Isotactic polypropylene foams crystallized from compressed propane solutions

Crystallization of isotactic polypropylene (iPP) from homogeneous solution in supercritical propane yields open-cell foams of high surface area (120–150 m²/g). Their morphology usually consists of microspheres with a dense core and a porous periphery of radiating fibrils. Pore radii covering the mesopore range (2–50 nm), making their largest contribution at 10–20 nm, were calculated from nitrogen adsorption isotherms. Surface areas of the correct order of magnitude are obtained by assuming that gas adsorption takes place on the surfaces of lamellar crystals. Crystallization of iPP from n-butane and n-heptane generates foams of lower mesoporosity and smaller surface area. These more “liquid-like” solvents do not allow the formation of an open network of mesopores or they promote its collapse upon their removal. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 617–627, 1998     

The recovery of gold from thiourea solutions with open-cell polyurethane foams

The recovery of the gold-thiourea complex from aqueous solutions with TBP-loaded and unloaded polyurethane foams was investigated in batch experiments. The rates of adsorption of the gold complex on various types of loaded and unloaded foams were studied in detail and compared with the rate of adsorption on active carbon. Loaded and unloaded polyurethane foams of the polyether or polyester type behaved similarly to active carbon. The adsorption capacity of the foams was lower than that of active carbon but the use of foam simplifies the procedure by eliminating the filtration process which is necessary with carbon.     

New views on hydrazone-enehydrazine tautomerism

A new proton transfer mechanism is proposed for hydrazone-enehydrazine tautomerism through the cyclic dimer of the phenylhydrazones that take part in the E. Fischer indolization process. The energy, structural, and electronic indices of the proposed dimers were calculated by the AM1 quantum-chemical method. The calculated data were used to derive a new equations for the constant of the hydrazone-enehydrazine tautomeric equilibrium in terms of the orders of the breaking and forming bonds.I. Dzhavakhishvili Tbilisi State University, Tbilisi, Georgia Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 752–756, June, 1999.     

Investigation of protein foams obtained by bubbling

Summary The foaminesses of bovine serum albumin solutions, (BSA) with and without buffer, salt and alcohol additives were measured by bubbling and their surface tensions were obtained as function of the timet. The timet _DG , which is necessary to attain the equilibrium surface tension is long (15 h). The area requirement of a single surface adsorbed moleculeA _j0 was obtained fromd/dc, wherec the surfactant concentration, by the Gibbs relation. By assuming the existence of a hydration complex, which consists of the surfactant andX water molecules, the,coordination numbers were estimated toX=12±1 fromA _j0 and the surface requirement of the hydrophilic group of the surfactant. The dependences of CMC andX on the additives are discussed. A good relation prevails between andt _DG . By applying the phase change model of Avrami for the adsorption and surface denaturation of theBS A, simple relation was found between the dimensionless surface tensionV = (₀ - _s) (_st-_s) and the timet:log (2.3 logV) =n logt + logb The good relations between andn as well as between andnb indicate the applicability of this model.

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Zusammenfassung Das Schaumbildungsvermögen von Rinderserumalbumin-Lösungen (BSA), mit und ohne Zusätze wurde gemessen und ihre Oberflächenspannung als Funktion der Meßzeit ermittelt. Die Einstellzeitt _DG der Gleichgewichtsoberflächenspannung _eq ist lang. Zwischen undt _DG läßt sich eine einfache Beziehung aufstellen. Aus der Änderung von _eq mit der bedarf des adsorbierten Molekel ermitteln. Durch die Anwendung des Modells von Steinbach kann gezeigt werden, daß sich der Flächenbedarf durch die Bildung eines Assoziates erklären läßt, bei dem das Wasser komplexartig um das Protein-Molekül lagert. Für die Koordinationszahl der WassermoleküleX ergab sichX=12±1.Durch das Kristallwachstumsmodell von Avrami, das von überreiter auf Polymeradsorption angewendet wurde, läßt sich die Zeitabhängigkeit der Oberflächenspannung beschreiben. Das Schaumbildungsvermögen kann man als einfache Funktion der Konstanten dieser Avrami-Gleichung darstellen.

     

New foams: Fresh challenges and opportunities

Some recent trends in foam research have been directed towards the rapid production of highly monodisperse bubbles, of diameter on a scale around or below 100 μm, with surprising consequences. Such foams remain wet under gravity and order spontaneously and rapidly, forming substantial microcrystals. Previously, ordered foams have resulted only from slow processes of deliberate fabrication, or from the influence of walls in confined geometry. This opens up a wide range of new topics of interest, analogous to those of metallurgy: equilibrium crystal phases, their stability, their defects and interfaces, and phase transitions between them. The ordered structures associated with confined geometries also offer opportunities for microfluidics. Other new kinds of foam incorporate particulate matter, and are intermediate between foam and granular matter. Remarkable properties are beginning to emerge for these as well, including “superstability”, that is, a high degree of stability with respect to both coarsening and rupture.     

New polyurethane foams modified with cellulose derivatives

New polyurethane foams were elaborated with different cellulose derivatives as raw material, by the one-shot process. The foams were submitted to soxhlet extraction in order to quantify the amount of cellulose derivative incorporated in the foam by chemical bonding. The foams were characterized by means of FTIR, solid state ¹³C NMR spectroscopy, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy and dynamic mechanical analysis (DMA). The FTIR- and solid state ¹³C NMR showed characteristic peaks for cellulose derivatives and polyurethane. DMA measurements indicated that storage modulus increased with increasing content of cellulose derivatives. The highest value was obtained for foams prepared with cellulose sulphate.     

Electrostatic effects on the yield stress of whey protein isolate foams

The mechanisms responsible for foam structure are of practical interest within the food industry. The yield stress (tau) of whey protein isolate (WPI) foams as affected by electrostatic forces was investigated by whipping 10% (w/v) protein solutions prepared over a range of pH levels and salt concentrations. Measurements of foam overrun and model WPI interfaces, i.e. adsorption kinetics as determined via dynamic surface tension and dilatational rheological characterization, aided data interpretation. Interfacial measurements were also made with the primary whey proteins, beta-lactoglobulin (beta-lg) and alpha-lactalbumin (alpha-la). Yield stress of WPI foams was dependent on pH, salt type and salt concentration. In the absence of salt, tau was highest at pH 5.0 and lowest at pH 3.0. The addition of NaCl and CaCl2 up to 400 mM significantly increased tau at pH 7.0 but not at pH 3.0. Furthermore, at pH 7.0, equivalent molar concentrations of CaCl2 as compared to NaCl increased tau to greater extents. Salts had minimal effects on tau at pH 5.0. Comparisons with interfacial rheological data suggested the protein's capacity to contribute towards tau was related to the protein's potential at forming strong, elastic interfaces throughout the structure. The dynamic surface tension data for beta-lg and alpha-la were similar to WPI, while the interfacial rheological data displayed several noticeable differences.     

Microcellular foams made from gliadin

We have generated closed-cell microcellular foams from gliadin, an abundantly available wheat storage protein. The extraction procedure of gliadin from wheat gluten, which involves only the natural solvents water and ethanol, respectively, is described with emphasis on the precipitation step of gliadin which results in a fine dispersion of mostly spherical, submicron gliadin particles composed of myriad of protein molecules. A dense packing of these particles was hydrated and subjected to an atmosphere of carbon dioxide or nitrogen in a high-pressure cell at 250 bar. Subsequent heating to temperatures close to but still below 100 °C followed by sudden expansion and simultaneous cooling resulted in closed-cell microcellular foam. The spherical gliadin templates along with the resulting foam have been analyzed by scanning electron microscope (SEM) pictures. The size distribution of the primary particles shows diameters peaked around 0.54 μm, and the final foam cell size peaks around 1.2 μm, at a porosity of about 80 %. These are the smallest foam cell sizes ever reported for gliadin. Interestingly, the cell walls of these microcellular foams are remarkably thin with thicknesses in the lower nanometer range, thus nourishing the hope to be able to reach gliadin nanofoam.     

Human serum albumin adsorption on TiO2 from single protein solutions and from plasma

In the present work, the adsorption of human serum albumin (HSA) on commercially pure titanium with a titanium oxide layer formed in a H(2)O(2) solution (TiO(2) cp) and on TiO(2) sputtered on Si (TiO(2) sp) was analyzed. Adsorption isotherms, kinetic studies, and work of adhesion determinations were carried out. HSA exchangeability was also evaluated. Surface characterization was performed by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and wettability studies. The two TiO(2) surfaces have very distinct roughnesses, the TiO(2) sp having a mean R(a) value 14 times smaller than the one of TiO(2) cp. XPS analysis revealed consistent peaks representative of TiO(2) on sputtered samples as well as on Ti cp substrate after 48 h of H(2)O(2) immersion. Nitrogen was observed as soon as protein was present, while sulfur, present in disulfide bonds in HSA, was observed for concentrations of protein higher than 0.30 mg/mL. The work of adhesion was determined from contact angle measurements. As expected from the surface free energy values, the work of adhesion of HSA solution is higher for the TiO(2) cp substrate, the more hydrophilic one, and lower for the TiO(2) sp substrate, the more hydrophobic one. The work of adhesion between plasma and the substrates assumed even higher values for the TiO(2) cp surface, indicating a greater interaction between the surface and the complex protein solutions. Adsorption studies by radiolabeling of albumin ((125)I-HSA) suggest that rapid HSA adsorption takes place on both surfaces, reaching a maximum value after approximately 60 min of incubation. For the higher HSA concentrations in solution, a multilayer coverage was observed on both substrates. After the adsorption step from single HSA solutions, the exchangeability of adsorbed HSA molecules by HSA in solution was evaluated. The HSA molecules adsorbed on TiO(2) sp seem to be more easily exchanged by HSA itself than those adsorbed on TiO(2) cp after 24 h. In contrast, after 72 h, nearly all the adsorbed albumin molecules effectively exchange with other albumin molecules.     

Competitive adsorption from mixed nonionic surfactant/protein solutions

A thermodynamic model is derived which is suitable to describe adsorption from a mixed protein/surfactant solution. The comparison with experimental data for HSA mixed with the nonionic surfactant decyl dimethyl phosphine oxide shows good agreement. Some model calculations are discussed in terms of the competitive character of the process of adsorption from mixed protein/surfactant solutions. The behavior of globular (HSA) and flexible (beta-casein) proteins appears to be quite different due to the possibility of changing the molar area of adsorbed protein molecules.     

Structuring bubbles and foams in gelatine solutions within a circular microchannel device

A flow-focusing device with circular cross-section to produce monodispersed air bubbles and foams in several gelatine solutions is presented. Four flow regimes were studied by varying the gas pressure: dripping, bi-disperse bubbly, bubbly and foam flows. Bubble formation at the flow-focusing exit is discussed in detail and compared with that in rectangular microchannels. The bubble volume was shown to depend on the viscosity of the gelatine solution but not on the surface tension. For the bubbly flow, the frequency of bubble formation in this geometry was similar to that found in rectangular microchannels. For the foam flow the frequency was independent of the pressure. Study in the outlet microchannel for the bubbly and foam flows showed that the gas flow followed a power law with the applied pressure. Finally, the viscous resistance was measured and a pressure drop law was determined for each regime.     

New developments in chemical modification of fire-safe rigid polyurethane foams

This work reports the preparation of polyurethane-polyisocyanurate (PUR-PIR) foams containing different amounts of flame retardants (FRs) and a layered silicate nanoclay. An environmentally friendly blowing agent, a mixture of 1,1,1,3,3-pentafluorobutane and 1,1,1,2,3,3,3-heptafluoropropane (HFC 365/227), with small amount of water was used. The flame retarded PUR-PIR foams showed better fire resistance in comparison to classical PUR and unmodified PUR-PIR foams without deterioration of their functional properties. It was observed that when nanoclay was used in conjunction with flame retardants containing reactive bromine and phosphorus compounds, and zinc stannate, the flammability was significantly reduced. Expandable graphite was also used in some samples. As control samples for reference purposes three foam systems without any flame retardant were frothed: PUR, PUR-PIR and foams PUR-PIR modified by carbodiimide groups.     

A multi point conductivity measurement system for characterisation of protein foams

Protein foams play an important role in both food and biotechnological processes. A sound understanding of foaming properties of proteins relevant to such processes is useful e.g. to allow adequate control of unwanted foams and appropriate choice of protein-physical system when foams of certain characteristics are required. In general, measurements of changes in foam volume (volumetric method) are used for foam characterisation. However, recently there has been increased interest in the use of measurement methods based on conductivity and capacitance. Simple relative techniques based on electrical conductivity measurements provide information on both foamability and foam stability. A multi point conductivity measurement system has been designed and used for characterisation of model protein foams (0.1 and 1.0 mg ml⁻¹ Bovine serum albumin, BSA). The solution of BSA was sparged with nitrogen or carbon dioxide gas at constant flow rate (90 cm³ min⁻¹) via a stainless steel sinter (0.5 or 2.0 μm in pore size). A comparison of foaming properties determined by volumetric and conductimetric techniques is provided. Both methods show that more stable foams are obtained for solutions at higher BSA concentrations. At all BSA concentrations, higher foamability and stability are achieved with a smaller sinter pore size. When nitrogen rather than carbon dioxide is used as a dispersed phase, higher foamability and foam stability are obtained. The conductivity measurements indicate that foamability is dependent on gas type, whereas, volumetric measurements do not show such differences.     

Determination of protein in solutions from absorption in the ultraviolet region

A comparison of spectrophotometric methods of determining protein in solutions from absorption in the UV region has shown the advantage of a procedure based on measuring the optical densities at 235 and 280 nm and the possibility of its use for the analysis of plant proteins.     

Determination of protein in solutions from absorption in the ultraviolet region

A comparison of spectrophotometric methods of determining protein in solutions from absorption in the UV region has shown the advantage of a procedure based on measuring the optical densities at 235 and 280 nm and the possibility of its use for the analysis of plant proteins.Scientific-Research Institute of Biology, Dnepropetrovsk State University. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 693–695, September–October, 1989.     

Smooth transition from metastability to instability in phase separating protein solutions

For insight into the structure and dynamics of phases emerging upon crossing the metastability/instability boundary we monitor with optical microscopy, in real time and in real space, the generation of a dense liquid phase in high-concentration solutions of the protein lysozyme after temperature quenches into thermodynamically defined metastable and unstable regions. We show with this system, which is a poor fit to mean-field assumptions, that the evolution of the structure factor during nucleation is similar to that during spinodal decomposition and reveals no singularity predicted upon crossing the metastability boundary. We introduce two kinetic definitions of the metastability/instability boundary that yield values within approximately 1.5 K, i.e., the boundary appears as an area rather than a line, which is near and above the thermodynamic prediction. Delay times for the appearance of the new phase in the unstable regime are significant, i.e., new-phase growth is hindered by kinetic barriers. While our results agree with predictions of the non-mean-field theories of phase transformations, the experimentally observed behavior is richer than the one envisioned by theory.     

Radiation effects on viscosimetry of protein based solutions

Due to their good functional properties allied to their excellent nutritional value, milk protein isolates and soy protein concentrates have gained a crescent interest. These proteins could have their structural properties improved when some treatments are applied, such as gamma irradiation, alone or in presence of other compounds, as a plasticizer. In this work, solutions of those proteins were mixed with a generally recognized as safe plasticizer, glycerol. These mixtures (8% protein (w/v) base) at two ratios 1:1 and 2:1 (protein:glycerol) were submitted to a gamma irradiation treatment (⁶⁰Co), at doses 0, 5, 15 and 25 kGy, and their rheological performance was studied. As irradiation dose increased viscosity measurements decayed significantly (p<0.05) for mixture soy/glycerol and calcium caseinate/glycerol. The mixture sodium caseinate/glycerol showed a trend to form aggregation of macromolecules with dose of 5 kGy, while the apparent viscosity for dispersions containing whey/glycerol remained almost constant as irradiation dose increases. In the case of soy protein isolate and sodium caseinate, a mixture of 2:1 showed a significant higher viscosity (p<0.05) than a mixture of 1:1.