Reactive Acrylic Adhesives

Reactive acrylic adhesives (sometimes called tough acrylics, reactive fluids, second-generation acrylics or methyl methacrylate adhesives are based on acrylate and methacrylate monomers, and have been used commercially for 50 years. Reactive acrylic adhesives are based on acrylic and methacrylic monomers, and polymerise via a free-radical route similar to catalysed anaerobic adhesives. However, very significant differences exist. Whereas the monomers in anaerobics are predominantly difunctional or trifunctional to achieve highly crosslinked thermoset systems, reactive acrylics are based mainly on monofunctional monomers e.g., methyl methacrylate, or cyclo hexyl methacrylate  

These products are supplied as two separate components that can be mixed before application or each component can be applied to separate surfaces. 

Historically, three types of systems have evolved  

Lord Corporation introduced adhesives containing methacrylated phosphate monomers that gave much-improved thermal and atmospheric durability, and Dymax Corporation introduced their aerobic acrylics that were less sensitive to inhibition by atmospheric oxygen. Dow Automotive, 3M, and Loctite recently introduced two-part acrylic-based adhesives that can bond many low-surface-energy plastics, including many grades of polypropylene, polyethylene, and thermoplastic polyolefins without special surface preparation (see Section 4.2.2 for a description of this technology). 

Type of adhesive Major ingredients Distinctive features 

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Damico DJ. Reactive acrylic adhesives. In Pizzi A, Mittal K, eds. Handbook of Adhesive Technology. Marcel Dekker 1994 [Chapter 28]. 

Damico, D. J., Reactive Acrylic Adhesives, Handbook of Adhesive Technology, Ch. 28, (A. Pizzi and K. Mittal, eds.), Marcel Dekker (1994)... 

A new type of nonvolatile reactive acrylic adhesive, bridging the gap between anaerobic acrylic and volatile reactive acrylic adhesives, has recently been developed. The term "aerobic" acrylic adhesives has been coined solely to identify and to set apart these adhesives from other acrylics it does not necessarily describe their cure mechanism. Their term "aerobic" will be used to refer to a diminished sensitivity to air inhibition of thick layer curing properties and the ability to cure between two surfaces regardless of the presence or the absence of air. 

Reactive acrylic adhesives do not require the longterm or sophisticated fixturing techniques usually required for epoxies and urethanes. They do not require the application of heat, nor is scrupulous surface preparation required in the majority of instances. 

In spite of this impressive list of characteristics the use of reactive acrylic adhesives has been limited to selected high-performance adhesive markets. Their growth otherwise, has been less rapid than expected (10). One of the principal reasons is due to the toxicity characteristics associated with methyl methacrylate and methacrylic acid monomers, major formulation constituents of "second-generation" acrylic adhesives, with regard to inhalation, ingestion and skin contact. Compositions containing large quantities of these monomers have been rejected on certain production lines such as automotive assembly. The low flash point and resultant flammability hazard have also been important contributors to the restricted use of modified acrylic adhesives (9 and 11). 

Recently, technique or "use" problems have been cited as inhibitions to the growth of reactive acrylic adhesives. The main problems are described as a high sensitivity to the concentration of activator and movement in the substrate prior to fixturing, both of which cause less than optimal... 

This article examines a new reactive acrylic adhesive that overcomes most of these disadvantages. This new family of adhesives, called aerobic acrylics, maintains, and in some cases improves upon, the performance advantages of second-generation acrylics. The products are low in odor, essentially nonflammable, and lower in toxicity. Their higher speed of cure and fixture rate of 10 to 60 seconds and their solvent-diluted activators have minimized the other problems associated with acrylic adhesives namely, sensitivity to high concentrations of activator and movements in the substrates prior to fixture. 

Reactive acrylic adhesives generally consist of a solution of a toughening rubber (chlorosulphonated polyethylene) in a partly polymerized mixture of monomers this is mainly methylmethacrylate but ethane diol dimethacrylate is added as a cross-linking agent. The remaining monomer is polymerized in a free radical chain polymerization redox initiation involves an organic peroxide and a tertiary amine. Acrylic cements consist of a partly polymerized acrylic monomer containing an initiator. Cure is established by the thermal or UV decomposition of the initiator (see Radiation-cured adhesives). 

Takami, M. and Eastop, D. (2002). The conservation of a Korean painted silk banner, c. 1800 paint analysis and support via solvent-reactivated acrylic adhesive. In R. Vontobel (Ed.), 13th triennial meeting, Rio de Janeiro, 22-27 September 2002 Preprints 747-754, James James. 

Table 2.4 Major types of reactive acrylic adhesives ...

Mrxable reactive acrylic adhesives have become very important in bonding fibreglass in this industry because of their high performance... 

Mannfacturers of photovoltaic system are beginning to nse reactive acrylic adhesives in place of mechanical fasteners to streamline costs, decrease maintenance, and improve dnrability and product life expectancy of the solar energy systems. 

Polymers are the major components of all adhesives, and thus have a dominant influence on their properties. There is relatively little specific information in the literature on the thermal properties of adhesives therefore, we must depend on the properties of the polymer to know about an adhesive. Examples are that polymethylmethacrylate can be used as a model for reactive acrylic adhesives, polydimethylsiloxane for silicone adhesives, and nylons for polyamide hot-melts. 

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