Sealants, acrylic

Solvent-releasing acrylic sealants, 22 43 Solvent-releasing butyl sealants, 22 43-44 Solvent resistance, of polycarbonates, 79 799-801... 

Conde-Salazar L, Guimaraens D, Romero L Occupational allergic contact dermatitis from anaerobic acrylic sealants. Contact Derm 18 129-132, 1988... 

Acrylics. There are two principal dasses of acrylic sealants latex acrylics and solvent-rdease acrylics. 

Future developments are likely to feature the production of more silicone sealants that do not pick up dirt, more latex acrylic sealants that have high performance properties, urethanes that have improved uv stability, and high performance polysulfides that are made in the United States. 

Acrylics. There are two principal classes of acrylic sealants latex acrylics and solvent-release actylics. High molecular weight latex acrylic polymers are prepared by emulsion polymerization of alkyl esters of acrylic acid, The emulsion polymers are compounded inlo sealants by adding fillers, plasticizers, freeze-thaw stabilizers, thickeners, and adhesion promoters. As is true of the silicone lalex sealants, die acrylic latex sealants are easy to apply and clean with water. 

Another class of acrylic sealants arc the solvent-releasing acrylics. Acrylic monomers are polymerized in a solvent. The natural adhesion of most of the solvent-releasing acrylics produces some of the best unprimed adhesion in the sealant industry. However, slow, continual cure generally produces large compression sets and limits their use to low movement applications. Also, the relatively high amounts of solvent and traces of acrylic monomer in these formulations limits their use to outdoor applications, usually in construction,... 

Solvent-based acrylic sealants are semi-elastomeric because of their thermoplastic nature. The movement accommodation factor is approximately 20%. However, these sealants perform best in the area from 7.5%... 

Table 5.3 Properties of solvent-based acrylic sealants... 

Initially, these sealants exhibit a shore A hardness of 25 to 35, which increases slowly with time. A good solvent-based acrylic sealant does not exceed 55 shore A. A higher hardness limits the movement capability and may result in adhesive or cohesive failure of the sealant. 

Solvent-borne acrylic sealants have very good weathering properties and exhibit excellent adhesion to a wide variety of substrates without the use of primers. These sealants can even be applied to substrates where slight contamination occurs (Brieton, 1994). 

Solvent-based acrylic sealants are used for areas where there is limited movement, such as perimeter joints around doors and windows, wood sashes and wood-to-masonry joints, precast joins, panel-to-panel joints and stone cladding. The properties of solvent-based acrylic sealants are summarised in Table 5.3. 

Water-based acrylic sealants are also referred to as acrylic emulsion sealants or latex sealants. These are one-component gun-grade material with a solid content ranging from 80%-85%. Curing occurs by evaporation... 

Typical areas of application for water-based acrylic sealants are gaps and joints subject to only a limited amount of movement, for example around door and window frames (Figure 5.1), fixtures and fittings and naturally occurring joints between different building materials. They are... 

Figure 5.1 Application of water-based acrylic sealant on window frames...

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. 

Acrylic adhesives first appeared about 1937 the acrylic resins may be considered as belonging to the vinyl family [1, p. 305], Today, acrylic adhesives appear in many forms as both pressure-sensitive and non-pressure sensitive formulations in organic solvent and emulsion forms as monomer and polymer cements as anaerobics as cyanoacrylates as so-called reactive or honeymoon two-part systems and as radiation curing formulations. Commercial production of acrylic polymers began in the late 1920s, but it was not until 1958 that the first aerylie sealant was developed [10, p. 226]. The solvent-based acrylic sealants were first introdueed to the eonstruction industry in about 1960 ... 

Chem. Descrip. y-Glycidoxypropyltrimethoxysilane CAS 2530-83-8 EINECS/ELINCS 219-784-2 Uses Adhesion promoter in water-borne acrylic sealants, urethane and epoxy coatings coupling agent in polysulfide and polyurethane caulks and sealants, min.-filled or glass-reinforced thermosets and thermoplastics, and in glass roving size-binders Properties Colorless transparent liq. m.w. 236.4 dens. 1.065-1.075 vise. 

Acrylic sealants are water-based but they may also contain ethylene and propylene glycols, mineral spirits and mineral oil. There are also solvent-based aerylie sealants which contain substantial amounts of solvents sueh as mineral spirits, toluene and xylene. Polysulfide sealants usually contain toluene but methyl ethyl ketone is also used. The group of class B sealants contains substantially more solvents (up to 40% by volume) but there are some exceptions. PVC sealants are based on plastisols and they ean be made without solvents. Butyl rubber based sealants usually eontain hydroearbons (Q-Cn). Styrene-buta-diene-styrene based sealants usually have a large amount of solvents seleeted from a group including toluene, heptane, hexane, methyl ethyl ketone, isobutyl isobutyrate, n-amyl acetate, n-amyl ketone. They are usually processed in solvent mixtures. Polyehloroprene is usually dissolved in a mixture of solvents ineluding ketones or esters, and aromatie and aliphatic hydrocarbons. The list includes naphtha, hexane, aeetone, methyl ethyl ketone, benzene, and toluene. 

Acrylic sealants, adhesives and coatings use m,p-cresol propoxylate (Macol 85) and alkyl benzyl phthalate (Santicizer 160) as permanent coalescing plasticizers. Acrylic based floor polishes use alkyl benzyl phthalate (Santicizer 160) and dialkyl adipate (Santicizer 141). These plasticizers are also permanent coalescing agents. 

Fillers and thixotropic agents are used widely throughout the various acrylic sealant and adhesive products. Fillers also form a significant component of epoxy-based adhesives. For example, if it is necessary to identify the filler used in the hardener component of an epoxy product, the isolation sequence involves initial centrifugation of the product to isolate the crude filler component. The latter is then washed repeatedly with acetone and dried thoroughly. The fine dry powder may then be used to prepare a standard KBr disk for IR analysis. 

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. 

In the absence of oxygen and in the presence of metals, anaerobic acrylic sealants, e.g., Loctite, Tree-bond and Sta-Lok, polymerize rapidly. Dimethacrylates are their principal components (Dempsey 1962 Ranch-off and Taylor 1985 Conde-Salazar et al. 1988 Kanerva et al. 1989). Diethylene glycol dimethacrylate oligomer is most commonly used for screw-thread locking, whereas urethane dimethacrylate is used for retaining and locking flat metal surfaces (Bjorkner 1995)-... 

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