Cyanoacrylate peel loads

Figure 1.4 Toughened cyanoacrylates offer better resistance to peel loads due to the presence of rubber particles in the adhesive matrix...

For example, polyethylene terephthalate (PET) plastic can be bonded with many different types of adhesives, including cyanoacrylates, UV acrylics and epoxies, and good strengths can be obtained on standard lap shear parts (1.6 mm thick). However, if thin films (<0.75 mm thick) of PET are to be bonded then it will be much easier to subject the adhesive to a peel load and the measured strength of the adhesive on the same grade of PET will be considerably lower. 

Fabric Peel Test Samples were cut from a plain weave cotton fabric (306 g/m ). Samples measuring 2.5 x 8 cm were cut, submerged in phosphate buffer (pH = 7.2), and allowed to air dry for 25 min. MFC measuring 350 (J-L (used as a model for cyanoacrylate-based tissue adhesives) was spread over a 2.5 X 6 cm area of one fabric sample, and a mating sample was placed on top. A 1200-g weight was set on top of the specimen for 1 min. The specimen was then allowed to cure for 1 h. The unglued portion was gripped into an MTS MiniBionix (Model 858) and the force required to separate the films at a displacement rate of 5.0 cm/min was measured. The maximum load after the initial peak was used to calculate the peel force of the adhesive joint. ... 

Designs deliberately incorporating flexible rubbery inserts between two stiff adherends are well known. For example, cyanoacrylate adhesives are successfully used to bond spectacle lenses to frames through an intermediate rubber layer. Without the rubber to dissipate peel and cleavage loads, the joint between the lens and the metal frame would be readily over-stressed, resulting in premature failure. 

Figure 10.6 The crack only gets as far as the rubber particle and the stress is dissipated. The crack then has to reform, only to meet another crack arrester . The resulting adhesive bond line is therefore considerably more resistant to peel and cleavage loads than a conventional cyanoacrylate...

Rigid adhesives (e.g., standard ethyl cyanoacrylates) are used for bonding assemblies when the joints can be designed to be subjected only to shear and normal static forces. If the application is subjected to peel stresses or impact loads, a toughened adhesive (e.g., epoxy, two-part acrylic or toughened cyanoacrylate) would be more suitable. 

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