Abnormal Tensile Creep Behavior of Annealed β-Nucleated Isotactic Polypropylene

Abstract

The microstructure changes of β-nucleated isotactic polypropylene (β-iPP) during the annealing process and the resultant macroscopic physical property responses were comparatively investigated. The results demonstrated that the annealing process not only increased the crystallinity of β-iPP samples but also enhanced the chain-segment mobility in the amorphous region. Interestingly, it was observed that the annealed β-iPP samples obtained at an appropriate annealing temperature exhibited accelerated creep deformation when the tensile creep measurement was carried out at relatively low environmental temperatures and/or small tensile stresses. However, at relatively higher measuring temperatures and/or larger tensile stresses, the role of the crystalline structure in influencing the creep deformation of β-iPP became dominant, and consequently, the creep resistance of β-iPP increased with increasing annealing temperature. Furthermore, it was demonstrated that the creep deformation of β-iPP is also highly dependent on the crystalline morphology.

Influence of different beta-nucleating agents on the morphology of isotactic polypropylene and their toughening effectiveness

“…A spherulitic structure has also been found in the literature for concentrations of 0.03e0.05 wt.% of beta Ref. [43] To the best of our knowledge, there are no studies about the exact kinetics of this self-assembly process of the additives used in this study. However, it is known that the formation of fibers depends on the cooling rate [14,23,41] and, that the structure formation of such self-assembly additives can be very slow and take up to several minutes, as shown by Libster et al for the sorbitol-based additive DMDBS [44].…”

Synergetic effects of a matrix crystalline structure and chain mobility on the low temperature toughness of polypropylene/ethylene–octene copolymer blends

“…11,23,[25][26][27][28][29][30] The amorphous chain mobility could be adjusted by annealing at elevated temperatures (lower than its melting point) aer the crystalline perfection and ner structure adjustment during annealing based on our recent results. [23][24][25]30,31 Not only will the interplay between crystalline structure and amorphous phase mobility be discussed, but also the toughness of the blends over a wide range of temperatures as well as their tensile properties will be investigated. This work will give a deeper understanding in the toughening mechanism at low temperatures, and meanwhile provide guidance for producing PP with stiffness-toughness balance.…”

Microstructural Evolution of Isotactic‐Polypropylene during Creep: An In Situ Study by Synchrotron Small‐Angle X‐Ray Scattering

“…According to a survey by Ceresana, the global market for PP was about 55 million tons in 2013 . Considering its ever‐increasing range of applications in our daily life and in the engineering field, it is of great significance to evaluate the microstructure response under mechanical load . Unlike to uniaxial drawing, compression, and impact tests, a creep test serves as an effective method for the long‐term life time assessment of polymer materials.…”

“…Sliding of tie chains and their detachment from lamellar blocks play a key role in the time‐dependent response of i PP . The mobility of chain segment in the amorphous phase influences the creep deformation of β‐ i PP . The increase of crystallinity, the presence of subsidiary lamellae in the amorphous region, and the integration of preexisting lamellar structure would enhance the creep resistance of i PP .…”