Characterisation of alumina-supported vanadium oxide catalysts by kinetic analysis of H2-TPR data

Alumina-supported vanadium oxide catalysts with vanadium contents of 2, 5 and 11 wt.% were prepared by incipient wetness impregnation and characterised by XRD, Raman spectroscopy and H₂-TPR. The catalysts with the low vanadium contents contained vanadium mainly in the well-dispersed phase, but the catalyst with the highest vanadium content contained also some crystalline AlVO₄ according to XRD and Raman spectroscopic results. The reduction kinetics of the vanadium catalysts was modelled based on the hydrogen consumption during the TPR. The reduction kinetics could be described with a single-reducible-site random nucleation model for the catalyst containing the lowest amount of vanadium. The reduction kinetic models for the other catalysts required a combination of multiple processes to describe the experiments properly. In the catalyst with 5 wt.% V, a part of vanadium species possibly reduces as a homogeneous random nucleation process, but topochemical reduction by nuclei growth also takes place. In the catalyst with 11 wt.% V, reduction by nuclei growth seems to be the predominant reduction mechanism. The characterisation of the reduced catalysts by XRD and during reduction by Raman spectroscopy enabled the identification of the features of the TPR profiles.     

Development of a phosphate-free home laundry detergent

A group of multifunctional surfactants was synthesized in order to arrive at materials which might function well in hard water. The salts of alkylaryl sulfopropionates, ; alkylaryl sulfonamides of taurine R-C₆H₄-SO₂NHCH₂CH₂SO₃Na; and the alkylaryl sulfonamide of aminoethylsulfuric acid R-C₆H₄-SO₂NHCH₂CH₂OSO₃Na were found to be quite effective. These compounds were synthesized via conventional routes and their biodegradability was established. These materials were formulated into the detergents with the aid of various organic and inorganic builders other than condensed phosphates. The detergency of these materials was evaluated with the aid of standard test cloths. Analogously formulated detergents based upon linear alkylbenzenesulfonate were also included for comparison in this evaluation study. It was found that a number of fairly satisfactory phosphate-free heavy duty detergent formulations could be developed. Presented at the AOCS Meeting, Houston, May 1971.     

Chemical in situ polymerization of polypyrrole on poly(methyl metacrylate) substrate

Combination of electrically and optically active organic materials in one fiber would enable to realize several interesting smart systems in a simple and cost effective manner. In this work the coating of plastic optical material-poly(methyl metacrylate)-was carried out by in situ chemical polymerization of polypyrrole (PPy). Two ways of chemical polymerization were compared: (a) using FeCl₃ and (b) using ammonium peroxydisulphate with p-toluene sulfonic acid. Both planar and fiber samples were prepared. The samples are characterized by their surface resistivity and surface morphology. The influence of polymerization conditions like temperature, time and reactant concentration on surface resistivity is discussed. Optical transmission properties of PPy films are presented. The ageing of samples was studied within 4 weeks time.     

Qualitative analysis of twin-screw extruder performance in stabilization pelletizing of HDPE resins

Two twin-screw extruders of different size and centerline distance C_L were compared. To understand better the performance of the extruders, the operation points were optimized for an HDPE (high-density polyethylene) film product, and the performance of screw configuration was qualitatively analyzed with some numerical methods at the operation points. The machinery with narrower C_L was found to have lower average shear rate, higher conveying capacity, and more channeling in the conveying flow. That means also a need for severe processing in the kneading zone. The extruder with narrow C_L had a narrow operation window, and that made it more difficult to combine homogenization and degradation of the product.     

Effect of heat‐treatment on the performance of gas barrier layers applied by atomic layer deposition onto polymer‐coated paperboard

The effect of heat treatment on the gas barrier of the polymer‐coated board further coated with an Al₂O₃ layer by atomic layer deposition (ALD) was studied. Heat treatment below the melting point of the polymer followed by quenching at room temperature was used for the polylactide‐coated board [B(PLA)], while over‐the‐melting‐point treatment was utilized for the low‐density polyethylene‐coated board [B(PE)] followed by quenching at room temperature or in liquid nitrogen. Heat treatment of B(PLA) and B(PE) followed by quenching at room temperature improved the water vapor barrier. However, because of the changes in the polymer morphology, quenching of B(PE) with liquid nitrogen impaired the same barrier. No improvement in oxygen barrier was observed explained by, e.g., the spherulitic structure of PLA and the discontinuities and possible short‐chain amorphous material around the spherulites forming passages for oxygen molecules. This work emphasizes the importance of a homogeneous surface prior to the ALD growth Al₂O₃ barrier layer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Stress–strain behavior of polyamide 6 staple fibers of punch-needled press felts under simulated wet-pressing conditions

This study evaluates the specific stress (tenacity) and strain (elongation) of polyamide 6 staple fibers, which were virgin, punch-needled on the press felt, and worn on the press felt under simulated wet-pressing conditions. The staple fibers were distinguished by molecular weights. The fiber deformation and defects were microscopically characterized after the felt preparation and aging. We discovered that the tensile breaking force and elongation of the polyamide 6 staple fibers decreased markedly during the felt preparation and aging. The mechanical reduction of staple fibers reflected their tenacity, work, and modulus values. Surprisingly, the linear density of staple fibers remained unchanged – although fibers strongly deformed and lost their mechanical properties after the felt aging. The results indicate that an increase in molecular weight improves the mechanical durability of staple fibers, the preparation of the press felt (punch-needling) decreases the tenacity and elongation of staple fibers, and humidity provokes their degradation.     

Morphologic changes in cat epithelium following continuous wear of orthokeratology lenses: a pilot study.

PURPOSE: To investigate the sequence of morphologic changes over time in cat epithelium during continuous wear of orthokeratology lenses. METHODS: Four 2-year-old female cats were used; one served as a no lens wear control and three wore custom designed Paragon CRT lenses for myopic and hyperopic correction in the right and left eyes, respectively. Lenses were worn continuously and animals were euthanased after 4h, 8h and 14 days. Corneal tissue was fixed then stained with hematoxylin and eosin for histologic evaluation and measurement of epithelial thickness. RESULTS: Average epithelial thickness of control eyes in the centre (38+/-1 microm) and mid-periphery (3.0 mm from the centre, 38+/-2 microm) of the cornea was similar. Epithelial thickness in myopic corrected eyes showed progressive thinning in the centre and progressive thickening in the mid-periphery with increased lens wearing time. Hyperopic corrected eyes showed the opposite pattern of progressive epithelial thickening in the centre and thinning in the mid-periphery with lens wearing time. CONCLUSIONS: The epithelium appears to play a major role in the changes induced by orthokeratology lenses. The epithelial effects were dependent on time and lens design. Further studies are needed to determine the mechanisms responsible for these changes.     

The influence of crack size on the fracture behaviour of short cracks

Crack size effects are investigated by applying local fracture criteria at a specific distance ahead of a crack tip, related to the material's microstructure. For sufficiently long cracks, the criteria are applied at points within the singularity-dominated region and then failure corresponds to the attainment of a critical intensity of the singularity but for shorter cracks this may not be the case and size effects may be anticipated.Comparisons of stress and strain fields around crack tips are made between cracked specimens and a boundary layer model which allows for a finite T-stress parallel to the line of the crack; these demonstrate that size effects can be characterized, for a useful range of crack sizes, in terms of the elasticT-term.The variation of the ductile-brittle transition temperature with crack size is studied on the basis of model calculations based on a power-law hardening material with temperature-dependent yield stress, coupled with two competing fracture criteria, chosen to model brittle or ductile crack extensions respectively. Generally, shorter cracks display lower transition temperatures and higher toughness. This potentially beneficial effect may, however, be nullified by stress triaxiality.     

Electrospinning of polyamides with different chain compositions for filtration application

Electrospinning of several polyamides, PA6, PA66, PA612, PA614, PA1012, and PA1014, having different chain compositions and lengths of diacid and diamine segments, was demonstrated. Electrospinnability and fiber production rate of these polyamides were evaluated. Electrospun fibers were characterized with regard to their use in air filtration by measuring fiber diameter and filtration efficiency of fiber coating. Longer nonpolar chain segments of higher polyamides could in theory indicate higher dielectricity compared to PA6 and PA66, which would be an advantage in filtration applications. The solubility in polar formic acid and electrospinnability of higher polyamides, on the other hand, were clearly impaired with increased length of chain segments. Hence, PA66 is our best choice, and PA612 and PA6 our second options for commercial filtration applications if fiber electrospinnability, production rate, fiber diameter, and its distribution are concerned. Filtration efficiency of more than 95% of the particles having a diameter of 0.16 μm and above was achieved with 0.5 g/m² coating of PA66 nanofibers. Further increase in coating weight mainly increased the pressure drop to an unusable range without a significant further improvement of filtration efficiency. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Abrasive wear resistance of starch consolidated and sintered high speed steel

The abrasive wear resistance of starch consolidated (SC) and super solidus liquid phase sintered (SLPS) M3/2 high speed steel (HSS) samples have been evaluated by a two-body micro-abrasion test (low stress abrasion), using 6 μm diamond abrasive particles, and a three-body abrasion test (high stress abrasion), using significantly larger abrasive particles of blast furnace slag (600 HV) and silicon carbide (2400 HV), respectively. In the tests a commercial powder metallurgical (PM) HSS was used as a reference material.The results show that the microstructure of the SC and SLPS HSS samples is strongly dependent on the sintering temperature used. With increasing temperature the microstructure ranges from a porous (5% porosity) relatively fine grained low temperature sintered microstructure to a fully dense relatively coarse grained high temperature sintered microstructure with eutectic carbides/carbide networks. However, despite the pronounced microstructural differences displayed by the as-sintered HSS microstructures these show a relatively high abrasive wear resistance, comparable with that of a HIPed HSS reference, both under low and high stress abrasion contact conditions. The characteristic features of the low and high temperature sintered microstructures, i.e. the pores and coarse eutectic carbides/carbide networks, only show a limited impact on the wear rate and the wear mode (dominant wear mechanism). The results obtained imply that near net shaped components manufactured by starch consolidation and super solidus liquid phase sintering might be of interest in tribological applications.