Flame-treated LDPE

A second relevant example is the surface oxidation of polyolefins, such as LDPE, which is carried out frequently for thick specimens using an oxidizing flame treatment. For instance, while untreated LDPE surfaces are non-polar and thus fairly hydrophobic, flame-treated LDPE possesses a much higher surface energy and therefore improve the binding of these surfaces with other substances, such as adhesives, printing inks, paints, and various metal surfaces. 

Force Titrations of Flame-Treated LDPE Sample Preparation Flame-treatment [29]... 

The FV data acquired are analyzed as sketched in the examples above. The pull-off force values for each f-d curve are estimated and a histogram of forces for each pH and treatment condition is calculated. In Fig. 4.11 some normalized force titration curves (average pull-off force as a reference of value at pH 4 versus pH) on flame treated LDPE are shown. These titration curves display a typical sigmoidal shape, while the untreated polymer exhibited by contrast an almost constant pull-off force over the entire pH range. 

Fig. 4.11 Normalized force titration curves showing the adhesive force between hydroxyl functionalized tips and flame treated LDPE films as a function of the solution pH. The average pull-off force at pH 4 was set as a reference for each sample. The solid lines have been added as guides to the eye. (a) Untreated LDPE. (b) LDPE flame-treated 50 times, (c) LDPE treated 100 times, (d) LDPE treated 200 times. Reproduced with permission from [29]. Copyright 2007. Elsevier...

LDPE films are flame-treated (50x, lOOx, and 200x) according to hands-on example 35. 

The object to be treated is passed over one or more burners, each of which possesses a large number of closely spaced jets. The burners are fed with an air-hydrocarbon gas mixture whose proportions are carefully controlled. Ayres and Shofher found that with methane the optimum treatment time for an unspecified polyolefin was 0.02 s. A study of the flame treatment of LDPE showed very high levels of oxidation, although the oxidized layer was only 4-9 nm thick. 

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