Investigation of uniaxially drawn polyethlene by positron annihilation

Positron annihilation lifetime spectra are measured in uniaxially drawn polyethylene (PE) at room temperature as function of deformation ϵ from 0 to 190%. The positron annihilation parameters are very sensitive to the microstructural changes of PE during the drawing process. In the elastic stage (ϵ = 0 to 20%), the amount and size of voids in amorphous regions and the size of defects in crystalline regions increase drastically with increasing deformation and reach a maximum at the yield point. In the strain softening stage (ϵ = to 40%), the fractional free volume f is nearly constant. When ϵ < 40%, i.e. in the plastic stage, the fractional free volume f continuously decreases, which shows that the degree of crystallinity increases owing to the orientation of chains and strain-induced crystallization. continuously decreases, which shows that the degree of crystallinity increases owing to the orientation of chains and strain-induced crystallization.