Polypropylene chemiluminescence

Figure 3 shows how the elementary structure of the polymer affects the observed patterns of chemiluminescence response in oxygen at 120°C. As expected, the oxidizability decreases in the order polyisoprene < polybutadiene < polypropylene < polyethylene. However, it is difficult to understand why the maximum light emission is almost 2x lower for polybutadiene than for PP. The oxidation of polybutadiene occurs via secondary peroxyl radicals, while in... 

Figure 3 Comparison of chemiluminescence runs from saturated and unsaturated hydrocarbon polymers having tertiary carbons (polypropylene, polyisoprene) in the main chain.

Figure 4 Chemiluminescence oxidation runs at 140°C in oxygen for films of polypropylene (PP), polyamide 66 (PA 66) and polyethylene (PE) (logarithmic time scale).

Figure 6 (A) Non-isothermal chemiluminescence runs for oxidation of polystyrene (PS), polyethylene terephthalate) (PETP) and polyfmethyl methacrylate) (PMMA), in oxygen, heating rate 2.5°C/min. (B) Non-isothermal chemiluminescence runs for oxidation of polypropylene (PP), polyamide 6 (PA 6), poly(vinyl pyrrolidone) (PVP), polyethylene (PE) and polyamide 66 (PA 66), in oxygen, heating rate 2.5°C/min.

Figure 7 Arrhenius plots for non-isothermal chemiluminescence runs of oxidized polymers, (1) polypropylene, (2) polyethylene, in oxygen, heating rate 2.5°C/min. 

Figure 13 Comparison of DSC and chemiluminescence scans of the oxidation of polypropylene films.

Figure 14 Chemiluminescence oxidation runs at 120°C in oxygen for polypropylene powder samples of different molar mass. The numbers against each curve express the average molar mass in g/mol. 

Figure 15 Chemiluminescence oxidation runs for polypropylene powder at different temperatures the average molar mass of the polymer is 180 kg/mol. 

Figure 18 Chemiluminescence during oxidation of a non-stabilized polypropylene film and a stabilized film containing 0.1% (w/w) of the phenolic antioxidant Irganox 1010 at 140°C, in an oxygen atmosphere.

Table 4 The effect of antioxidants on induction time of oxidation of polypropylene determined at 150°C from chemiluminescence measurements...

Figure 19 Chemiluminescence from oxidation of polypropylene containing 0.5 % wt. of Irganox 1010 at 150°C in oxygen. Line 1 represents the original polymer film line 2 is the same sample after 7,890 s of annealing at 130°C.

L. Rychla and J. Rychly, New concepts in chemiluminescence at the evaluation of thermooxidative stability of polypropylene from isothermal and non-isothermal experiments. In A. Jimenez and G.E. Zaikov (Eds.), Polymer Analysis and Degradation, Nova Science Publishers, New York, 2000 p. 124. 

Abstract The oxidation of polymers such as polypropylene and polyethylene is accompanied by weak chemiluminescence. The development of sensitive photon counting systems has made it comparatively easy to measure faint light emissions and polymer chemiluminescence has become an important method to follow the initial stages in the oxidative degradation of polymers. Alternatively, chemiluminescence is used to determine the amount of hydroperoxides accumulated in a pre-oxidised polymer. Chemiluminescence has also been applied to study how irradiation or mechanical stress affects the rate of polymer oxidation. In recent years, imaging chemiluminescence has been established as a most valuable technique offering both spatial and temporal resolution of oxidation in polymers. This technique has disclosed that oxidation in polyolefins is non-uniformly distributed and proceeds by spreading. 

Keywords Chemiluminescence Imaging chemiluminescence Polyethylene Polypropylene Oxidation PP PE... 

Comparison of Chemiluminescence with Impact Strength for Monitoring Degradation of Irradiated Polypropylene... 

The loss of Impact strength of polypropylene was followed from sheets stored In air at 25°C and 60°C after irradiation with electron beams. A marked difference in efficacy of phenolic and thioether-based stabilizers at the two temperatures was found, with the thioether active alone at 60°C but only synergistically at 25°C. This difference was also reflected qualitatively in differences in chemiluminescence emission from the samples. 

In this study we measured chemiluminescence of polypropylene stabilized with different combinations of antioxidants and irradiated to different extents, and made correlations with conventional impact strength measurements of the same materials. 

Chemiluminescence has been used by a number of workers to characterize the thermal oxidation of polypropylene ( 1 2). This study allowed an opportunity to use fiber-optics for transmitting chemiluminescence from the heated sample to the detector, which promises to simplify greatly the apparatus required for the technique. 

Table II. Chemiluminescence (counts/2 min.) at ambient temperature from polypropylene irradiated at day 0 with a dose of 5MR.

Inhibitors reduce oxidative chemiluminescence by reducing the rate of light-producing peroxyl self-terminations (Scheme 1), by quenching electronically excited states (9) or simply by absorption of emitted light. The second factor may be much less important in polymers because of lowered rates diffusion (10). The rate of diffusion of 2,4-dihydroxybenzophenone in polypropylene has been... 

Figure 7. Top and Middle Loss of impact strength of polypropylene, irradiated to 5MR, vs. storage time at 25 and 60°C. Bottom Ambient chemiluminescence from irradiated (5MR) polypropylene samples vs. storage time at 25°C.

The above considerations bear on the ambient chemiluminescence from polypropylene, although at 150°C one would still expect that the fluorescence emission from singlet carbonyls would be relatively unaffected by quenching from stabilizers in our samples. One can also infer that physical quenching alone is not sufficient to explain the decrease in light from the polypropylene sample with both phenol and thioether (Table II, comb), since the initial reduction in intensity is more than can be accounted for by the combined effects of the additives separately. 

Chemiluminescence at ambient temperature and at 150°C of several irradiated (electron-beam) polypropylene formulations can be qualitatively correlated with loss of impact strength. The correlation with chemiluminescence is preserved at high vs. low temperatures, even though the ranking changes. 

The chemiluminescence curves of unstabi-and stabilized (B) polypropylene samples. 

Table I. The evaluation of polypropylene thermal oxidative stability by the chemiluminescence and oven aging methods at 150°C...

G.A. George and M. Ghaemy, The effect of stabilizers on integrated chemiluminescence in the early stages of polypropylene photo-oxidation, Polym. Degrad. Stab. 1991, 34, 37-53. 

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