Photocuring of cycloaliphatic epoxy formulations using polyesters with multiarm star topology as additives

Multiam star polyesters were synthesized by growing poly(ε‐caprolactone) (PCL) arms from hyperbranched polyesters cores of different molecular weight and used as polymeric modifiers in UV‐curable cationic formulations based on a biscycloaliphatic epoxy resin. The effect of the multiarm stars on the curing kinetics has been investigated by real‐time FTIR. The thermal‐mechanical properties of the photocured thermosets have been studied with calorimetry and dynamomechanical and thermogravimetric analysis. Impact strength tests have been performed to assess their effect on the toughness of the cured materials. An accelerative effect of these modifiers has been observed as a consequence of the participation of the hydroxyl groups of the modifiers in the cationic curing of the epoxy resin. A modest increase in toughness accompanied by a decrease in the glass transition are observed, as a consequence of the incorporation of the modifiers into the network structure, leading to homogeneous, in situ reinforced materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40005.     

Formic acid decomposition on Au catalysts: DFT,microkinetic modeling,and reaction kinetics experiments

A combined theoretical and experimental approach is presented that uses a comprehensive mean‐field microkinetic model, reaction kinetics experiments, and scanning transmission electron microscopy imaging to unravel the reaction mechanism and provide insights into the nature of active sites for formic acid (HCOOH) decomposition on Au/SiC catalysts. All input parameters for the microkinetic model are derived from periodic, self‐consistent, generalized gradient approximation (GGA‐PW91) density functional theory calculations on the Au(111), Au(100), and Au(211) surfaces and are subsequently adjusted to describe the experimental HCOOH decomposition rate and selectivity data. It is shown that the HCOOH decomposition follows the formate (HCOO) mediated path, with 100% selectivity toward the dehydrogenation products (CO₂ + H₂) under all reaction conditions. An analysis of the kinetic parameters suggests that an Au surface in which the coordination number of surface Au atoms is ≤4 may provide a better model for the active site of HCOOH decomposition on these specific supported Au catalysts. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1303–1319, 2014     

Potential dermal exposure to deltamethrin and risk assessment for manual sprayers: influence of crop type

A comparison of the Potential Dermal Exposure (PDE) of workers to the insecticide deltamethrin was made as a function of crop type, in small agricultural production units in Argentina. Seven experiments were done with two different crops (maize and broccoli, treated area between 600 and 1000 m(2)) with three different operators under typical field conditions using a lever operated knapsack. The methodology is based on the whole body dosimetry technique, presenting separately the data for mixing/loading and application activities. These results indicate a higher concentration of pesticide in lower body sections for broccoli and a wider distribution for maize. The risk inherent in these agricultural procedures is estimated through Margin of Safety (MOS) values and was found to be generally safe. Preliminary results of a mass balance distribution of the pesticide between crop, soil and operator are also presented.     

Assessment of Novel Water-Borne Coatings Obtained from Composite Latex Particles and Reinforced with TiO2 Nanotubes

Novel, environmentally friendly waterborne coatings were obtained from the filmification of nanostructured latex particles reinforced with inorganic nanotubes. The latex used to form the coatings consists of core-shell particles with a shell functionalized with different amounts of acrylic acid (AA). This external polymer layer was doped, in some cases, with TiO₂ nanotubes at three different concentrations: 100, 500 and 1000 ppm. The composite particles were synthesized in two steps by semi-continuous emulsion polymerization at 75°C. A series of films was prepared by employing core-shell particles with different sizes, core cross-linking and shell functionalization. The coatings obtained were characterized by infrared spectroscopy (FTIR), tapping mode atomic force microscopy (TM-AFM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetrical analysis (TGA). Drying rates and tests were also performed to further evaluate these films. It was observed that the addition of small amounts of TiO₂ nanotubes contributes to improve the application properties, mainly adhesion to metallic substrates and water impermeability. The resistance to thermal degradation was also strongly increased, as showed by the DSC and TGA analyses.