Studies on irradiated polypropylene, its copolymers and blends .1. ESR studies

The following polymer materials: (i) isotactic polypropylene, (ii) low-density polyethylene, (iii) blends of polypropylene and polyethylene with various content of polyethylene, and (iv) natural copolymers of polypropylene with the same amount of ethylene as in blends, were irradiated and subsequently investigated using electron spin resonance (ESR) technique. Polymer samples have been irradiated by applying high-energy electrons from 13 MeV linear electron accelerator (LAE 13/9) over the dose range 10-50 kGy. For controlling radiation degradation of polymers (i), radiation sterilization of medical equipment (ii), and evaluation of radiation resistance of the investigated materials (iii), the following dose ranges have been applied: 10-25 kGy, 20-35 kGy, and similar to 50 kGy, respectively. The nature and the yield of primary radicals has been analyzed as a function of the absorbed dose for different polymer types by means of ESR using a Bruker ESP-300 spectrometer. The yield of peroxy radicals for various polymers and for their different composition has been also evaluated. Basing on the ESR results the mechanism of radiation-induced copolymerization of polymers in solid state has been proposed.