Elastomeric sealants

Uses ndReactions. Some of the principal uses for P-pinene are for manufacturing terpene resins and for thermal isomerization (pyrolysis) to myrcene. The resins are made by Lewis acid (usuaUy AlCl ) polymerization of P-pinene, either as a homopolymer or as a copolymer with other terpenes such as limonene. P-Pinene polymerizes much easier than a-pinene and the resins are usehil in pressure-sensitive adhesives, hot-melt adhesives and coatings, and elastomeric sealants. One of the first syntheses of a new fragrance chemical from turpentine sources used formaldehyde with P-pinene in a Prins reaction to produce the alcohol, Nopol (26) (59). 

HEPA filters consist of a filter pack sealed into a case. The filter pack or core is made by pleating a continuous web of fiberglass paper back and forth over corrugated separators. The filter pack is sealed into a full-depth wood or steel casing using a elastomeric sealant. Gasketing is a critical item to ensure that the filter passes the air leakage tests. 

Most elastomeric sealants used in structural glazing applications are organic polymers or elastomers. Because organic materials degrade, some changes in the properties of the elastomer can be expected to occur with pas-... 

In addition to the petrolatum tapes and those based on a laminate of p.e. or p.v.c. with an elastomeric sealant or pressure-sensitive adhesive layer, recent developments have centred around self-adhesive bituminous laminates. These tapes are commonly constructed with a p.v.c. backing, whose thickness ranges from 0 08 to 0 75 mm and a bituminous adhesive compound layer to provide a total tape thickness of up to 2 mm. In order to maintain conformability without compromising impact values, tapes may also be manufactured with a fabric reinforcement within the bituminous layer. 

The room temperature cured epoxy adhesives discussed thus far exhibit a general lack of flexibility, especially when considered next to elastomeric sealants. Flexibility is generally desired when the performance requirements include high peel strength, impact strength, and resistance to thermal shock or thermal cycling. 

C 603 C 711 Test Method for Extrusion Rate and Application Life of Elastomeric Sealants Test Method for Low Temperature Flexibility and Tenacity of One Part Elastomeric Solvent Release Type Sealants... 

MIL-A-8576 MIL-A-9117 MIL-A-12850 MIL-C-14064 MIL-C-15705 MIL-C-18255 MIL-C-18969 MIL-C-23092 MIL-C-27315 MIL-C-27725 MIL-C-5539 MIL-C-7438 Adhesive, Acrylic Monomer Base Synthetic Elastomeric Sealant Natural Liquid Rubber Cement Grinding Disk Cement Caulking Compound Caulking Compound with Synthetic Rubber Base Caulking Compound—Watertight Exterior Hull Seams of Vessels Cement, Natural Rubber Coating Systems, Elastomeric Coating, Corrosion, Preventative, Air Fuel Tanks Natural Rubber Cement Core Material, Aluminum, for Sandwich Construction... 

The coating is two-component and needs mixing on-site prior to application. It can be applied either using conventional airless spray equipment or by brush or roller. A final thickness of 1 mm to 2 mm can be obtained with two coats. Pretreatment of the substrate with an epoxy primer ensures good adhesion. Defects in the concrete or brickwork are sealed with an elastomeric sealant which is resistant to the fluid being stored in the tank. 

C-603 TM for extrusion rate and application life of elastomeric sealants. 

C-792 TM for effects of heat ageing on weight loss, cracking and chalking of elastomeric sealants. 

Plasticizers improve the working properties of the compound while lowering its modulus. Control of modulus is extremely important in an elastomeric sealant to ensure that the adhesive strength of the compound does not exceed the structural strength of the substrate to which it is applied. 

Cure time testing tends to be somewhat subjective, but again there are methods available, such as ASTM C-679, Tack-Free Time of Elastomeric Sealants. Tack-free time is the curing time required for the product to develop a skin that is not damaged when subjected to application and removal of a plastic film. It is important in all cases to determine the cure characteristics of the product in actual working conditions. Since most silicones cure by reaction with moisture in the air, the sensitivity of cure time to humidity should be determined. Surface cure rates can usually be tailored to meet application requirements. 

A large variety of different sealant products are available, ranging from plastomeric oil-based mastics that are little more than joint fillers, to high-performance elastomeric sealants, which are capable of withstanding large joint movements of np to 60% of the nominal joint width. 

The rest of the sealants in Table 1 are said to be elastomeric they will aU withstand some degree of joint movement and undergo change to a more or less elastic state after application. Elastomeric sealants that are predominantly plastic in character but which show limited deformations are termed plasto-elastic. The butyl rubber and acrylic sealants are typical of this type and are limited in their uses to joints in which moderate movement occurs and to pointing around window and doorframes. Most of these change to a plasto-elastic state by loss of volatile constituents, which can cause shrinkage, and this must be borne in mind when designing joints. 

When the amplitude of joint movement is likely to be 20% or more of the joint width, it is essential to use one of the elasto-plastic or elastic types of elastomeric sealant. 

The ATF chanistry required to achieve a positive p-v curve to prevent shudder and maintain a sufficiently high friction level to provide adequate torque capacity will depend on the chemistry of the friction materials and the type of materials used to construct the transmission clutches [20]. A typical transmission clutch uses a cellulosic friction material in combination with steel plates. Other friction materials like carbon fiber are also used. Instead of steel plates, aluminum, copper, bronze, tin, and other metallic materials can also be used. In addition to these materials, plastic, nylon, and a variety of elastomeric sealant materials are used to construct other components of the automatic transmission. More recently, ATFs are required to be compatible with electronic circuitry and sensors [21]. Thus, changes in transmission design and materials have a direct effect on the... 

Active cracks may be sealed with an elastomeric sealant. Dormant cracks may be sealed with a fluid epoxy sealer that can be pumped into the crack or allowed to flow in by gravity. An epoxy sealer of 100 percent sohd content will seal the crack without shrinkage and will join the crack faces to re-form a monolithic structure.This seal will be strong enough to resist further cracking. However, should stress stiU occur, cracking will take place somewhere else in the structure. 

The elastomeric sealants should be based on polysulfide or urethane rubbers (preferably a two-component formulation in traffic grade) and comply with Federal Specification TT-S-00227E. The epoxy sealers may be epoxy-polysulfides (complying with Corps of Engineers Specification MMM B-350A) or epoxy-polyamides (complying with Specification M-200-65 of the American Association of State Highway and Transportation Officials). The epoxy compounds are described in Table 5.65. 

Some mortar joints, especially very narrow ones, may be sealed with an elastomeric sealant applied by a caulking gun. Cracked bricks may also be repaired by widening the crack and sealing it with an elastomeric sealant. 

PMMA migrate to the interfaces (i.e. act as a surfactant) and effectively compatibilise the polymer blend [234], TEM analysis of nanostructured cured elastomeric sealant compositions prepared by sonicating a mixture of silylated apophyUite filler in PDMS showed unambiguously that silicate layers are exfoliated [235]. Watkins et al. [174] have studied platinum/poly(4-methyl-l-pentene) (PMP) nanocomposites by means of TEM. For nanocomposite science and technology, cfr. also ref. [236]. 

SilverBond ground crystalline silica is the performance standard by which other crystalline fillers are measured. Completely inert, SilverBond provides excellent tint retention in exterior architectural finishes and helps prevent atmospheric degradation at the surface interface. Low oil absorption allows for high loadings, and its neutral pH makes SilverBond the preferred filler in catalyzed two-component systems. A hard filler, SilverBond imparts excellent abrasion and scratch resistance when incorporated into industrial paint and coatings, grouts, elastomeric sealants and high performance epoxies. 

Polysulfide sealants have found wide acceptance in construction, aircraft, automotive, marine, and insulating glass. In fact, polysulfide sealants were the first elastomeric sealants used in the construction industry and continue today, to a large extent, to be the standard with which other sealants are compared. 

Polysulfide sealants, although facing strong challenges from silicones and polyurethanes, continue to be the dominant segment of the elastomeric sealant market (Table 1) [2],... 

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