Structural characterization of electron-beam crosslinked thermoplastic elastomeric films from blends of polyethylene and ethylene-vinyl acetate copolymers

Films were prepared from a blend of low-density polyethylene (LDPE) and ethylene-vinyl acetate (EVA) containing 45% VA and ditrimethylol propane tetraacrylate (DTMPTA). Electron-beam initiated crosslinking of these films was carried out over a range of radiation doses (20-500 kGy), concentrations of DTMPTA (1-5 parts by weigth), and blend compositions. The IR studies revealed that oxidation and crosslinking dominated up to an irradiation dose of 100 kGy. At higher irradiation doses chain scission and disproportionation predominated among all the competitive processes for the 50:50 blend without DTMPTA. The gel ii-action of the films increased with the increase in irradiation dose, DTMPTA level, and EVA content of the blends. X-ray diffraction and differential scanning calorimetry studies showed that the crystalline portion of the blends was only affected by radiation at higher irradiation doses (greater than or equal to 200 kGy). Scanning electron microscopy studies indicated that in the 50:50 blend the LDPE formed the continuous phase, which was further confirmed by atomic force microscopy and transmission electron microscopy studies. However, a co-continuous morphology was formed when the EVA content was increased. When DTMPTA was added to the blends (greater than or equal to3 wt %), the 50:50 blend exhibited a co-continuous morphology. (C) 2001 John Wiley & Sons, Inc.