Bonding as a joining technique is usually classified as ‘nondetachable’. To date, this has applied to many applications, and particularly to structural adhesive-bonded joints. However, this classification is incorrect whenever ‘nondetachability’ is defined as an inherent property of a joint not to allow separation (and reconstitution) of the joint without irreversibly changing its elements (or adding new elements). This is illustrated by the following two examples.
First, in olden days, knife blades were mounted into the handles made from precious materials (e. g. silver) by bonding the shank and using rosin as the adhesive. When the blade needed to be replaced due to corrosion or damage, the handle was gently heated with a flame to melt the rosin, the shank was carefully removed from the handle, and a new blade immediately mounted. Dexterous fingers achieved this without applying any new adhesive.
Second, all of us know the Post-it® notes that are manufactured by the 3M company. These notes are easily removed from the block without leaving any residues (at least on visual inspection), and can be reattached to the block or to other surfaces, again and again (see Section 8.17.5.1).
No further attempt to clarify the definition of‘detachability’ will be made here, because tricky discussions of terminology hinder rather than benefit the development of a technique. In the following sections the detachability of a bond will be confined to the possibility of separating a bond on demand, easily and without leaving major residues. This is particularly interesting with regards to repair and recycling aspects, which are reflected by a variety of applications that have been filed for patents during the past few years. A choice of investigations is presented in Refs [122-124].