The effect of crystallization conditions on the radiation-induced crosslinking in polyethylene

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Abstract
Polyethylene irradiated by doses below the gelation level, hence where the sample is still fully soluble by our tests, has been examined as regards viscosity, light scattering and recrystallization behaviour. In the course of this the molecular dispersion of the material previously designated as soluble was verified. The intrinsic viscosities pass through a minimum followed by a maximum with increasing dose while light scattering indicates steadily increasing molecular weight, this increase being in the expected relation to the appropriate gel points. On irradiation the molecular weight distribution widens and the molecules become more compact, increasingly so with the larger molecules. It is concluded (in conjunction with results in Parts I-IV) that there can be only very little if any crosslinking between molecules in a given layer and that the crosslinks which lead to an increase of the molecular weight even below the gel point must be those which link the different layers together. Most of the ineffective links should be in the fold and some could be multiple ones between molecules in consecutive layers. Accordingly crosslinking must be highly selective and the type of selectivity inferred here demands regularity at the fold surface.