Selection of sealants

The selection of sealants must be discussed in detail with sealant manufacturers. The final choice will, however, be a compromise, as no one product has all the above mentioned... 

Hydrocarbon resins are used extensively as modifiers in adhesives, sealants, printing inks, paints and varnishes, plastics, road marking, flooring, and oil field appHcations. In most cases, they ate compounded with elastomers, plastics, waxes, or oils. Selection of a resin for a particular appHcation is dependent on composition, molecular weight, color, and oxidative and thermal stabiHty, as weU as cost. A listing of all hydrocarbon resin suppHers and the types of resins that they produce is impractical. A representative listing of commercially available hydrocarbon resins and their suppHers is included in Table 6. 

Filter pack. Filter pack is the term used to describe the materials placed in the annular space between the screen and the formation (Figure 1). Aller et al. and Driscoll provide a discussion of the purpose and selection of filter pack materials. The filter pack serves a number of important mechanical functions. During well construction, it helps to keep the well screen centered in the borehole and acts to block the sealant from entering the well screen. The filter pack also improves hydraulic conductivity between the well screen and the formation, prevents formation materials from migrating to the well screen by acting as a filter, and helps support the screen and borehole. ... 

We can tune the physical characteristics of polyurethanes over a wide range by careful selection of their components. Polyurethanes are used extensively as foams, which range from soft and resilient to rigid. Solid polyurethanes range from soft moldings and elastic fibers to rigid injection molded items. Other uses of polyurethanes include coatings, sealants, and adhesives. 

Temperature sensitive mixtures, strategic separation schemes and, 22 3lit Temperature sensors, selection and installation of, 20 679-680 Temperature stability, of sealants, 22 29-30... 

Imai, T., Harte, B. R., and Giaicin, J. R. (1990). Partition distribution of aroma volatiles from orange juice into selected polymeric sealant films.. Food Sci. 55,158-161. 

Epoxy adhesives and sealants are generally not significantly affected by simple outdoor weathering. However, there are certain circumstances that could affect the permanence of joints exposed to outdoor service, ft is important that these be considered early in the design of the adhesive joint and selection of materials. 

The method used to apply the adhesive or sealant can have as much to do with the success of the joining operation as the kind of material applied. The selection of an application or dispensing method depends primarily on the form of the adhesive liquid, paste, powder,... 

Cure time is very important for sealants as well as adhesives. Often the sealant will be required to function as a barrier or resist the movement of substrates very soon after it is applied. With construction sealants, for example, it may not be possible to delay the environmental conditions until after the adhesive cures. Thus, curing time becomes a critical parameter in selection of the sealant. ASTM C 679 covers a method for determining the time that a mechanic can work the sealant into the joint before the sealant starts to skin or solidify. 

The selection of an alloy for a specific application is based on the cost and the corrosion resistance of the alloy in the environment of interest. It is also possible to subject the chosen alloy to a process by which the corrosion resistance of the selected material can be improved within the acceptable limits. Some of the corrosion prevention and protection strategies with respect to the aluminum-based alloys are (i) design (ii) alloy selection and joint sealants (iii) aluminum thermal spraying anodic coatings (iv) inhibitors (v) conversion and organic coatings and (vi) cathodic protection. 

It has also been found that the water flux depends on the osmotic pressure of the water/organic solvent mixture involved. When no pinholes are present, only water molecules can pass through a constriction to form menisci behind it. Thus a high separation factor can be attained. When selecting a sealant, considerations should be given to the chemical compatibility between the solvent and the membrane material. An example is the use of CA-modified membranes for acetone/water mixtures where acetone can conceivably dissolve some of the CA that plugs the pinholes. 

Corrosion control can be accomplished in the design and manufacturing phase as well as in the operation and maintenance phase of the aircraft. Proper design for corrosion control must include the selection of materials, coatings, sealants, and corrosion inhibitors. It is also necessary to avoid dissimilar metal contacts, access for maintenance, and proper drainage. 

Fillers increase the strength, impart needed rheological properties, and reduce the cost of sealants. Tensile properties are increased significantly, depending on the type of filler, its particle size, and the type of cure. Improper filler selection can ruin the performance of a polysulfide sealant. Calcium carbonates (wet or dry ground limestone, precipitated), carbon blacks (furnace, thermal), calcined clays, silica and silicate fillers, and rutile titanium dioxide are typical fillers used in polysulfide sealants. Generally, combinations of fillers are used in formulation. Plasticizers improve the working properties while... 

The application of IR spectroscopy to organic sorbates has been primarily limited to gas-phase a orption kinetics and gas-phase catalysis (21). The usefrilness of IR for investigating sorption/desorption processes in situ, has been demonstrated for the selectivity of conformer adsorption at mineral surfaces (22). Strong absorption of H O vibrational modes by IR radiation has been a major hindrance in the application of IR spectroscopy to study organic sorption at aqueous-mineral interfaces. Attenuated total reflectance-IR (ATR-IR) spectroscopy and the use of DjO in the aqueous phase minimizes the water absorption problem. Figure 3 details the ATR setup used in this study. Clay pastes were loaded into Teflon plaques and clamped to both sides of a vertical ATR prism. Silicon sealant around the edges of the plaques prevented water evaporation during extended data collection times (up to 2 days). The area of the D O... 

Naturally, swelling may be undesirable in many instances as well. For example, swelling of organic polymer based membranes decreased selectivity. Other possible deleterious effects could include malfunctions due to solubilization and swelling of sealants such as gaskets or o-rings. 

Based on the limited evaluation of the synthesized compounds, the following conclusions can be made a) The synthetic process developed for introduction of methacrylate groups into hydroxyl containing polyester systems appears to be a viable route for modification of other hydroxyl containing monomers and polymers, b) Additional development work on selected systems to define optimum formulation recipes will be required, c) The materials evaluated have potential application in the areas of sealants, coatings and adhesives. 

The term primer is used to describe any liquid preparation used to modify the surface of an adherend. While there are some primerless systems, the sealants used in construction often require primers as the surface condition may be extremely variable (See Sealant joint design, Seaiants in doubie giazing and Selection of joint sealants). 

Performance of primers has been studied both in general construction and water-retaining structures.Further information may be found in articles on Selection of joint sealants. Sealant joint design, Paint primers and Primers for adhesive bonding. 

A preliminary article indicates the scope and types of Sealants. In designing a sealant joint, it is essential to select a snitable sealant with adequate capability to withstand the expected movement at the joint... 

When calculating the design width of joints in a building, it is essential to take account of the tolerances on the relevant dimensions of the components and the accuracy in placing them that is likely to be achieved on site. For these reasons, there may, in practice, be considerable variation in the widths of a number of ostensibly identical joints. The joint width for the design must ensure that in no joint will the sealant be subjected to a level of compression or extension that, when expressed as a proportion of the achieved joint width, exceeds its movement capability. (See the Selection of joint sealants, where Table 1 gives maximum movement permitted for each major type of sealant.) However, considerable variation in formulation and properties may occur between different brands of the same chemical type, which may affect this value. The maximum tolerable joint movement quoted by the manufacturer should be used in joint design calculations. 

British Standards Institution, Guide to the Selection of Construction Sealants, BS 6213, BSI, London, 2000. 

The most common system for the outer or secondary sealant used is based on polysulfide polymers cured with manganese dioxide where the physical properties have been modified by the use of a low-volatility plasticizer such as a higher phthalate. Recent developments have seen an increase in the use of polyurethanes because of their higher adhesion potential. All the systems are required to have oil resistance when used in timber windows (from the glazing putt and preservatives) (see Selection of joint sealant). 

---