Effect of radiation on the crystals of polyethylene and paraffins: 2. Phase separation in γ-irradiated paraffins

Paraffins are observed to respond to γ radiation in a manner which is distinctly different from the behaviour of polyethylene. Namely, the lattice spacings and crystal perfection are virtually unaffected, the destruction of crystallinity becoming manifest through the reduction of the amount of crystalline material and the concurrent increase in the amount of amorphous material (‘paraffin-like’ behaviour) as opposed to the changes in the crystal lattice and concomitant deterioration of lattice order in polyethylene (‘polyethylene-type’ behaviour, Part 1). By application of calorimetry, X-ray diffraction and g.p.c. it is seen that the cause underlying the ‘paraffin-like’ behaviour is a phase segregation between the crosslinked and the still unaffected chains into a liquid-like and an undamaged crystal phase, respectively. There is a thermodynamic equilibrium between these two phases with a limited mutual solubility. The temperature dependence of the latter accounts satisfactorily for the observed melting behaviour (‘heterophase’ melting) of the irradiated product.