Rubber-toughened epoxy adhesives energy

Figure 7.16 The effect of joint width upon the maximum adhesive fracture energy, Clem, for a rubber-toughened epoxy adhesive bonding steel substrates using a TDCB geometry [106].

Sprenger and coworkers used a room-temperature curing rubber-toughened epoxy adhesive with a Tg of 70°C (Kinloch et al. 2003 Sprenger et al. 2003 2004). The addition of only 4 wt% of 20 nm diameter silica nanoparticles doubled the fracture energy, fi om 1,200 to 2,300 J/m. The addition of the nanoparticles also increased both the lap-shear and peel strength, as shown in Pig. 55.10. 

In contrast to polyethylene and EVAs, Epoxide adhesives are thermosets and are much stiffer and less ductile. The adhesion fracture energy (Gc, see Fracture mechanics), between both unmodified and rubber-toughened epoxies (see Toughened adhesives) and several metals has generally been found to be much higher when microfibrous surfaces were involved (Table 2) ... 

A further important parameter is the adhesive thickness within a joint. In certain adhesive systems such as rubber-toughened epoxies, there is an optimum thickness of adhesive within which energy-dissipation processes can take place. Above and below this critical size, the adhesive fracture energy will be lower. 

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