Effect of annealing on fracture behavior of poly(propylene‐block‐ethylene) using essential work of fracture analysis

Abstract

The influence of annealing conditions on the fracture behavior of poly(propylene-block-ethylene) sheets was investigated by means of the essential work of fracture method, and was complemented by the study of the effect of annealing on crystal structure, using differential scanning calorimetry. It was shown that both the crystal perfection degree and crystallinity could be improved substantially as annealing temperature (Ta) increased, while the prolonged annealing time at 808C mainly resulted in the improvement of crystallinity. The reasons for an increase in the specific essential work of fracture and a decrease in the specific plastic work item as crystal perfection degree and crystallinity grew are discussed. The displacement to failure of double edge notched tension specimens decreased gradually with increasing T a , and the double-plastic zone could be observed in all specimens. In addition, a novel method to aid the accurate measurement of intense stress-whitening outer plastic zone height by adjustment of illumination conditions is proposed.

Abnormal Tensile Creep Behavior of Annealed β-Nucleated Isotactic Polypropylene

“…On the other hand, the stress-drop phenomenon became inconspicuous when the sample was annealed at relatively high temperature (130 °C). This indicates that the structural discrepancy was weakened, and the microstructure in the annealed sample became more homogeneous, so that stress transfer in the sample became easier during the tensile process . Obviously, the formation of new lamellae in the amorphous region and the increase in crystallinity of the material mainly contribute to the decreased structural discrepancy.…”

“…This indicates that the structural discrepancy was weakened, and the microstructure in the annealed sample became more homogeneous, so that stress transfer in the sample became easier during the tensile process. 48 Obviously, the formation of new lamellae in the amorphous region and the increase in crystallinity of the …”

Influence of Annealing on Microstructure and Mechanical Properties of Isotactic Polypropylene with β-Phase Nucleating Agent

“…The similar results have been reported by others, and the reason is partly ascribed to the improvement of crystal perfection degree without the excessive reduction of the tie molecules number. 52,53 However, for nucleated iPP, one can observe a typical brittle-ductile-brittle (B-D-B) transition in impact strength with the increase of T a . At relatively low T a (<110 °C), the impact strength enhances slightly.…”

Effect of annealing on the microstructure and mechanical properties of polypropylene with oriented shish‐kebab structure

“…Due to their importance in polymer processing, the formation mechanism 1–3 and threshold flow conditions required for the onset 4–8 of an oriented shish‐kebab structure has drawn considerable interest over the past decades. In contrast, little attention has been paid to the annealing of flow‐oriented polymers,31–36 although annealing below the melting temperature is thought to be effective in inducing chain rearrangement in semicrystalline polymers and then improving their physical properties 37–43. Moreover, to our best knowledge, up to now most studies have been limited to thin films and fibres,31, 32, 34–36 and no effort has been made on the injection‐moulded parts probably because it is difficult to obtain highly oriented structures percolating through the moulded parts.…”