Polymers dispersion effects

Bicomponent technology has been used to introduce functional and novelty effects other than stretch to nylon fibers. For instance, antistatic yams are made by spinning a conductive carbon-black polymer dispersion as a core with a sheath of nylon (188) and as a side-by-side configuration (189). At 0.1—1.0% implants, these conductive filaments give durable static resistance to nylon carpets without interfering with dye coloration. Conductive materials such as carbon black or metals as a sheath around a core of nylon interfere with color, especially light shades. 

The most effective and widely used dispersants are low molecular weight anionic polymers. Dispersion technology has advanced to the point at which polymers are designed for specific classes of foulants or for a broad spectmm of materials. Acrylate-based polymers are widely used as dispersants. They have advanced from simple homopolymers of acryflc acid to more advanced copolymers and terpolymers. The performance characteristics of the acrylate polymers are a function of their molecular weight and stmcture, along with the types of monomeric units incorporated into the polymer backbone. 

Intermolecular forces are generally less than lOkcal/mole. In polymers, in the absence of hydrogen bonding, the intermolecular force is primarily due to dispersion effects. 

Another excellent but expensive acrylic acid terpolymer is Acumer 5000, a silica and magnesium silicate dispersant. Although this polymer remains effective well above 600 psig (42 bar), it is recommended that at or above this pressure, FW silica should be removed at source, using DI or some other appropriate external treatment process. 

Low iron levels in the feed are essential to avoid damage to the electrode from iron deposition. This is achieved only by correct condensate line corrosion treatment. Polymer dispersants should be fed direct to the feed line and boiler to ensure particulate iron is effectively removed with the BD. 

Nappom WT, Laborde H, Leger J-M, Lamy C. 1995. Flectro-oxidation of Ci molecules at Pt-based catalysts highly dispersed into a polymer matrix Effect of the method of preparation. J Electroanal Chem 404 153-159. 

Dispersion of soluble rhombic sulphur does not usually create problems in most polymers, but addition of the insoluble form can create problems of incorporation into the rubber compound due to insolubility in the rubber. The insoluble sulphur particles tend to agglomerate into small lumps, which cannot then be dispersed effectively. Various treated insoluble sulphur products are available which aid incorporation. 

Much work on the preparation of nonaqueous polymer dispersions has involved the radical polymerization of acrylic monomers in the presence of copolymers having the A block the same as the acrylic polymer in the particle core 2). The preparation of polymer dispersions other than polystyrene in the presence of a PS-PDMS diblock copolymer is of interest because effective anchoring of the copolymer may be influenced by the degree of compatibility between the PS anchor block and the polymer molecules in the particle core. The present paper describes the interpretation of experimental studies performed with the aim of determining the mode of anchoring of PS blocks to polystyrene, poly(methyl methacrylate), and poly(vinyl acetate) (PVA) particles. 

TXRF was used to characterize high-viscosity polymer dispersions [83], with special attention being paid to the different drying techniques and their effect on the uniformity of the deposited films. TXRF was also used as a means to classify different polymers on the basis of their incoherently scattered peaks [84], Dispersive XRF has been used to assess the level of aluminum in antacid tablets [85]. 

We see that the second monomer greatly improves the dispersing effect. Here again we can note that a low molecular weight polymer gives a good ageing behaviour. 

Surfactants enable the polymer particles to disperse effectively without coagulation in the mortar and concrete. Thus, mechanical and chemical stabilities of latexes are improved with an increase in the content of the surfactants selected as stabilizers. An excess of surfactant, however, may have an adverse effect on the strength because of the reduced latex film strength, the delayed cement hydration and excess air entrainment. Consequently, the latexes used as cement modifiers should have an optimum surfactant content (from 5 to 30% of the weight of total solids) to provide adequate strength. Suitable antifoamers are usually added to the latexes to prevent excess air entrainment increased dosages causes a drastic reduction in the air content and a concurrent increase in compressive strength [87, 92-94]. 

Throughout this summary we have neglected the effect of dispersion on the overall transport of mass and heat. This is due to the fact that if dispersion is included, dispersion tensors must be determined before the equation can be solved. This can be done by solving the appropriate transport equation within a unit cell. Because a unit cell cannot be defined in most reinforcements used in polymer matrix composites, however, dispersion tensors cannot be accurately determined, so we have left dispersion effects out of our equations. In general, we anticipate dispersion to play a minor role in the IP, AP, and RTM processes. This assumption can be checked, however, by evaluating the dispersion terms using an approach similar to [16] where experiments and correlations are used to determine the importance of dispersion. 

The dispersion effect of water-soluble polymers on a heme aggregate is mentioned below. However, these water-soluble polymers have no coordinating ability and are not polymer ligands. It is well known that heme and its complexes easily aggregate in aqueous solution by stacking interaction, and that stable monomeric dispersed heme complexes are formed under restricted conditions such as extremely low concentration and low ionic strength21,22 ... 

Coleman et al. 2471 reported the spectra of different proportions of poly(vinylidene fluoride) PVDF and atactic poly(methyl methacrylate) PMMA. At a level of 75/25 PVDF/PMMA the blend is incompatible and the spectra of the blend can be synthesized by addition of the spectra of the pure components in the appropriate amounts. On the other hand, a blend composition of 39 61 had an infrared spectrum which could not be approximated by absorbance addition of the two pure spectra. A carbonyl band at 1718cm-1 was observed and indicates a distinct interaction involving the carbonyl groups. The spectra of the PVDF shows that a conformational change has been induced in the compatible blend but only a fraction of the PVDF is involved in the conformational change. Allara M9 250 251) cautioned that some of these spectroscopic effects in polymer blends may arise from dispersion effects in the difference spectra rather than chemical effects. Refractive index differences between the pure component and the blend can alter the band shapes and lead to frequency shifts to lower frequencies and in general the frequency shifts are to lower frequencies. 

Considering heterogeneous models for the film structure, we realize that if PVC with its low permeability were the continuous phase, there should only be small increases in permeability with the addition of EVA polymer. Such effects have been observed for a system of butadiene-based polymer modifier added to PVC to increase the impact strength (1). Addition of 15% modifier increased the permeability less than 10%. Electron micrographs of this film showed that the butadiene-based modifier was dispersed in the PVC phase. 

In order to ascertain that the selective dispersion effect of PAAX was truly due to the modified polymer itself and not to the associated poly-sulfides in the crude reaction, the flocculation testing was repeated with the purified PAAX solution. By using 300 mg/l of the purified PAAX solution, about 96 percent of the coal suspension flocculated in 5 minutes, while the pyrite suspension remained stable. These tests confirmed that the selective dispersion action was due to the PAAX (polyxanthate polymer) itself. 

On the other hand, there is a technological trend towards a high solid content of polymer formulations, e.g., to minimize shrinkage effects or to shorten processing times. A high polymer content at reasonable processing viscosities can only be obtained by polymer dispersions, either in water or hydrocarbon solvents. 

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