Phosphorescence polyolefins

The changes in the luminescence properties of polyolefins with degradation have been attributed to the formation of a, P-unsaturated ketones (or ene-ones) (Jacques and Poller, 1993, Allen and Owen, 1989b), which may have a pro-oxidant effect. While these species emit strong phosphorescence, the detection of these and other conjugated sequences by fluorescence has been suggested (Jacques and Poller, 1993, Allen and Owen, 1989b). 

T uminescence studies of commercial polymers have provided valuable -L information on the nature of some of the light absorbing chromophoric impurities believed to be responsible for sunlight-induced oxidation (1-13). The luminescence (fluorescence and phosphorescence) from commercial polyolefins has been attributed to the presence of impurity carbonyl groups (1,2,5,6,8), and recent work on polypropylene has indicated that these groups are conjugated with ethylenic unsaturations... 

Fluorescence characteristics of some common polymers have been listed [505]. Fluorescence analysis of polyolefins has been the subject of much controversy but is generally now considered to be associated with the presence of low levels of cyclic a, -unsaturated carbonyl compounds of the enone or enal type [514]. Fluorescence and phosphorescence excitation and emission of LLDPE, HDPE and mPE were reported [515]. 

Figures 1.6 and 1.7 show fluorescence and phosphorescence of polyolefins, respectively [69]. Figure 1.6 shows that fluorescence of polyolefins cannot be attributed to the presence of polynuclear aromatic hydrocarbons (e.g. naphthalene), because the positions of emitted bands differ significantly. On the other hand phosphorescence emission (Fig. 1.7) shows the presence of a,)S-unsaturated carbonyl groups. These results indicate the presence in polyolefins of enone and/or dienone chromophoric groups which are responsible for the observed luminescence.

Ultraviolet irradiation of polyolefins in vacuum causes increased absorption (Fig. 3.1), fluorescence (Fig. 3.2) and phosphorescence (Fig. 3.3) absorptions. 

Anatase (but not rutile) has been found to quench the long-lived phosphorescence emission from polyolefins [97,102,2266]. The following electron transfer mechanism between a triplet excited (Tj) carbonyl group and Ti02 has been reported [2266] ... 

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