Cavitation during tensile drawing of annealed high density polyethylene

Abstract

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

Structural mechanics of semicrystalline polymers prior to the yield point: a review

“…Otherwise, fragmentation of crystal lamellae is preferred. This outcome is compatible with the independent observations of Pawlak and Galeski [15]. In their former work [11], it was found that cavities are formed readily in HDPE, i-PP, and POM while they do not occur in lowdensity polyethylene (LDPE), PA6, and ethylene-octene copolymer.…”

“…Along with the well-established data, new findings regarding structural defects occurring at small strains as well as their role in the global deformation behavior of semicrystalline polymers will be highlighted. At low strain level, stretching favors the occurrence of different structural defects such as nanocavities in the interlamellar amorphous layers [8][9][10][11][12][13][14][15][16][17][18][19] and damages of crystalline lamellae [20][21][22]. These imperfections could lead either to softening or modification of the plastic deformation mechanisms of semicrystalline polymers.…”

Macroscopically homogeneous deformation in injection molded polypropylene induced by annealing studied with microbeam X-ray scattering

“…14. In the case of PP-N ( Fig. 14 (a)), the SAXS profiles showed a monotonic-like decrease without a distinct peak at each layer, which is usually observed in the void formation in semi-crystalline polymers [29,30,49]. This result indicates that inhomogeneous voids with a broad size distribution were formed in PP-N.…”

“…Annealing also changes the cavitation behavior, which is closely related to the deformation mechanism [27e29]. For example, Pawlak and Galeski investigated the effect of annealing on the cavitation behavior of various high-density polyethylene samples with a spherulite structure [30]. They reported that the annealing induced a massive cavitation, giving rise to a decrease in the localization of the plastic deformation after the yielding.…”

Cavitation Behavior of Semi-Crystalline Polymers during Uniaxial Stretching Studied by Synchrotron Small-Angle X-Ray Scattering

“…Cavitation behavior has been found in many semi-crystalline polymers, including isotacticpolypropylene (iPP) [1,2], polyethylene (PE) [3,4], poly(1-butene) (P1B) [5], and so on, when these polymers are stretched above their glass transition temperature. Stress whitening can be regarded as the scattering of visible light by voids detected by naked eye.…”