Compatibilization of a polyolefin blend through covalent and ionic coupling of grafted polypropylene and polyethylene. II. Morphology

The morphology of a polypropylene/polyethylene (PP/PE) blend and a maleic anhydride modified PP and PE (PPg/PEg) blend was studied. The initial morphology, at the extruder die, after the melt blending into a twin‐screw extruder, was first characterized. Then, the evolution of this initial morphology was followed after a injection molding operation, and during annealing in an oven at 200°C. The influence of the compatibilization of the blend by coupling reactions through covalent (with 1,12‐diaminododécane) and ionic reactions (with zinc acetate and sodium hydrogenocarbonate) was also investigated. At the extruder die, the viscosity ratio proved to be a determinant factor governing the dispersed phase diameter of the droplets, and as a second factor, the addition of small amounts of coupling‐agents together with (PPg/PEg) to (PP/PE) resulted in a decrease of the diameter of the droplets. The injection molding of these initial blends resulted in important coalescence and in an elongation of the dispersed phase. This was observed for the non compatibilized and also for some of the compatibilized blends. The ionic coupling showed a good stabilization of the morphology. Finally, the morphology of the non compatibilized blends was found to be instable when the material was annealed at 200°C. The average size of the dispersed phase increased. The coupling reactions delayed the occurrence of the coalescence about 5 min and limited its effects. The extent of the coarsening depended strongly on the composition of the blend and on the nature of the coupling. Still, the ionic agents appeared more effective. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2237–2244, 2004     

Larvicidal Effect of a Cell-Wall Fraction Isolated from Alder Decaying Leaves

Decaying alder leaves in water from Alpine Aedes breeding sites, particularly their toxicity to larval Culicidae, were investigated and characterized with comparative toxicological and chemical methods. Bioassays that used third-instar Aedes aegypti as a reference species indicated that the larvicidal effect of crude leaf litter varied with decaying age of the litter, while no toxicity was detected from leaching water of the mosquito breeding sites. Ten-month-old leaf litter was the most toxic. Comparison of the different soluble and insoluble fractions obtained after sequential extraction of decomposed litter allowed us to localize the toxicity factor to an insoluble cell-wall fraction. The toxicity seems to be linked to phenolic activity. It is higher than that found for tannic acid solutions used as a reference to mimic the larvicidal effects of the molecules naturally occurring in decaying litter. The pattern of establishing the larvicidal effect of alder leaf litter in water of Alpine Aedes breeding sites is discussed.     

Creep Behavior of a Pitch-Based Carbon Filament

New fabrication techniques were developed for uniaxial creep specimens of high-strength, high elastic modulus, pitch-based, carbon filaments, with a matrix-free test section. Experiments show that pitch-based carbon filaments with a tensile modulus of 896 GPa can exhibit, under high stress, large creep deformation without necking. The stress exponent for the pitch-based fibers in the Dorn equation is much lower than that for PAN-based fibers, while the activation energy is the same. The activation energies and activation volumes determined from the experiments suggest mechanisms of creep deformation.     

Spin coating of hydrophilic polymeric films for enhanced centrifugal flow control by serial siphoning

In this paper, we implement rotational flow control on a polymeric microfluidic “lab-on-a-disc” platform by combining serial siphoning and capillary valving for sequential release of a set of on-board stored liquid reagents into a common (assay) channel. The functionality of this integrated, multi-step, multi-reagent centrifugal assay platform critically depends on the capability to establish very reproducible, capillary-driven priming of the innately only weakly hydrophilic siphon microchannels made from common poly(methyl methacrylate) (PMMA) substrates. Due to the relatively high contact angle of the native PMMA substrate, it was practically impossible to ensure sequential release of on-board stored reagents using the capillary-driven serial siphon valves. In this work, we demonstrate that spin-coated hydrophilic films of poly(vinyl alcohol) (PVA) and (hydroxypropyl)methyl cellulose (HPMC) provide stable contact angles on PMMA substrates for more than 60 days. The deposited films were characterized using contact angle measurements, surface energy calculations and X-ray photoelectron spectroscopy spectra. The PVA and HPMC films reduced the water contact angle of the PMMA substrate from 68° to 22° and 27° while increasing their surface energies from 47 to 62 and 57 mN m^?1, respectively. On the centrifugal microfluidic platform, the films were validated to enable the effective and reproducible priming of the serial siphon microchannels at low rotational frequencies while ensuring that the in-line capillary valves are not opened until their respective burst frequencies are passed. Furthermore, the biocompatibility of the proposed surface modification method was examined, and the platform was used to run a sandwich immunoassay for the detection of human immunoglobulin G, and its performance was proven to be comparable to dynamic coating using surfactants.     

UV‐Induced Cross‐Linking of Poly(ethylene oxide) in Aqueous Solution

Summary: Hydrogels of high‐molecular‐weight poly(ethylene oxide) (PEO) have been obtained in situ by applying a very simple procedure that involves UV cross‐linking of PEO in aqueous solution. The efficiency of the photoactivated cross‐linking of thin layers of PEO in aqueous solution in the presence of (4‐benzoylbenzyl) trimethylammonium chloride as a photoinitiator has been determined at room temperature and in a frozen state (?25 °C). It was found that the efficiency varies with the concentration of PEO solution, the molecular weight of PEO, and especially with the temperature. When the UV cross‐linking was performed in the frozen state, porous hydrogels with very high yield of gel fraction (above 90%) and high cross‐linking density were obtained. After drying the hydrogels, films of 50–150 μm thickness were prepared. The films swell extremely fast in water and act as asymmetric membranes.

SEM of a dried PEO hydrogel obtained by UV cross‐linking of an aqueous solution at room temperature.     

Introduction of disulfide bonds into Bacillus subtilis neutral protease

The effects of engineered disulfide bonds on autodigestion andthermostability of Bacillus subtilis neutral protease (NP-sub)were studied using site-directed mutagenesis. After modellingstudies two locations that might be capable of forming disulfidebonds, both near previously determined autodigestion sites inNP-sub, were selected for the introduction of cysteines. Analysisof mutant enzymes showed that disulfide bonds were indeed formedin vivo, and that the mutant enzymes were fully active. Theintroduced disulfides did not alter the autodigestion patternof the NP-sub. All mutant NP-subs exhibited decreased thermostability,which, by using reducing agents, was shown to be caused by theintroduction of the cysteines and not by the formation of thedisulfides. Mutants containing one cysteine exhibited intermoleculardisulfide formation at elevated temperatures, which, however,was shown not to be the cause of the decreased thermostability.Combining the present data with literature data, it would seemthat the introduction of disulfide bridges is unsuitable forthe stabilization of proteases. Possible explanations for thisphenomenon are discussed.     

A Cmos Interface for Thermocouples with Reference-Junction Compensation

This paper presents a CMOS interface for a thermocouple, includingreference-junction compensation. The interface contains a first-orderoscillator whose period is modulated by the signal from the thermocouple(V_X) and two other signals generated internally. One is abase-emitter voltage (V_BE) and the other is a PTAT voltage(V_PTAT). Linear combinations of the periods corresponding tothese two voltages are made by a µC, to obtain a reference signal anda temperature-dependent signal. The internal signals are required to provideauto-calibration for offset and gain and to measure the interface internaltemperature. Dynamic Element Matching is applied to generate an accurate andreliable PTAT voltage. The inaccuracy in the base-emitter voltage iscalibrated using a vertical PNP substrate transistor with multi-emitterareas. The applied modulator used in the circuit has a second-orderfiltering which suppresses low-frequency (1/f) noise. This filteringproperty enables the use of a low-cost CMOS process for the implementationof the circuit. The interface is able to measure a voltage(V_X) in the range of –27 mV to 100 mV, the measuredaccuracy of the system over a temperature range of –25°C to75°C is 550 ppm of V_X ± 2µV. The inaccuracyin determining the reference-junction temperature is 0.6 K. The measuringtime is 50 ms.     

Modelling and experimental evaluation of reaction kinetics in reactive extraction for chiral separation of amines, amino acids and amino-alcohols

This paper reports on determination of the intrinsic reaction kinetics in reactive extraction of chiral compounds. It is important to know the mass transfer rates and reaction kinetics separately for a reliable scale-up. A kinetic model is developed to interpret the experimental data from the selected model reactor, the modified Lewis cell. The two-phase homogeneous reaction model was selected over the interfacial reaction model, because physical partitioning is considerable in all systems studied. It was shown by simulations and by theoretical considerations that conventional regime analysis fails for reactive extraction in a number of regimes, because the conditions of an irreversible reaction and a negligible resistance to mass transfer in the non-reactive phase are generally not fulfilled in reactive extraction. Furthermore, it follows from the simulations that enhancement of mass transfer by reaction may be partly invisible. Finally, it becomes clear that only the fraction of the species that is in the right ‘extractable’ form should be used in the calculations. As the conventional regime analysis cannot be applied to determine the reaction kinetics in the chiral systems, first the mass transfer rate was measured during physical extraction to determine the location of the main resistance to mass transfer. Then the enhancement of mass transfer was measured during reactive extraction. By model simulation, it was determined how much enhancement of mass transfer should be observable. In this way, it was concluded that the reaction kinetics of the azophenolic crown ether system are between fast and instantaneous, and the reaction kinetics of the Cu(II)-N-dodecyl-L-hydroxyproline system are between slow and fast. The Lewis cell is not the most suitable model contactor to determine reaction kinetics in reactive extraction systems.     

Electrical Systems for Automatic Handling and Electric Heating of Slabs

The availability of large quantities of electrical power and sophisticated means of control has justified the use of induction methods in heating large steel slabs to rolling mill temperatures. Capable of delivering 210 MW, a unique power system, comprising power transformers, autotransformers, static switches, and capacitor banks, provides eighteen induction heaters with controlled electrical energy. The entire system can deliver 600 ton/h of steel to the rolling mill. The basic overall automatic control scheme involves the operations of slab handling control, heater control, static power switching, and computer control. The control functions, including phase balance and demand limit control, are described and discussed. The features and operation of the static power switch, capable of switching close to 10 000 A, are presented. Used as a protective device, the switch can clear up to 210 000-A faults in less than one cycle.     

Improving light fastness of natural dyes on cotton yarn

The objectives of this study were to evaluate the light fastness of selected natural dyes (madder, weld and woad) and the effect of some commonly used antioxidants and UV absorbers on the light fastness of these dyes.

The photofading rate curves of madder and weld fixed on cotton correspond to type II fading rate curves described by Giles. These results are in concordance with those of Cox-Crews. The woad presents a type III fading rate curve, similar to the indigo fading rate curve presented by Cox-Crews.

A poor light fastness of the three natural dyes in comparison with synthetic ones is established beyond question. Nevertheless, the use of some additives can improve this default of natural dyes. In all the cases, the use of UV absorbers or antioxidants improved the light fastness of dyed fabrics. The most effectives were the vitamin C and the gallic acid.