Thermodynamic investigation of thermoresponsive xanthan‐poly (N‐isopropylacrylamide) hydrogels

Polysaccharide‐based hydrogels, such as xanthan maleate/poly(N‐isopropylacrylamide) (PNIPAAm) interpenetrated polymer networks, are thermostimulable materials of interest for the controlled release of biologically active components due to conformation changes at the low critical‐solution temperature (LCST) PNIPAAm phase transition. The phase transition of these interpenetrated polymer network hydrogels, where PNIPAAm is in a ‘confined’ environment, was examined by high resolution magic angle spinning nuclear magnetic resonance and differential scanning calorimetry. High resolution magic angle spinning nuclear magnetic resonance spectroscopy allows the accurate determination of LCST and an evaluation of the corresponding thermodynamic data. More particularly, the evolution of these data as a function of the composition of the hydrogel, and of the external parameters such as pH and ionic strength, was considered. LCST shows a minimal value with increasing xanthan content. Moreover, it was possible to calculate, as a function of temperature, the fraction of NIPAAm which remains uncollapsed. The data obtained for pure PNIPAAm hydrogels are in good agreement with recently published results. The phase transition of PNIPAAm in a diphasic hydrogel is broader when PNIPAAm is ‘confined’ within an interpenetrated polymer network than in a pure PNIPAAm crosslinked network. The widening of the transition with increasing xanthan content indicates a reduction of the PNIPAAm interchain aggregation in a network structure. Copyright © 2011 Society of Chemical Industry     

Microstructure and phase composition of cordierite-based co-clinker

The aim of this work is to study the effect of phase composition and microstructure of cordierite-based co-clinkers on the electrical properties and coefficient of thermal expansion of cordierite briquettes. To achieve this aim talc and kaolinite samples were collected from quarries in the Egyptian desert. The samples are characterized using XRD, XRF, polarized light, cathodoluminescence and SEM microscopy attached with EDAX, in addition to X-ray micro-computed tomography (3D- µXCT). The electrical properties and coefficient of thermal expansion of the cordierite briquettes are determined using HiTESTER instrument and automatic Netzsch DIL402 PC dilatometer, respectively.Five talc-based batches were shaped and fired in the temperature range 1000–1350 °C for 2 h. The microstructural and physical characteristics of the resulted cordierite-based co-clinkers depend mainly on the viscosity of the liquid phase developed during firing. The microchemistry of the cordierite briquettes confirms their enrichment of both cordierite and ferroan-cordierite crystallized directly from locally developed melts. The dielectric constant and loss factor values for cordierite briquettes allow their possible use as insulator components in electronic applications.     

Loss of nitrogen from urea applied to rainfed wheat in varying rainfall zones in northern Syria

Fertilizer-applied Nitrogen (N) may be lost from the soil by various mechanisms, i.e., runoff, leaching, denitrification, and volatilization. The latter process is of primary concern in calcareous soils of arid and semi-arid regions, especially when urea is used. In this field study from northern Syria, urea alone, urea with either an incorporated urease inhibitor, phenylphosphorodiamidate, or an experimental bran-wax coating were evaluated on wheat for two cropping seasons at two experimental stations with varying average seasonal rainfall (340 mm, 270 mm). Loss of N was assessed with ¹⁵N by mass balance, i.e., the amount of N applied minus the crop N uptake and N remaining in the soil. Crop yields and N uptake were related to seasonal rainfall. Losses of N, apparently as volatilized NH₃, were relatively low at both sites, i.e., 11–18%. However, compared to the unmodified urea, neither the incorporated urease inhibitor nor the bran-wax coating had any effect on yields, N uptake or N loss. While urea hydrolysis is normally rapid, it may be delayed by dry conditions at the soil surface; similarly, unusually cold periods may delay nitrification following hydrolysis. Thus, under the cool-season conditions of rainfed cropping in the Middle East, efficient use of urea is not likely to be achieved by modification of the urea but by conventional management practices that ensure pre-plant soil incorporation or topdressing during early spring rains.     

Swelling and electrical properties of rubber vulcanizates loaded with paraffin wax

The influence of the concentration of paraffin wax on the penetration rate, P, and the average diffusion coefficient, D, of kerosene in an SBR–NR composite and also on the coefficient of viscosity were investigated. All decreased with the addition of wax. Also, the effect of the concentration of paraffin wax on both the current–voltage characteristics and the temperature dependence of the dc electrical conductivity were studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3169–3177, 2001     

Yielding behaviour of thermoplastic/elastomer blends cured by gamma irradiation

Mechanical blends of thermoplastic medium density polyethylene (MDPE) and elastomeric ethylene propylene diene monomer (EPDM) have been prepared with a fixed composition of 60/40 wt%. They have been used either in their gum form or loaded with two different reinforcing fillers, high abrasion furnace (HAF) carbon black or precipitated SiO₂ (Hi Sil) of concentration 25–100 phr (parts per hundred parts of resin) with respect to the blend. Curing was achieved by gamma irradiation. Yielding properties (yield stress, yield strain and cold drawing) have been followed as a function of irradiation dose for different blend compositions. Yield stress values increased with irradiation dose and with the content of the reinforcing filler, but yield strain and cold drawing values decreased with irradiation dose and also with the filler content. The data obtained reveal that Hi Sil is more effective as a reinforcing filler, and the prepared blends are suitable for load‐bearing applications. © 2001 Society of Chemical Industry     

Dielectric analysis of α‐relaxation process of chlorinated poly(vinyl chloride) stabilized with nitro‐phenyl maleimide

Nitro‐phenyl maleimide (NPM), is the organic stabilizer for poly (vinyl chloride) (PVC), has been investigated as thermal plasticization for rigid chlorinated poly (vinyl chloride) (CPVC). Dielectric relaxation of CPVC stabilized with 10 wt% of NPM has been studied in temperature and frequency ranges of 300–450 K and 10 kHz–1 MHz, respectively. An analysis of the dielectric constant, ε′ and dielectric loss index, ε″, was performed assuming a plasticization effect of NPM molecules. The plasticization effect of NPM molecules was confirmed by the behavior of the dielectric modulus M′ and M″ spectra. A clear dielectric α‐relaxation process has been obtained in the studied temperature range. The results showed that NPM reduce the glass transition temperature, T_g, of CPVC by about 20 K. This effect has been assigned to the plasticization effect of NPM. At lower temperatures, dielectric modulus spectra reveal that there is a role of the effect of the electrode polarization in the relaxation process. The behavior AC conductivity, σ_ac, indicated that the conduction mechanism in all CPVC samples is hopping type conduction. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

New polymer synthesis. XXX. Synthesis and thermal behavior of new organometallic polyketones and copolyketones based on diferrocenylidenecycloheptanone

A new interesting category of organometallic polyketones and copolyketones was synthesized via Friedel–Crafts reactions through the polymerization of 2,7‐bis[(2‐ferrocenyl)methylene] cycloheptanone ( II ) with different diacid chlorides. The model compound was synthesized by reacting monomer II with benzoyl chloride and characterized by ¹H‐NMR, IR, and elemental analyses. The polyketones and copolyketones were insoluble in most organic solvents but easily soluble in concentrated H₂SO₄. The thermal properties of these polyketones and copolyketones were evaluated and correlated to their structural units by TGA and DTG measurements and had inherent viscosity of 0.32–0.65 dI g^?1. Moreover, the electrical conductivity of polyketone Va and copolyketone VI was investigated above the temperature range (300–500 K) and followed an Arrhenius equation with activation energy 2.09 eV. Also, the morphological properties of selected example of polyketones were detected by scanning electron microscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2394–2401, 2005     

Synthesis of a new sulphonated cation exchange resin and its application in catalysed hydrolysis of esters

Samples of an acidic cation exchanger have been prepared by sulphonation of acrylonitrile butadiene styrene copolymer previously cross-linked with phenol-formaldehyde resin. The samples having a cation exchange capacity of 3.48 meqg^–1, are being introduced as new catalysts in the hydrolysis of ethyl acetate. The synthesized cation exchanger shows good thermal and chemical stability. Hydrolysis rate constants (K _r values) for the catalysed reaction have been determined. The efficiency of the resin catalyst,q, is shown to be a function of resin concentration.     

Brain-potential evidence for the time course of access to biographical facts and names of familiar persons.

On seeing familiar persons, biographical (semantic) information is typically retrieved faster and more accurately than name information. Serial stage models explain this pattern by suggesting that access to the name follows the retrieval of semantic information. in contrast, interactive activation and competition (IAC) models hold that both processes start together but name retrieval is slower because of structural peculiarities. With a 2-choice go/no-go procedure based on a semantic and a name-related classification, the authors tested differential predictions of the 2 alternative models for reaction times (RTs) and lateralized readiness potentials (LRP). Both LRP (Experiment 1) and RT (Experiment 2) results are in line with IAC models of face identification and naming. (PsycINFO Database Record (c) 2011 APA, all rights reserved)