Flame Treatment of 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. 

In this hands-on example we follow closely a recently published procedure [171]. Additive free LDPE films (with a thickness of 0.2 mm, e.g. obtained from DSM, Geleen, the, Netherlands) is cut into pieces of ca. 1 x 1 cm2 prior to treatment. To remove contaminants, the samples are refluxed in dichloromethane for 30 min, followed by a rinse with ethanol and drying in a stream of nitrogen immediately prior to use. For the flame treatment a mixture of natural gas and air are combusted by a nozzle type burner (using a typical flow rate of the mixture of natural gas and air of ca. 12.3 cm3/s and an equivalence ratio, which is defined as the stoichiometric oxidizer fuel ratio divided by the actual oxidizer fuel ratio of ca. 0.93). The LDPE 

The operation and adjustment of the TM-AFM are identical to the procedures discussed in example 34 (oxyfluorinated iPP). 

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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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