Synthesis and characterization of new imidazole and fluorene–bisphenol based polyamides: Thermal,photophysical and antibacterial properties

A new para-linked diether-diamine, 9,9-bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-aminophenoxy] phenyl}fluorene (III), bearing fluorene–bisphenol and two ortho-linked diaryl-substituted imidazole rings were synthesized by the catalytic reduction of the nitro groups of compound (II), 9,9-bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-nitrophenoxy]phenyl}fluorene, by using hydrazine monohydrate in the presence of Pd/C. Compound (II) was synthesized by the nucleophilic chloro displacement reaction of the synthesized 2-(2-chloro-5-nitrophenyl)-4,5-diphenyl-1H-imidazole with 9,9-bis(4-hydroxyphenyl)fluorene in refluxing DMAc in the presence of potassium carbonate. This diamine was condensed directly with aliphatic and aromatic diacids via the Yamazaki–Higashi phosphorylation method in the presence of triphenylphosphite (TPP), pyridine (Py) and halide salt to give high molecular polyamides (PAs). The synthesized PAs were obtained in quantitative yields with inherent viscosities between 0.51 and 0.76 dL g^?1. The structures of diamine and PAs were characterized by elemental analysis, FT-IR and NMR spectroscopy, and properties of PAs were investigated by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and UV–visible and fluorescence spectroscopy. The PAs showed good solubility in aprotic and polar organic solvents, with high thermal stability exhibiting the glass transition temperatures (T_gs) and 10% weight loss temperatures (T_10%) in the range of 226–330 °C and 400–466 °C in air, respectively, and fluorescence emission with maximum wavelengths (λ_em) in the range of 417–473 nm with quantum yields (Φ_f) of 9–35%. Two of these polymers together with compounds (II) and (III) were also screened for antibacterial activity against Gram positive and Gram negative bacteria.     

Investigating the role of surface treated titanium dioxide nanoparticles on self-cleaning behavior of an acrylic facade coating

In this study, the addition of silane treated TiO₂ nanoparticles on the self-cleaning properties of an acrylic facade coating was evaluated. Tetraethoxyorthosilicate, TEOS, was used for surface treatment of TiO₂ nanoparticles. The silica grafting on the TiO₂ nanoparticles was characterized via Fourier Transform Infrared spectroscopy, specific surface area measurement, pore size distribution, and real density measurements. The effect of surface treatment and content of nanoparticles on the photocatalytic activity of acrylic coating and self-cleaning properties was studied. For this purpose, the photodegradation of Rhodamine B (Rh.B) dyestuff, as a colorant model, was investigated by colorimetric technique, while the coating samples were exposed to UVA irradiation. Performance of the acrylic coating films was evaluated by gloss change during accelerated weathering conditions. Also, the surface morphology of the coating films was studied using SEM analysis. The results showed that the addition of both treated and untreated TiO₂ nanoparticles provides self-cleaning property to the acrylic coatings. However, silica surface treatment of TiO₂ nanoparticles reduces the coating degradation caused by TiO₂. This is more evident when higher concentrations of the treated TiO₂ nanoparticles are used.     

Fabrication of low surface free energy automotive clear coats: Mechanical and surface chemistry studies

This work aims at improving the surface chemistry and the mechanical properties of a commercial acrylic–melamine clear coat using a functional siliconized additive. The resistance of films against biological degradation was then investigated using pancreatin (simulated bird droppings) and Arabic gum (simulated tree gum). Variations in the surface and bulk chemical structures, as well as the thermomechanical characteristics of the clear coats at different concentrations of the additive, were investigated by a wide range of techniques inclusive of contact angle measurement, gonio‐spectrophotometery, dynamic mechanical thermal analysis (DMTA), energy‐dispersive spectroscopy, atomic force microscope, optical microscope, and attenuated totalreflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. Negligible effect of additive on color change was revealed. It was shown that even at low loadings of additive it could migrate to the surface, producing hydrophobic films with very low surface free energies with water contact angle exceeding 100°. In addition, it was found by DMTA and ATR‐FTIR studies that the functional additive was covalently attached to the acrylic–melamine chains through its hydroxyl groups. However, phase separation was observed at high concentrations of additive, leading to reduced crosslinking density. The clear coat resistance against pancreatin and Arabic gum was improved using optimum concentrations of the additive. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermomechanical and chemorheology properties of a thermosetting acrylic/melamine clearcoat modified with a hyperbranched polymer

The work presented here aims at studying the thermomechanical and chemorheological properties of an automotive clearcoat containing an acrylic/melamine resin modified with a hyperbranched poly ester‐amide (HBP) additive. Rheological experiments were conducted at ambient (25°C) and curing temperature (140°C). Dynamic mechanical thermal analysis and hardness measurements were performed to reveal the influence of HBP content on the behavior of the cured samples. It was found that the viscosity of the resin containing HBP samples considerably decreased. Although curing degree and mechanical properties were improved at low HBP loadings, a reverse effect was seen at higher contents. Dynamic rheological results during curing showed that although low amount of HBP resulted in an early gel point (GP), higher HBP loading postponed the GP. This loading‐dependent behavior was explained by the influence of HBP on viscosity and reactivity of the system on which the curing performance was influenced oppositely. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of different silicon-based surface active additives on degradability of clearcoats exposed to bird droppings

A series of clearcoats separately loaded with different concentrations of functional silicon–polyacrylate and polydimethyl siloxane additives were prepared. Optical performances of the cured films were studied by gonio-spectrophotometry. Dynamic mechanical thermal analysis was used in order to investigate viscoelastic properties of the additive-containing films. Contact angle measurements, (FTIR) spectroscopy, scanning electron microscopy equipped with energy-dispersive analysis of X-ray, and atomic force microscopy techniques were utilized to evaluate surface properties of the clearcoats. It was shown that clearcoat surface free energy decreased and its crosslinking density increased in the presence of the additives. Results revealed that addition of both additives to the clearcoat enhanced its resistance against pancreatin (simulated bird droppings). A decrease in surface degradation was observed in the presence of the additives. Results also showed that functional polydimethyl siloxane influenced coating viscoelastic, surface chemistry, and biological resistance more effectively compared to that of the functional silicon–polyacrylate one.     

Studying the effects of the chemical structure of an automotive clearcoat on its biological degradation caused by tree gums

The effects of artificial and natural tree gums on the mechanical, chemical, and aesthetic performances of two automotive acrylic/melamine clearcoats were studied. To this end, two clearcoats with different acrylic/melamine ratios were investigated. Biological experiments were performed under post-aging conditions using an accelerated weathering test. Analytical techniques including optical microscopy, scanning electron microscopy (SEM), gloss measurement, FTIR, and DMTA analyses were utilized to reveal the responses of the coating system upon exposure to the aforementioned biological materials. Contact angle measurements were also conducted to estimate the surface energy of the coatings. Greater crosslinking density, together with a higher T _g and damping behavior of the clearcoat, indicative of a greater degree of cure, were obtained as the ratio of melamine crosslinker increased. It was shown that both Arabic and natural tree gums could strongly attach to the clearcoats’ surface, imposing a significant stress during the drying process, thereby leading to a physical failure. In addition, the acidic nature of these biological materials leads to a chemical alteration in the clearcoats’ structure. The greater crosslinking density and lower hydrophilicity of the clearcoats containing higher melamine crosslinker were responsible for the weaker interaction of gums with the surface. This showed a greater capability for stress damping. Small surface cracks with fracture morphology on the coatings exposed to biological materials at higher exposure times (in the xenon test) were also observed. This is discussed based on the adhesion of the coatings to gums at longer exposure times, because of significant stress.     

CFD modeling of the effect of absorbent size on absorption performance of a packed bed column

This paper reports a study on the ability of the computational fluid dynamics (CFD) modeling for analyzing the fluid flow hydrodynamics and absorption in a packed bed column. The water absorption by silica gel absorbents in an experimental packed bed was investigated, and the absorption performance of two different sizes of absorbent was studied. A series of experiments were carried out for five setups which are different in the weight ratio of the employed big to small absorbents. The CFD modeling was carried out for all five experimental setups. The predicted results show that by more replacing of the big absorbents with the small ones the water absorption increased. On the other hand, a greater pressure drop was observed as more small absorbents were used. The predicted absorption rates were compared with the measured values and on average a consistency within 11.6% was observed.     

Characteristics of Natural Organic Matter and Formation of Chlorinated Disinfection By-Products from Two Source Waters that Respond Differently to Ozonation

This study investigated the characteristics of natural organic matter (NOM) in two different raw surface water sources that respond differently to ozonation: one for which ozonation decreases the disinfection by-product (DBP) formation potentials (i.e., Capilano Reservoir, Vancouver, Canada), and one for which ozonation does not (i.e., South Thompson River, Kamloops, Canada); and evaluated the effect of ozonation on these characteristics and on the DBP formation potential of the different size and polar fractions of the NOM. Although the South Thompson River and the Capilano Reservoir waters had relatively similar total organic carbon concentrations, the characteristics of the NOM (e.g., size and polar distribution, specific UV absorption), in these water sources differed significantly. In general, no clear and consistent trend was observed with respect to the tendency of different size and polar fractions of NOM to generate DBPs. Nonetheless, the results from the present study suggest that hydrophobic NOM has a higher tendency to form DBPs. In addition, when considering individual size and polar fractions, specific UV absorption was a good overall indicator of the DBP formation potential for a given water source. The effect of ozonation on South Thompson River and Capilano Reservoir waters also differed significantly. For both source waters, ozonation appeared to have a greatest effect on the more hydrophilic fractions, generally increasing the DBP formation potential of the smaller more hydrophilic NOM, while generally decreasing that of the larger more hydrophilic NOM. The beneficial effect of ozonation on reducing haloacetic acid (HAA) formation potentials was due to a reduction in both the dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) formation potentials, while the negative effect of ozonation on increasing HAA formation potentials was due to an increase in the DCAA formation potentials. The results from the present study clearly indicate that the use of ozone as a primary disinfectant does not necessarily reduce the DBP formation potential of NOM in all water sources, further demonstrating the complex structure of NOM and the fact that NOM from different sources cannot be simply treated as one entity and compared with one another.