Crystalline modification of a rare earth nucleating agent for isotactic polypropylene based on its self-assembly

Abstract

In this paper, the crystalline modification of a rare earth nucleating agent (WBG) for isotactic polypropylene (PP) based on its supramolecular self-assembly was investigated by differential scanning calorimetry, wide-angle X-ray diffraction and polarized optical microscopy. In addition, the relationship between the self-assembly structure of the nucleating agent and the crystalline structure, as well as the possible reason for the self-assembly behaviour, was further studied. The structure evolution of WBG showed that the self-assembly structure changed from a needle-like structure to a dendritic structure with increase in the content of WBG. When the content of WBG exceeded a critical value (0.4 wt%), it self-assembled into a strip structure. This revealed that the structure evolution of WBG contributed to the Kβ and the crystallization morphology of PP with different content of WBG. In addition, further studies implied that the behaviour of self-assembly was a liquid–solid transformation of WBG, followed by a liquid–liquid phase separation of molten isotactic PP and WBG. The formation of the self-assembly structure was based on the free molecules by hydrogen bond dissociation while being heated, followed by aggregation into another structure by hydrogen bond association while being cooled. Furthermore, self-assembly behaviour depends largely on the interaction between WBG themselves.

β-Nucleation of isotactic polypropylene: Chain structure effects on the effectiveness of two different nucleating agents

“…The 0.01 wt% of CGNA-7588 based on experience was found to be satisfactory. Despite the fact that with 0.21 wt% a concentration of WBG was chosen, which was assumed to be 'safe' and clearly in the saturation range in terms of β-phase formation according to literature [12,14], the higher sensitivity towards chain regularity of iPP as well as the more limited impact strength increase (see Figure 5) are evident. The results from compositions based on SSC-PPH and ZNC-RACO indicate some β/α-duality of WBG, actually resulting in an increase of γ-phase content and a rather low impact strength.…”

“…This paper of Liu et al is just one of the most recent examples in a long row of publications on the application of WBG. Several working groups evaluated the performance of this β-nucleating agent alone [7][8][9][10][11][12][13], varying dispersion mode, cooling history, and base polymer type. Comparisons to α-nucleation [14][15][16][17][18] or other types of β-nucleating agents were done as well.…”

Lightweight and High Impact Polypropylene Foam Fabricated via Ultra‐Low Gas Pressure Injection Molding

“…This phenomenon could be ascribed to the added 𝛽-nucleating agent, which contributed more heterogenous nucleation sites, both the nucleating agent itself and the small crystals formed due to its promotion of crystallization can play a role of heterogenous nucleating sites in the foaming process. [33,34] Compared with homogeneous nucleation, the energy barrier of heterogenous nucleation is lower thus the heterogenous nucleation plays a dominant role in cell nucleation. [26] Especially for our current work, the low gas pressure FIM, the pressure of the N 2 we used was only 6.5 MPa.…”

Effect of rare earth nucleating agent on supercritical CO2 foaming behavior of block copolymerized polypropylene

“…Rare earth compounds have been known as stabilizers in polymers, but they are still a new research field in the modification of polyolefins. 45,46 As a new and high efficient β-nucleating agent, rare earth is safe, non-toxic, and non-radioactive.…”