Thermal properties of ion beam irradiated engineering thermoplastics

Abstract

Thermal properties and recrystallization ability of commercial grade poly(para-phenylene sulphide) (PPS) and poly(ethylene terephthalate) (PET) thin foils, bombarded with 380 keV He+ ions, were studied by Differential Scanning Calorimetry (DSC) and X-ray Diffractometry (XRD). The following phenomena are observed on bombarded targets: a) decrease of the enthalpy of fusion (ΔHf ) and recrystallization (ΔHrc ) and b) decrease of the onset of the melting and recrystallization temperature. This behaviour indicates amorphisation of crystalline phases, increase of imperfections in the remaining crystallites, and loss of the recrystallization ability of the amorphous zones upon repeated thermal cycles. The amorphisation fluence, for which no crystalline regions were detected by DSC and XRD, is 2 × 1014 He+ / cm2 for PPS and 1014 He+ / cm2 for PET. However, the irradiated targets lose their ability to recrystallize at much lower fluences, around 4 × 1013 He+/cm2 for PPS and 2 × 1013 He+/cm2 for PET. The loss of crystallization ability is attributed to the presence of reactive defects on the bombarded targets which may generate crosslinks (and chain scissions) during the heating stage of the DSC run.