Cohesive weight

The critical compressibility factor, Z, calculated from the relation pV = nZ KT., is 0.282. A parameter representing the number of associated molecules of a fluid at the critical composition, and derived from a generalized equation of state, has been described as the cohesive weight [288a]. Under such conditions the cohesive weight of phosgene is said to correspond to the stoicheiometry, (COCi,). ... 

Asphaltenes are obtained in the laboratory by precipitation in normal heptane. Refer to the separation flow diagram in Figure 1.2. They comprise an accumulation of condensed polynuclear aromatic layers linked by saturated chains. A folding of the construction shows the aromatic layers to be in piles, whose cohesion is attributed to -it electrons from double bonds of the benzene ring. These are shiny black solids whose molecular weight can vary from 1000 to 100,000. 

For benzene at 25°C this becomes AU = 33,900 - 8.314 (298) = 31,400 J mol". The molar volume of a compound is given by V° = (molecular weight)/ (density). For benzene at 25°C, this becomes V° = 78.0/0.879 = 88.7 cm mol". Tlie cohesive energy density is simply the ratio AUy/V°, but in evaluating this numerically, the question of units arises. By convention, these are usually expressed in calories per cubic centimeter, so we write... 

To produce a spandex fiber by reaction spinning, a 1000—3500 molecular weight polyester or polyether glycol reacts with a diisocyanate at a molar ratio of about 1 2. The viscosity of this isocyanate-terrninated prepolymer may be adjusted by adding small amounts of an inert solvent, and then extmded into a coagulating bath that contains a diamine so that filament and polymer formation occur simultaneously. Reactions are completed as the filaments are cured and solvent evaporated on a belt dryer. After appHcation of a finish, the fibers are wound on tubes or bobbins and rewound if necessary to reduce interfiber cohesion. 

Polyurethane adhesives are known for excellent adhesion, flexibihty, toughness, high cohesive strength, and fast cure rates. Polyurethane adhesives rely on the curing of multifunctional isocyanate-terrninated prepolymers with moisture or on the reaction with the substrate, eg, wood and ceUulosic fibers. Two-component adhesives consist of an isocyanate prepolymer, which is cured with low equivalent weight diols, polyols, diamines, or polyamines. Such systems can be used neat or as solution. The two components are kept separately before apphcation. Two-component polyurethane systems are also used as hot-melt adhesives. 

Introduction. Crosslinking of the acrylic polymer can be a very important factor in formulating a PSA. As can be expected, for a given PSA composition, it is typically observed that the cohesive strength of a non-crosslinked polymer decreases with the decreasing molecular weight. This drop in performance can be... 

The presence of these low molecular weight tackifiers and plasticizers may also have other negative effects on the PSA performance. For example, the reduced entanglement of the polymer typically reduces the cohesive strength of the PSA, although crosslinking may be used to compensate for this loss in property. Plasticizers and tackifiers may also be susceptible to migration and/or oxidation, both... 

The main characteristics of NR latex are as follows high gel content high molecular weight high cohesive strength high self tack and high rubber content. 

Cohesive strength of these adhesives can be modified by blending butyl rubber and polyisobutylene. Higher strength is obtained by using high molecular weight PIB or butyl rubber. On the other hand, blends of butyl rubber or PIB with chlorinated butyl rubber show improved cure properties. 

The broad molecular weight distribution (MWD) and low cohesive strength of... 

Standard-grade PSAs are usually made from styrene-butadiene rubber (SBR), natural rubber, or blends thereof in solution. In addition to rubbers, polyacrylates, polymethylacrylates, polyfvinyl ethers), polychloroprene, and polyisobutenes are often components of the system ([198], pp. 25-39). These are often modified with phenolic resins, or resins based on rosin esters, coumarones, or hydrocarbons. Phenolic resins improve temperature resistance, solvent resistance, and cohesive strength of PSA ([196], pp. 276-278). Antioxidants and tackifiers are also essential components. Sometimes the tackifier will be a lower molecular weight component of the high polymer system. The phenolic resins may be standard resoles, alkyl phenolics, or terpene-phenolic systems ([198], pp. 25-39 and 80-81). Pressure-sensitive dispersions are normally comprised of special acrylic ester copolymers with resin modifiers. The high polymer base used determines adhesive and cohesive properties of the PSA. 

Rubber powder from scrap tires readily absorbs oil floating on water and forms a cohesive mass, which can be easily removed. The amount of oil take up and weight of oil absorbed depends on the particle size of waste tire powder, temperature, and type of oil the weight of oil absorbed is directly proportional to the amount of rubber powder [65]. The oil uptake time decreases as the particle size decreases. 

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