EFFECTS OF AGING AND WASHING ON UV AND OZONE-TREATED POLY(ETHYLENE-TEREPHTHALATE) AND POLYPROPYLENE

In this study we investigated the stability of poly(ethylene terephtha late) (PET) and polypropylene (PP) surfaces modified using three combi nations of UV light and ozone: ozone only, UV light in air (producing ozone), and UV light in air supplemented by additional ozone in the in coming air. Analysis was done using X-ray photoelectron spectroscopy a nd dynamic contact angle measurements. Our results showed that PET fil m is oxidized using these treatment conditions and it changes signific antly within the first week of aging and after washing with water. The se changes are reflected in the decrease in the Delta(O:C) ratio and t he increase in the contact angle. Conversely, PP changes very little o n aging or washing. Low-molecular-weight oxidized material (LMWOM), pr oduced on the polymer surfaces treated with UV/air or UV/air + ozone, is easily removed with water washing. On aging PET, a number of the ox idized groups at the surface disappear, seeming to migrate into the bu lk. The PP, however, does not favour migration as a path to reduce the overall free energy of the system, so the oxidized groups remain at t he surface. Treatment with ozone only, in the absence of UV light, is a much different modification process in terms of the mechanism and th e functional groups formed on the surface. This is reflected in the ag ing and washing behaviour of both the PET and the PP treated with ozon e only.