Force volume imaging of defects in highly drawn high-density polyethylene

The internal structure of highly drawn high-density polyethylene (HDPE) of various draw ratios was studied. An atomic force microscope (AFM) in force volume (FV) mode was used to reveal the difference in mechanical properties of different regions of the cut surface of the sample. It was found that different regions have very similar mechanical response to the tip of the microscope. The only observable difference that allows an image to be constructed is the tip-surface adhesion force of the retracting line. It was found that the areas which appear as entire bands under the scanning electron microscope (SEM) have much lower adhesion force than the areas in between those bands. A mechanism of defect formation based on the changes in mechanical response is proposed.