Viscosity index defined

This technology has been utilized by BP Chemicals for the production of lubricating oils with well defined characteristics (for example, pour point and viscosity index). It is used in conjunction with a mixture of olefins (i.e., different isomers and different chain length olefins) to produce lubricating oils of higher viscosity than obtainable by conventional catalysis [33]. Unichema Chemie BV have applied these principals to more complex monomers, using them with unsaturated fatty acids to create a mixture of products [34]. 

In a polymer solution the specific viscosity is defined as tjsp — (tj — ri0)/t]0 with the solution and solvent viscosity i] and i]lt, respectively. The intrinsic viscosity (Staudinger index) of a polymer is defined as... 

Materials (ASTM) introduced the so-called viscosity index (VI). It is based on the values of kinematic viscosity at 40° C and 100°C, which are compared to the respective viscosities of two reference oils. One reference oil is standard paraffin oil. Its viscosity only weakly depends on temperature. It was given a viscosity index of 100. The other reference is a standard naphthenic oil with a high temperature dependence. Its viscosity index is defined as zero. A low viscosity index indicates a relatively strong dependence of viscosity on temperature, a high viscosity index, a small dependence. 

Lubricants are formulated products composed of a base stock, which is either a mineral or synthetic oil, and various specialty additives designed for specific performance needs. Additive levels in lubricants range from 1 to 25% depending on the application. Synthetic base stocks are oligomers of small molecules, synthesized to a defined molecular weight. Important performance indicators include viscosity index which measures the viscosity index behavior over a temperature range, oxidative stability, and pour point. The performance of synthetic and mineral oils (Morse, 1998 Shubkin, 1993) is summarized in Table 2.7. 

Base stock specifications, as defined by the producer or the purchaser, largely enumerate the physical properties required for the fluid—typically density, viscosity at two temperatures, viscosity index (VI), low temperature performance measures, flash and volatility properties, and solubility information from aniline point or viscosity-gravity constant (VGC)—the latter two are usually for naphthenic base stocks. While chemical composition is responsible for physical properties, it usually only surfaces as measurements of heteroatom content—sulfur and nitrogen—and aromatics content (or conversely that of saturates). Sulfur and aromatics levels in paraffinic base stocks are now criteria for American Petroleum Institute (API) classifications. However, detailed chemical compositional information is needed to understand the chemistry of the unit processes, the effects of changes in feeds, catalysts, and operating conditions, and behaviors of finished lubricant products. 

Ye and co-workers exploited the shear stability of highly branched, high molecular weight polyethylenes (PEs) as lubricant viscosity index improvers [252, 253]. Viscosity index of a lubricant is a critical parameter which defines its quality and application temperature range. They synthesized PEs with controllable chain topologies ranging from linear to a hyperbranched dendritic structure by chain walking polymerization [254]. The PE samples were blended into a base paraffinic oil (density 0.8659 g mL at 15 °C, kinematic viscosity 30.06 cST at 40 °C) to form lubricants. The lubricants were subjected to the Kurt Orbahn (KO) test to measure the shear stability index, which is expressed by... 

The API has defined the base oils in five categories on the basis of viscosity index, snUur content and percentage saturates. The details are provided in Table 1. A number... 

While the viscosity-temperature plots provide a clear visual estimate of fragility, it is more convenient to establish a single parameter that provides a quantitative measure of fragility. Several measures have been proposed, but the most commonly used fragility index is the "m fragility" or "steepness index" defined as [52, 55] ... 

The viscosity of an oil at various temperatures csm be determined by plotting a line on ASTM viscosity paper. Experimental determinations at two temperatures serve to define the strmght line, o r if the Viscosity Index is known, the viscogty at one temperature suffices. Figure 4-45 shows two such viscosity-temperature lin ... 

In all complex mixtures, such as petroleum, it is difficult to define what is meant by pure raffinate R) and pure extract (jB), and hence the RE scale is not read directly in percentages of R and E but by some significant property such as specific gravity or Viscosity Index. Experimental data are necessary in order to draw the diagrams. 

Other terms relating to physical properties include viscosity refractive index pour point, ie, the lowest temperature at which the oil flows flash point, ie, the temperature at which the oil ignites and aniline point, ie, the minimum temperature at which equal volumes of oil and aniline are completely miscible. These are determined under defined conditions estabHshed by ASTM. 

The melt flow index describes the viscosity of a solid plastic. It is the weight in grams of a polymer extruded through a defined orifice at a specified time. The melt viscosity and the melt flow index can measure the extent of polymerization. A polymer with a high melt flow index has a low melt viscosity, a lower molecular weight, and usually a lower impact tensile strength. 

A convenient term for the rheological properties of an unvulcanised elastomer (see Rheology). It has been defined as the susceptibility to, and retentivity of deformation , and also the degree of flow which takes place under given conditions of temperature and pressure . The use of the term viscosity is a more appropriate description. Plasticity Retention Index... 

Various correlations for mean droplet size generated by plain-jet, prefilming, and miscellaneous air-blast atomizers using air as atomization gas are listed in Tables 4.7, 4.8, 4.9, and 4.10, respectively. In these correlations, ALR is the mass flow rate ratio of air to liquid, ALR = mAlmL, Dp is the prefilmer diameter, Dh is the hydraulic mean diameter of air exit duct, vr is the kinematic viscosity ratio relative to water, a is the radial distance from cup lip, DL is the diameter of cup at lip, Up is the cup peripheral velocity, Ur is the air to liquid velocity ratio defined as U=UAIUp, Lw is the diameter of wetted periphery between air and liquid streams, Aa is the flow area of atomizing air stream, m is a power index, PA is the pressure of air, and B is a composite numerical factor. The important parameters influencing the mean droplet size include relative velocity between atomization air/gas and liquid, mass flow rate ratio of air to liquid, physical properties of liquid (viscosity, density, surface tension) and air (density), and atomizer geometry as described by nozzle diameter, prefilmer diameter, etc. 

Some fermentation broths are non-Newtonian due to the presence of microbial mycelia or fermentation products, such as polysaccharides. In some cases, a small amount of water-soluble polymer may be added to the broth to reduce stirrer power requirements, or to protect the microbes against excessive shear forces. These additives may develop non-Newtonian viscosity or even viscoelasticity of the broth, which in turn will affect the aeration characteristics of the fermentor. Viscoelastic liquids exhibit elasticity superimposed on viscosity. The elastic constant, an index of elasticity, is defined as the ratio of stress (Pa) to strain (—), while viscosity is shear stress divided by shear rate (Equation 2.4). The relaxation time (s) is viscosity (Pa s) divided by the elastic constant (Pa). 

VGC (viscosity-gravity constant) an index of the chemical composition of crude oil defined by the general relation between specific gravity, sg, at 60°F and Saybolt Universal viscosity, SUV, at 100°F ... 

Kinetic studies of primary and higher order star formation concluded that well-defined first order stars with narrow molecular weigth distribution could be prepared with [SiH]/[C=C] = 1.25 at room temperature whereas higher order stars were obtained with [SiH]/[C=C]=4.0 at 120 °C. While primary star formation was very slow and could require up to a week to complete at room temperature, higher order star formation was essentially complete in 24 h. Higher order stars with up to 28 arms have been prepared by this method. Intrinsic viscosities and branching index g were also studied. The intrinsic viscosities of stars were much lower than those of linear PIBs of the same MW. As expected, it was found that g values of stars depend on the number of arms and not on the MW of the arms. The stars were found to be resistant to acids and bases suggesting that the PIB corona protects the vulnerable core. 

Weir (1963) defined the mouldability index, aSTv (the index STV stands for shear-temperature-viscosity), as follows ... 

The application of refractive index and differential viscometer detection in SEC has been discussed by a number of authors [66-68]. Lew et al. presented the quantitative analysis of polyolefins by high-temperature SEC and dual refractive index-viscosity detection [69]. They applied a systematic approach for multidetector operation, assessed the effect of branching on the SEC calibration curve, and used a signal averaging procedure to better define intrinsic viscosity as a function of retention volume. The combination of SEC with refractive index, UV, and viscosity detectors was used to determine molar mass and functionality of polytetrahydrofuran simultaneously [70]. Long chain branching in EPDM copolymers by SEC-viscometry was analyzed by Chiantore et al. [71]. 

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