Viscosity surface treatments

Nevertheless, from a practical viewpoint physical reasons for viscosity reduction during the surface treatment of the filler play a minor role first of all the effect of viscosity reduction itself is significant. 

Filler surface treatments, such as fatty acids, are very useful for reducing melt viscosities and some fillers would be impossible to use at the loadings needed for certain applications such as fire retardancy without some form of surface treatment. In some cases melt viscosities can be maintained at similar levels to the unfilled polymer, even in highly filled systems, despite the use of high filler loading [9]. 

Polypropylene compositions containing magnesium hydroxide, with and without magnesium stearate surface treatment, were characterised at low and high shear rates using dynamic and capillary measurement techniques [36]. A significant reduction in viscosity was observed when surface treatment was present, particularly at low shear rates. In addition, with this system, the yield stress for the onset of flow was markedly reduced (Compare magnesium hydroxide variants A and E in Fig. 9). 

A number of chapters have been overhauled so thoroughly that they bear only minor resemblance to their counterparts in the first edition. The thermodynamics of polymer solutions is introduced in connection with osmometry and the drainage and spatial extension of polymer coils is discussed in connection with viscosity. The treatment of contact angle is expanded so that it is presented on a more equal footing with surface tension in the presentation of liquid surfaces. Steric stabilization as a protective mechanism against flocculation is discussed along with the classical DLVO theory. 

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. 

Many mineral fillers are also commercially available with an organofunctional silane surface treatment. Suppliers of treated mineral fillers are shown in Table 10.2. These fillers are used in a variety of applications having critical property requirements that must be protected from moisture. Surface treatment of the mineral fillers also provides the formulator with a tool to reduce the viscosity of highly filled systems. 

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.

Figures 9.23 and 9.24 show that complex viscosity decays with time of mixing. The magnitude of this decay depends on the surface treatment of the filler as well as on its concentration. Again the conditions of the experiment influence the...

The application of polymer affects choice of filler. For example, to prepare conductive materials, special fillers must be used to obtain the required properties. Also, the method of processing imposes certain constraints on the choice and treatment of the filler before its use. For example, polymers processed at high temperature require fillers which do not contain moisture. This affects both the choice of the filler and/or its pretreatment. The choice of additives used to improve the incorporation of the filler depends on the application and the properties required from a product but it is also determined by the processing method. For example, the viscosity of a melt is reduced by special lubricating agents whereas the viscosity of filler dispersions is controlled by the surface treatment of filler. In some cases, the order of addition is important or a special filler pretreatment is used to achieve the desired results. These methods are discussed in special section in the table. Some fillers simply caimot be used with some polymers. In other cases, special care must be taken to ensure polymer stability or filler may interact with some vital components of the formulation. This subject is discussed in special considerations of filler choice. 

Finally, if heavy beads such as silica (SG = 2.1) are used, they can be assembled into a regular matrix by sedimentation [20]. One particular advantage of silica beads is that, after assembling them in a glass cell, sucrose can be added to the electrophoresis buffer to closely match the index of refraction of silica. This leads to a transparent material that is ideal for optical detection (at the expense of separation time, since sucrose increases the medium s viscosity, and thus reduces electrophoretic mobility). A second advantage is that some of the well-documented surface treatment strategies against electroosmosis developed for capillary electrophoresis can be directly transposed. 

Surface treatments for Cab-O-Sil influence the viscosity and thixotropic properties of an adhesive as shown in Figure 3.19 where MS-5 is untreated Cab-O-Sil , TS-720 is treated with polydimethylsiloxane, and TS-610 and TS-530 are treated with dimethyldichlorosilanes. The silica filler treated with polydimethylsiloxane (TS-720) produces greater van der Waals forces of attraction and thus higher viscosity compared to TS-610 and TS-530. ... 

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