Irradiated polypropylene impact strengths

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. 

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.

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 thioether ester (DLTDP) shows a very strong synergistic effect with the phenolic stabilizer at room temperature, and is active alone at 60°C for protection from loss of impact strength of the irradiated polypropylene. 

In general, the tensile strength was found to be improved with perlite addition at higher radiation doses, especially for 15% and 30% perlite compositions. The ultimate elongation also decreased with addition of perlite and the radiation dose, but not as fast as observed in nnfllled polypropylene, especially when 50% perlite composites are considered. The impact strength, as can be expected, decreased with perlite addition for nonirradiated polypropylene composites, but it was found that gamma irradiation for both unfilled polypropylene and filled polypropylene did not much alter the impact strength. 

---