Plastic Deformation of High Density Polyethylene with Extended-Chain Crystal Morphology

Abstract

Samples of polyethylene with extended-chain crystal morphology, obtained by crystallization under high pressure, were subjected to uniaxial compression to various strains. Accompanying structural changes were analyzed using scanning electron microscopy. At the true strain of e = 0.2–0.3 the microbuckling instability was observed in longitudinally loaded lamellae, resulting in the formation of angular kinks. This induced a rapid reorientation of the lamellae, facilitating their further deformation by crystallographic slip. Microbuckling instability was found to occur earlier than in samples with folded-chain crystal morphology (e = 0.3–0.4) due to a smaller ratio of the amorphous to crystalline layer thickness. SEM observations demonstrated that the microbuckling instability begins with small undulation in long lamellae. Sharp angular lamellar kinks develop from the initial undulation through intense plastic deformation by crystallographic slip along the chain direction. The same slip system was found to operate throughout the kink, including the tip region as well as both limbs. In contrast to thin folded-chain lamellae that often undergo fragmentation during deformation, the thick extended-chain lamellae deform stably by chain slip and retain their continuity up to high strains, e > 1.6. This stability of deformation is related to the large thickness of extended-chain lamellae.

Deformation Instabilities and Cavitation in Plastic Deformation of Semicrystalline Polyethylene

“…The dashed-line arrows connect the characteristic points of the nominal stress−extension curves (Figure 2a) with corresponding points in the true stress−true strain curves (Figure 2b). Additionally, the true stress−true strain curve determined for the same neat HDPE material deformed in uniaxial compression 27 is presented for comparison. The tensile true stress−true strain curves appear very similar in shape to that obtained for the same neat polymer in uniaxial compression, which suggests that the same deformation mechanisms had to be active in both deformation modes, in similar sequence.…”

“…24−26 Once the kink is formed, the angle at its tip tightens and the lamellae forming the kink arms gradually tilt in the direction of drawing, likely due to intense chain slip mechanism activated in the lamellae just reoriented in the kink. 27 At local true strains e H(load) ≥ 0.9, the effect of another deformation instability can be recognized in the form of extensive fragmentation of the lamellae due to slip localization (cf., green-highlighted areas in the micrographs for e H(load) ≥ 1.07). The intensity of such fragmentation increases significantly with increasing strain and ultimately leads to the complete destruction of the original lamellar morphology, which is replaced with a microfibrillar structure, at strains above e H(load) ≈ 1.3.…”

Effect of zinc oxide surface treatment concentration and nanofiller loading on the flexural properties of unsaturated polyester/kenaf nanocomposites

“…If the interfacial bonding is weak, the nanoparticles can experience relative motion within the matrix under applied stress. Furthermore, Polymers typically exhibit a certain degree of chain mobility, allowing them to undergo plastic deformation [ 55 ]. When stress is applied to the composite material, the polymer chains can rearrange and flow around the nanoparticles, facilitating their movement within the matrix [ 56 ].…”

Bio-high density polyethylene films embedded with organoclay and zinc pyrithione

“…The essential parameters for studying thermal properties were Tm and Xc. BHDPE had a Tm around 130°C [25,44,45] . Compositions with clay reduced of approximately 5°C for PC3 and 18°C for PC6 relative to BHDPE.…”

“…Generally, the predominance of ductile behavior can be observed where the material presents elastic behavior at low deformations. After a specific stress, the film plastically deforms up to the rupture stress [45] . The BHDPE films obtained a tensile strength of 58.8 ± 7.6 MPa, while the PC3 and PC6 films showed a reduction of 34.3% and an increase of 41.5%, respectively.…”