Hard Chain Research Articles

El desplazamiento de las fuentes de agregación de valor en la cadena de maíz duro ecuatoriana

Este estudio estima el desplazamiento de las fuentes de agregación de valor en Ecuador según la lógica de la “curva agregada de la sonrisa” que recepta los cambios entre los insumos participes–primarios, secundarios, terciarios–. Con base a los costos de los productores de la cadena de maíz amarillo, se determina ese tipo de desplazamientos mediante una estimación de corte transversal cuya inclinación resulta más a tono con la detectada por Baldwin et. al., 2014 en varios países asiáticos entre 1985-1995, y no tanto la que encuentran entre 1995- 2005 cuando se aprecia una tercerización más clara de la producción. Palabras clave: Fuentes de agregación de valor, tercerización de la producción, cadena productiva del maíz amarillo. URL: http://revistas.uta.edu.ec/erevista/index.php/bcoyu/article/view/678

Solubility of gases in ionic liquids using PHTC equation of state

In our previous work, a perturbed hard trimer chain (PHTC) equation of state (EOS) was used to compute the volumetric properties of several ionic liquids (IL) (M. M. Alavianmehr et al., Ionics (2016) 2447–2459). In the present study, the proposed EOS is employed to model the solubilities of CO2, H2S and R143a gases in some ionic liquids for temperatures ranging from 282 K to 353.15 K and at pressures (gas mole fractions) up to 5 MPa (0.8). The proposed EOS is applied to estimate Henry's constant and Gibbs energy of solvation of CO2 in [C8mim][PF6] ionic liquid. The outcomes of the results for the Henry constant on the mole fraction scale are compared with the experimental data. Parameters appeared in the EOS for pure ILs and considered gases are obtained using densities given in literature over a broad range of temperature. Using three parameters together with one binary interaction parameter one can predict solubility parameters with acceptable accuracies.

Microphase-separated structure and mechanical properties of cycloaliphatic diisocyanate-based thiourethane elastomers

Polythiourethane (PTU) and polyurethane (PU) elastomers were prepared from poly(oxytetramethylene) glycol, 1,4-bis(isocyanatomethyl) cyclohexane and a dithiol or diol chain extender with two methylene numbers (tetramethylene (C4) and pentamethylene (C5)). The effect of dithiol and diol and the methylene length of the chain extenders on the microphase-separated structure and mechanical properties of PTU and PU were evaluated. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction measurements revealed that the degree of ordering of hard segment chains in PTUs is lower than that for PU elastomers. However, it was revealed from the DSC, small-angle X-ray scattering and temperature dependent dynamic viscoelasticity measurements that the degree of microphase separation in the PTUs became stronger than that for the PUs. As a result, the mechanical property of PTUs is comparable with PUs. Furthermore, the glass transition temperature for the soft segment of PTU became lower than that for PU. PTU and PU exhibited a larger degree of microphase separation and mechanical property when the chain extender was composed of a tetramethylene (C4) chain compared to a pentamethylene (C5) chain. Polythiourethane (PTU) elastomers, which are obtained by the reaction between polyol, diisocyanate, and dithiol, are expected to have some properties that polyurethanes (PUs) do not have. Herein, the microphase-separated structure and mechanical properties of the 1,4-bis(isocyanatomethyl) cyclohexane-based PTUs were investigated. It was revealed from the differential scanning calorimetry, small-angle X-ray scattering and dynamic viscoelasticity measurements that the PTUs possess a stronger degree of microphase separation and lower glass transition temperature of soft segment compared to that of PUs.

Improving and Estimating the Precision of Bounds on the Worst-Case Latency of Task Chains

One major issue that hinders the use of performance analysis in industrial design processes is the pessimism inherent to any analysis technique that applies to realistic system models. Indeed, such analyses may conservatively declare unschedulable systems that will in fact never miss any deadlines. We advocate the need to compute not only tight upper bounds on worst-case behaviors but also tight lower bounds. As a first step, we focus on uniprocessor systems executing a set of sporadic or periodic hard real-time task chains. Each task has its own priority, and the chains are scheduled according to the fixed-priority pre-emptive scheduling policy. Computing the worst-case end-to-end latency (WCEL) of each chain is complex because of the intricate relationship between the task priorities. Compared to the state of the art, our analysis provides upper bounds on the WCEL in the more general case of asynchronous task chains, and also provides lower bounds on the WCEL both for synchronous and asynchronous chains. Our computed lower bounds correspond to actual system executions exhibiting a behavior that is as close to the worst case as possible, while all other approaches rely on simulations. Extensive experiments show the relevance of lower bounds on the worst-case behavior for the industrial design of real-time embedded systems.

Critical Properties of n-Alkanes Binary Mixtures Based on Equations of State

The aim of this work is the parameters test of the equation of state for hard convex body chain in predicting the critical properties of binary mixtures of n-alkanes. The predicted critical properties agree closely with the experimental results and are better than the predicted values both from the hard convex body equation of state and the Guggenheim equation of state for hard spheres. The agreement between theoretical and experimental results of the critical properties of n-alkanes appears to be improved negligibly, even if the shape of the molecule is considered. However, an improvement in the accuracy of the result is obtained with the equation of state of the hard convex body chain compared to the simple hard convex body equation of state.

Modeling of n-alkanes and refrigerants with a hard convex body chain equation of state

In this work an equation of state which was previously given for the hard convex body chain molecules was modeled to n-alkanes and refrigerants. The equation of state parameters and the application ranges of density and temperature were determined through fitting with the experimental data. It was found that the collision diameter and the nonspherical geometry parameter are temperature dependent and the relations were also given for their temperature dependencies. The compressibility factor, the reduced bulk modulus and the reduced isobaric expansion coefficient were calculated using the obtained parameters and compared with their experimental values. It was shown that the errors in the properties prediction are within experimental uncertainty. The results show that the equation of state is applicable for alkanes and refrigerants in both subcritical and supercritical region, but the error increases a little in the region away from the critical point.

Rheological and mechanical properties of thermoplastic polyurethane elastomer derived from CO2 copolymer diol

ABSTRACTCO2 copolymer diol‐based thermal polyurethane elastomers (PPC‐TPU) were prepared by the reaction of CO2 copolymer diol and methylene diphenyl diisocyanate and chain extender (ethylene glycol/1,4‐butanediol/1,6‐hexanediol) (EG/BDO/HG). The rheological and mechanical properties of PPC‐TPU were analyzed. The effects of shear rate, shear temperature, hard segment content, and variety of chain extender on the properties of PPC‐TPU were studied. The results showed that the apparent viscosity (η) of PPC‐TPU decreased with the increasing shear rate (τ), and the non‐Newtonian index (n) was less than 1. PPC‐TPU exhibited a typical character of pseudoplastic non‐Newtonian rheological behavior. The degradation during the processing was obviously inhibited by adding plasticizer and antioxidant. It was also discovered that the apparent viscosity varied with the content of hard segment and chain extender. Under the same temperature (185 °C) and shear rate (50 s−1), the apparent viscosity increased considerably with the raise of hard segment content, and the apparent viscosity and tensile strength of PPC‐TPU with EG as chain extender was the maximum. It can be seen that with the apparent shear rate increasing, the variation tendency of apparent shear stress levels off, and the nonlinear relationship of τ–γ curve tended to be obvious. PPC‐TPU exhibited a typical character of pseudoplastic non‐Newtonian rheological behavior. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45974.

Sowing date and maize grain quality for dry milling

Abstract Argentina is the single exporter of non-gmo hard endosperm maize to the European Union, and is internationally known for its grain hardness. This special hard endosperm maize supply chain follows strict regulations to ensure a high quality grain. Specific values for test weight, flotation index, grain vitreousness, and screen retention are demanded by the dry milling industry. Central temperate Argentinean production system is currently changing to later sowings, and there is limited information on the effect of contrasting sowing dates over specific grain quality attributes of interest for the industry. In this study we explored the effects of delaying maize sowing dates from September-October to December on maize dry milling grain quality in the central temperate area. Eighteen commercial genotypes differing in grain hardness were sown during two growing seasons and two sowing dates. Measured traits were grain yield, individual grain weight, dry milling quality (test weight, floaters, vitreousness, 8 mm screen retention), and composition (oil, protein, starch). Grain yield varied significantly among genotypes (p

Design of Polyurethane Composed of Only Hard Main Chain with Oligo(ethylene glycol) Units as Side Chain Simultaneously Achieved High Biocompatible and Mechanical Properties

In order to create a novel rigid polymer material for biomedical application, we designed the polymer structure of polyurethane, bearing oligo(ethylene glycol) (OEG) as the side chain, which was synthesized by only hard main chain using diisocyanate and short diol monomers. We investigated the effect of the graft structure of OEG units on polymer properties using pentaethylene glycol (OEG5) or propanediol (PDO) in the main chain as the other diol monomers. Furthermore, the rigid 4,4′-methylenebis(cyclohexyl isocyanate) (HMDI) and symmetric hexamethylene diisocyanate (HDI) were selected for the isocyanate monomers. As a result, there is a significant difference in various properties, depending on both the existence and the position of OEG units in the polymer structure. For example, differential scanning calorimetry (DSC) showed that the graft structure of OEG caused a decrease in the glass transition temperature from 73 to 35 °C in the case of using HMDI as well as a disappearance of the melting point in ...

Effect of hard segments on the thermal and mechanical behaviour of a novel hybrid silicon thermoplastic elastomer

A novel hybrid organic silicon thermoplastic elastomer (Si-TPE) was copolymerized by adopting branched organic polysiloxane and diphenyl methane diisocyanate, and the thermal processing mechanism and the effect of hard segments on the thermal processability and mechanical properties of Si-TPE were studied. The results showed that Si-TPE presents excellent thermal processability ascribed to its reversible physical crosslinking, i.e. hydrogen bonding between NH–C=O of the hard chains, and could be stably thermally processed into different products including films, tubes, tapes and sheets at 160–180 °C. With increasing hard segment content, the hydrogen bonding in the system was enhanced, leading to increases in both the melt viscosity and the softening temperature of Si-TPE. Simultaneously, the mechanical properties of Si-TPE were improved. When the hard segments increased to 20.3%, the tensile strength and Young’s modulus of Si-TPE reached 13.4 MPa and 43.8 MPa, respectively.

A new equation of state for modeling thermodynamic properties of some fatty acids alkyl esters, methyl ester-based biodiesels and their blends

A perturbed hard trimer chain (PHTC) equation of state (EOS) is developed for several biomaterials. This model employs a trimer expression from the statistical associating fluid theory-Trimer (SAFT-T). The performance of this model has been checked by predicting 3039 volumetric data points related biomaterials for pressures and temperature up to 210 MPa and 393 K, respectively. The average absolute deviation (AAD) of the predicted densities from the experimental ones for 3039 data points of studied biomaterials and also 407 data points of biodiesel blends were found to be 0.13% and 0.14%, respectively. Besides, the isothermal compressibility (κT), liquid bulk modulus (BT), isobaric expansivity coefficients (αP), heat capacity at constant pressure (CP) and speed of sound (u) have been estimated by the proposed model and compared with literature data.

Superior Properties of Polyurethane Elastomers Synthesized with Aliphatic Diisocyanate Bearing a Symmetric Structure

Polyurethane elastomers (PUEs) containing trans-1,4-bis(isocyanatomethyl)cyclohexane (1,4-H6XDI) have been synthesized by polymerizing 1,4-H6XDI with poly(oxytetramethylene) glycol and 1,4-butanediol. The molecular aggregation state and mechanical properties of these PUEs have been compared with those exhibited by PUE analogues made of MDI and diols. The hard segment chains in the 1,4-H6XDI-based PUEs are found to readily crystallize and form strong hydrogen bonds due to a high symmetry of 1,4-H6XDI molecule. Consequently, the 1,4-H6XDI-based PUEs exhibit well-organized hard segment domains. This leads to their generally superior mechanical properties as compared to those of the well-known MDI-based PUEs. 1,4-H6XDI’s lack of aromatic moieties is expected to greatly enhance color stability of resulting PUEs. All the above features suggest 1,4-H6XDI could replace MDI in a range of applications.

Tuning nanophase separation behavior in segmented polyhydroxyurethane via judicious choice of soft segment

Polyhydroxyurethane (PHU) is of major research interest because it is a non-isocyanate polyurethane-like (NIPU) polymer. Here, we demonstrate the ability to tune nanophase separation in linear, segmented PHU copolymers via the soft segment. PHUs were synthesized from polytetramethylene oxide (PTMO)- and polybutadiene-co-acrylonitrile (PBN)-based soft segments, with divinyl benzene dicyclocarbonate and Dytek-A as hard segment and chain extender, respectively. These NIPU polymers were characterized by small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and tensile testing. SAXS reveals that the NIPUs with 30–40 wt% hard segment are nanophase separated with interdomain spacings of 9–16 nm. DMA reveals that PTMO-based PHUs have broad interphases with a range of local compositions and glass transition temperatures (Tgs), with tan δ ≥ 0.3 over temperature ranges exceeding 70 °C in breadth. In contrast, PBN-based PHUs have sharper interphases, evidenced by narrow tan δ peaks near soft-segment and hard-segment Tgs as well as by DSC and AFM data. FTIR shows that the ratio of hydrogen-bonded carbonyl to free carbonyl is higher in PBN-based PHU than in PTMO-based PHU, consistent with the absence and presence of intersegment hydrogen bonding in PBN-based PHU and PTMO-based PHU, respectively.

Direction and pressure response of osmotic pressure in binary polymer solutions

Using a molecular equation-of-state (EOS) theory, I discuss the direction and pressure response of osmotic pressure П for a composite system with a pure solvent and its non-ideal solution of a polymeric component separated by a semi-permeable membrane. A perturbed hard sphere chain model is chosen here for the EOS to estimate П in a general way while pressure is applied. It is shown that П is a phase behavior in connection with the phase stability of the solution. In case of an incompatible pair upon forcing a single phase, there exists a region inside the binodal line for negative П possessing a spinodal point as the threshold of П=0. It is the potential energy term that contributes to the negative П and drives solvent molecules away from polymers. Those actions are reversed when phase separation occurs on the solution side. In addition, it is revealed that the solution responds to pressure with either increase or decrease in П upon pressurization, which depends on the pressure coefficients of spinodals and solvent compressibility.

Renormalization group corrections to the modified perturbed hard sphere chain equation of state for vapor liquid equilibria and interfacial tension of pure and binary mixtures

The interfacial tensions of pure fluids and binary fluid mixtures are described following an investigation of phase behavior. A modified version of the perturbed hard sphere chain (PHSC) equation of state (PHSC-CL EOS) is developed by applying the chain length dependence contribution to the PHSC EOS. The density gradient theory (DGT) is combined with the proposed model to account for both the phase equilibria and the interfacial tension. The influence parameter, the only input of the DGT with EOS to calculate the interfacial tension of the fluid, is considered an adjustable parameter for each fluid. The PHSC-CL EOS accurately describes the vapor liquid equilibria (VLE) and interfacial tensions of fluids away from the critical region. It is combined with a renormalization group theory to consider the contribution of long range fluctuations in the near critical region. The calculation procedure is based on White's work and the phase space cell approximation is adopted for mixtures. The VLE and interfacial tensions are obtained with good agreement to experimental data for linear alkanes, cyclo hexane, benzene, toluene, carbon dioxide, and their binary mixtures.

The effect of humidity on the CO2/N2 separation performance of copolymers based on hard polyimide segments and soft polyether chains: Experimental and modeling

In this work, we studied two copolymers formed by segments of a rubbery polyether (PPO or PEO) and of a glassy polyimide (BPDA-ODA or BKDA-ODA) suitable for gas separation and CO2 capture. Firstly, we assessed the absorption of water vapor in the materials, as a function of relative humidity (R.H.), finding that the humidity uptake of the copolymers lies between that of the corresponding pure homopolymers values. Furthermore, we studied the effect of humidity on CO2 and N2 permeability, as well as on CO2/N2 selectivity, up to R.H. of 75%. The permeability decreases with increasing humidity, while the ideal selectivity remains approximately constant in the entire range of water activity investigated. The humidity-induced decrease of permeability in the copolymers is much smaller than the one observed in polyimides such as Matrimid® confirming the positive effect of the polyether phase on the membrane performance.Finally, we modeled the humidity-induced decrease of gas solubility, diffusivity and, consequently, permeability, using a suitable approach that considers the free volume theory for diffusion and LF model for solubility. Such model allows estimating the extent of competition that the gases undergo with water during sorption in the membranes, as a function of the relative humidity, as well as the expected reduction of free volume by means of water molecules occupation and consequent reduction of diffusivity.

Thermodynamic modeling of CO2 absorption in 1-butyl-3-methylimidazolium-based ionic liquids

There are a number of methods to capture the carbon dioxide; among them ionic liquids are the recent magical solvents as gas absorption agents. To understand and predict the phase behavior of CO2+ionic liquid mixtures, a convenient thermodynamic model such as an equation of state is required. In this study, Perturbed Hard Sphere Chain Equation of State (PHSC) has been selected to model CO2 absorption in a series of ionic liquids including 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4], 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6], 1-butyl-3-methylimidazolium methylsulfate [BMIM][MeSO4], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl−mide) [BMIM][Tf2N]. Three molecular-based parameters, i.e. hard-sphere diameter, the non-bonded interaction energy and the number of segments per molecule have been employed as scaling constants. It is the advantage of PHSC EoS that works satisfactorily by regression of only one binary interaction parameter. The binary interaction parameter is enhanced with rising temperature due to the lower interaction of CO2 with ionic liquids.

Thermodynamic modeling of wax disappearance temperature in n-alkane mixtures by perturbed hard sphere chain equation of state

In this study, the perturbed hard sphere chain equation of state (PHSC EoS) has been used for the prediction of the wax disappearance temperature (WDT) in n-alkane mixtures. The PHSC EoS can thermodynamically predict the properties of high-molecular-weight compounds and chain-like molecules. The WDT of binary and ternary n-alkane mixtures have been predicted thermodynamically without using any fitting parameter. The liquid and solid phases are described by PHSC EoS based on multi-solid phase theory. The results have shown that the PHSC EoS is capable to predict the WDT of a n-alkane mixture by reasonable accuracy in comparison with experimental data.

Stabilizing the hexagonal close packed structure of hard spheres with polymers: Phase diagram, structure, and dynamics.

We study the phase behaviour of a binary mixture of colloidal hard spheres and freely jointed chains of beads using Monte Carlo simulations. Recently Panagiotopoulos and co-workers predicted [Nat. Commun. 5, 4472 (2014)] that the hexagonal close packed (HCP) structure of hard spheres can be stabilized in such a mixture due to the interplay between polymer and the void structure in the crystal phase. Their predictions were based on estimates of the free-energy penalty for adding a single hard polymer chain in the HCP and the competing face centered cubic (FCC) phase. Here we calculate the phase diagram using free-energy calculations of the full binary mixture and find a broad fluid-solid coexistence region and a metastable gas-liquid coexistence region. For the colloid-monomer size ratio considered in this work, we find that the HCP phase is only stable in a small window at relatively high polymer reservoir packing fractions, where the coexisting HCP phase is nearly close packed. Additionally we investigate the structure and dynamic behaviour of these mixtures.

Density and Volumetric Behavior of CO2 + Undecane System from 313.15 to 353.15 K and Pressures up to 19 MPa

Densities of compressed CO2 + undecane binary mixtures were measured using a magnetic suspension balance (MSB). Measurements were made at temperatures ranging from 313.15 to 353.15 K and pressures ranging from 8 to 19 MPa at CO2 mole fractions (x1) of 0, 0.2483, 0.4641, 0.6797, and 0.8874. The mixture densities were found to increase linearly with pressure and decrease with temperature; this behavior is similar to that of CO2 + decane or dodecane mixtures. The mixture densities show a crossover with composition when the CO2 mole fraction is high. The densities of alkanes increase almost linearly with carbon number, as do the densities of CO2 + alkane mixtures. With the of CO2 mole fraction, the mixture densities increase at first, then decrease. The increase of pressure makes the excess molar volume less negative, whereas the increase of temperature makes it more negative. Densities calculated from the perturbed hard chain equation of state (PHSC EOS) with improved parameters are in good agreement with the experimental densities. Adopting the constant binary interaction parameter kij for different alkanes in the PHSC EOS slightly enlarge the model deviation but simplifies the calculation.