Morphological Evidence for the Two-Step II–I Phase Transition of Isotactic Polybutene-1

The Shear-Accelerated II-I Phase Transition of Isotactic Poly(1-Butene)

The II-I phase transition of isotactic poly(1-butene) (iPBu) leads to improved mechanical performance. However, this will take several weeks and increase storage and processing costs. In this work, shear forces are introduced into the supercooled iPBu melt, and the effects of isothermal crystallization temperature (Tc) and shear temperature (Tshear) on crystallization and phase transition are explored. Shear-induced transcrystalline morphology of Form II with a significantly shortened crystallization induction period can be observed at relatively high Tc (105 °C). Besides, the shear-induced Form II can transit to Form I faster than the unsheared one. In addition, the phase transition rate increases as the Tshear decreases, with the fastest rate occurring at Tshear of 120 °C. The half transition time (t1/2) is measured as 6.3 h when Tc = 105 °C, Tshear = 120 °C, which is much shorter than the 20.7 h required for unsheared samples. The accelerated phase transition of iPBu can be attributed to the stretching of molecular chains, resulting from shear treatment. This study provides a quantitative analysis of the influence of the shear treatment and the Tshear on the II-I phase transition rate. It also presents a cost-effective and straightforward approach for expediting the phase transition process.

Investigation of the synergistic effect of melt-extension and nanofiller on the crystal-crystal phase transition from form II to I of isotactic polybutene-1

New questions and conjectures are raised on the crystal-crystal phase transition of isotactic polybutene-1 (iPB-1) containing nanofiller in the flow field. In this work, we investigate the phase transition from flow-induced oriented form II to I in iPB-1 blends with multi-walled carbon nanotubes (MWCNTs) with a homemade two-drum extensional rheometer combined with in situ wide-angle X-ray diffraction (WAXD) measurements. The MWCNTs show a limited promoting effect on the phase transition kinetics under quiescent conditions, while the phase transition kinetic is highly accelerated with the impose of melt-extension. When the loading extension strain is 0.5 or 2.0, the half time of phase transition (t_1/2) is shortened from tens of hours to a few hours, depending on the melt-extension strain and the MWCNTs content in iPB-1. When the extension strain increases to 3.5, t_1/2 decreases to about 30 min, which is independent of the MWCNTs content in all iPB-1 blends except in blends with MWCNTs content of 1%, where the phase transition rate in the middle and late stages is restrained. It's speculated that flow-induced molecular orientation or shish-kebab morphology affects the internal stress or stress transfer. The addition of a nanofiller enlarged the effect of melt-extension through strengthening the localized intensity of flow field. In general, the combination of nanofiller and melt-extension can obviously promote the phase transition kinetics.

Crystal structures, crystallization and II-I transition behaviors of iPB-1 in iPB-1/UHMWPE blends - Part 1. Crystal structures and crystallization behaviors

Isotactic polybutene-1 (iPB-1) is of particular commercial interest due to its excellent mechanical performances. The form I polymorph is preferred in most industrial applications, while the form II is kinetically...

Concepts of Nucleation in Polymer Crystallization

Nucleation plays a vital role in polymer crystallization, in which chain connectivity and thus the multiple length and time scales make crystal nucleation of polymer chains an interesting but complex subject. Though the topic has been intensively studied in the past decades, there are still many open questions to answer. The final properties of semicrystalline polymer materials are affected by all of the following: the starting melt, paths of nucleation, organization of lamellar crystals and evolution of the final crystalline structures. In this viewpoint, we attempt to discuss some of the remaining open questions and corresponding concepts: non-equilibrated polymers, self-induced nucleation, microscopic kinetics of different processes, metastability of polymer lamellar crystals, hierarchical order and cooperativity involved in nucleation, etc. Addressing these open questions through a combination of novel concepts, new theories and advanced approaches provides a deeper understanding of the multifaceted process of crystal nucleation of polymers.

A new perspective to enhance the II–I transition of polybutene-1

The bottleneck for the application and potential utilization of polybutenene-1 (PB-1) with excellent physical and mechanical properties is its inevitable phase transition.