Adhesion and Hydrolytic Stability of the Interface Between High-Modulus Polyethylene Fibers and Acrylic Resins

The effects of oxyen plasma treatment on the surface chemistry of Spectra 1000® high modulus polyethylene fibers and on the mechanical properties of fiber-reinforced composites of the fibers in a Bis-GMA based acrylic resin have been studied. X-ray photoelectron spectroscopy and diffuse reflectance FTIR spectroscopy have been used to show that the majority of oxygen on the fiber surface exists mostly in the form of ether and/or epoxy linkages, with carbonyl-, carboxylic- and ester-containing compounds accounting for less than 10 percent of the total. While the untreated and plasma-treated fibers have similar chemical compositions, the surfaces of the plasma-treated fibers are more polar and the oxygen is chemically bonded instead of being merely physisorbed. The interfacial shear strength between the fibers and the acrylic resin is increased by a factor of 2.3 by the plasma treatment indicating the presence of a weak boundary layer on the surface of the untreated fibers. The hydrolytic stability of the composite interfaces was investigated for fibers sized with several Bis-GMA-based adhesives. Maximum stability was attained by sizing with Bis-GMA containing a peroxide catalyst or an amine accelerator. The flexural properties of composites utilizing plasma-treated and untreated fibers were compared in three-point bending. The ultimate bending loads for composites using treated fibers were much higher than those for composites with untreated fibers, but only a fraction of that for glass or Kevlar®-reinforced materials.     

CONCENTRATION POLARIZATION OCCURRING INSIDE THE MEMBRANE DURING STEADY STATE PERVAPORATION

Experimental profiles of a single penetrant (water) across the membrane have been established at different downstream pressures during steady state pervaporation. The profiles ofacetic acid-water binary penetrant system across the membrane were also measured at different downstream pressures, temperatures and compositions during steady state pervaporation. A stack of identical pre-characterized symmetric aromatic polyamide membranes was used for the profile study. The theoretical prediction of concentration polarization from mathematical equations has been confirmed by the experimental profile data for a binary penetrant system.     

BOILING OF MIXTURES IN A NARROW SPACE

Nucleate pool boiling of binary mixtures composed of water and normal propyl alcohol (NPA) within a narrow space between heated and unheated horizontal-parallel surface has been investigated under atmospheric pressure. The electrically heated lower surface is made of a sheet of stainless steel 304 with the dimension of 145 x 22 x 0.05 mm and the unheated upper plate is a stainlesssieel cylinder with a diameter of 20 mm. The periphery of the confined space is open and the size of the gap can be varied from 0 to 10 mm. Experimental results show that the heat transfer coefficient of nucleate pool boiling of binary mixture in a narrow space is much greater than that of conventional nucleate pool boiling. It is due to the evaporation of a thin liquid film under the deformed bubble. Experimental results also show that mass diffusion effect is important in both nucleate pool boiling in a narrow space and in conventional nucleate pool boiling. Based on the experimental results, the microlayer evaporation, mass diffusion and the film flow driven by the gradient of the disjoining pressure and the Marangoni effect are discussed.     

Hydrogenation of aromatics under mild conditions on transition metal complexes in zeolites. A cooperative effect of molecular sieves

The hydrogenation of aromatics, i.e. benzene, toluene, -methylstyrene, anisole, and ethyl benzoate, can be carried out under a very low (1/12000) catalyst to substrate ratio, and mild reaction conditions (80°C, 6 atm of H₂O), on Rh and Ni organometallic complexes anchored on USY zeolites. A strong cooperative effect between the faujasite surface and the transition metal surface complex is thought to be responsible for the simultaneous enhancement of concentrations of arene and H₂ in the neighborhood of the catalytic centers, and for the observed electronic effects.     

Spontaneous change in porosity of a reacting pressed material and non-one-dimensional regimes of diffusion combustion

Essentially non-one-dimensional regimes of synthesis-wave propagation are considered within the framework of a model describing two-dimensional diffusion combustion and taking into account a change in porosity of a reacting composition attributed to a change in its physical and chemical properties. The surface and layer-by-layer burning of a pressed specimen in gas is described qualitatively as well as the interaction front propagation wherein unreacted material remains in skin layers of the specimen. The conditions of development of a gastight layer on the specimen surface and incomplete material conversion because of pore volume exhaustion have been determined. Dynamics of a number of unstable regimes of front propagation is studied. The role of diffusion supply of a gaseous reagent is analyzed under the conditions of changing porous space in the reacting material. The surface and layer-by-layer burning of pressed specimens, with the reagents interacting in an unstable regime, is considered.Institute of Structured Macrokinetics, Russian Academy of Sciences, Chernogolovka. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 2, pp. 47–58. March–April, 1995.     

High-performance size-exclusion chromatographic studies on a high-oleic acid sunflower oil during potato frying

The behavior of a high-oleic acid sunflower oil used for 75 repeated deep-fat fryings of potatoes, with a fast turnover of fresh oil during frying, was evaluated by measuring the total polar content isolated by column chromatography. The total polar content increased in the oil from 3.6 ± 0.1 (mean ± SD) mg/100 mg unused oil to 7.6 ± 0.4 mg/100 mg oil after being used in 20 repeated fryings, followed by a tendency to reach a near-steady state throughout the successive fryings. Further, the polar fraction was examined by high-performance size-exclusion chromatography. Triacylglyceride dimers increased continuously from 0.18 ± 0.01 mg/100 mg unused oil to 2.42 ± 0.12 mg/100 mg oil at the 40th frying with no further significant changes. The amount of triacylglyceride polymers increased from 0.03 ± 0.00 mg/100 mg unused oil to 0.70 ± 0.01 mg/100 mg oil at the 60th frying, but did not increase further with continued frying. Oxidized triacylglycerides also significantly increased from 1.13 ± 0.06 mg/100 mg oil to 3.58 ± 0.09 mg/100 mg oil at the 50th frying to reach a near-steady state in successive fryings. Diacylglycerides and free fatty acids levels, related to hydrolytic alteration, did not change from the starting oil after continued fryings. Data from this study indicated that repeated fryings of potatoes in high-oleic sunflower oil with a frequent turnover of fresh oil throughout the frying slightly increased the level of polar material in the fryer oil during the first fryings, followed by minor changes and a tendency to reach a near-steady state in successive fryings.     

Soil effects due to sewage sludge application in agriculture

Field trials show that increased nutrients (mainly P) and heavy metals in soil due to agricultural use of sewage sludge have mainly to be expected when sludge is applied in too high amounts. The biological effects of heavy metals on plants are determined by their solubility which is increased by pH decrease and degradation of organic matter. Normally, it should be expected that the microbial activity in soil would increase with the application of organic matter in sewage sludge. But, also negative effects on the microflora by simultaneous enrichment of organic matter or inorganic and organic pollutants were found. The most important deleterious effects on soil microorganisms are the reduction in size of the total biomass, a reduced nitrogen fixing activity and changes in the composition of microbial populations of the soil. At what stage heavy metal toxicity to soil microorganisms or to microbial processes in soil is likely to become evident is unfortunately still uncertain. Again, the soluble fraction of heavy metals (also of organic pollutants) is a determing factor. To minimize the shown environmental risks an adequate sludge management is proposed.     

Oscillations of CO and CO + H2 oxidation in air over supported and unsupported Pt catalysts

Oscillation behaviour of the oxidation of CO (0.2–2.2%) in air over Pt wire coils and over Pt/Al₂O₃ catalysts deposited onto the coils (pellistors) has been investigated. The waveforms differ considerably between the two catalytic systems. Over unsupported Pt at 240–260° C, regular oscillations were accompanied by slowly declining activity and by deposition of carbon. Over supported Pt at 110–180°C, relatively complex but sustained oscillation occurred by a different mechanism. This oscillation was greatly enhanced by H₂ (0.25–1.0%), and may involve fluctuations in the concentrations of CO and H₂ around the supported catalyst.     

Downward movement of nitrate and ammonium nitrogen in a flatland ultisol

Three field trials were conducted in the early and late rainy season on a Piarco Series soil (Aquoxic Tropudults) in Central Trinidad to monitor downward movement of NH ₄ ⁺ -N and NO ₃ ^- -N under flat-tilled and ridge-tilled conditions as affected by mulch application. The first experiment was carried out in the early rainy season under bare-fallowed conditions, while okra (Abelmoschus esculentus) was the test crop used in the two remaining trials, which were conducted during the early and late rainy season periods. The plots were fertilized with urea seven days after crop emergence and 14 days after land preparation for the cropped and bare-fallowed experiments respectively. Soil samples were collected weekly after fertilizer application and analyzed for NH ₄ ⁺ -N, NO ₃ ^- -N and soil water.Urea application increased NH ₄ ⁺ -N levels in the soil and NH ₄ ⁺ -N was the dominant inorganic N form observed for the first four weeks after fertilization. Mulch application decreased NH ₄ ⁺ -N and NO ₃ ^- -N soil levels. Ridging the soil increased downward movement of NH ₄ ⁺ -N and NO ₃ ^- -N. Under bare-fallowed conditions, downward movement of NH ₄ ⁺ -N was noted in the 30 to 45 cm soil layer at seven days after fertilization, while under cropped conditions its movement was restricted to the 15 to 30 cm layer within the same period. In bare-fallowed soil, increased NO ₃ ^- -N and its downward movement was noted after four weeks of fertilization. In the cropped soil, downward movement of NO ₃ ^- -N was observed one week after fertilization in the early rainy season and three weeks after fertilization in the late rainy season.     

Anode-support system for the direct electrorefining of cement copper Part I: Process conditions using horizontal rotary cathodes

This paper describes a preliminary study towards a modified anode-support system for the direct electrorefining of cement copper. The proposed system is an alternative process for small mines that produce cement after leaching of copper oxide minerals. It is feasible to utilize a cell provided with a horizontal AISI-316 stainless steel mesh covered with a layer of cement copper as anode system. As cathode system, several horizontal rotary cylinders of AISI-316 stainless steel can be used. The rotary cylinders, partially immersed in acidic copper sulphate electrolyte, must have an internal electrical contact with a copper shaft and two or more isolated slots at the surface to permit the stripping of the copper deposits in the form of thin sheets. The cement copper must be maintained wet to avoid rapid oxidation. The use of pulsed current permits control of the formation of a non-conductive copper sulphate layer on the cement surface, avoiding a continuous increase in cell voltage. As operating conditions a solution of CUSO₄.5H₂O (160 g dm^–3) and H₂SO₄ (50 g dm^–3) with j _c = 5.0 A dm^–2, T = 40 °C, u = 200 rpm; and pulsed current with t _d = 3 min and t _d/t ₀ = 20 can be used. At this stage of the study cement copper (90–95% purity) was utilized.