Minimum processing viscosity

The most common method of measurement is to run the compound in the mooney viscometer until the viscosity shows a 5 point rise above the minimum. The viscosity of the compounded rubber at the processing temperatures can also be obtained from the minimum of the curve. The values normally taken from the cure curve are ... 

The Delta Mooney (A Mooney) test is an extension of the Mooney used on empirical grounds as a general indication of processibility for non-pigmented oil extended emulsion styrene/butadiene rubber. It quantifies the changes that occur in Mooney viscosity with time, either as the difference between viscosities recorded at two specified times or as the difference between the minimum viscosity recorded immediately after the commencement of the test and the subsequent maximum viscosity. Several alternative Delta Mooney values are defined depending on the times, whether minimum/maximum viscosity difference is used and whether or not the sample has been massed on a mill. Procedures for Delta Mooney are standardised in ISO 289-341, BS 903 Part A58-142 and in ASTM D334643. 

For fiber preparation, a lyotropic solution is best processed at a solids concentration near the minimum solution viscosity and at a temperature close to its anisotropic transition temperature (Figure 13.2). These conditions maximize solution ordering prior to spinning. 

An oil/brine/surfactant/alcohol system often forms a middle phase microemulsion in an appropriate salinity range. The salinity at which the middle phase microemulsion contains an equal volume of oil and brine is defined as the optimal salinity (9). At the optimal salinity, the interfacial tension is in the millidynes/cm range at both oil/microemulsion and microemulsion/brine interfaces, and the oil recovery is maximum (6,9). Moreover, we have shown (10) that at optimal salinity, the coalescence time or phase-separation time is minimum for oil/brine/surfactant/alcohol systems. When these systems are pumped through porous media, a minimum pressure drop or apparent viscosity is observed at the optimal salinity (10). All these phenomena occurring at optimal salinity are summarized in Figure 11. In a recent study, we have also found that the surfactant loss in porous media is minimum at the optimal salinity. Therefore, besides ultralow interfacial tension, a favorable coalescence process for mobilized oil ganglia and the minimum apparent viscosity (or minimum AP) of the oil bank and the minimum surfactant loss are the other factors contributing towards the maximum oil recovery at the optimal salinity. 

Among the physical properties of great importance in determining the mass transfer rates in supercritical extraction processes, viscosity affects significantly the efficiency of the extraction system. In fluids, high temperature and pressure directly affect viscosity, for example, at constant pressure, viscosity decreases with an increase in temperature (Brunner, 1994). With respect to the viscosity behavior of the fluids, Brunner (1994) stated that at temperatures above the minimum, the fluid behaves like a gas, and below this minimum, it behaves like a liquid. 

The focus of this chapter is more specifically blends in which the reinforcing species is a thermotropic LCP which is blended in a rather conventional way with isotropic thermoplastics (TP). This exploits the inherent strength and low viscosity of the LCP in a way which leads to maximum benefit at minimum processing complexity. This has been an actively studied area of polymer engineering for 40 years and continues to be of interest. We note that though much work has been done on the science of LCP blends, there is also a need to review the exploitation aspects in terms of cost considerations, patents and commercial products. 

During the press operation, which is actually a form of compression mol ding, the resin-treated laminate pHes are heated under pressure and the resins cured. The initial heating phases cause the resin to melt and flow into voids in the reinforcing ply and bond the individual pHes together. The appHed heat simultaneously causes the resin to polymerize and eventually to cross-link or gel. Therefore, resin viscosity reaches a minimum during the press cycle. This is the point at which the curing process becomes dominant over the melt flow process. Dynamic mechanical and dielectric analyses (11) are excellent tools for study of this behavior. 

Electrodeposition This method of paint application is basically a dipping process. The paint is water-based and is either an emulsion or a stabilised dispersion. The solids of the paint are usually very low and the viscosity lower than that used in conventional dipping. The workpiece is made one electrode, usually the cathode, in a d.c. circuit and the anode can be either the tank itself or suitably sized electrodes sited to give optimum coating conditions. The current is applied for a few minutes and after withdrawal and draining the article is rinsed with de-ionised water to remove the thin layer of dipped paint. The deposited film is firmly adherent and contains a minimum of water and can be stoved without any flash-off period. This process is used for metal fabrications, notably car bodies. Complete coverage of inaccessible areas can be achieved and the corrosion resistance of the coating is excellent (Fig. 14.1). 

Filter aids are widely used in die fermentation industry to improve the efficiency of filtration. It is a pre-coated filter medium to prevent blockage or blinding of the filter by solids, which would otherwise wedge diemselves into the pores of the cloth. Filter aid can be added to the fermentation broth to increase the porosity of the cake as it formed. This is only recommended when fermentation product is extracellular. Filter aid adds to the cost of filtration. The minimum quantity needed to achieve the desired result must be established experimentally. Fermentation broths can be pretreated to improve filtration characteristics. Heating to denature proteins enhances the filterability of mycelial broths such as in penicillin production. Alternatively, electrolytes may be added to promote coagulation of colloids into larger, denser particles, which are easier to filter. The filtration process is affected by the viscosity and composition of the broth, and the cell cake.5... 

It is also important to note Ca, , says nothing about the drop sizes produced upon breakup The value of Ca t only gives the maximum drop size that can survive in a given flow in the absence of coalescence. This result may appear to suggest that the most effective dispersion—leading to the finest drop sizes—occurs when viscosities are nearly matched. As we shall see later on, this perception turns out to be incorrect. Nevertheless, an understanding of Fig. 14 constitutes the minimum level of knowledge needed to rationalize dispersion processes in complex flows. 

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