Two-part Acrylics

Two-part acrylics are available either as two-part resins or as a resin for Part A with Part B as a liquid activator. The two-part resin products are formulated with Part A and Part B of similar viscosities and designed to be dispensed as bead-on-bead or mix-in-the-nozzle. 

Two-part acrylics (also referred to as methyl methacrylates or methylmethacrylates (MMA)) can offer benefits over cyanoacrylates with improved gap fill and typically 

They are comparatively inexpensive and although earlier versions were brittle when cured, the more recent developments are significantly tougher and more flexible generally give improved peel strength over cyanoacrylates. 

Some toughened acrylic grades can be difficult to dispense due to the stringiness of the additives in the adhesive matrix and so difficult to manage on small component parts. They often have a high odour (although low-odour versions are available) and 

MMA have proved to be extremely useful in the bonding of larger plastic components such as bonding automotive bumpers, fibreglass components and assembling boats. 

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FIGURE 15.21 Shear strength of mild steel joints, (a) two-part epoxy, (b) two-part acrylic, (c) anaerobic acrylic, (d) cyanoacrylate, (e) PVC plastisol, (/) one-part heat cured epoxy. ... 

In all of these applications the adhesive bond must remain sufficiently strong and stiff over the 20-40 year life of the rolling stock the adhesive itself must also remain sufficiently flexible to allow joint deformation under impact loading. In these respects British Rail have favoured two-part acrylics, at least for use with zinc-coated steels. 

Figure 5.30 (upper) Effect of temperature on adhesive shear behaviour (from reference 5.18). (lower) Effect of immersion in water of ERP/two-part acrylic adhesive/ERP joints on the tensile... 

Two-part acrylic adhesive An initiator, such as peroxides, polymerises acrylate groups of the main component... 

Methylmethacrylate - Two part Acrylic - Two part, with sur e activator ... 

Notes - Notes Structural Adhesives Ltd. have a wide range of two-part acrylic ... 

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). 

It is worth noting here some low volume, non-epoxy usage. The bonding of some brackets, etc., makes use of a two-part acrylic system. 

Figure 8.7 Effect of immersion in water at 40 °C on the tensile lap-shear strength of glass fibre reinforced plastic (GRP) substrates bonded with a two-part acrylic adhesive [40]. The surface pretreatment was simply an abrasion/solvent-cleaning process.

Bumpers - Automobile bumpers are now made from a range of polymers ineluding polycarbonate, polyester thermoplastic elastomers, and reaction injection molded methanes. These are being bonded to the automobile using a variety of adhesives such as two part acrylics and polymethanes as well as RTV silieones. 

Depending on the chemistry of the adhesive, the adhesion to different substrates (Dettner 1991) and the tolerance for surface contamination is different. Epoxy and acrylic-based adhesives bond well to a variety of different surfaces like metals, aluminium, or composites and tolerate some degree of surface contamination like oil if cured by heat. They do not adhere well to low-energy surfaces like plastic. Two-part epoxy formulations need a cleaning of the surface to remove any contamination. Special two-part acrylic-epoxy hybrid adhesives are able... 

As an environmental durability test, measurement of lap-shear strength after exposure to 95% RH at 40° C was carried out. The only adhesive that met all of the requirements was a two-part acrylic adhesive. That adhesive also had the desired cure characteristics (work life 5 min, de-jig time 30 min). 

The UV acrylic gave excellent results on the grade of polyethersulfone tested [2] (Table 2.8) but good results were also achieved with the specialist polyolefin bonder , a 10 1 two-part acrylic. 

Polyethylene has a low surface energy (31 mN/m) and so will generally require surface preparation prior to bonding. The two-part acrylic polyolefin bonder showed good strengths in these trials [2] (Table 2.9). 

Structural adhesives for plastics are more often than not epoxies, two-part acrylics, cyanoacrylates or UV-cure adhesives. 

Two-part acrylics (or MMA) bond exceptionally well to many thermoplastics and these products are often used for the assembly of point-of-sale plastic assemblies where ease of application, strength and aesthetics are important. 

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