Factors affecting the mechanical properties of mica-filled polypropylenes

Water-ground Phlogopite mica (Kemira Siilinjarvi phlogopite) has been evaluated as a reinforcing filler in polypropylene. The major factors which influence the composite strength and modulus include the size, aspect ratio, and uniformity of the mica flakes. Aqueous delamination permits the production of very small flakes (less than 44 microns diameter) with aspect ratios near 50. Such small flakes impart greater tensile and modulus values to polypropylene than larger flakes and the former can also be reprocessed many times without any deterioration of properties. Surface treatment is necessary for adequate dispersion and coupling, particularly with the finely divided mica fillers. Other properties such as the heat-distortion temperature, fracture toughness, and gas permeability are also influenced by the mean size and aspect ratio of the mica filler. Guidelines are presented to indicate the preferred characteristics of mica fillers for optimum performance.     

C,CO and CO2 hydrogenation on cobalt foil model catalysts: evidence for the need of CoO reduction

The hydrogenation of C, CO, and CO₂ has been studied on polycrystalline cobalt foils using a combination of UHV studies and atmospheric pressure reactions in temperature range from 475 to 575 K at 101 kPa total pressure. The reactions produce mainly methane but with selectivities of 98, 80, and 99 wt% at 525 K for C, CO, and CO₂, respectively. In the C and CO₂ hydrogenation the rest is ethane, whereas in CO hydrogenation hydrocarbons up to C₄ were detected. The activation energies of methane formation are 57, 86, and 158 kJ/mol from C, CO, and CO₂, respectively. The partial pressure dependencies of the CO and CO₂ hydrogenation indicate roughly first order dependence on hydrogen pressure (1.5 and 0.9), negative first order on CO (–0.75) and zero order on CO₂ (–0.05). Post reaction spectroscopy revealed carbon deposition from CO and oxygen deposition from CO₂ on the surface above 540 K. The reduction of cobalt oxide formed after dissociation of C-O bonds on the surface is proposed to be the rate limiting step in CO and CO₂ hydrogenation.     

Blends of natural rubber and polyurethane latices studied by 1H wideline and 13C MAS solid‐state NMR

¹H wideline and ¹³C magic‐angle spinning NMR have been used to study the morphology and dynamics of latex‐cast and solution‐cast film blends of natural rubber (NR) and a polyurethane (PU) based on poly(?‐caprolactone) diol and isophorone di‐isocyanate. ¹H T₁ and T_1ρ relaxation times have been measured, and the extent of interpenetration of the NR and PU constituents has been monitored using the Goldman–Shen technique. The NMR spectra and relaxation properties indicated that the NR and PI constituents largely occupy separated domains on a distance scale of >10 nm. The Goldman–Shen experiments indicated that there was slightly greater contact between NR and PU in the solution‐cast samples than in the latex‐cast. The tensile properties of the films have been measured. The tensile strength and initial Young's modulus pass through a maximum at a PU content of about 50 wt%. © 2002 Society of Chemical Industry     

Fabrication and Characterization of Large Free-Standing Polarizer Grids for Millimeter Waves

Construction of large aperture free-standing metal wire grids is demonstrated for the lower end of the millimeter wave spectral region. For the constructed two grids the co-polarized and cross-polarized components of transmitted power were measured at 45° oblique incidence. The measurements were performed as a function of wire orientation angle and in more detail at selected angles. The results are in good agreement with the theoretical results presented in the literature. In order to save time and costs the construction apparatus was simplified from those reported previously by other authors. It was shown that for this frequency range the grid characteristics are not degraded when such an apparatus is applied. One of the constructed grids will be used in a calibration system of the Helsinki University of Technology (HUT) polarimetric radiometer.     

Variational formulation of open-ended coaxial line in contact withlayered biological medium

An open-ended coaxial probe designed to measure layered biological media is analyzed with a new method. The probe is considered as an electrostatic circuit element whose capacitance is solved using a stationary functional. The fundamental transverse electric and magnetic field (TEM)-mode and the series of evanescent wavemodes in the coaxial cable are used as basis functions. The field outside the probe is solved using a Hankel transform. The capacitance is calculated for homogeneous materials and two-layer structures and the results are compared with values measured with a phantom model. The method can be easily extended for structures with an arbitrary number of layers. A practical approximation for two-layer cases, originally developed to take into account the effect of subcutaneous fat in skin measurements, is presented and its validity for different combinations of dielectric constants and the thickness of the first layer is demonstrated. The static approximation limits the frequency range, but it covers biological measurements up to 500 MHz. The developed method is accurate and easy to adopt in practice     

Applications of positron techniques to surface studies and catalysis

Positrons can be used to obtain unique information on solids. The life and annihilation of this anti-matter particle is extremely sensitive to the atomic and electronic environment. Studies of solid surfaces with monoenergetic positron beams have found increasingly interesting applications and many new techniques have been introduced with unique results. The more traditional techniques using polyenergetic positrons have been utilized in the study of internal surfaces closely related to catalysis. In this review different positron techniques are described and their applications in the field of surface science and catalysis are presented.     

Aqueous poly(urethane–urea) dispersions and cast films based on m‐TMXDL. 1. Structure–property relationships

Aqueous poly(urethane–urea) dispersions were prepared from polycaprolactone diol, α,α,α′,α′‐tetramethyl‐1,3‐xylylene diisocyanate (m‐TMXDI) and α,α‐dimethylol propionic acid (DMPA) using a prepolymer mixing process. In the process, polyurethane prepolymers were neutralised with triethylamine and the chains extended in water with either hydrazine, 1,2‐ethylene diamine or 1,2‐propylene diamine. For comparison, some samples were prepared from a more commonly used diisocyanate, isophorone diisocyanate (IPDI). Dispersion characteristics and basic structure–property relationships of the cast films were determined. m‐TMXDI provided some advantages over IPDI in the preparations since its use gave lower prepolymer viscosities and better resistance to elevated temperatures. Films prepared from m‐TMXDI dispersions exhibited considerably lower values of Young's modulus and hardness and higher elongations at break than those prepared from IPDI‐based dispersions for analogous compositions, whereas differences in the average particle sizes or viscosities of the dispersions were only small. When the DMA content was varied, the dispersions and cast films of m‐TMXDI‐based systems showed similar changes as are known to occur in IPDI‐based systems: as the DMPA content was increased, the average particle size of the dispersions decreased and the viscosity increased, and for the cast films, the Young's modulus and tensile strength increased and the maximum elongation at break decreased. Changing the chain‐extension agent from hydrazine to 1,2‐ethylene diamine, to 1,2‐propylene diamine and had little effect on the particle size of the dispersions, but increased the Young's modulus and hardness of the respective cast films. Molar masses of the chain‐extended polymers were unexpectedly low. DSC analysis of cast films indicated that the degree of crystallisation of the soft or hard domains was low. © 2002 Society of Chemical Industry     

The effect of reaction conditions on the oxidation of veratryl alcohol catalyzed by cobalt salen-complexes

Cobalt salen-type [salen=N,N′-bis(salicylidene)ethylenediamine] complexes 1–6 were studied as catalysts for dioxygen activation in the oxidation of veratryl alcohol in basic aqueous conditions. The complexes Co(salen) (1), Co(CH₃salen) (2) [CH₃salen=N,N′-bis(methylsalicylidene)ethylenediamine], Co(4OHsalen) (3) [4OHsalen=N,N′-bis(4-hydroxosalicylidene)ethylenediamine], Co(sulfosalen) (4) [sulfosalen=N,N′-bis(5-sulfonatosalicylidene)ethylenediamine], Co(acacen) (5) [acacen=N,N′-bis(acetylacetone)ethylenediamine) and Co(N-Me-salpr) (6) [N-Me-salpr=bis(salicylideniminato-3-propyl)methylamine] were chosen to examine the influence of ligand structure on the catalytic activity. The effect of reaction conditions on the oxidation of veratryl alcohol was studied by varying temperature, pH, time or the nature and amount of the axial base needed to enhance the activity of complexes 1–5. The catalytic behaviour of the studied complexes was shown to be very depended on the applied conditions and distinct differences could be observed among the complexes. In all reactions, veratraldehyde was the only product observed. The unsubstituted complex 1 was the most efficient catalyst in the studied system achieving turnover numbers of up to 28 at 80 °C and pH 12.5.     

Cyclohexene dehydrogenation and hydrogenation on Pt(111) monitored by SFG surface vibrational spectroscopy: different reaction mechanisms at high pressures and in vacuum

The hydrogenation and dehydrogenation reactions of cyclohexene on Pt(111) crystal surfaces were investigated by surface vibrational spectroscopy via sum frequency generation (SFG) both under vacuum and high pressure conditions with 10 Torr cyclohexene and various hydrogen pressures from 30 up to ~600 Torr. At high pressures, the gas composition and turnover rate (TOR) were measured by gas chromatography. In vacuum, cyclohexene on Pt(111) undergoes a change from π/σ‐bonded, σ‐bonded cyclohexene and c‐C₆H₉ surface species to adsorbed benzene when the surface was heated from 130 to 330 K. A site‐blocking effect was observed at saturation coverage of cyclohexene that caused dehydrogenation to shift to somewhat higher surface temperature. At high pressures, however, none of the species observed in vacuum conditions were detectable. 1,4‐cyclohexadiene (1,4‐CHD) was found to be the major species on the surface at 295 K, even with the presence of nearly 600 Torr of hydrogen. Hydrogenation was the only detectable reaction at the temperature range between 300 and 400 K with 1,3‐cyclohexadiene (1,3‐CHD) on the surface, as revealed by SFG. Further increasing the surface temperature results in a decrease in hydrogenation reaction rate and an increase in dehydrogenation reaction rate and both 1,3‐CHD and 1,4‐CHD were present on the surface simultaneously. The simultaneous observation of the reaction kinetic data and the chemical nature of surface species allows us to postulate a reaction mechanism at high pressures: cyclohexene hydrogenates to cyclohexane via a 1,3‐CHD intermediate and dehydrogenates to benzene through both 1,4‐CHD and 1,3‐CHD intermediates. Isomerisation of the 1,4‐CHD and 1,3‐CHD surface species is negligible. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of four methods to enumerate probiotic bifidobacteria in a fermented food product

Four methods of enumeration were compared by monitoring levels of probiotic bifidobacteria in fermented oat drink during storage. Strains of Bifidobacterium longum and B. lactis were quantified by plate counts, fluorescent in situ hybridization (FISH), quantitative real-time PCR and commercial LIVE/DEAD BacLight bacterial viability kit, and the methods were further developed to suit the enumeration of bifidobacteria in fermented foods. Plate counts of both B. lactis and B. longum were lower than the PCR and FISH counts. The LIVE/DEAD counts of B. lactis were comparable to PCR and FISH counts. The plate counts of B. lactis were slightly but significantly lower than LIVE/DEAD counts, suggesting that the cells that were not able to grow on plates may have become dormant. The plate counts of B. longum were several log units lower than LIVE/DEAD counts, suggesting that a remarkable part of the cells were dormant. Real-time PCR and FISH were shown to suit the quantification of the total amount of probiotic bifidobacteria in foods. Plate counts and LIVE/DEAD counts provided conflicting information on viability especially in the case of B. longum. We conclude that the choice of enumeration method for probiotic bacteria may have significant effect on the results of the analysis. The strain-specific properties and the objects of the analysis should be taken into account when enumeration methods for different probiotic strains are chosen.