Deformation and entanglement in semicrystalline polymers

Abstract

Transmission electron microscopy and optical studies of thin films of isotactic polystyrene (iPS) and polyoxymethylene (POM) provide evidence for a distinction between crazing mechanisms in semicrystalline polymers above and below Tg. In the latter temperature regime, deformation in iPS and POM crystallized at high supercooling has been discussed in terms of existing models for crazing in amorphous glassy polymers, based on entanglement ideas. Above Tg, where the difference in mechanical behavior of the amorphous and crystalline regions becomes marked, the fibrillar nature of local deformation appears to be a consequence of the inhomogeneity of the undeformed polymer.

Fatigue and Fracture in Polyacetal Resins

“…It has been observed previously [17,18], that cavitation in POM is similar to the dilatational yielding behaviour observed for many toughened polymers and recently quantitatively accounted for [19,20]. It has been observed previously [17,18], that cavitation in POM is similar to the dilatational yielding behaviour observed for many toughened polymers and recently quantitatively accounted for [19,20].…”

“…It is known that POM is a mixture of a rigid (crystalline) matrix and a rubber (amorphous) phase [15][16][17]. As in rubber toughened polymers, yielding at room temperature in bulk POM is accompanied by extensive cavitation and stress whitening [15][16][17].…”

The chemistry, manufacture and tensile behaviour of polyester fibers

“…Owing to a rise in yield stress, the localization of deformation increases. Moreover, similar to amorphous polymers, the entanglement density plays an important role in the failure behavior of semicrystalline polymers, which was already suggested by Bastiaansen et al [273] and Plummer and Kausch [274]. The entanglement density affects the strain hardening behavior of the polymers, which affects the amount of stabilizing of deformation in strain localization zones.…”

The structural evolution of high-density polyethylene during crazing in liquid medium

“…Deformation of semicrystalline polymers may also be accompanied by the development of crazes analogous to crazes in amorphous glassy polymers [75][76][77]. The growth of crazes and the development of deformation by the mechanism of crazing rather than shear depend primarily on the density of the effective entanglement network and the surface energy of a polymer irrespective of whether the polymer is amorphous or semicrystalline [78].…”

“…When a semicrystalline polymer is stretched at a temperature above the glass-transition temperature of its amorphous phase, the deformation may also lead to the nucleation of cavitations in the interlamellar region [6,7], and their subsequent development may be accompanied by the development of crazes characterized by a typical fibrillar-porous structure [75][76][77]. This type of crazing may be referred to as ''intercrystallite'' or ''interlamellar'' crazing.…”