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In this study, various effects on the properties of the material, such as free-radical (FR) processes, oxygen induction time (OIT), melting temperature and melting heat are examined during several stages of the polyethylene (PE) pipe extrusion process. The spectra in the Electron Spin Resonance (ESR) are researched between 77–293 K and in a wide range of magnetic fields. At 77 K a triplet signal in ESR is observed. The parameters of the signal are ΔH m1  ≅ 1:4 – 1:6 mT; ΔH m2  ≅ 1 – 1:2 mT; ΔH m3  ≅ 0:6 – 0:8 mT and g 1  ≅ 2:020; g 2  ≅ 2:011; g 3  ≅ 1:99 and Hyper Fine Structure constant ΔH 12  ≅ 2:1 mT; ΔH 23  ≅ 5:3 mT. As the temperature increase from 77 K up to 293 K, the signal for g 4  ≅ 2:02 (ΔH m 4 ≅ 0:7 – 0:8 mT) appears and intensity of signals increase. It is also thought that the triplet observed at 77 K belongs to macroradicals of alkyl (–CH 2 –CH–CH 2 ), alyl(~CH 2  C HCH = CHCH 2 ~), carboanions and the acyl (H C O) radicals of the fourth signal. At room temperature, all the FR's transform into peroxide radicals. The total concentration of the FR's is minimum at 463 K and increases at the outlet of the extruder and the pipe sample.

Free-radical Reactions and Thermal Effects in PE during Pipe Extrusion