Phase separation in segmented polyurethanes derived from mixtures of polyether polyols with different functionality

A series of segmented polyurethanes containing 60 wt° of hard segments (HS) was prepared from MDI (4,4-diphenylmethane diisocyanate) ethylene glycol and mixtures of a polyoxyethylene end-capped polyoxypropylene triol and a polyoxyethylene end-capped polyoxypropylene diol. The effects of the content of polyether diol in polyether polyols on phase separation and properties was investigated by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and investigation of tensile properties. The DSC and DMA results indicate that the polyurethane derived from only polyether triol exhibits obvious phase separation and that the HS is immiscible with the SS, but that the HS is compatible with the HS for the polyurethane derived from polyether diol. As the content of polyether diol increases, the compatibility between HS and SS increases. As the content of polyether diol increases, the tensile strength. elongation. toughness and tear resistance of the polyurethanes increases. but their moduli decrease. The modulus-temperature dependence in the temperature region of –30 to 65 °C increases as the polyether diol content increases.     

Structure-property relations in non-linear,segmented copolyureas formed by reaction injection moulding,RIM

Summary Segmented copolyureas have been formed by RIM using a MDI-based polyisocyanate (RMA400) and mixtures of a polyether triamine (Jeffamine T5000) and diethyltoluene diamine (DETDA) chain extender. Hard segment (HS) content was varied between 35 and 65% w/w at a constant overall stoichiometric ratio of -NCO to -NH₂ groups of 1.03. All the copolyureas were translucent and DSC confirmed their totally amorphous structure.The copolyureas were shown by dynamic mechanical-thermal analysis to possess a two-phase morphology comprising polyether soft segments of constant Tg^s of –40°C and aromatic polyurea hard segments with Tg^H increasing from 215 to 236°C as HS content increased. The ratio of flexural moduli at –35 and 65°C, decreased from 4.9 to 2.2 at 65% HS, and mechanical integrity was retained at temperatures in excess of 250°C, with flexural moduli of 10MPa at 270°C.Tensile stress-strain studies showed the polyureas to range from semi-rigid elastomers to stiff plastics with moduli greater than IGPa. Postcuring significantly improves materials toughness at high HS contents.     

Rates and controls on denitrification in an agricultural soil fertilized with liquid lagoonal swine waste

Under laboratory conditions, we studied rates and controls on denitrification and denitrification potential (denitrifying enzyme activity, DEA) in agricultural soils in the southeastern United States that had been repeatedly fertilized with liquid lagoonal swine effluent. This is a waste management practice commonly employed by large-scale swine production facilities that have proliferated regionally in the past 10 years. The microbial community was rapidly responsive to the added waste, as denitrification N flux (N₂ + N₂O) from intact soil cores increased from about 200 to as high as 2850 g N m^–2 h^–1, usually within 1 day of application. Elevated rates of denitrification were short-lived (3 days), as the combination of coarse soil texture (rapid drainage) and low mineralization potential (low organic content) of the waste rapidly restored aerobic conditions. Although <2% of the fertilizer-N was lost to denitrification by the time rates had returned to pre-fertilization values after 8–12 days, soil NO₃^––N levels increased from 5 g N g_dw soil^–1 to as high as 43 g N g_dw soil^–1, providing not only substrate for additional denitrification following rainfall, but also a mobile N source for both offsite transport by surface and groundwater and assimilation by plants. Both N₂O and N₂ production from denitrification were unresponsive to changes in soil moisture until field capacity was approached or exceeded. Temperature coefficients (Q₁₀) for DEA varied from 1.6 to 2.8 between 7 and 30 °C, depending on the temperature interval, while high DEA between 20 and 40 °C pointed to a denitrifying community well-adapted to regional summer soil temperatures. Glucose-C or NO₃^––N amendments proved equally stimulatory to DEA in homogenized soils relative to water-only controls. However, addition of the combined substrates gave the best response, indicating that these chemical factors were equally important controls on potential denitrification in these soils once anaerobic conditions had become established.     

Synthesis and interfacial properties of montmorillonite/polypyrrole nanocomposites

Montmorillonite/polypyrrole (MMT/PPy) nanocomposites were prepared by the in situ polymerization of pyrrole in the presence of MMT. The morphology of the MMT/PPy nanocomposites as examined by scanning electron microscopy differs slightly from that of the untreated MMT but markedly from that of polypyrrole. X-ray photoelectron spectroscopy (XPS) showed that the materials have MMT-rich surfaces, an indication that polypyrrole is essentially intercalated in the host clay galleries. The transmission electron microscopy showed, that the interlamellar spacing of the untreated MMT increased from 1.25 to 18.9 nm, when compared to nanocomposite MMT/10.8% PPy. Moreover, XPS highlighted the cation exchange of Na⁺ from montmorillonite by K⁺ (from the oxidant) and by the positively charged polypyrrole chains. Inverse gas chromatography indicated that the nanocomposites are high surface energy materials with a dispersive contribution to the surface energy reaching 200 mJ/m² at 150 °C, for a PPy loading of 21.4 wt%. The values of the MMT/PPy nanocomposites were correlated to the changes in the specific surface area of the MMT induced by the intercalation of polypyrrole.     

High-temperature chlorine corrosion of technical carbons Part II. Anodic corrosion in chloride melt

Medium (200 to 400°C) to high (600 to 800°C) temperature corrosion of technical carbons (Acheson graphites) have been investigated in alkali chloride melts at chlorine evolving anodes. At low temperature in chloride melts containing free Lewis acid (AlCl₃) no chlorine is evolved — even at high current densities — because chlorine, together with aluminium chloride, instantaneously form intercalation compounds with graphite and, as a consequence, the carbon desintegrates very rapidly. At 200°C carbon is consumed anodically in a C/Cl of molar ratio 70/1. With increasing temperature Scheson graphites become more stable so that at 700°C short term destruction cannot be observed in melts which contain free Lewis acid. Chlorine corrosion of carbon electrodes in purified basic alkali chloride melts, which are free of oxygen carriers and, in particular, free of water at temperatures between 600 and 800°C in basic chloride melts, is an electrochemical reaction proceeding at low current densities slower than anticipated from thermodynamic data for carbon chlorination equilibria. The anodic carbon corrosion reaction has an activation energy of only 50 kJ mol^–1 and its rate increases with increasing anode potential, or anodic current densities (rate: exp (i)). At a technical current density of 0.4 A cm^–2 at 700°C the corrosion rate is estimated to be of the order of centimeters per year, rendering carbon anodes dimensionally unstable. Most important is to note that apart from CCl₄, chlorinated carbon compounds (olefins and arenes) are generated as side-products which are noxious and ecologically dangerous and must not be released from processes which use carbon anodes for chlorine evolution from salt melts.This paper is dedicated to Professor Dr Fritz Beck on the occasion of his 60th birthday.     

Partial oxidation of methane to syngas over Co/MgO catalysts. Is it low temperature?

Co/MgO catalysts with high Co-loading (>28 wt%) are able to initiate the reaction of methane with oxygen at temperatures around 500 °C. High conversions of methane ( 70%) and very high selectivities for hydrogen and carbon monoxide ( 90%) are obtained at very high reactant gas space velocities (10⁵–10⁶ h^–1). The temperature of the catalyst at the conditions of partial oxidation of methane to form syngas was found to be extremely high (1200–1300 °C); it is about 600–850 °C higher than that previously reported by others. At these temperatures, high temperature homogeneous reactions may prevail. It is suggested that combustion of methane to carbon dioxide occurs on the catalyst with major heat release and that methane and water, respectively methane and carbon dioxide are reformed thermally in an endothermic reaction leading to syngas.     

The synthesis and characterization of polydibromoacetylene

Summary Polydibromoacetylenes were synthesized under different polymerization conditions and with Al-Ti coordinative catalysts. For the characterization of the polymers and for the study of the correlation between polymerization conditions and properties of the polymers, ¹³C MAS NMR, ESR and UV spectroscopies were used. The electrical conductivity of the polymers was measured in dependence on temperature. The energy gap decreased with increased crystallinity. As compared to polyacetylene the conductivity of polydibromoacetylenes was lower, but the stability against oxygen was higher. The polydibromoacetylenes were thermal stabile up to 200°C.Dedicated to Professor Dragutin Fle on the occasion of his 70th birthday     

Synthesis and Properties of New Aromatic Polyimides Based on 2,6-Bis(4-aminophenoxy)naphthalene and Aromatic Tetracarboxylic Dianhydrides

A series of new aromatic polyimides containing bis(phenoxy)naphthalene units were synthesized from 2,6-bis(4-aminophenoxy)naphthalene (2,6-BAPON) and various aromatic tetracarboxylic dianhydrides by the conventional two-stage procedure with thermal imidization of poly(amic acid) films. The intermediate poly(amic acid)s obtained had inherent viscosties of 1.60–3.31 dL/g, and they could be solution cast and thermally converted into transparent, flexible, and tough polyimide films. The resulting polyimide films had tensile moduli of 1.5–2.3 GPa, tensile strengths of 105–124 MPa, and elongations at break of 7–22%. The polyimide derived from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) was readily soluble in polar aprotic solvents. The glass-transition temperatures of these polyimides, except for that from pyromellitic dianhydride (PMDA), were recorded between 255 and 295°C by differential scanning calorimetry (DSC). The softening temperatures of all the polyimide films stayed within 246–286°C according to thermomechanical analysis (TMA). Thermogravimetic analyses (TGA) established that these polymers were fairly stable up to 500°C, and the 10% weight loss temperatures were recorded in the range of 543–563°C in nitrogen and 535–563°C in air atmosphere.     

Commercial grades of alumina

Conclusions In an investigation of the properties of alumina GO, GK, and GU of Soviet origin and of the Hungarian alumina GV it was shown that the chemical composition is similar in all these materials but the alkali content is highest in the Hungarian alumina.The density of the alumina depends on the corundum content and increases in the order GOGU GVGK.Preliminary roasting of the alumina reduces the shrinkage of the specimens produced from these materials (with the exception of alumina GK) as a result of the formation of corundum during the roasting. The shrinkage of all specimens was similar when they were produced from alumina roasted at 1550°C.The porosity of the specimens depends primarily on the firing temperature. Firing the specimens at 1750°C resulted in complete sintering regardless of the temperature at which the original alumina was roasted. The cold-crushing strength was also at maximum in this case.Translated from Ogneupory, No. 3, pp. 46–52, March, 1976.     

Mechanical Properties of Ceramics Prepared from a Nanocrystalline ZrO2 – 3 mol.% Y2O3 Powder

Ceramics of ZrO₂ – 3 mol.% Y₂O₃ composition prepared from commercial raw materials by cold isostatic pressing technique at sintering temperatures from 1100 to 1500°C are studied. Best mechanical properties were found in material sintered at 1350°C: density, 5.95 g/cm³; bending strength, 1200 MPa, and crack resistance, about 18 MPa m^1/2. The mechanical properties of ceramic materials sintered at 1300 and 1500°C are inferior by roughly a factor of 1.5, despite virtually the same density and grain size. This difference is explained as due to the different properties of the intergranular material in ceramics sintered at different temperatures.     

Thermal conductivity of insulating refractories measured by the standard method and by the cylinder method

Conclusions The coefficients of thermal conductivity of insulating refractories measured by the method prescribed in GOST 12170-66, using the recommended thermometers with a scale division of 0.1°C and thermal insulation made from firebrick with an apparent density of 1.0 g/cm³, are appreciably higher than data obtained by the cylinder method. At average temperatures of 200–500°C (400–1000°C on the hot face) the discrepancy comes within the range 50–200%; when T_mean=600–700°C (1200–1300°C on the hot face) the discrepancies diminish to 0–30%.The maximum apparatus error in determining the thermal conductivity according to GOST 12170-66 with the use of Beckmann thermometers and low thermal-conducting linings is 10–30% for – 0.2–1.0 kcal/(m·h·deg), which greatly exceeds that indicated in the standard, ±10%. The maximum proportion in the error comes from the measurement of the drop in water temperature as it passes through the calorimeter. Consequently, the use of the standard recommended thermometers with scale divisions of 0.1°C is unacceptable for measurements on materials with a low thermal conductivity, since it may lead to errors of about 100%.Detailed comparison of the results of measuring this factor on standard equipment using the Beckmann thermometers, and on the improved instrument designed by the Ukrainian Institute (the cylinder method), showed that the mean square deviation of the experimental values for thermal conductivity for identical specimens with respect to the interpolation curves in the case of standard determinations is 2–3 times greater than the corresponding deviation for the cylinder method.In most experiments the interpolation curves =f(T) for the standard method is different by ±15–25% from the curves obtained with the cylinder method. This displacement apparently is due to certain constant errors connected with the unaccounted-for sources of error in the standard methods.The proposed method of determining the coefficient of thermal conductivity is of interest for scientific-research work. The use of the cylinder method is industry is associated with difficulties in preparing the specimens — Editors.Translated from Ogneupory, No. 8, pp. 45–52, August, 1971.     

Structure and Surface Transformations of Humic-Adsorbed Synthetic Hydrotalcite-Like Materials

Hydrotalcite-like material of Mg–Al-carbonate system (MACH) was prepared and its heat-treated product (MACHT) was obtained by calcination at 500°C, for 3 hours at atmospheric condition. The resulting materials were used as adsorbents for removal of humic substance (HS) from synthetic peat water (SPW) and natural peat water (NPW). Batch kinetic study showed that MACH or MACHT adsorb the humic substance with maximum adsorption capacities of around 15 mg of humic substance per g of adsorbent, when SPW was used compared to 78 mg/g when NPW was used. The humic substance uptake on MACH and MACHT from SPW and NPW followed the Langmuir model of adsorption. X-ray diffractograms showed that the layered structure of MACH collapsed when it was heated at 500°C and a new amorphous-like phase was observed. Due to the memory effect property of hydrotalcite, the regeneration of MACH from MACHT was observed when MACHT was treated with humic substance from SPW or NPW, and the basal spacing of around 7.9 Å was restored. The BET surface area increased by about a factor of 3, from 68.0 in MACH to 201.9 m²/g in MACHT, but the micropore surface area decreased by about 20%, from 12.3 in the former to 9.9 m²/g in the latter. Expulsion of water molecules and carbon dioxide from carbonate in the interlayer together with the formation of an amorphous-like phase was thought to be the reason for the increase of the BET surface area. The decrease in the micropore area is possibly due to collapse of the layered structure of MACH. The BET surface area for MACH and MACH-humic substance-adsorbed from SPW or NPW is similar. On the other hand, a high reduction in surface area was observed for MACHT-adsorbed humic substance from SPW or NPW, by about 80% in the latter compared to about 90% in the former when compared to MACHT. The regeneration of MACH from MACHT together with the adsorption of humic substances presumably contributed to a high reduction in surface area of humic substance-adsorbed MACHT samples     

Propane oxidative dehydrogenation on silica based oxide catalysts

The oxidative dehydrogenation of propane to propylene with molecular O₂ (PPD) has been investigated on commercial bare SiO₂ and medium loaded V₂O₅ and MoO₃ catalysts at 450–525°C. The direct relationship between the density of reduced sites (, 10¹⁶ s_r g _cat– ¹ ), evaluated in steady-state conditions by O₂ chemisorption, and the POD reaction rate proves the occurrence of a concerted reaction mechanism involving the activation of gas-phase O₂ on the reduced sites of the catalyst surface. A straight-line correlation between the activity of such silica based catalysts in POD and methane partial oxidation to formaldehyde (MPO) at 525°C has been disclosed.     

Synthesis, Characterization and Anti-microbial Activity of Oligo-N-2-aminopyridinylsalicylaldimine and Some Oligomer-metal Complexes

The oxidative polycondensation and optimum reaction conditions of N-2-aminopyridinylsalicylaldimine using air oxygen, H₂O₂ and NaOCl were determined in an aqueous alkaline solution between 40–90°C. Oligo-N-2-aminopyridinylsalicylaldimine (OAPSA) was characterized by using ¹H-NMR, FT-IR, UV-vis and elemental analysis. N-2-aminopyridinylsalicylaldimine was converted to oligomer by oxidizing in an aqueous alkaline medium. The number average molecular weight (M _n), weight average molecular weight (M _w) and polydispersity index (PDI) values were found to be 7487 gmol^–1, 7901 gmol^–1 and 1.06, respectively. According to these values, 70% of N-2-aminopyridinylsalicylaldimine turned into oligo-N-2-aminopyridinylsalicylaldimine. During the polycondensation reaction, a part of the azomethine (–CH=N–) groups oxidized to carboxylic (–COOH) group. Besides, the structure and properties of oligomer-metal complexes of oligo-N-2-aminopyridinyl salicylaldimine (OAPSA) with Cu (II), Ni (II), and Co (II) were studied by FT-IR, UV-vis DTA, TG and elemental analysis. Anti-microbial activities of the oligomer and its oligomer-metal complexes have been tested against C. albicans, L. monocytogenes, B. megaterium, E. coli, M. smegmatis, E. aeroginesa, P. fluorescen and B. jeoreseens. Also, according to the TG and DTA analyses, oligo-N-2-aminopyridinylsalicylaldimine and its oligomer-metal complexes were found to be stable thermo-oxidative decomposition. The weight loss of OAPSA found to be 20%, 50% and 98% at 350°C, 535°C and 1000°C, respectively.     

Nitrate accumulation, yield and leaf quality of turnip greens in response to nitrogen fertilisation

Two pot and two open-field experiments were conducted to determine the influence of N fertilisation on nitrate accumulation, yield, and leaf quality of turnip greens (Nabiças, Brassica rapa var. rapa). The pot experiments were conducted: (1) in a controlled environment (24 h photoperiod at 250±25 mol s^-1 m^-2, and 20±1 °C ), and (2) outdoors (315 w m^-2 mean solar radiation, and daily mean air temperature between 19 and 26 °C). The response of plant biomass to N from 0 to 250 g m^-3 of pot-soil, in each of the two experiments, was characterised by a steep increase in weight until the level of N reached 100 g m^-3, with a tendency to stabilisation thereafter. There was a clear turning point around 100 g m^-3 N, beyond which plant biomass did not significantly increase in response to N application. When fertilisation with N was increased from at 100 to 250 g m^-3, plant fresh weight increased by 7.4 and 8.6% and nitrate concentration by 279 and 1315%, respectively, in both growth-room and outdoors pot experiments, showing that turnip greens may easily reach conditions of luxury consumption of N. In the two open-field experiments, turnip plants were grown in a clay soil, in winter and in spring at Lisbon, Portugal. Increasing N fertilisation from 0 to 200 kg ha^-1 resulted in plants with higher fresh weight both in winter and spring. Plant nitrate concentration in winter was higher than in spring at the same applied N. The increase of plant fresh weight in response to N had a clear asymptotic tendency at N exceeding 160 kg ha^-1, but the increase of leaf nitrate had a linear trend showing a clear tendency for nitrate accumulation in the leaves. N induced a darker green leaf colour but had no effect on leaf taste and texture. Increasing N fertilisation up to 200 kg ha^-1 seemed to be an effective means of improving yield and quality of turnip greens and of shortening the cropping cycle.     

Hydroboration polymerization of dicyano compounds

Summary Hydroboration polymerization of various ,-dicyanoalkanes with thexylborane produced the corresponding poly(cyclodiborazane)s, that consist of boron-nitrogen four-membered rings. The structures of the obtained polymers were confirmed by spectroscopic analyses such as ¹H-, ¹¹B-NMR and IR spectra. From the result of thermogravimetric analysis of the polymer prepared from adiponitrile and thexylborane, 12% of the inorganic materials remained after heating at 900°C. *** DIRECT SUPPORT *** AEB03051 00003     

High strength and high modulus fibers of poly(p-xylylene)

Summary High strength and high modulus fibers of poly(p-xylylene) (PPX) were obtained by drawing of as-polymerized films (molecular weight 5×10⁵) at 420 °C in the conformationally disordered ₂ phase. Fibers of PPX have been obtained having a tensile strength at break of 3.0 GPa, a Young's modulus of 102 GPa and a strain at break of 3 %. The theoretical strength of PPX was calculated to be 23 GPa.     

Measurement of through-plane effective thermal conductivity and contact resistance in PEM fuel cell diffusion media

An experimental study was performed to determine the through-plane thermal conductivity of various gas diffusion layer materials and thermal contact resistance between the gas diffusion layer (GDL) materials and an electrolytic iron surface as a function of compression load and PTFE content at 70 °C. The effective thermal conductivity of commercially available SpectraCarb untreated GDL was found to vary from 0.26 to 0.7 W/(m °C) as the compression load was increased from 0.7 to 13.8 bar. The contact resistance was reduced from 2.4×10⁻⁴ m²°C/W at 0.7 bar to 0.6×10⁻⁴ m²°C/W at 13.8 bar. The PTFE coating seemed to enhance the effective thermal conductivity at low compression loads and degrade effective thermal conductivity at higher compression loads. The presence of microporous layer and PTFE on SolviCore diffusion material reduced the effective thermal conductivity and increased thermal contact resistance as compared with the pure carbon fibers. The effective thermal conductivity was measured to be 0.25 W/(m °C) and 0.52 W/(m °C) at 70 °C, respectively at 0.7 and 13.8 bar for 30%-coated SolviCore GDL with microporous layer. The corresponding thermal contact resistance reduced from 3.6×10⁻⁴ m²°C/W at 0.7 bar to 0.9×10⁻⁴ m²°C/W at 13.8 bar. All GDL materials studied showed non-linear deformation under compression loads. The thermal properties characterized should be useful to help modelers accurately predict the temperature distribution in a fuel cell.     

An examination of the thermorheological and drug release properties of zinc tetraphenylporphyrin-containing thermoresponsive hydrogels, designed as light activated antimicrobial implants

This study describes the thermorheological, mechanical and drug release properties of novel, light-activated antimicrobial implants. Hydrogels, based on N-isopropylacrylamide (NIPAA) and hydroxyethylmethacrylate (HEMA) and either devoid of or containing zinc tetraphenylporphyrin, were prepared by free radical polymerisation and characterised using oscillatory rheometry and texture profile analysis. Drug release was studied at both 20 and 37 °C. Hydrogels containing NIPAA exhibited a sol-gel temperature (Tm), which increased as the proportion of HEMA increased and was . The viscoelastic properties (storage modulus G^′, loss modulus G^″, loss tangent and dynamic viscosity η^′) were affected by hydrogel composition and temperature, with the copolymers exhibiting lower values of G^′,G^″ and η^′ values than either homopolymer. Similar relationships between the composition of the hydrogels and the textural/mechanical properties were observed. At 37 °C rheological structuring (increased G^″,G^″,η^′ and reduced loss tangent) occurred for all NIPAA-containing polymers and increased as the NIPAA content increased. At 20 °C drug release was diffusion controlled, the rate of which was similar for all NIPAA-containing polymers and was lower than drug release from p(HEMA), despite the greater elasticity of this homopolymer. At 37 °C drug release from the NIPAA-containing hydrogels was initially non-diffusion controlled, following which drug release levelled. Drug release decreased as the NIPAA content increased and correlated to hydrogel elasticity. It is suggested that the ability to engineer the release of Zn-TPP from these hydrogels, in conjunction with their acceptable mechanical properties, may be clinically advantageous for the treatment of infection.     

Effects of calcining conditions of kaolinite on pore structures of mesoporous materials prepared by the selective leaching of calcined kaolinite

This paper describes the effects of calcining conditions of kaolinite on pore structures of the porous materials obtained from the selective leaching of calcined kaolinite using KOH solution. Mesoporous -Al₂O₃ was the predominant crystalline phase in the samples calcined in the temperature range between 950°C and 1050°C for 24 h. The mean specific surface area of these samples was approximately 250 m² · g^–1 and the mean total pore volume was approximately 0.8 ml · g^–1. The pore size distribution curves of these samples showed a sharp peak at around 2–3 nm pore radius. This peak was sharper for the sample calcined at 1000°C for 24 h. On the other hand, the pore sizes of the sample calcined at 1100°C for 24 h increased abruptly to 10–20 nm and this change corresponded to the formation of mullite in the sample. The pore sizes of the samples calcined at 1100°C varied with calcining time. The specific surface area and total pore volume decreased, the longer the calcining time of the samples, and this was correlated with an increase in the amount of mullite in the samples.