Polyethylene sample, radical formation

Figure 3 shows the dose-yield relationship for the formation of the alkyl radical at 77 K, together with the ESR spectrum in the insert, we observed for polyethylene sample of Mv = 2.3 x 104 and density = 0.963 (CX-36F from the Showa Denko Co.). The slope of the initial linear portion gives the G value of 3.3 in accordance with the values reported previously [21, 24], Above 30 kGy, the slope of the dose-yield curve gradually declines probably because of the overlapping of spurs. 

Anotner organic ferric compotuid,namely the ferric acetyl acetonate (PemAcAo) has been found to be an effective initiator for the photodegradation of polyethylene (65) and poly(vinyl chloride)(66). These ferric compounds are easily oxidized and photolyz eT. The following mechanism for radical formation in polyethylene sample was proposed (67,68)1... 

The ends of the microfibrils create about Itf m point vacancies in the microfibrillar superlattice (Fig. 11). Under applied tensile load they may fail first, eventually by microcrack formation so that the adjacent microfibrils have to carry a heavier load than the rest of the sample. Hence they are first candidates for rupture detectable by the rascals formed at the rupture of tie molecules in at least one amorphous layer of the microfibril affected. Depending on the ratio of axial strength to lateral adhesion of the microfibrils the microcracks will grow parallel (high ratio) or perpendicular (low ratio) to the fibre axis yielding a large number of broken, chains and radicals in the former and a small one in the latter case. Nylon is an example of the former and linear polyethylene of the latter type. 

---