Localised thermal analysis of a packaging film

A scanning probe microscope fitted with a fine platinum wire active heating element was used to examine the topography of a 300 mu m thick cross-section of a seven-layer polyolefin laminate designed for a food packaging application. Localised thermomechanical analysis was carried out by positioning the probe over selected regions and heating the wire whilst detecting the change in cantilever deflection using the microscope stage. Different grades of polyethylene and a poly(ethylene-vinyl alcohol) barrier layer could be identified by softening behaviour at a resolution of 10 mu m or better - even in cases where there were no obvious changes in image contrast. (C) 1999 Elsevier Science B.V. All rights reserved.