Zishou Zhang

Non-isothermal crystallization kinetics and morphology of wollastonite-filled β-isotactic polypropylene composites

To obtain wollastonite-filled β-iPP composites, the wollastonite with β-nucleating surface (β-wollastonite) was prepared through chemical reaction between wollastonite with α-nucleating surface (α-wollastonite) and pimelic acid. The formation of calcium pimelate on the surface of wollastonite was proved using Fourier transform infrared spectrometry and scanning electron microscopy. The crystallization behavior, melting characteristics, non-isothermal crystallization kinetics, and crystalline morphologies of α- and β-wollastonite-filled iPP composites were studied by differential scanning calorimetry and polarizing optical microscopy. It is found that the crystallization peak temperatures of β-wollastonite-filled iPP composites were higher than that of α-wollastonite-filled iPP composites, which indicated that wollastonite with β-nucleating surface has stronger heterogeneous nucleation than that of wollastonite with α-nucleating surface. Although the crystallization temperatures of iPP and iPP composites decreased with increasing cooling rates, α-wollastonite-filled iPP composites mainly crystallized in α-spherulite and β-wollastonite-filled iPP composites formed β-spherulite. In addition, the spherulite size of β-wollastonite-filled iPP composites was smaller than that of α-wollastonite-filled iPP composites. Jeziorny and Mo methods were applicable to study the non-isothermal crystallization kinetics of wollastonite-filled iPP composites. The activation energy (∆E) and the nucleation efficiency (EN) of non-isothermal crystallization were calculated by Kissinger method and the equation proposed by Fillon, respectively. The β-wollastonite-filled iPP composites exhibited higher crystallization rate, activation energy, and EN than that of α-wollastonite-filled iPP composites.

Non-isothermal crystallization kinetics of montmorillonite filled β-isotactic polypropylene nanocomposites

Abstract Montmorillonite filled isotactic polypropylene nanocomposites (iPP/MMT) generally form α-modification due to the heterogeneous α-nucleation of MMT for iPP crystallization. To obtain MMT filled β-iPP nanocomposites, MMT with β-nucleating surface (β-MMT) was prepared by supporting calcium pimelate (CaPA) as β-nucleator on the surface of MMT particles. The crystallization behavior, melting characteristics, and non-isothermal crystallization kinetics and crystallization activation energies of MMT and β-MMT filled iPP nanocomposites were studied by differential scanning calorimetry. It is found that the crystallization peak temperatures of β-MMT filled iPP nanocomposites were higher than those of β-iPP and MMT filled iPP nanocomposites, which indicated that the heterogeneous nucleation of β-MMT is stronger than that of MMT. Jeziorny and Mo methods were applicable to study the non-isothermal crystallization kinetics of iPP and its nanocomposites. Addition of CaPA, MMT and β-MMT can increase the crystallization rate. The crystallization activation energies were calculated by Friedman methods, and nucleating activities were calculated by Dobreva methods. It is indicated that β-nucleation decreased the crystallization activation energy of iPP, and the nucleating activity of β-MMT is higher than that of CaPA and MMT.

Effect of blending way on β -crystallization tendency of compatibilized β -nucleated isotactic polypropylene/poly(ethylene terephthalate) blends

The main purpose of this study is to investigate the β-crystallization tendency in the β-nucleated iPP blends. The β-nucleated iPP/compatibilizers blends, β-nucleated iPP/PET blends and its compatibilized versions with four kinds of compatibilizers (PP-g-MA, PP-g-GMA, POE-g-MA, and EVA-g-MA) were prepared by different blending ways. The effect of compatibilizers and blending ways on the non-isothermal crystallization and melting characteristics and the β-crystallization tendency of β-nucleated iPP blends were studied by differential scanning calorimetry. The relative content of the β-phase were characterised by the kβ values determined on the basis of the wide angle X-ray diffractogram. The results indicated that the β-crystallization tendency of β-nucleated iPP blends depends on the kinds of compatibilizer. Addition of PP-g-MA significantly reduced the β-crystallization tendency of β-nucleated iPP, while PP-g-GMA, POE-g-MA, and EVA-g-MA have little effect on it. In the compatibilized β-nucleated iPP/PET blends, the blending ways, which controlled the dispersion of β-nucleating agent, influences the β-crystallization tendency intensively. The high β-crystallization tendency and β-crystal content were obtained for compatibilized β-nucleated iPP/PET blends prepared firstly at high temperature and β-nucleating agent added into blends at low temperature; however, the type of compatibilizers has little effect on β-crystallization tendency and melting behavior of blends.

Molecular chain bonding synthesis of nanoporous, flexible and conductive polymer composite with outstanding performance for supercapacitors

Molecular chain bonding is, for the first time, developed to synthesize a nanoporous, flexible and conductive polymer composite by converting a single polymer phase matrix to two phases of interpenetrating polymer networks. Significantly, the porous polymer composite not only presents ultra-high mechanical properties, durability and conductive stability, but also enhances the capacitance by 7-fold.

Preparation and characterization of wollastonite with a β-nucleating surface and its filled isotactic polypropylene composites

To transform α-nucleation into β-nucleation of wollastonite surface for isotactic polypropylene (iPP), the wollastonite with a β-nucleating surface was prepared through the chemical reaction between wollastonite and pimelic acid in both liquid mixing (method A) and powder mixing (method B). The wollastonite with a β-nucleating surface was confirmed using differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy analysis, wide-angle X-ray diffraction under different temperatures, thermogravimetry coupled with Fourier transform infrared spectrometry, and scanning electron microscopy. The crystallization and melting behavior and the crystalline morphology of iPP composites filled by wollastonite with a β-nucleating surface were investigated by DSC and optical microscopy. The results indicated that wollastonite filled iPP composites predominantly crystallize in the α-phase iPP and iPP composites filled by wollastonite with a β-nucleating surface mainly form β-phase iPP. It is proved that heterogeneous nucleating mechanism has been changed from α-nucleation into β-nucleation of wollastonite surface for iPP crystallization. What deserves to be mentioned is that the nucleation density of flat surface in the end of needle-like wollastonite is higher than that of curved surface of wollastonite.

The β-nucleating effect of wollastonite-filled isotactic polypropylene composites

Wollastonite (W) with β-nucleating effect (β-W100) for iPP crystallization was obtained through reaction between Ca2+ in wollastonite and pimelic acid (PA) and the β-iPP composites filled by different content of β-W100 were prepared. The effect of PA and wollastonite contents on β-nucleation, crystallization and melting behavior, and crystalline morphology of W and β-W100-filled iPP composites was investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction, and polarizing optical microscopy. The results indicated that incorporation of W and β-W100 increase the crystallization peak temperature of iPP due to its heterogeneous nucleating ability. And iPP/W composites predominantly crystallize in the α-phase iPP and iPP/β-W100 composites in the β-phase iPP. The results of DSC multi-scanning in same and different melting temperatures showed that β-W100 not only has strong heterogeneous β-nucleating effect but also DSC multi-scanning in same and different melting temperatures has no influence on the heterogeneous β-nucleating effect of β-W100. The β-iPP containing high wollastonite content with high β-phase content can be easily prepared.

Preparation and crystallization of aluminum hydroxide-filled β-polypropylene composites

Aluminum hydroxide-filled polypropylene composites generally form α-crystal due to the strong heterogenous α-nucleation of filler. In order to utilize β-crystal PP with high toughness to prepare aluminum hydroxide-filled PP composites, the aluminum hydroxide-filled PP composites nucleated by calcium pimelate and PP composites filled by calcium pimelate-supported aluminum hydroxide were fabricated. The crystallization and melting behavior of filled composites were compared by differential scanning calorimetry. The influence of aluminum hydroxide contents on the β-crystal content in the filled PP composites was discussed. It is a novel effective method to prepare aluminum hydroxide-filled β-PP composites with calcium pimelate-nucleated aluminum hydroxide.

A novel polypropylene composite filled by kaolin particles with β-nucleation

Kaolin-filled polypropylene (PP) composites generally form α-crystal due to the effect of kaolin with α-nucleation. The transition from α- to β-nucleation of kaolin has been investigated, and a novel kaolin with β-nucleation (β-kaolin) and kaolin-filled PP composites with high β-crystal content were prepared first. The DSC and WAXD results indicated that the β-kaolin exhibits stronger β-nucleating ability than CaPA as β-nucleating agent for PP crystallization. It is found that the β-crystal content has been influenced little by filler contents in β-kaolin-filled PP composites. Mechanical properties and spherulitic morphology of filled PP composites was characterized. The synergistic effect of filler and β-crystal significantly improved impact strength of kaolin-filled PP composites.

Enhanced ultraviolet resistance of polypropylene random copolymer filled by ZnO-supported mesoporous zeolite

To enhance the ultraviolet resistance of ZnO based polymer materials, ZnO-supported mesoporous zeolite (M-ZnO) was prepared and characterized by atomic absorption spectroscopy and scanning electron microscopy. The ultraviolet resistance, crystallization behavior and melting characteristics of ZnO and M-ZnO filled PPR composites were compared by FTIR spectra and differential scanning calorimetry. The ultraviolet resistance of M-ZnO filled PPR composites is higher than that of ZnO filled PPR composites, indicating higher ultraviolet resistance of M-ZnO than that of ZnO. The crystallization temperatures of mesoporous zeolite filled PPR were higher than those of M-ZnO and decreased with increasing UV-irradiation time. But the crystallization temperatures of M-ZnO filled PPR composites were not influenced by UV-irradiation time. The ZnO supported on the surface of zeolite is effective in enhancing the ultraviolet resistance of ZnO based polymer materials.

Long-Life and High-Power Binder-Free Cathode Based on One-Step Synthesis of Radical Polymers with Multi-Pendant Groups

The main bottlenecks for the widespread application of radical polymers in organic radical batteries are poor cycling stability, due to the dissolution of radical polymers into the electrolyte, and the low efficiency of multi-step synthesis strategies. Herein, a kind of electrolyte-resistant radical polymer bearing multi-pendant groups (poly(ethylene-alt-TEMPO maleate) (PETM)) is designed and synthesized through a one-step esterification reaction to graft 4-hydroxy-2,2,6,6-teramethylpiperidinyl-1-oxy into the commercially available poly(ethylene-alt-maleic anhydride). Interestingly, PETM is hardly soluble in the ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate-based electrolyte, showing an extremely low solubility of 0.59 mg mL-1 , but is easily soluble in tetrahydrofuran and N-Methyl pyrrolidone. The derived binder-free PETM cathode exhibits nearly 100% utilization of the grafted nitroxide radicals (88 mA h g-1 ) and excellent rate capability with almost invariant capacitance from 10 C to 40 C. Significantly, the PETM cathodes retain 94% of the initial capacity after 1000 cycles, outperforming most reported radical polymer-based cathodes.