Effects of flame treatment on the interfacial energy of polyethylene assessed by contact mechanics

The effects of flame treatment of low-density polyethylene (LDPE) on the work of adhesion (W) and energy release rate (G) were assessed by a custom-built adhesion testing device (ATD). The contact area and the vertical displacement between planar LDPE films and PDMS lenses (untreated and UV/ozone treated) were varied as a function of the applied load, P. The adhesion and pull-off forces between the extracted PDMS lenses and the LDPE films were studied as a function of the duration of the flame treatment expressed in treatment numbers. A fracture mechanics approach was used to relate the applied load and the radius of the contact area to the energy release rate (G). The difference between the energy release rate and the thermodynamic work of adhesion, defined as the adhesion hysteresis (G - W), increased systematically with increasing treatment numbers for both lens types. In addition, the adhesion hysteresis appeared to be dependent on the contact time. Finally, the origin of the adhesion hysteresis was discussed. It was concluded that bonding by surface functional groups may be the dominating mechanisms for the changes in the observed hysteresis.