Chemiluminescence-HDPE

FIGURE 3.1 Chemiluminescence spectra under nitrogen of HDPE, LLDPE, and mPE polymers at 170°C. 

Fig. 22 Comparative results for thermal degradation of some polyolefins by (a) chemiluminescence measurements and (b) oxygen uptake. Testing temperature 140 °C. The data were taken from [9001]. (1) HDPE, (2) P4MP, (3) PP, (4) PB.

Camacho and Karlsson [35] investigated the thermal and thermo-oxidative stability of recycled PP, HDPE and a 20 80 PP/HDPE blend. These samples were subject to extrusion cycles. The oxidation induction time of all three samples decreased with the number of extrusion cycles, as did the temperature of oxidation. Chemiluminescence runs showed two peaks one sharp peak (corresponding to PP) and the other bimodal in shape (corresponding to PE). 

Figure 2.8 shows the chemiluminescence curves of PP, HDPE and their blend after the first extrusion step. The PP exhibits a sharp peak at the maximum on chemiluminescence intensity, whereas the HDPE curve shows a broad bimodal behaviour [36]. In the chemiluminescence curves of the blend, all these features were observed. This may be a strong indication of the existence of a two-phase system in the molten state, which was also pointed out by Braun and co-workers [37], although this was based on peroxide treatment of PP/PE blend melts. It appears that PP oxidises first and the oxidation sites created during this process accelerate, to some extent, the oxidation of PE phase. The overlap between the PP and PE traces in the blend can be interpreted as the interface of these two phases where the PE starts oxidising. In addition, the shape of the curves confirms that the oxidation mechanisms of these resins are different, and that this difference remains during the oxidation of the hlend in the molten state. 

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