Optimization of the synthesis of polyhydroxyurethanes using dynamic rheometry

Polyhydroxyurethanes (PHUs) produced by the reaction between dicyclocarbonate and diamine groups are often presented as possible candidates to substitute for classical polyurethanes based on isocyanate precursors. In the literature, the synthesis of this class of polymers is often performed according to arbitrary conditions of time and temperature without any scientific justification. As such, the real potential of PHUs is probably not fully known. Numerous contradictions in previously published results seem to support this hypothesis. Our paper proposes two methodologies based on dynamic rheometry to determine optimized conditions for the synthesis of PHUs. The case of a PHU formed by the reaction between 1,10‐diaminodecane and a dicyclocarbonate bearing a central aromatic group is described more precisely. The first approach consists of conducting various rheological experiments (kinetics, thermomechanical analyses) in situ on the reaction mixture. The second one retains the same technique to qualify the viscoelastic properties of PHUs synthesized according to various conditions. In this latter case, all samples show thermomechanical behaviour of amorphous thermoplastic polymers. But discrepancies are observed with regard to the value of the glass transition temperature and the existence or not of a rubbery zone. Comparison of these data with size exclusion chromatography results shows that these differences are direct consequences of the polymer molecular weight that can be predicted using macromolecular theory. The properties of the PHUs obtained after optimization of the polymerization reaction were compared with literature data in order to complete the evaluation of the efficiency of the rheological methodology. Copyright © 2012 Society of Chemical Industry     

Modeling nitrous oxide emissions from tile-drained winter wheat fields in Central France

Modeling nitrous oxide (N₂O) emissions from agricultural soils is still a challenge due to influences of artificial management practices on the complex interactions between soil factors and microbial activities. The aims of this study were to evaluate the process-based DeNitrification-DeComposition (DNDC, version 9.5) model and modified non-linear empirical Nitrous Oxide Emission (NOE_V2) model with weekly N₂O flux measurements at eight sites cropped with winter wheat across a tile-drained landscape (around 30-km²) in Central France. Adjustments of the model default field capacity and wilting point and the optimum crop production were necessary for DNDC95 to better match soil water content and crop biomass yields, respectively. Multiple effects of varying soil water and nitrate contents on the fraction of N₂O emitted through denitrification were added in NOE_V2. DNDC95 and NOE_V2 successfully predicted background N₂O emissions and fertilizer-induced emission peaks at all sites during the experimental period but overestimated the daily fluxes on the sampling dates by 54 and 25 % on average, respectively. Cumulative emissions were slightly overestimated by DNDC95 (4 %) and underestimated by NOE_V2 (15 %). The differences between evaluations of both models for daily and cumulative emissions indicate that low frequency measurements induced uncertainty in model validation. Nonetheless, our validations for soil water content with daily resolution suggest that DNDC95 well represented the effect of tile drainage on soil hydrology. The model overestimated soil ammonium and nitrate contents mostly due to incorrect nitrogen partitioning when urea ammonium nitrate solution was applied. The performance of the model would be improved if DNDC included the canopy interception and foliar nitrogen uptake when liquid fertilizer was sprayed over the crops.     

CARBON-13 MOLECULAR STRUCTURE PARAMETERS OF RTFOT AGED ASPHALTS: THREE PROPOSED MECHANISMS FOR AROMATIZATION.

ABSTRACT

The determination of average molecular structural parameters of asphalts represents an important step in describing their skeleton. Using a new method based only on the analysis of carbon-13 nuclear magnetic resonance measurements, the average molecular parameters were determined for three asphalts before and after Rolling Thin Film Oven Test aging. From the analysis of the changes in the parameters, three mechanisms are proposed to explain the aromatization process in asphalts during oxidation.     

NITROGEN REAGENTS IN METAL ION SEPARATION. PART IX. EXTRACTION OF COBALT AND NICKEL USING IMIDAZOLE DERIVATIVES

ABSTRACT

The extraction capability of derivatives of imidazole towards Co(II) and Ni(II) has been investigated in dilute acid medium in the presence of each of chloride, perchlorate and thiocyanate ions. The influence of the stereochemistry of the substituted imidazole on the extraction behaviour has been investigated. Two-phase potentiometric titrations were employed to determine the nature of the metal species extracted into the organic phases. The electronic spectra of the extracted metal species have been employed to provide information of the nature of such species.     

Determination of Parabolic Rate Constants from a Local Analysis of Mass-Gain Curves

A method is proposed to allow a more accurateevaluation of thermogravimetric data to identifydiffusion or partial diffusion control of scalingkinetics. This method is based on the fitting ofmass-gain data to a parabola over a short time interval.The translation of the time interval over the entiretest time period provides an actual instantaneousparabolic rate constant independently of any transient stage or simultaneous reaction steps. Theusefulness and limitations of this procedure areillustrated from oxidation tests performed on severalmetallic materials (pure nickel, single-crystalsuperalloys, and NbTi-Al alloy).     

Chemical Differences Between the Wood Extracts of Jack Pine (Pinus Banksiana), Black Spruce (Picea Mariana) and Balsam Fir (Abies Balsamea) from Eastern Canada

Abstract

Differences in the chemical composition of the wood of balsam fir (Abies balsamea (L.), jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.)) were determined by GC analysis of their hexane extracts. Certain constituents such as juvabione, (E)-α-atlantone and α-cadinene were shown to be present only in the heartwood of balsam fir. Analysis of the sapwood of the three species also revealed the presence of certain constituents such as juvabione, dehydrojuvabione and (E)- α-atlantone, all found only in balsam fir and an unidentified compound found only in jack pine. The chromatograms of the hexane extracts of both sapwood and heartwood showed characteristic patterns for each of the three species of conifers.     

Effect of process unit operations and long-term storage on catechin contents in EGCG-enriched tea drink

Due to the increasing market for functional foods and the chemopreventive action of (?)-epigallocatechin gallate (EGCG), manufacturers produce ready-to-drink green tea infusions enriched or not in EGCG. However, the maintenance of green tea catechins stability in drinks is always a challenge. In this context, the objectives of this study were (1) to assess the catechin stability in tea drink during a 6-month storage, (2) to evaluate the impact of process unit operations on catechin stability and (3) to compare the catechin and caffeine contents of commercially available tea drinks. It appeared that the stability of catechins during long-term storage was optimum at low temperature (4 °C) and acidic pH (pH 4.0). During the processing of the EGCG-enriched green tea drink, all the process unit operations, except heat-treatment, had no impact on catechin concentrations. In addition, in commercially available tea drinks, except enriched green tea drinks, their catechin contents are very low to provide health benefits.     

CFD modeling of heat transfer and flow field in a bakery pilot oven

A bakery pilot oven is modeled using computational fluid dynamics software. This approach relies on integration of an instrument into modeled geometry. The instrument is a heat flux measuring device that can be used in the industrial baking process. All three heat transfer mechanisms are considered and coupled with turbulent flow. Turbulence is taken into account via the k–ε realizable model whereas the surface-to-surface model simulates the radiation. Additionally, buoyancy forces are introduced by means of a weakly compressible formulation. The model predictions show a good qualitative agreement with the experimental measurements. A quantitative agreement was obtained to some extent. Limitations came from the difficulty to measure the temperature of the radiant surfaces of the oven. Operating conditions used are typical of bakery products and, as expected, radiation was the dominant mode of heat transfer. The integration of the instrument was useful for assessing the model. Since it is designed for industrial use, it may be a valuable tool for future challenges in the field, such as simulation of an industrial scale oven.