Behavior of Individual Polymers under Ionizing Radiation

In the early 1950s, polyethylene was the first plastic material used for radiation curing. Today, approx. 150 Mio. meters of polyethylene pipe are radiation cured for under floor heating and drinking water lines. The pipes exhibit higher heat distortion temperatures with simultaneous improvement in their characteristic creep data under compression and considerably higher resistance to stress cracking [716]. 

Radiation-induced crosslinking in polyethylene affects mainly the amorphous, interlamellar regions and leads to hardening and embrittlement [89]. 

Formation of carbonyl groups (detected by FTIR) on the surface of PE-FtD films following electron irradiation in a vacuum and subsequent storage in air [599] 

Eigure 5.128 shows that strain at break and ultimate tensile strength behave entirely differently when polyethylene is irradiated. Eor strain at break the halfvalue dose is determined as 0.4 MGy. For ultimate tensile strength, no half-value dose can be determined. 

The ultimate tensile strength of polyethylene first increases under irradiation in a vacuum at low doses, reaches a peak at approx. 400 kGy, decreases with medium doses (600 to 6000 kGy), and increases again following a minimum at approx. 6000 kGy. This is explained as the result of changes in crosslinking and crystallinity caused by irradiation as well as crystallization processes during the tensile test [711]. 

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Behavior of Individual Polymers under Ionizing Radiation. 557... 

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