Acid-catalyzed moisture-curing polyurea/polysiloxane ceramer coatings

The para-toluene sulfonic acid (p-TSA) was used to catalyze the moisture curing of an organic/inorganic hybrid coating system. The organic phase was based on the isocyanurate of 1,6-hexamethylene of diisocyanate (HDI). The inorganic phase was based on the prepolymerized oligomers of tetraethyl orthosilicate (TEOS). An alkoxysilane-functionalized HDI isocyanate was added into the coating formulation to aid in phase miscibility. The general coating and tensile properties were evaluated as a function of the acid catalyst concentration. In addition, the films were analyzed using differential scanning calorimetry (DSC) and dynamical mechanical thermal analysis (DMTA). The results indicated that the acid catalyst enhanced the adhesive properties of the hybrid coatings. The addition of the acid catalyst increased the changed crosslink density of films and decreased the crystallinity of the organic phase.     

Analysis of exempt paint solvents by gas chromatography using solid-phase microextraction

Acetone, methyl acetate, and parachlorobenzotrifluoride (PCBTF or Oxsol? 100) have been exempted as VOC solvents by the U.S. Environmental Protection Agency. In measuring coating VOC content, separate methods for determining exempt solvents are required. One such method utilizes solid-phase microextraction (SPME) to sample the headspace of solvent-based coatings to which the surrogates acetone-d6, methyl acetate-d3, and/or metachlorobenzotrifluoride have been added. The sampled exempt coating solvents are thermally desorbed and analyzed using gas chromatography with flame ionization or mass spectral detection. The SPME headspace method has also been used to analyze MEK, butyl acetate, tert-butyl acetate, toluene, and xylene in solventborne coatings, and alcohols in waterborne systems. This paper presents the results obtained for acetone and toluene in a large number of aerosol paints. Additionally, the results from a round-robin study for acetone, methyl acetate, and parachlorobenzotrifluoride in commercial solvent-based coatings are reported.     

Epoxidized soybean oil-based ceramer coatings

New inorganic/organic hybrid coating containing epoxidized soybean oil were prepared. Three sol-gel precursors [titanium (IV) i-propoxide, titanium (IV) di-i-propoxide bis-acetoacetonate, and zirconium n-propoxide] were utilized as the inorganic phase. Various coating properties, including adhesion, hardness, impact resistance, flexibility and tensile properties, were investigated as a function of sol-gel precursor type and concentration. All ceramer coatings exhibited excellent flexibility and hardness. Tensile strength and hardness increased with sol-gel precursor concentration. A slight decrease in adhesion and impact resistance was observed with increasing precursor content.     

Moving Averages of Random Vectors with Regularly Varying Tails

Regular variation is an analytic condition on the tails of a probability distribution which is necessary for an extended central limit theorem to hold, when the tails are too heavy to allow attraction to a normal limit. The limiting distributions which can occur are called operator stable. In this paper we show that moving averages of random vectors with regularly varying tails are in the generalized domain of attraction of an operator stable law. We also prove that the sample autocovariance matrix of these moving averages is in the generalized domain of attraction of an operator stable law on the vector space of symmetric matrices.
AMS 1990 subject classification. Primary 62M10, secondary 62E20, 62F12, 60F05.     

Synthesis of metatungstate pillared layered double hydroxides with variable layer composition. Effect of the Mg:Al ratio on the microporous structure

A series of layered double hydroxides (LDHs) pillared with the Keggin ion H₂W₁₂O₄₀⁶⁻ has been synthesized with final Mg:Al ratios of 1.75:1, 2.31:1 and 3.51:1 by ion exchange reaction of the LDH-hydroxide and LDH-adipate precursors. In each case, the pillared product was characterized by specific BET N₂ surface areas of more than 110 m² g⁻¹ and micropore volumes in excess of 0.026 ml g⁻¹. The micropore size distribution plots obtained from the argon adsorption isotherms indicate that the micropore diameters become smaller as the surface charge density of the LDH increases. A study was also performed on each of the LDH precursors in order to determine any problematic steps in the overall synthesis. Significant differences were noticed in the POXRD patterns of the LDH-adipate precursor; these are believed to be due to differences in the orientation and degree of order of the adipate anions in the gallery space of the LDH. It was found that adipate anions orientated with the long axis perpendicular to the inorganic layers were easier to exchange than those where the long axis was aligned parallel to the inorganic layers.     

Effect of pulsing on reaction outcome in a gas–liquid catalytic packed-bed reactor

A novel experiment is described for studying the effect of flow regime on reaction outcome for a consecutive-parallel reaction. By taking advantage of the convective nature of disturbances that grow into pulses in gas–liquid packed-bed reactors, it is shown that it is possible to compare reaction behavior for pulsing and trickling at the same flow rates. This contrasts previous studies where effects of regime were found, but at different flow rates. This experiment is accomplished by packing the column with mostly inert particles and confining the catalytically active region either near the inlet, where pulses have not yet formed, or near the end where they have developed. It is found that for the reaction of phenylacetylene to styrene and ethylbenzene over a platinum/alumina catalyst, where pulses are present in the bottom of the reactor but not at the top, about a 15% increase in styrene concentration, as an intermediate, occurs under pulsing conditions.     

Effect of composition on the mechanical response of agglomerates of infant formulae

The objective of this paper is to investigate the relationship between the compositions of four typical infant formulae, the evolution of key quality characteristics during pneumatic conveying and the mechanical properties of individual agglomerates. Conveying experiments were conducted using a lab-scale rig. Four quality characteristics were measured before and after conveying: bulk density, volume mean diameter, wettability and percentage free fat. Relative breakages were calculated from particle size distributions. Uniaxial compression experiments were performed on individual agglomerates, giving forces and strains at failure and agglomerate stiffnesses. Coefficients of restitution of the agglomerates were obtained by video analyses of drop tests. The data indicate that bulk densities before conveying and the force and the strain of individual agglomerates at failure were related to the protein content. The force at failure and agglomerate stiffness were strongly correlated, and generally increased with increasing protein to fat ratio while the strain at failure decreased.     

Dynamic and kinetic modeling of isotopic transient responses for CO insertion on Rh and Mn–Rh catalysts

Isotopic transient tracer techniques have been employed to study heterogeneous hydroformylation on Rh/SiO₂ and Mn–Rh/SiO₂. Pulse injection of D₂ and allowed tracing of the deuterium and CO incorporation pathway into the aldehyde product. The d₁- and d₂-propionaldehyde responses showed a double-peak, or two-hump, response to the D₂ pulse, while showed a single-hump response to the pulse. Analysis of the product responses to the D₂ pulse in CO/H₂/C₂H₄ and CO/H₂/C₂H₄/C₂H₅CHO suggests that the first hump of the d₁- and d₂-propionaldehyde responses was due to rapid H/D exchange with adsorbed propionaldehyde via enol intermediates. The decay of the second hump was due to reaction of adsorbed acyl with spillover hydrogen/deuterium. The response was due to CO insertion followed by acyl hydrogenation. Compartment modeling of the product responses from the and D₂ pulse inputs allowed determination of residence times of adsorbed intermediates, surface coverages of adsorbed intermediates, and the elementary rate constants for acyl hydrogenation and CO insertion. Elementary rate constants for acyl hydrogenation determined from this study were consistent with the value calculated by transition state theory (TST). The addition of Mn promoter to Rh/SiO₂ increased coverages of , , and and shifted the rate-limiting step for propionaldehyde formation. Acyl hydrogenation is the rate-limiting step on Rh/SiO₂ while CO insertion and acyl hydrogenation are both kinetically significant on Mn–Rh/SiO₂.