Morphological Characteristics of β-Nucleating Agents Governing the Formation of the Crystalline Structure of Isotactic Polypropylene

An efficient β-nucleating agent with high lattice matching rate for plate-like crystallization of polypropylene random copolymer

It is challenging to naturally produce large amounts of β-crystals by directly adding a commercial β-nucleating agent (β-NA) into polypropylene random copolymer (PPR) at present. In this work, a novel rare earth β-NA WBN-28 was directly introduced into PPR to prepare β-PPR with high β-crystal conversion. The results of differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) indicated that it is an efficient β-NA for PPR. The β-conversion rate (β-CR) could surpass 85% when the nucleating agent content was mere 0.05%. With the further increment of nucleating agent, the β-CR increased gradually, which could reach 89.5% and 86.9% respectively calculated by DSC and WAXD when the addition amount was 0.4%. The incredible high β-CR delayed the βα-recrystallization in isothermal crystallization. The fusion peak of α-crystal was unobserved below the isothermal crystallization temperature of 122 °C when the addition amount was more than 0.2%. Furthermore, there was a highly ordered structure in WBN-28 with the periodicity of 12.89 Å, which was approximately twice of the unit cell parameter in the c direction of β-PP, indicating a high lattice matching rate between them. Intuitively observed by polarizing optical microscope (POM), the crystal grains of the blends with β-NA were more refined and finally crystallized in a plate-like shape. The forming process of the plate-like β crystalline regions were proposed by scanning electron microscope (SEM) and POM.

β-Nucleated Polypropylene: Preparation, Nucleating Efficiency, Composite, and Future Prospects

The β-crystals of polypropylene have a metastable crystal form. The formation of β-crystals can improve the toughness and heat resistance of a material. The introduction of a β-nucleating agent, over many other methods, is undoubtedly the most reliable method through which to obtain β-PP. Furthermore, in this study, certain newly developed β-nucleating agents and their compounds in recent years are listed in detail, including the less-mentioned polymer β-nucleating agents and their nucleation characteristics. In addition, the various influencing factors of β-nucleation efficiency, including the polymer matrix and processing conditions, are analyzed in detail and the corresponding improvement measures are summarized. Finally, the composites and synergistic toughening effects are discussed, and three potential future research directions are speculated upon based on previous research.

Effect of Shear Stress during Processing on Structure, Morphology, and Properties of Isotactic Polypropylene Nucleated with Silsesquioxane-Based β-Nucleating Agent

The study aimed to determine the influence of shear stress during real-life industrial processes such as compression molding and injection molding to different cavities on the crystallization of the isotactic polypropylene nucleated with a novel silsesquioxane-based β-nucleating agent. Octakis(N²,N⁶-dicyclohexyl-4-(3-(dimethylsiloxy)propyl)naphthalene-2,6-dicarboxamido)octasilsesquioxane (SF-B01) is a highly effective nucleating agent (NA) based on the hybrid organic-inorganic silsesquioxane cage. The samples containing various amounts of the silsesquioxane-based and commercial iPP β-nucleants (0.01-0.5 wt%) were prepared by compression molding and injection molding, including forming in the cavities with different thicknesses. The study of the thermal properties, morphology, and mechanical properties of iPP samples allows for obtaining comprehensive information about the efficiency of silsesquioxane-based NA in shearing conditions during the forming. As a reference sample, iPP nucleated by commercial β-NA (namely N²,N⁶-dicyclohexylnaphthalene-2,6-dicarboxamide, NU-100) was used. The static tensile test assessed the mechanical properties of pure and nucleated iPP samples formed in different shearing conditions. Variations of the β-nucleation efficiency of the silsesquioxane-based and commercial nucleating agents caused by shear forces accompanying the crystallization process during forming were evaluated by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). The investigations of changes in the mechanism of interactions between silsesquioxane and commercial nucleating agents were supplemented by rheological analysis of crystallization. It was found that despite the differences in the chemical structure and solubility of the two nucleating agents, they influence the formation of the hexagonal iPP phase in a similar way, taking into consideration the shearing and cooling conditions.

Temperature Effects on the Crystalline Structure of iPP Containing Different Solvent-Treated TMB-5 Nucleating Agents

TMB-5 nucleating agent (NA) treated by different solvents were used as the β-NA of iPP. The effects of temperature on the crystalline structure of different iPP/TMB-5, as well as the crystallization and melting behaviors were investigated. It was found that strong polar solvent treated TMB-5 (TMB-5_DMSO and TMB-5_DMF) could induce more β-crystal at high T_c = 140 °C than the other TMB-5 NAs, while the β-crystal inducing efficiency of untreated TMB-5 (TMB-5_UT) and non-polar solvent treated TMB-5 (TMB-5_LP) is seriously reduced at high T_c = 140 °C. TMB-5_DMSO can induce a high and stable content of β-crystal with K_β = 83-94% within T_c = 90-140 °C, and TMB-5_ODCB can induce a high content of β-crystal with K_β > 91.3% within T_c = 90-130 °C. TMB-5_DMF is the most temperature-sensitive one, but can induce a high fraction of β-crystal with K_β > 92% both at low T_c = 90 °C and high T_c = 140 °C. High temperature pre-crystallization at T_pc = 150 °C tremendously reduces the β-crystal inducing efficiency of all TMB-5 NAs. TMB-5_UT and TMB-5_LP exhibit higher nucleating efficiency than TMB-5_DMSO, TMB-5_DMF and TMB-5_ODCB. During the non-isothermal crystallization process, TMB-5_UT induced β-crystal possesses higher structural perfection and stability, while TMB-5_LP is more likely to induce α-crystal with considerable quantity and stability. The structural perfection and stability of TMB-5 induced β-crystal can be enhanced with appropriate increasing of T_c.

The Influence of Metal Lithium and Alkyl Chain in the Nucleating Agent Lauroyloxy-Substituted Aryl Aluminum Phosphate on the Crystallization and Optical Properties for iPP

In this work, a kind of aryl phosphate salt nucleating agent (APAl-12C) was synthesized, which was replaced in the hydroxyl group on the aluminum hydroxy bis [2,2′-methylene-bis(4,6-di-tert-butylphenyl) phosphate] (APAl-OH) by lauroyloxy, which could improve the dispersion between the nucleating agent and the iPP matrix and reduce the migration potential of the nucleating agent in the iPP matrix by increasing the molecular weight. The structure of the nucleating agent APAl-12C was analyzed by fourier infrared spectroscopy (FT-IR ) and ¹H NMR. The differential scanning calorimeter (DSC) results indicated that the addition of APAl-OH or APAl-12C alone was inferior to the commercial nucleating agent NA-21 (compounds of APAl-OH and Lithium laurate) in terms of the crystallization behavior, which may be due to the importance of metal Li in the crystallization property. Thus, the iPP/A12C-Li composites were prepared with APAl-12C, lithium laurate (lilaurate) and the iPP matrix. The crystallization behavior, morphology, optical and mechanical properties for the iPP/A12C-Li composites were systematically studied and compared with that of the iPP/NA-21 composite. Among the iPP/A12C-Li composites with the addition of 0.5 wt%, APAl-12C/Lilaurate had the fastest crystallization rate and reduced the haze value of the neat iPP from 36.03% to 9.89% without changing the clarity, which was better than that of the iPP/NA-21 composite. This was due to the weakening of the polarity of the APAl-12C after lauroyloxy substitution and better dispersion in the iPP matrix, resulting in a significant improvement in the optical properties.

A ternary hybrid nucleating agent for isotropic polypropylene: Preparation, characterization, and application

A ternary hybrid nucleating agent (THNA) powder was prepared by co-spray drying the fluid mixture of Si-MP/SNa slurry. The THNA was characterized by Fourier transform infrared and thermogravimetric analyses; the results showed that THNA was prepared successfully. The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that THNA was ring-shaped or mushroom cap-shaped and it was uniformly dispersed in the iPP matrix. With the incorporation of THNA (0.2 wt%), the crystallization peak temperature of iPP/THNA increased effectively. The nucleation efficiency and crystallinity were improved to 69% and 58%, respectively. Moreover, the flexural strength, flexural modulus, tensile strength, and impact toughness of iPP/THAN were enhanced to 49.3 MPa, 1,988 MPa, 42 MPa, and 4.93 kJ·m−2, respectively. The transparency was increased to 77.7%, and the haze was reduced to 14.1%. The compound of sodium laurate and inorganic silica/aromatic phosphate had an obvious synergistic effect.

Crystalline Characteristic Effect of In Situ Interaction between ZnO and Pht on Inducing β Nucleation of Isotactic Polypropylene

The β-nucleating agent (β-NA), zinc phthalate (ZnPht), was prepared from a mixture of zinc oxide (ZnO) and phthalic anhydride (Pht) during the extrusion of isotactic polypropylene (iPP). To establish the relationship between the crystalline characteristic of ZnO and the crystallization of iPP, single-crystalline ZnO (ZnO(S)) and polycrystalline ZnO (ZnO(P)) were selected and mixed with Pht, respectively, to in situ inducing the β-crystal form of iPP (β-iPP). Compared to ZnO(S)/Pht, ZnO(P)/Pht has the selectivity of β-crystal nucleation during the crystallization of iPP; indeed, the relative content of β-crystal ( $k_{\beta }$ ) improved from 18.0% for ZnO(S)/Pht/iPP to 84.6% for ZnO(P)/Pht/iPP. Moreover, the impact strength of the ZnO(P)/Pht/iPP was nearly 2.0 times greater than pure iPP; for ZnO(S)/Pht/iPP, it was approximately 1.4 times greater than pure iPP. To explain these phenomena, we propose a mechanism that the content of ZnPht generated by ZnO(P)/Pht is more than that of ZnO(S)/Pht during its in situ reaction; evidence from Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, and thermogravimetric infrared spectroscope analysis was consistent with this mechanism. This study may provide a new perspective to control the crystal type of polymorphic polymer by adjusting the crystalline characteristic of the nucleating agent.

The Influence of Melt Status and Beta-Nucleation Agent Distribution on the Crystallization of Isotactic Polypropylene

Although being investigated extensively in past decades, the factors affecting β-crystallization in β-nucleating agent/iPP composites have not been identified completely. In this study, β-crystallization in mesomorphic melt and free melt...

Investigation on the Effects of MXene and β-Nucleating Agent on the Crystallization Behavior of Isotactic Polypropylene

The effects of MXene on the crystallization behavior of β-nucleated isotactic polypropylene (iPP) were comparatively studied. The commonly used MXene Ti3C2Tx was prepared by selective etching and its structure and morphology were studied in detail. Then MXene and a rare earth β-nucleating agent (NA) WBG-II were nucleated with iPP to prepare samples with different polymorphic compositions. The crystallization, melting behavior, and morphologies of neat iPP, iPP/MXene, iPP/WBG-II, and iPP/MXene/WBG-II were comparatively studied. The crystallization behavior analysis reveals that a competitive relationship exists between MXene and WBG-II when they were compounded as α and β nucleating agents. In the system, the β-nucleation efficiency (NE) of WBG-II is higher than α-NE of MXene. The β-phase has relatively low thermal stability and would transform to α-phase when cooled below a critical temperature.