Solution Processing of Composites

Common traditional approaches for the fabrication of CNT-polymer composites include solution processing of composites, melt spinning, melt processing, in situ polymerization, processing of composites based on thermosets, electrospinning and coagulation spinning for composite fibers and yam production [92]. 

A typical process for the preparation of an acryUc solution terpolymer of composition 27.5% 2-ethyIhexyl acrylate—41.3% methyl methacrylate—31.2% hydroxyethyl methacrylate begins with the following charges ... 

During the processing of composite materials in a hot press or an autoclave, the laminate is usually kept flat until cure is complete. If the platen surfaces are assumed frictionless, the effect of the constraints is to require that the curvatures K] and k2 be zero throughout cure. To develop the elastic solution under these constrained conditions, the laminated plate theory may be used with conditions of N = 0 and jc, = 0. The resulting midplane strains are given by... 

The early work on properties of molecular composites was done by Hwang et al. (1983a, b). They performed experimental studies of solution processing of films based on poly(p-phenylene benzobisthiazole) with both poly(2,5 (6 ) benzimidazole (ABPBI) and poly(2,5 (6 ) benzothiazole) (ABPBT). The films were shown to possess very high modulus and strength values, which improve upon heat treatment. The uniaxial modulus of highly oriented molecular composites was shown to follow the linear rule of mixtures. 

Wan et al. directly added whiskers into absolute ethyl alcohol solution containing polyethylene glycol. The ratio of whiskers, polyethylene glycol, and absolute ethyl alcohol is 10 3 300. Stir for 5 hours. Then the dispersed whiskers are filtered and dried, and modified whiskers are obtained. Then in situ polymerization between the prepared whiskers and matrix will occur during the preparation process of composites. 

If two phases of a mixture are in thermal equilibrium, they generally have a different composition. The relation between the compositions of the phases, which varies from case to case, is the basis of all methods of thermal separation. Thus, information on liquid-vapour equilibrium is needed for the understanding and calculation of distillation and rectification. The equilibrium between a solid or a gas that is to be dissolved and the liquid solvent is important for solution processes. Of technical importance is also the equilibrium between a substance to be dried and air with a certain humidity. 

Development efforts at Celanese Research Co. estabHshed soHd-state polymerization as the most practical process for engineering scale-up. Homogeneous solution polymerization of PBI in polyphosphoric acid was eliminated because of the need to work with low soHd compositions (in the range of 3—5%) during the precipitation, neutralization, and washing steps required for isolation of the product. 

The first commercial plant to use CYANEX 272 became operational in 1985. An additional three plants were constmcted between 1985 and 1989. Of the four, one is in South America and three in Europe. An additional three plants have been built two in Europe (1994) and one in North America (1995). Approximately 50% of the Western world s cobalt is processed using CYANEX 272. Both high purity salts and electrolytic cobalt metal are recovered from solutions ranging in composition from 30 g/L each of cobalt and nickel to 0.2 g/L Co, 95 g/L Ni Operating companies usually regard use of CYANEX 272 as confidential for competitive reasons and identities cannot be disclosed. CYANEX 272 is being evaluated on the pilot-plant scale in many additional projects involving the recovery of cobalt and other metals. 

An excellent review of composite RO and nanofiltration (NE) membranes is available (8). These thin-fHm, composite membranes consist of a thin polymer barrier layer formed on one or more porous support layers, which is almost always a different polymer from the surface layer. The surface layer determines the flux and separation characteristics of the membrane. The porous backing serves only as a support for the barrier layer and so has almost no effect on membrane transport properties. The barrier layer is extremely thin, thus allowing high water fluxes. The most important thin-fHm composite membranes are made by interfacial polymerization, a process in which a highly porous membrane, usually polysulfone, is coated with an aqueous solution of a polymer or monomer and then reacts with a cross-linking agent in a water-kniniscible solvent. 

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