Single polymer composites

The polymeric material produced in a single stirred-tank reactor will, except for stochastic variations, be of uniform composition. This polymer composition can be significantly different from the composition in the monomer feed mixture unless the conversion is high. If several tanks are connected in series the composition of the polymer produced in each reactor can be quite different. Since most particles are formed in the first reactor this change in composition in the following reactors can yield polymer particles in which composition varies with radius within the particles. 

Yonemura, H., Yamamoto, Y, Yamada, S., Fujiwara, Y. and Tanimoto, Y. (2008) Magnetic orientation of single-walled carbon nanotubes or their composites using polymer wrapping. Sci. Technol. Adv. Mater., 9 (024213), 1-6. 

Anisotropic materials have different properties in different directions (1-7). 1-Aamples include fibers, wood, oriented amorphous polymers, injection-molded specimens, fiber-filled composites, single crystals, and crystalline polymers in which the crystalline phase is not randomly oriented. Thus anisotropic materials are really much more common than isotropic ones. But if the anisotropy is small, it is often neglected with possible serious consequences. Anisoiropic materials have far more than two independent clastic moduli— generally, a minimum of five or six. The exact number of independent moduli depends on the symmetry in the system (1-7). Anisotropic materials will also have different contractions in different directions and hence a set of Poisson s ratios rather than one. 

Yavin, B., Gallis, H. E Scherf, J., Eitan, A. and Wagner, H. D., Continuous monitoring of the fragmentation phenomenon in single fiber composite materials, Polym. Composites, 12, 436 (1991). 

Both z/Mw and B show the same trend with increasing hydroxyl content of the copolymer, faffing rapidly in the range 0-4 mole % HEMA but showing only a small decrease for the addition for a further 5 mole % HEMA. For a flexible polymer, it has been calculated (35) that B should decrease from 5 X 10"4 in a good solvent to zero in a poor solvent at the 0 temperature. There is ample experimental evidence to confirm this for a single polymer in a series of solvents (19). Here we appear to have produced the same effect by varying the composition of the polymer rather than of the solvent. 

The traditional model used to explain the properties of the (partly) crystalline polymers is the "fringed micelle model" of Hermann et al. (1930). While the coexistence of small crystallites and amorphous regions in this model is assumed to be such that polymer chains are perfectly ordered over distances corresponding to the dimensions of the crystallites, the same polymer chains include also disordered segments belonging to the amorphous regions, which lead to a composite single-phase structure (Fig. 2.10). 

Non-Aqueous Processes. Dispersions of composite particles in non-aqueous media (12) have been prepared. The particles were sterically stabilised to prevent flocculation and aggregation. This was achieved by physical absorption of amphipathic graft or block copolymer (13,14) or by covalent attachment of diluent-soluble oligomer or polymer chains (15) at the particle surface so that by definition different polymers were situated at the surface and in the bulk of the particles, even for single-polymer particles. Composite particles were prepared by slow addition of the second monomer which was fully miscible with the diluent phase, obviating a monomer droplet phase further monomer-soluble initiation and amphipathic graft stabiliser was included as appropriate so that the process comprised continued dispersion... 

In the last decade several studies focused on the pyrolysis of plastic mixture in BFB reactors, operated under different conditions of temperatnre, flnidizing gas, bed material, reactor size and geometry [10, 12, 26, 27, 48], Particnlar attention has been devoted to the effect of PVC presence on the determination of yield of chlorinated aromatics [10, 12, 27]. The effect of temperature, which has been also well stndied [12, 27, 48], appears to be in accordance with that described for single polymer feeding an increase of temperature leads to an increase of yields in gas and aromatics and to a decrease of waxes. It is however noteworthy that the temperature value has to be selected on the basis of mixture composition, in order to optimize the desired products. In fact, most of polymers produces aromatics at higher temperatures and residence times (PE, PP) while others (like PS) do so at lower temperatures. 

Bliznyuk VN, Singamaneni S, Sanford RL, Chiappetta D, Crooker B, Shibaev PV (2006) Matrix mediated alignment of single wall carbon nanotubes in polymer composite films. Polymer 47(11) 3915-3921... 

DengL, Young RJ, Zwaag SVN, Picken S (2010) Characterization of the adhesion of single-walled carbon nanotubes in poly(P-Phenylene Terepthalamide) composite libers. Polymer... 

There are essentially four different types of membranes, or semipermeable barriers, which have either been commercialized for hydrogen separations or are being proposed for development and commercialization. They are polymeric membranes, porous (ceramic, carbon, metal) membranes, dense metal membranes, and ion-conductive membranes (see Table 8.1). Of these, only the polymeric membranes have seen significant commercialization, although dense metal membranes have been used for commercial applications in selected niche markets. Commercial polymeric membranes may be further classified as either asymmetric (a single polymer composition in which the thin, dense permselective layer covers a porous, but thick, layer) or composite (a thick, porous layer covered by a thin, dense permselective layer composed of a different polymer composition).2... 

There has been very little progress in the last five years in improving the performance of single polymer asymmetric membranes. Meanwhile, the composite membranes have been improved and they exhibit a higher flux and better re-... 

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