Surface treatments dispersants

How does surface treatment of polar solid additives lead to better dispersion and distribution of the additive in the polymer matrix ... 

Various particle surface treatments have been used to delay polymer hydration until polymer particles have been thoroughly dispersed. These include guar treatment with borax (2,94) and HEC treatment with glyoxal (95). 

This technique involves the dispersion of a nanomaterial in a monomer (Fig. 4.8). This step requires a certain amount of time that depends on the polarity of the monomer molecules, the surface treatment of the nanomaterial, and the swelling temperature. For thermoplastics, the polymerization can be initiated either by the addition of an agent or by an increase in temperature. For thermosets such as epoxies or unsaturated polyesters, a curing agent or peroxide can be added in order to initiate the polymerization. Functionalized nanomaterials can improve their initial dispersion in the monomer and consequently in the composites. In the case of layered materials, such as clays or graphene, the most important step is the penetration of the monomer between the sheets, thus allowing the polymer chains to exfoliate the material. The... 

For instance in azo pigment manufacture, the crude product is given some form of surface treatment, such as with rosin, to control crystal growth, control aggregation and to aid in dispersion. 

The surface tension of two thermoplastics and three fillers are listed in Table 2. Large differences can be observed both in the dispersion, but especially in the polar component. The surface tension of the majority of polymers is in the same range, in fact between that of PP and PMMA. Those listed in Table 2 represent the most important particulate fillers, and also reinforcements used in practice, since clean glass fibers possess similar surface tensions to Si02. Surface treatment lowers the surface tension of fillers significantly (see Sect. 6.1). 

As an inorganic mineral, most unmodified nanoadditives are strongly hydrophilic and are generally compatible and miscible only with a few hydrophilic polymers, for instance, clay can only be made into PNs with polyethylene oxide),27 poly(vinyl alcohol),28 and a few other water soluble polymers. Most polymers are hydrophobic and thus they are neither compatible nor miscible with the unmodified nanoadditives, leading to an inability to achieve a PN with a good nanodispersion in most cases. Therefore, for most nanoadditives that have been used to prepare the PNs, an important and necessary feature is their surface treatment that provides compatibility to the nanoadditives and enables them to be uniformly dispersed (and/or separated into single nanoparticles) in the polymer matrix. 

The clay is first dispersed in water or an aqueous system (to form a suspension) and the modifier that has been pre-dissolved in water (or an aqueous system) is then gradually (drop-wise) added to the clay suspension. The organo-modifier will be anchored onto the surface of the clay platelets immediately after it is added but further stirring for some more time up to a few hours may be needed to achieve homogeneous and complete ion exchange. Some representative modifiers (in both cationic and anionic form) that have been used as surface treatment for the clays in the literature are shown in Figure 11.9. 

Solvent blending Solvent blending, also called solution intercalation in the case of clay and other nanolayers, involves both dispersing the nanoadditive and dissolving the matrix polymer in a solvent or a solvent mixture. Three parameters have been considered to be important, particularly for clays, in choosing the surface treatment of the nanoadditives with this process The structure of the modifier, its miscibility with the polymer, and its thermal stability. The miscibility of the modifier here has two meanings miscibility with both the final polymer and the solvent chosen to dissolve the polymer. The modifier structure and its miscibility are perhaps more important than the thermal... 

Particle interactions resulting in aggregates of particles will adversely affect dispersion. Special surface treatments are provided to reduce these aggregation forces and achieve higher loadings and better suspension stability with less effect on viscosity. These surface treatments can be applied directly to the filler, and many grades of treated fillers are commercially available. 

Figure 10.6. Surfactant demand curves of 70% (weight) dispersions of Ti02 pigments with various levels of alumina treatment. Dispersions were prepared in DIDP plasticizer on a highspeed disk mill. Survactant used was Disperbyk I. Pigment A titania surface, no alumia surface treatment. Pigment B 1.5% alumina surface treatment, minimum viscosity achieved at 2.36% surfactant based on pigment weight. Pigment C 3.0% alumina surface treatment, minimum viscosity at 3.9% surfactant.

Given the potential consequences of inadequately dispersed pigments, pigment manufacturers apply proprietary surface treatments to make their products easier to disperse, and colorists who formulate with these pigments devote at least as much effort to dispersion technology as they do to color formulation technology. 

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