Dispersion in unions

Phloroglucinol is Hsted in the Colourindex as Cl Developer 19. It is particularly valuable in the dyeing of acetate fiber but also has been used as a coupler for azoic colors in viscose, Odon, cotton (qv), rayon, or nylon fibers, or in union fabrics containing these fibers (157). For example, cellulose acetate fabric is treated with an aromatic amine such as (9-dianisidine or a disperse dye such as A-hydroxyphenylazo-2-naphthylamine and the amine diazotizes on the fiber the fabric is then rinsed, freed of excess nitrite, and the azo color is developed in a phloroglucinol bath at pH 5—7. Depending on the diazo precursor used, intense blue to jet-black shades can be obtained with excellent light-, bleach-, and mbfastness. 

Dispersion in column frits was originally thought to be large and thus, made a significant contribution to the overall extra column variance. It was not until the introduction of low-dispersion unions that it was found that most of the dispersion that was thought to occur in the frits, actually occurred in the unions that contained the frits. Scott and Simpson (11) measured the dispersion that occurred in some commercially available column frits and demonstrated that their contribution to dispersion to be insignificant compared with other sources of extra column dispersion. 

As previously pointed out, this book deals mostly with colloidal silicas, that is, disperse systems in which the disperse phase is silica in the colloidal state of subdivision. The colloidal state of subdivision comprises particles with a size sufficiently small (<1 fim) not to be affected by gravitational forces but sufficiently large (>1 nm) to show marked deviations from the properties of true solutions. In this particle size range, 1 nm (10 A) to 1 /xm (1000 nm), the interactions are dominated by short-range forces, such as van der Waals attraction and surface forces. On this basis the International Union of Pure and Applied Chemistry (IUPAC) suggested that a colloidal dispersion should be defined as a system in which particles of colloidal size (1-1000 nm) of any nature (solid, liquid, or gas) are dispersed in a continuous phase of a different composition or state (6). If the particles are solid they may be crystalline or amorphous. The disperse phase may also be small droplets of liquids, as in the case of emulsions, or gases, as for example in foams. 

Some of the particles were studied after supercritical point drying. The particles were dispersed in acetone by several centrifugation steps (45,000 X g). In a critical point dryer (Balzers Union, CPD 020), the carbon-coated grids and the dispersion in acetone were placed. Under pressure, the acetone was exchanged against liquid CO2 after increasing the temperature and passing the critical point, the particles adsorbed on the film were supercritically dried. 

In gas phase processes, gaseous propylene comes into contact with the solid catalyst which is intimately dispersed in dry pol5aner powder. Industry uses two different methods of carrying out this reaction depending on the chosen method of heat removal. The Unipol PP process uses a modification of the Unipol polyethylene fluidised bed system. The Novolen PP process and Innovene PP process use mechanically agitated dry powder beds with evaporative cooling in vertical and horizontal reactors, respectively. Unipol PP was originally developed by Union Carbide and Shell, the Novolen PP process by BASF and the Innovene PP process by Amoco. 

Starting from simple consideiations about the basic objectives of mixing, with reference to recent results for rubber-filler morphology, attention was paid to fundamenlal aspects of this processing step. Investigations into the kinetic aspects of carbon black dispersion in robber and the relationships that could be demonstrated between bound robber and flow properties showed that these were important criteria in rmderstanding the complexity of robber mixing. 22 refs. EUROPEAN COMMUNITY EUROPEAN UNION FRANCE WESTERN EUROPE... 

In the manufacture of highly resident flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. Graft polyols are dispersions of free-radical-polymerized mixtures of acrylonitrile and styrene partially grafted to a polyol. Polymer polyols are available from BASF, Dow, and Union Carbide. In situ polyaddition reaction of isocyanates with amines in a polyol substrate produces PHD (polyhamstoff dispersion) polyols, which are marketed by Bayer (21). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion. The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM appHcations where elastomers of high modulus, low thermal coefficient of expansion, and improved paintabiUty are needed. 

It is seen that the normal union can cause significant dispersion and, by drilling out the union, the dispersion is greatly reduced. It must be assumed that the dispersion caused by the modern reduced volume union would fall somewhere between these two extremes. The same authors also measured the dispersion arising from stainless steel frits and their results are shown in Table 4. 

Extra-column dispersion can arise in the sample valve, unions, frits, connecting tubing, and the sensor cell of the detector. The maximum sample volume, i.e., that volume that contributes less than 10% to the column variance, is determined by the type of column, dimensions of the column and the chromatographic characteristics of the solute. In practice, the majority of the permitted extra-column dispersion should... 

When the CMC determination is made by surface tension measurements, the resulting curve appears without minimum as a single surfactant. It is probable that an inversion takes place through the adsorption of the LSDA onto the surface of the Ca soap micelle, so that complete precipitation does not occur [23]. Zhang and Xiao [32] are of the opinion that the dispersion comes from the union of LSDA with the free ionic soap molecules. The particles from the soap-LSDA mixture are far larger than the corresponding soap molecules in soft water and therefore result in turbidity in hard water. 

Military weapons tests conducted at the Pacific Proving Grounds in the 1940s and 1950s resulted in greatly elevated local concentrations of radionuclides, and an accident at the Chernobyl nuclear power plant in the former Soviet Union in 1986 resulted in comparatively low concentrations of radionuclides dispersed over a wide geographical area. Both cases are briefly reviewed. 

The effect of environmental concerns on future developments in the paint industry is discussed. Particular attention is paid to volatile organic compound regulations, developments in powder coatings, and radiation-curable coatings. Tabulated information is presented on applications, backbone type and typical mechanical properties of Incorez W830 series PU dispersions and Incorez W2000 series uiethane/aciylic hybrids. 10 refs. EUROPEAN COMMUNITY EUROPEAN UNION UK WESTERN EUROPE... 

It is highly improbable that a nuclear fission power plant would ever explode like a nuclear bomb, but a loss of coolant accident could result in a melt down condition. In a melt down, a large amount of radiation can be released at ground-level. A nuclear or conventional chemical or steam explosion could disperse much of the radioactive particles into the atmosphere. This is essentially what happened when the Chernobyl gas explosion occurred in the Soviet Union in 1986. 

One recent development in Ziegler Natta catalysts was in producing catalyst particles that expanded as the polymerization reaction occurred. In this polymer the catalyst remains dispersed throughout the polymer, retaining its activity. This led to the development of fluidized bed processes to make polyethylene and polypropylene in which a sphere of polymer formed around each initial catalyst particle, and the polymer remained sohd as the reaction proceeded, rather than requiring a liquid solution. A major class of these catalysts and fluidized bed reactor was developed by Union Carbide and by Shell Oil and called the Unipol process. In this process a very active solid catalyst is introduced into the reactor, and reaction occurs on the catalyst particles, which expand to maintain active sites on the growing polymer sphere. 

These two characteristic qualities of the gels are best interpreted on the assumption that the disperse phase does not consist of isolated particles but that union between a number of these particles takes place to form relatively short fibrils of threads, which intersect one another to form a felt in the irregular meshes of which the mobile liquid phase penetrates. The fibrils in the case of gelatine would, according to Bancroft, consist of a viscous water in gelatine solution, and, according to Hardy, a solid solution of water in gelatine. 

---