AGING EFFECTS OF POLYPROPYLENE USED IN HEATING-SYSTEMS

The aging effects of polypropylene targets used in heating systems wer e investigated using the nuclear reaction analysis (NRA) technique. De uterium beams of energies 900, 1200 and 1500 keV, supplied from the Un iversity of Jordan Van de Graaff accelerator, were employed. Different working times between 1 and 6 years were investigated in addition to a new fresh sample which was considered as standard. The reactions res ulting from C-12(d,p)C-13, O-16(d,p1)O-17 and N-14(d,alpha1)C-12 were monitored. The oxygen and nitrogen concentrations data reveal similar behavior for both elements. The initial concentration of both quantiti es resulting from fusion, processing and storage times decreases and t hen gradually increases to reach higher levels than those initially, a s the working time is increased. A model, based on mass transfer of ai r-oxygen and nitrogen and solubility of polypropylene to both elements , was proposed to explain our observation. The uptake of these light i mpurities and their presence at high concentration levels in the therm opipes material, in addition to microstructural effects, are responsib le for the degradation of many of its observed properties. The main ef fect was demonstrated by the influence of several parameters on streng th and embrittlement.