Characterisation and comparison of industrially pre-treated homopolymer polypropylene, HF 135M

The effects of 13 pre-treatments were examined to determine their effect on the surface region of homopolymer polypropylene. Five of the pre-treatments were examined in detail due to excellent joint strengths. They were: corona discharge, flame, fluorination, low-pressure vacuum plasma and atmospheric plasma. The pre-treatments were examined using X-ray photoelectron spectroscopy (XPS), angle resolved XPS (AR-XPS) and atomic force microscopy (AFM), to determine surface chemistry and topography. Of the 13 pre-treatments examined, it was found that the first five all showed the highest surface chemical modification of the pre-treatments studied. It was identified that the surface chemistry, concentration depth and topography varied widely across the five pre-treatments. However, all have been shown to have similar bond strengths with polyurethane adhesives, indicating that a number of significant factors were responsible for bond strength. It is surmised that the depth of the functional group concentration is the determinant joint strength parameter and not the O : C ratio or surface roughness.