Role of tie molecules in the yielding deformation of isotactic polypropylene

Abstract

We examined the effects of the tie‐molecule fraction on the yielding behavior of two isotactic polypropylenes, one having little ethylene content and the other as the homopolymer with no ethylene. The tie‐molecule fraction of the samples used in this study was controlled by blending ethylene‐α‐olefin of an α‐olefin content above 50 mol % in the blend of which the copolymers were incorporated into the amorphous regions of polypropylene (PP). An excellent linear relationship was observed between the measured yield stress and the tie‐molecule fraction estimated from the Huang–Brown model, suggesting that the tie‐molecule fraction and lamellar stiffness determine whether the lamellar fragmentation is easily activated or not, depending on the PP composition. Furthermore, an extended Huang–Brown model predicts a lamellar cluster connecting about five lamellae, which has a potential to account for morphological transformation of the spherulitic structure into a fibrillar one. Comparing the immiscible blends showing a phase‐separated morphology with the partially miscible blends mentioned above, the yield stress was lowered by the presence of rubber phase, apparently in a similar manner; but the yielding processes were clearly discriminated between both cases when the yield stress was plotted against the tie‐molecule fraction. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 357–368, 1999

The effect of annealing on the elastoplastic response of isotactic polypropylene

“…The strains ε and e * that characterize transitions to steady plastic flows at active loading and unloading, respectively, are rather close to each other and are weakly affected by thermal treatment. This result confirms the hypothesis [4,34] that elastoplastic deformation of a semicrystalline polymer in a sub-yield region is mainly associated with transformations in the amorphous phase.…”

Raman Spectroscopic Analyses of Structure–Mechanical Properties Relationship of Crystalline Polyolefin Materials

“…According to their results, the fraction of consecutive trans sequences increased markedly in the elastic region; this was followed by a plateau region beyond the yield point, which was similar to the strain dependence on molecular orientation. These results are in good agreement with the typical deformation model that the tie chains connecting the adjacent lamellar crystalline layers are elongated into the stretching direction in the elastic region 81,82) .…”

Modeling the Large Deformation of Spark Plasma Sintered Polytetrafluoroethylene Under Uniaxial Tension by Phenomenological Approaches

“…The opposite trend shown in our study agrees with the work reported by Jordan et al [10] and references therein on PTFE and other semicrystalline polymers. This behavior is consistent with the well-established understanding that the mechanical response of semicrystalline polymers is not governed solely by crystallinity, but strongly depends on other microstructural features including the degree of perfection and orientation of the crystallites [61], formation of fibrous structure under large deformation [7,62], density and morphology of inter-crystalline connections [63] density of chain entanglements, presence of tie molecules [17,64,65] and the magnitude of the sample to highlight the so-called SIC phenomenon under deformation. This complex scheme is challenging and needs a precise characterization of all effects as a whole across multiple scales.…”