The chemical bonding mechanism suggests that primary chemical bonds may form
across the interface. Chemical bonds are strong and make a significant
contribution to the intrinsic adhesion in some cases.
For example, primary chemical forces have energies
ranging between 60-1100 kJ/mol, which are considerably higher than the bond
energies secondary forces have (0.08-5 kJ/mol) . We should also mention the coupling agents and adhesion promoters
that are used to help in fixing the adhesive at the surface by chemical