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.
Highlights
In the last decade, isotactic polypropylene (PP) has attracted common attention owing to its favourable price/performance ratio and many possible modifications
This paper focuses on the crystalline modification of a rare earth nucleating agent for PP, the selfassembly behaviour, as well as the relationship between the topological structure of the nucleating agent and the crystalline structure
The experimental results showed that the self-assembly structure changed from a needle-like structure to dendritic structure with increase in the content of WBG
Summary
Isotactic polypropylene (PP) has attracted common attention owing to its favourable price/performance ratio and many possible modifications. PP crystallizes into an α-crystal, which has low toughness, while the β-phase shows excellent toughness as well as thermal performance [3,4,5]. The formation of a β-crystal needs special conditions: temperature gradient [6], quenching [1], shearing [7,8,9] and adding β-nucleating agents [10,11,12] Among these methods, adding β-nucleating agents is considered to be the most efficient one
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