The mechanical interlocking theory of adhesion states that good adhesion occurs
only when an adhesive penetrates into the pores, holes and crevices and other
irregularities of the adhered surface of a substrate, and locks mechanically to
the substrate. The adhesive must not only wet the substrate, but also have the
right rheological properties to penetrate pores and openings in a reasonable
time.
This theory explains a few examples adhesion such as rubber bonding to textiles
and paper. Since good adhesion can occur between smooth adherend surfaces as
well, it is clear that while interlocking helps promote adhesion, it is not
really a generally applicable adhesion mechanism.
Pretreatment methods applied on surfaces enhance
adhesion [13]. These pretreatments (especially
plastic surface treatments) result in microroughness on the adherend
surface, which can improve bond strength and durability by providing mechanical
interlocking. Beyond mechanical interlocking, the enhancement of the adhesive
joint strength due to the roughing of the adherend surface may also result from
other factors such as formation of a larger surface, improved kinetics of
wetting and increased plastic deformation of the adhesive [14-15].
