Viscosity and Process

Extruded Articles. In an extruded article, the most important parameters are scorch safety and flow characteristics (49). The bisphenol/onium cure system provides the best scorch resistance. Gum viscosities and process aids affect flow characteristics. Typical formulations for extrusion-grade fluorocarbon elastomers are given in Table 8. 

Chain branching with high polymerization temperature and high monomer conversion results in reduced stability in polymer viscosity and processing properties deteriorate. 

Arthur BL, Edwin JW (1956) Composition comprising a polyhalogenated ethylene polymer and viscose and process of shaping the same. In Google Patents... 

Polypropylene (PP) and polysulfone (PSU) were successfully blended despite viscosity and processing temperature variations. These blends showed structure-property improvements with the addition of functional polyolefins. A series of membranes were made using an environmentally-friendly process. 

This section will firstly consider the properties of oils in the reservoir (compressibility, viscosity and density), and secondly the relationship of subsurface to surface volume of oil during the production process (formation volume factor and gas oil ratio). 

Viscosity and Density - which help determine how easily the fluids will move through the process facility. 

Steam is injected into a reservoir to reduce oil viscosity and make it flow more easily. This technique is used in reservoirs containing high viscosity crudes where conventional methods only yield very low recoveries. Steam can be injected in a cyclic process in which the same well is used for injection and production, and the steam is allowed to soak prior to back production (sometimes known as Huff and Puff). Alternatively steam is injected to create a steam flood, sweeping oil from injectors to producers much as in a conventional waterflood. In such cases it is still found beneficial to increase the residence (or relaxation) time of the steam to heat treat a greater volume of reservoir. 

Like steam injection, in-situ combustion is a thermal process designed to reduce oil viscosity and hence improve flow performance. Combustion of the lighter fractions of the oil in the reservoir is sustained by continuous air injection. Though there have been some economic successes claimed using this method, it has not been widely employed. Under the right conditions, combustion can be initiated spontaneously by injecting air into an oil reservoir. However a number of projects have also experienced explosions in surface compressors and injection wells. 

Nikowa L, Schwarzer D, Troe J and Schroeder J 1992 Viscosity and solvent dependence of low barrier processes photoisomerization of c/s-stilbene in compressed liquid solvents J. Chem. Phys. 97 4827... 

This produces even greater increases in viscosity, with the attendant increase in the difficulty of heat removal and processing. 

Eactors that could potentiaHy affect microbial retention include filter type, eg, stmcture, base polymer, surface modification chemistry, pore size distribution, and thickness fluid components, eg, formulation, surfactants, and additives sterilization conditions, eg, temperature, pressure, and time fluid properties, eg, pH, viscosity, osmolarity, and ionic strength and process conditions, eg, temperature, pressure differential, flow rate, and time. 

AvaUabUity and cost of raw materials and processing equipment Simplicity and cost of manufacture and inspection Manufacturing hazards PropeUant viscosity and flowabUity Environmental considerations... 

Lubricating Oil Extraction. Aromatics are removed from lubricating oils to improve viscosity and chemical stabihty (see Lubrication and lubricants). The solvents used are furfural, phenol, and Hquid sulfur dioxide. The latter two solvents are undesirable owing to concerns over toxicity and the environment and most newer plants are adopting furfural processes (see Furan derivatives). A useful comparison of the various processes is available (219). 

The problems of monomer recovery, reaction medium viscosity, and control of reaction heat are effectively dealt with by the process design of Montedison Fibre (53). This process produces polymer of exceptionally high density, so although the polymer is stiU swollen with monomer, the medium viscosity remains low because the amount of monomer absorbed in the porous areas of the polymer particles is greatly reduced. The process is carried out in a CSTR with a residence time, such that the product k jd x. Q is greater than or equal to 1. is the initiator decomposition rate constant. This condition controls the autocatalytic nature of the reaction because the catalyst and residence time combination assures that the catalyst is almost totally expended in the reactor. 

Flow processes iaside the spinneret are governed by shear viscosity and shear rate. PET is a non-Newtonian elastic fluid. Spinning filament tension and molecular orientation depend on polymer temperature and viscosity, spinneret capillary diameter and length, spin speed, rate of filament cooling, inertia, and air drag (69,70). These variables combine to attenuate the fiber and orient and sometimes crystallize the molecular chains (71). 

Its early commercial success owed much to the flammabUity disadvantages of the Chardoimet process, but competition from the viscose process led to its decline for aU but the finest filament products. The process is stiU used, most notably by Asahi in Japan where sales of artificial sHk and medical disposable fabrics provide a worthwhile income. However, its relatively high cost, associated with the cotton fiber starting point, prevented it from reaching the large scale of manufacture achieved by the viscose rayon process. 

Asahi Chemical Industries (ACl, Japan) are now the leading producers of cuprammonium rayon. In 1990 they made 28,000 t/yr of filament and spunbond nonwoven from cotton ceUulose (65). Their continuing success with a process which has suffered intense competition from the cheaper viscose and synthetic fibers owes much to their developments of high speed spinning technology and of efficient copper recovery systems. Bemberg SpA in Italy, the only other producer of cuprammonium textile fibers, was making about 2000 t of filament yam in 1990. 

Asahi s innovations have done much to transform the cuprammonium process from an uneconomic competitor for viscose and synthetics into the fastest wet-spinning system in the world. They now cl aim it to be competitive both economically and environmentally with the viscose filament process. 

Fabrication and Processing. PVDF is available in a wide range of melt viscosities as powder or pellets to fulfill typical fabrication requirements latices are also commercially available. 

A type of physical stabili2ation process, unique for poly(vinyl chloride) resias, is the fusion of a dispersion of plastisol resia ia a plastici2er. The viscosity of a resia—plastici2er dispersioa shows a sharp iacrease at the fusioa temperature. Ia such a system expansioa can take place at a temperature corresponding to the low viscosity the temperature can then be raised to iacrease viscosity and stabili2e the expanded state. 

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