Performance of hybrid reinforcements in PVC composites. II: Use of surface-modified mica and different cellulosic materials as reinforcements

The effect of the composition of various wood fibers and surface-treated mica as well as different surface treatments of cellulosic materials on the mechanical properties of PVC composites has been evaluated. Cellulosics were surface modified by prior coating with maleic andydride (MA), mixtures of MA and Na-silicate and isocyanate. The filler concentration was fixed at 25 wt%. Both tensile strength and modulus of composities filled solely with mica are superior to those of non-treated wood fiber-filled composities. while the reverse is true for impact strength (except for bagasse-filled composities), ultimate elongation, and tensile toughness. Moreover, the mechanical properties of composities, with the exception of modulus, filled only with mica and/or non-treated wood fibers are inferior to those of unfilled PVC. Compared to non-treated fiber-filled composites, properties improved when surface-modified wood fibers were used alone, or along with mica. Isocyanate-coated wood fibers ranked best with regard to the mechanical properties of the composities. Properties also changed with the change of wood species and compositions of mica and wood fibers. Experimental results indicate good compatibility between surface-treated wood fibers/mica and PVC composities.     

Diffusion-controlled adsorption processes

Numerical solutions of differential equations for diffusion-controlled adsorption processes in spherical particles are presented for slow diffusion of gaseous molecules followed by rapid adsorption according to the Langmuir isotherm. As the parameter in the denominator of the Langmuir equation is increased the rate increases and the generalized rate curves shift progressively from that for the linear isotherm, the Langmuir parameter = 0, to the curve of the parabolic law. Adsorption and desorption cycles are considered and parameters are provided for relating any of these processes to the generalized curves. A simple linear equation was shown to approximate the rate curves with moderate accuracy.     

Spontaneous combustion regimes

Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 5, pp. 13–27, September–October, 1992     

Fluidization studies in large gas—solid systems. Part IV. Similarity criteria for different size systems

Time average differential pressure profiles have been recorded at the base of fluidized beds with cross-sectioned areas of 0.375 and 1.5 m², both being fitted with uniform resistance gas distributors and containing various materials. For beds of a specific material, with equal ratios of defluidized bed depth/bed width (within the limits 0.375 – 1.5), a common relationship was found between the time average differential pressure difference between the centre and corners at the bed base (expressed as a fraction of total theoretical bed pressure drop at incipient fluidizing conditions) and superficial gas velocity.     

Esters of hydroxystearic acids as primary low-temperature plasticizers for a vinyl chloride—Vinyl acetate copolymer

Summary Thirty-one acyloxy or aryloxy esters prepared from hydroxystearic acids have been evaluated as plasticizers for a vinyl chloride-vinyl acetate copolymer (95∶5). Many of them were found to be primary plasticizers, having outstanding low-temperature performance when employed at the 35% level. Formulations with these compounds compared quite favorably in tensile properties with those containing the di-2-ethylhexyl esters of phthalic, sebacic, azelaic, and adipic acids. Volatility losses were similar to those of the four di-2-ethylhexyl esters. The loss of plasticizer through migration was equal to or less than that from compositions containing the esters of sebacic, azelaic, and adipic acids but was greater than that of the phthalate ester. A mechanistic scheme of plasticizer-polymer interaction has been presented, proposing that the rate of diffusion of plasticizer through the polymer mass is a controlling factor in both good low-temperature performance and the resulting high migration losses. Methyl esters, some aromatic esters, and esters containing three or more polar centers have improved permanence but show a more rapid change in torsional modulus as the temperature is lowered during the determination of the Clash-Berg stiffening temperature. Eastern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

The effect of heat on metal incorporated silica gels

Silica gel prepared under varying conditions indicated that, in addition to the pH and kind of acid, the mode of adding the solutions govern the evolution of surface area of the produced xerogel. Co-precipitation with the oxides of iron, copper, or nickel showed a marked effect in decreasing the surface area of the dry gel. Xerogels incorporated with iron oxide suffered from a sharp sintering that appeared upon heating to 900 °C. Copper oxide-incorporated silicas showed a small decrease in surface area at the same temperature. However, silica incorporated with nickel oxide seems to be resistant to heat treatment at 900 °C, and exhibits only a small change in surface area. Acid treatment of the incorporated silicas resulted in negligible variations in surface area, probably due to the low content of oxides.     

The Role of Cations in Some Inorganic Hydrolysis Reactions

Cations which shift certain equilibria from left to right by forming a compound with one of the reaction products were investigated with respect to their kinetic role in the process. Silver ions have no influence on the rate of the hydrolysis of cyanogen iodide. Similarly, cations which form sparingly soluble carbonates do not influence the rate of hydration of carbon dioxide. On the other hand, the hydrolysis of chlorine is accelerated by Ag⁺ and, to a lesser extent, by Cd²⁺ and Fe(III). It is shown that the effect is not due simply to a bimolecular reaction between chlorine and the cation. In the case of Ag⁺, heterogeneous catalysis may play some role, in analogy with the solvolysis of organic halides. In the case of Cd²⁺, there is spectrophotometric evidence for compounds between Cl₂ and HOCl on the one hand, and the cation on the other. It is suggested that these compounds interconvert more rapidly than do the parent substances. A similar mechanism may be operative in the case of Fe(III), and, possibly, also in the case of Ag⁺.     

Comportement des lits fluidisés en milieu viscoélastique

The flow of various fluids of different rheological behaviour has been studied in both fixed and fluidized beds. These fluids were water and aqueous solutions of glycerin, Carbopol and Separan AP-30. For small Deborah numbers, the flow of Carbopol and Separan AP-30 solutions thorough fixed beds is well described by the Ergun relation using the generalized Reynolds number of Christopher and Middleman (1965). Deviations from this behaviour are observed in fluidized beds as preferential flow paths easily occur near the distributor. These deviations are small for Newtonian fluids but take more importance with non-Newtonian solutions and are increased by viscoelasticity.     

The removal of radioactive caesium contaminants from simple aqueous solutions

Cs ions can be removed from aqueous solutions by forming a precipitate of copper ferrocyanide which, having occluded the Cs ions, can in turn be floated by means of an anionic collector. Collection was achieved with either α-sulphopalmitic acid or sodium dodecyl sulphate depending on what interfering ions were initially present in the solution. Recoveries of 98–99% were obtained on batch scale experiments and 97.5–98.5% on continuous scale operation. The investigations of the flotation parameters of pH, gas-rate, concentrations of precipitating reagents and collector, as well as the interference effects of other ions are discussed. Using data obtained in batch scale tests, continuous scale experiments were designed and operated.