Filler robustness

The second path in Fig. 3 outlines the approach to a more robust tape designed by Drew [21]. Here the milled rubber and filler are combined with tackifiers and other additives/stabilizers in an intensive dispersing step, such as a Mogul or Banbury mixer. Next, a phenolic resin or an alternative crosslinker is added and allowed to react with the rubber crosslinker to a point somewhat short of crosslinking. The compounded mixture is then charged to a heavy duty chum and dissolved in a suitable solvent like mineral spirits. To prepare a masking tape. 

Water penetration rates are usually calculated according to the gas laws from measurement of pressure decay upstream of the filler over the whole period of testing with the gas (air) volume above the fluid held constant. They are therefore subject to temperature variations. Although the principle of the water penetration test is sound, and the avoidance of the use of potentially adulterating solvents is attractive, the low rates of water penetration calculable from only very small pressure drops within test systems have raised doubts about the robustness of the method for routine application in its contribution to the decision-making process. 

As with carbon blacks, silica fillers are characterized on the basis of primary particle size and specific area. The smallest observable single filler particles (primary) have diameters of about 15 nm. The surface forces of the primary filler particles are so high that thousands of them agglomerate to form extremely robust secondary particles that cannot be broken apart. These secondary particles further agglomerate to form chain-like tertiary structures, many of which can be more or less degraded by shear forces. Determination of surface areas is done using the BET nitrogen absorption method. 

Suzuki, N. Kiba, S. Kamachi, Y. Miyamoto, N. Yamauchi, Y., Mesoporous Silica as Smart Inorganic Filler Preparation of Robust Silicone Rubber with Low Thermal Expansion Property. J. Mater. Chem. 2011,21,5338-5344. 

Composite materials of these aluminosilicate binders with a quartz sand filler show an excellent water resistance (100 °C, 6 h) and demonstrate high compressive strength up to 70 N/mm for robust construction components. 

Many alternatives exist and the choice between thermoplastic and thermosetting resins depends on the expected lifetime and maximum operating temperature. Styrene-butadiene block copolymers and acrylic resins can be used to produce low-end adhesives with an acceptable stability up to 100°C, whereas epoxy and silicone thermosets are preferred for their robustness at 150-200°C. In the most severe environments, poly(imide-siloxanes) and polyimides can sustain medium-term exposures to 250 and 300°C, respectively. Various conductive fillers are cited in the literature, including noble metals such as gold or silver, and low-cost metals such as copper, nickel, chromium, and soft solders. 

The studies of Aerts et al. (2001) and Kelley et al. (2002) discussed in Section 33.5 demonstrated that UTDR can be used to determine the effectiveness of fillers and cross-linking to improve the compaction resistance of membranes. This application needs to be explored by membrane manufacturers in order to create a new generation of more robust membranes. 

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