Sealants curing

Silicones. Commercially avaHable sHicone sealants are typicaHy one of three curing types moisture-reactive (curing) sealants, moisture-releasing (latex) sealants, and addition-curing sealants. Of these three types, moisture-curing sHicones make up the vast majority of sHicone sealants sold. 

The role played by the various ingredients in the composition of sealant, and in particular on the durability of adhesion has been discussed recently [77]. Inert plasticizers, such as trimethylsilyl-endblocked-PDMS, are typically added to silicone sealant compositions in order to adjust the rheology of the uncured sealant. They result in a reduction of the modulus and hardness of the cured sealant. Differences in the durability of silicone sealants are found to be due to differences in their cure chemistry, and more specifically to the nature and... 

However, the primary emission sources of these compounds in the museum environment are-besides acid-curing sealants and cleaning agents-without con-... 

The average shore A hardness of the cured sealant is 20 to 25 but increases with ageing. Resistance to ultraviolet radiation is excellent, but this is not important for indoor applications. The maximum movement accommodation factor (MAF) can be 15% of the total joint width. Joints should be designed so that movement due to shrinkage and thermal changes does not exceed the maximum MAF, related to the joint width. Table 5.4 lists the properties in general for acrylic emulsion sealants. These properties are summarised from the commercial literature of several acrylic emulsion sealant manufacturers and should not be considered as specifications. Table 5.5 lists the standard specifications for these sealants. 

In amine systems ammonia is released during the cure. This system can be used with alkaline materials. The cured sealant possesses the lowest modulus of all such systems. 

Butt joint Expansion joint Lap joint glass-to-glass concrete-to-concrete Triangular joint High-modulus or mid-modulus, acetic-cured or neutral cured sealant Low-modulus neutral cure sealant, to accommodate the movement in the joint Mid-modulus or high-modulus, neutral cure sealant Low-modulus, neutral cure sealant High-modulus or mid-modulus, acetic-cured or neutral cure sealant... 

X2 Construction sealants. Silicone sealants have proven to be very useful in a number of applications related to concrete construction (Figure 6.5). Systems based on neutral or alcoholic cure are suitable. Acetoxy-cured sealants are not suitable because of the evolution of acetic acid by-product, which reacts with calcium-bearing surfaces such as concrete and mortar, resulting in uncertain adhesion (Spells and Klosowki, 1981). 

Mid-to-high-modulus acetoxy-cured sealants are the most common. In certain applications, neutral cure silicones are also employed. Whatever the curing system, a sanitary sealant should be equipped with a fungicide. The sanitary field includes bathrooms (Figure 6.7), kitchens, refrigerators or cold storage rooms. 

Owing to their long curing period, one-component polysulphide sealants are not generally used in joints with dynamic movements. When a joint opens and closes under stress and under variations in temperature, a slow-curing sealant may experience cohesive failure as well as deformation. 

The cured sealant gives a tough, elastic, rubber-like seal and gives excellent adhesion to concrete and masonry, glass, aluminium and stainless steel. The shore A hardness ranges from 15-35. The movement accommodation factor is 25% in butt joints and 50% in lap joints. These sealants have the capacity to accommodate continuous and pronounced cyclic movements. They are suitable for joints where the joint width may range between 5 mm and 50 mm. Joints which are expected to experience cyclic movements should have a width depth ratio of 2 1. Minimum sealant depths recommended for different environments are mentioned in Table 7.8. Primers... 

Physical properties were evaluated using standard DIN or ASTM specifications. The sealants were filled into Teflon molds to form homogeneous test pieces of comparable thickness. The specimens were then moisture cured and conditioned at 25 °C and 50% relative humidity for 14 days before mechanical property testing. The hardness of the cured sealant samples was measured by Shore A. Shelf life at 50 °C was determined for a maximum of 21 days. Tack-free times were determined by finger touch under ambient conditions. For adhesion testing the substrates were first wiped with either methyl ethyl ketone (aluminum, steel, glass, concrete, wood) or methanol (PVC, PMMA, ABS, polystyrene), then washed with detergent, rinsed with distilled water, and allowed to air dry prior to preparation of the test specimens. Specimens were cured for 14 days at ambient conditions. 

Krieble, R.H. (1962) Anaerobic Curing Sealant Having Extended Shelf life , US Patent 3,043,820, Rocky Hill, Connecticut. 

Since the use of sealants and caulking compositions is essential for energy conservation in the construction of modern buildings, large quantities of hot melt and room temperature curing sealants and caulking compounds were used worldwide in... 

Emulsions of polyvinyl acetate and polyalkyl acrylates have been used as tub caulking compositions, spackling compounds and as building sealants.22 Acrylic sealants which harden in the presence of powdered iron or copper meet Federal Specifications TT-S-00230C. 27 Liquid monomers, such as polyethylene glycol dimethacrylate and butyl alpha—cyanoacrylate have been used as room temperature curing sealants.22 22. 

Sealants made with this silicone polymer are extrudable over a wide temperature range they can be applied in winter on the Alaskan North Slope or in the heat of an Egyptian summer. When the polymer is then crossllnked into a three-dimensional network to form the cured sealant, the rubberlness, or extensibility, does not change significantly with temperature. A sealant used in Alaska will continue to stretch easily and seal when temperatures are far below freezing. 

All chemically curing sealants employ catalysts, and silicone sealants are no exception. 

Resistance to Hardening or Cracking. Fully cured sealants... 

The amount or type of plasticizer used must be compatible in the cured sealant and its volatility should be adequate for its intended use. Table V and FIGURE 4 show the effect of three typical plasticizers on the properties of a polysulfide compound. 

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