Cavitation during tensile drawing of annealed high density polyethylene

Annealing of semicrystalline polymers usually leads to refinement and thickening of crystals. It appears that also cavitation is affected during tensile drawing. In the uniaxially drawn high density polyethylene massive cavitation was detected by X-ray scattering in the samples previously annealed at 125 °C. The number of voids depends on the annealing time, while their size and orientation depends on the local strain. Cavitation resulted in 30% increase in volume for the annealed samples, strained to 4-5. Cavitation and volume increase were not observed for small and intermediate strains if polyethylene samples were not annealed. The decrease in the drawing rate results in the reduction of cavitation and void stability - at the low strain rate voids were detected during tensile drawing, though they disappeared after unloading the sample.