Rheology of epoxy networks near the gel point

Summary Curing and gelation of diglycidyl ether of Bisphenol A with poly(oxypropylene)-diamine (Jeffamine D 400) was followed using dynamic mechanical measurements. The gel point was determined rheologically and the characteristic value of the loss factor tan at the gel point, (tan)_gel, was found to depend on the structure of the polymer. A negative normal force is generated in the shear dynamic mechanical measurement at the gel point.Dedicated to Dr. Karel Duek on the occasion of his 60th birthday for his important contribution to polymer science     

Polymerization of dicyclopentadiene: A new reaction injection molding system

Dicyclopentadiene was polymerized by reaction injection molding (RIM) using a catalyst system based on WCl₆ and diethylaluminium chloride. Ring opening polymerization results in formation of a crosslinked polymer with a high crosslink density. The kinetics of the fast exothermic reaction was followed by the adiabatic temperature rise method. In addition to the “adiabatic” polymerization, isothermal reactions were carried out in a thin mold. The properties of the cured samples were determined by dynamic mechanical measurements, solgel analysis, gas chromatography, mass spectrometry, DSC, and IR spectrometry. Gel fraction, glass transition temperature, content of the unreacted monomer, the modulus, and the degree of swelling were used to characterize the cured samples. The system shows very low critical conversion at the gel point (α_c < 0.01) proving a chainwise mechanism of the polymerization. Possible participation of a cationic mechanism is discussed. We found the specific reaction temperature range (T = 100–140°C) for optimum properties of the cured samples. Deterioration of properties (decrease in the crosslinking density, etc.) at a high temperature is a result of a faster deactivation of catalytic centers and a reversibility of the exothermic ring opening polymerization. Reverse cyclodegradation is preferred at a higher temperature.     

Kinetic experiments and modeling of NO oxidation and SCR of NOx with decane over Cu- and Fe-MFI catalysts

The kinetic model of the reduction of NO to N₂ with decane, developed based on the experimental data over Fe-MFI catalyst, has been applied for the oxidation of NO to NO₂ and reduction of NO₂ to N₂ with decane over Cu-MFI catalyst. The model fits well the experimental data of oxidation of NO as well as reduction of NO to N₂. Remarkable differences have been found in performance of Cu-MFI and Fe-MFI catalysts. While Fe-MFI is more active in oxidation of NO to NO₂, Cu-MFI exhibits much higher activity in the reduction of NO with decane. The kinetic model indicates that the significantly lower activity of Fe-MFI in comparison with Cu-MFI in transformation of NO_x to nitrogen is due to higher rate of transformation of NO₂, formed in the first step by the oxidation of NO, back to NO instead to molecular nitrogen.     

Application of water jet description on the de-scaling process

The paper is dealing with application of theoretical equations derived for rock disintegration onto materials with similar behavior—thick scales on hot metal rolling slabs. Penetration of water jet through a hot, rock-like material (e.g. scale) and work of the steam bubbles emerging from the water jet on the boundary between the scale layer and the hot metal material are described by a set of appropriate equations. The model is applied on the fan jets used for de-scaling process, and it provides both the qualitative and the quantitative results. These results make possible to determine the depth of penetration of water jet into the material of the scales and calculate the sizes of pieces of the disintegrated scales. Both mechanisms of water jet acting on scales, mechanical penetration to a certain depth in the material and the formation of steam bubbles inside the material, create mechanical stresses in the material of scales, especially the tensile and the shear ones. Pieces of scales are separated due to exceeding the limits of the stress and strain in the material of scales. The presented analytical equations describing the process in a simple way yield the quick and apprehensible calculation of applicable results. It is an alternative to solution of a rather complicated set of differential equations describing the mass and heat flow. The proposed theoretical base runs with technical factors and properties that can be obtained from tables or analogies with other materials or processes. The typical water pressure range of rolling mills is 16–24 MPa, the equivalent diameter of the applied water nozzle is 2 mm, the average traverse speed of the rolling slab is set to 1 m s^?1, and the mean stand-off distance of the nozzle from the steel slab surface is 150 mm. Calculated depth of penetration into scales is ranging from 5 to 18 mm for these parameters, while the real thickness of scales lies between 1 and 7 mm. Simultaneously, the calculated length of the peeled layer in the direction of the jet movement ranges from 30 to 70 mm and the cutting width determined from the jet shape and the stand-off distance is 80–120 mm. Therefore, the calculated size of the scale debris is 30?×?80 mm for layers thicker than 5 mm and 70?×?120 mm for the ones thinner than 2 mm. These theoretical values correspond with sizes of real scale debris picked at the rolling mill.     

The study of vapour phase hydrogen peroxide decontamination process as a potential method for degradation of organic pollutants

BACKGROUND: The work is focused on the application of vapour phase hydrogen peroxide (VPHP) as a highly promising and effective decontamination technique. The aim of this work was to assess the use of this validated technique for the removal of chemicals from contaminated surfaces and examine the impact of key parameters on the course of the decontamination process. RESULTS: Unique sophisticated laboratory equipment was developed to test the effect of VPHP on chemical substances. It was used for the evaluation of the role of crucial parameters such as the relative humidity, condensation and synergistic effect of UV radiation on the VPHP agent efficiency on a model compound (vanillin) degradation. The degradation rate of the model substance was notably affected by all these factors. CONCLUSION: VPHP could be used for an efficient decomposition of vanillin. The course of the decontamination process was strongly influenced by condensation (showing a substantial difference between ‘wet’ and ‘dry’ processes) and the synergistic effect of UV radiation influencing the reaction rate and degree of decomposition. Copyright © 2010 Society of Chemical Industry     

Aliphatic polycarbonate‐based polyurethane elastomers and nanocomposites. I. The influence of hard‐segment content and macrodiol‐constitution on bottom‐up self‐assembly

Aliphatic polycarbonate‐based polyurethane (PC‐PU) elastomers as well as their nanocomposites with organic‐modified clay (bentonite for organic system) were synthesized. Macrodiols (MD) (randomly copolymerized aliphatic PC‐glycols of molecular weight of about 2000: T5652, T4672, and T4692), hexamethylene diisocyanate, and butane‐1,4‐diol were used as starting materials. Solid‐state NMR and Fourier transform infrared spectroscopy, small‐angle X‐ray scattering, wide‐angle X‐ray diffraction, atomic force microscopy, and transmission electron microscopy were used for studying the bottom‐up self‐assembly of building units from the segmental level up that of organized structures of micrometer sizes. Contents of hard segments formed by the reaction of chain extender with diisocyanate plays a dominant role for the degree of ordering and related phenomena, while the MD chain has only limited effect on PC‐PU properties. The spectroscopy and scattering experiments suggest that bentonite particles incorporate well in the structure and promote the ordering of hard segment domains in PC‐PU matrix as compared with the nanofiller‐free analogue. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Novel Approaches in Mathematical Description of Hen Egg Geometry

Precise quantification of the profile of a hen egg can provide a powerful tool for analysis of egg shape and following solving of various technological problems. The article presents a new approach of the eggshell geometry determination using and analyzing the egg digital image and edge detection techniques. The detected points on the eggshell contour were fitted by the Fourier series. The obtained equations describing an egg profile were used to calculate the egg volume, surface area, and radius of curvature with a much higher degree of precision in comparison with previously published approaches. It was shown that radii of curvature at the critical points of the egg profile are independent on the egg shape index. The article shows and quantifies the limitations of the common and frequent procedures.     

The role of oleate-functionalized layered double hydroxide in the melt compounding of polypropylene nanocomposites

In this research, the oleate-functionalized magnesium and aluminum layered double hydroxide (LDH; Mg:Al = 3:1) o-LDH was applied as nanofiller in the melt blending of polypropylene (PP) nanocomposites, in order to understand its role in this process. o-LDH was prepared using the memory effect of the calcined carbonated LDH. Blending of PP and low o-LDH filler contents of 0.45 and 0.90 wt.% afforded the nanocomposites PP0.45 and PP0.90, respectively, which were characterized by transmission electron microscopy, X-ray diffraction, small angle X-ray scattering, thermo-gravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis. The oleate LDH surface functionalization enhanced the system compatibility as a relative regular dispersion of o-LDH tactoids was observed within the matrix, together with partial PP intercalation. This o-LDH incorporation increased the PP relative crystallinity, induced crystalline orientation and decreased the glass transition temperature. Furthermore, the nanocomposites showed improved initial resistance to decomposition and stiffness. These results showed that the o-LDH acted as both nucleating agent and plasticizer, and that the presented approach can be used for the development of PP nanocomposites with distinguished properties.