss in both the properties against accelerated artificial weathering. The composition of the additive mixture was simultaneously optimized by desirability function approach with a view to maximize UV radiation protection and minimize helium gas permeability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43529.     

Preparation of PEI nanofiber membrane based on in situ and solution crosslinking technology and their adsorption properties

Two kinds of PEI (Polyethyleneimine) nanofibers membrane were successfully prepared by electrospinning and crosslinking technology, which were insoluble in water. One Polyethyleneimine/ Epichlorohydrin/ Polyacrylonitrile nanofibrous films (abbreviated as PEI/ EPI/ PAN NFs) was prepared by in situ crosslinking of PEI/PAN nanofiber containing of EPI, and the other PEI/ PAN/ EPI NFs was prepared by crosslinking PEI/ PAN nanofibers using EPI solution. The composition and morphology of nanofibers before and after crosslinking were investigated by infrared spectroscopy and scanning electron microscopy. PEI/EPI/PAN nanofibers exhibited excellent adsorption properties toward heavy metal ions and methyl orange dyes, which can also be reused multiple times. The adsorption rate of methyl orange remained around 75% after 4 cycles, meanwhile, the adsorption rate of copper and lead still remained around 90% after 5 cycles. In addition, we found that PEI/ PAN/ EPI nanofibers prepared by solution crosslinking technology solved the problem of easy gel formation in in situ crosslinking technology and facilitated the continuous production of PEI/ EPI/ PAN nanofibers, which is better than in situ crosslinking technology. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48279.     

Chemical and bonding effects of exposing uncured PBI‐NBR insulation to ambient conditions

Uncured Polybenzimidazole‐Nitrile Butadiene Rubber (PBI‐NBR) insulation experiences altered chemical and bonding phenomena if exposed to ambient conditions while in a sheet‐stock configuration. Multiple lots of a PBI‐NBR formulation exposed to ambient and slightly elevated temperature (100°F) conditions experience bonding degradation when vulcanized to a metal substrate. Chemical analyses show that tallow amine (clay particle surfactant) accumulates at the surface of uncured NBR as a function of ambient and 100°F exposure time. Additionally, thin film analyses suggest surface oxidation of NBR polymers when exposed to the ambient environment. Mechanical and chemical observations imply a correlation between vulcanized bonding performance with tallow amine diffusion and polymer surface reaction. The diffusion and reactivity of chemical species found in the PBI‐NBR formulation has implications to other fields employing these components. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42636.     

Aging effect of atmospheric pressure plasma jet treated polycaprolactone polymer solutions on electrospinning properties

In previous work, an atmospheric pressure plasma jet was applied to successfully improve the electrospinnability of poly-ε-caprolactone (PCL) which enabled the fabrication of beadless nanofibers. In this paper, we report the aging effect of the plasma treatment to evaluate the robustness of the developed process. For this purpose, plasma-treated PCL polymer solutions with different exposure time were stored for 1 and 8 days and the aged solutions were analyzed in terms of conductivity, viscosity, surface tension, pH, and polymer molecular weight. During storage, the surface tension and acidity of the plasma-treated solutions were maintained constant. However, the viscosity was found to be significantly lower after 8 days which was attributed to PCL degradation. Electrospinning of all stored PCL solutions resulted in the generation of beadless PCL nanofibers. The plasma treatment effects were thus found to be highly stable over time and capable of producing high-quality PCL nanofibers up to 8 days. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48914.     

Sustained‐release properties of cotton fabrics impregnated with nanotuberose fragrance

Tuberose‐fragrance (TF) loaded polybutylcyanoacrylate nanoparticles were successfully prepared via emulsion polymerization. The nanotuberose fragrance (Nano‐TF) was directly impregnated into the cotton fabrics as an aromatic reagent. Dynamic light scattering and transmission electron microscopy showed that the average size of the spherical Nano‐TF was 202.4 nm. Fourier transform infrared spectroscopy demonstrated that TF was encapsulated into the BCA nanoparticles and that the Nano‐TF was in existence in the cotton fabrics. Thermogravimetric analysis showed that the loading TF content of the Nano‐TF was 50.9% and that 10.02% Nano‐TF had been impregnated into the fabrics. A lot of Nano‐TF was adhered onto the surface of the cotton fabrics after 50 washings, as shown by scanning electron microscopy and gas chromatography/hydrogen flame ionization detection (GC–FID). In addition, GC–FID demonstrated that most aroma compounds of the cotton fabrics impregnated with Nano‐TF only lost less than 20% of their aroma after 60 days of deposition and around 75% of their aroma after 6 h of deposition at 120°C, so they showed better sustained‐release properties than those with TF. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41678.     

Cold‐cured epoxy‐silica hybrids: Effects of large variation in specimen thickness on the evolution of the Tg and related properties

Experimental organic–inorganic hybrid systems, based on silane functionalized difunctional and trifunctional epoxy resins and an alkoxysilane precursor mixture, containing small amounts of ammonium molybdate, are evaluated for potential use as adhesives cured at ambient temperatures. The precursor resin mixtures are found to exhibit a large increase in viscosity with a pseudoplastic behavior. Scanning electron microscopy (SEM) analysis shows the existence of siloxane domains with nanometric dimensions, except for the presence of microscopic molybdate particles. By monitoring the evolution of the glass transition temperature (T_g) during curing, varying the thickness of the specimens between 0.2 and 4.5 mm, it is found that the organic–inorganic hybrids display a significant increase in the final T_g over the parent unmodified epoxy resins, particularly in thin specimens and when ammonium molybdate is added. Small‐angle X‐ray scattering (SAXS) spectra show that the dimensions and typographic features of thick and thin specimens are similar, both containing an agglomeration of primary particles of 5–6 nm. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Sol–gel preparation of ultralow refractive index silica coatings with hydroxypropyl‐beta‐cyclodextrin as porogen

Ultralow refractive index films were prepared based on a base‐catalyzed sol–gel process using methyltriethoxysilane (MTES), tetraethylorthosilicate (TEOS) as co‐precursors, and hydroxypropyl‐beta‐cyclodextrin (HPCD) as porogen. After further modification by hexamethylisilazane (HMDS), the lowest refractive index of these silica coatings obtained from the hybrid sol was 1.05 and the static water contact angles of the coatings increased from 66.4° to 128.7°. The effect of weight ratio of HPCD to SiO₂ on the refractive index and on the formation of coating films were systematically studied. The data showed that the films prepared with HPCD as porogen got a pore diameter around 4 nm. Compared with those templates such as poloxamer (F127), HPCD not only perform well in decreasing the refractive index of films, but also eliminate light scattering caused by mesopore of the film, will have potential value in the field of surfactant‐templated methods. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44686.     

Influence of electrochemical copolymerization conditions of 3‐methylthiophene and biphenyl on the morphology and nanomechanical properties of the films

The aim of this work is to synthesize novel 3‐methylthiophene (3MTh)/biphenyl (Biph) copolymer films by electropolymerization and study their mechanical properties through nanoindentation. The morphology, the chemical structure as well as the electrical conductivity of the copolymer films depended strongly on the electropolymerization conditions. It was found that the polymer deposition follow an instantaneous, two‐dimensional nucleation and growth mechanism leading to homogenous films. The copolymer films had higher Young modulus and nanohardness than poly(3‐methylthiophene) (3PMTh), indicating that the incorporation of Biph units within the P3MTh chain leads to a more densely packed structure and a more brittle polymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42575.