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The foaming of PP has encountered challenges because of its low melt strength and semi-crystalline characteristics. Introducing long chain branching (LCB) onto the PP backbone and the addition of particles as cell nucleating agent are the commonly used methods to improve the cell structure of PP foams. In this paper, clay-supported sodium benzoate (NaB-OMMT) was prepared from Na-montmorillonite (Na-MMT) via the partial ion exchange reaction with surfactant and subsequent reaction with benzoic acid. The as prepared NaB-OMMTs were then applied to prepare LCBPP/NaB-OMMT nanocomposites and their foams. The dispersion state of clay, crystallization behaviors and rheological properties of the nanocomposites, as well as the cell structure and compression properties of the foams were investigated. The results show that clay layers are mostly exfoliated in the nanocomposites with low NaB-OMMT content, while intercalated layers dominant with the content reaches 2% or higher. The melting temperature of the nanocomposites decreases and the crystallinity increases, while the spherulite size decreases compared to LCBPP. The melt viscosity and elasticity of nanocomposites increase significantly when the content of NaB-OMMT reaches 2% or higher. LCBPP/NaB-OMMT nanocomposites foams exhibit higher cell density, smaller cell size and its standard deviation. Therein, the foam with 1% of NaB-OMMT shows the maximum cell density and the minimum cell size. It is concluded that the cell structure of the foam is highly dependent on the content, dispersion state and structure of the cell nucleating agent. When NaB is supported on well dispersed and exfoliated clay layers, the cell nucleation efficiency is significantly enhanced. The compression properties of the foams depend on their cell structures and exhibit the similar variation trend with the latter with the content of NaB-OMMT increasing. Graphical Abstract [ABSTRACT FROM AUTHOR]

Long chain branched polypropylene/clay‐supported calcium pimelate (LCBPP/CaHA‐OMMT) composites and their foams were prepared using self‐made CaHA‐OMMTs. The CaHA‐OMMT showed high β‐nucleation efficiency, especially that with larger initial interlayer distance could induce 89% of β crystal in LCBPP with a dosage of 0.5%. Clay layers were mostly exfoliated in the composites with low CaHA‐OMMT content, while intercalated structure was dominant and agglomeration occurred when the content of CaHA‐OMMT was higher than 2%. The composite foams were prepared with improved compression molding. The cell structure of the composite foams is improved, that is, the density, cell size, and cell size distribution decreased, and the cell density increased compared with that of LCBPP foam. The minimum average cell size of LCBPP/CaHA‐OMMT foams was 77 μm and the maximum cell density was 2.8 × 106 cells/cm3 with the CaHA‐OMMT content of 2%. It is concluded that there are two requirements for high nucleation efficiency: the CaHA was supported on OMMT layers, and the OMMT platelets were dispersed well and exfoliated. The compression properties of the composite foams, including compression modulus, energy absorption density and failure strength increased first and then decreased with the increase of CaHA‐OMMT content. [ABSTRACT FROM AUTHOR]

Maleic anhydride-grafted carbon fiber (CF- g -MAH) was prepared by a solid-phase grafting method. The rheological behavior, morphology, mechanical properties, and nonisothermal crystallization behavior of pure poly(ethylene terephthalate) (PET) and PET/CF and PET/CF- g -MAH composites were investigated. The rheological analyses and mechanical tests show that the addition of CF or CF- g -MAH increased the complex viscosity and mechanical properties of PET. The morphology observations confirm that the introduction of the MAH group on the surfaces of the CF enhanced the interactions between the CF and PET, resulting in the fine dispersion of CF- g -MAH in the PET matrix. In addition, the analyses of the nonisothermal crystallization behavior of pure PET and the PET/CF and PET/CF- g -MAH composites show that CF or CF- g -MAH can act as a heterogeneous nucleating agent in PET and accelerate its crystallization. Compared to CF, CF- g -MAH is a more effective nucleator for PET. [ABSTRACT FROM AUTHOR]

ABSTRACT Improvement of mechanical and thermal properties is always the goal of high-performance general plastic for engineering applications. Herein, isotactic polypropylene/glass fiber/tetrapod-shaped zinc oxide (iPP/GF/T-ZnOw) composites are developed via melt-extrusion on twin-screw extruder. To improve the distribution of T-ZnOw in iPP matrix, T-ZnOw is first modified by various silane coupling agents and its structure is characterized by scanning electron microscopy, Fourier transform infrared spectra, and X-ray diffraction (XRD). The optimized treatment condition is determined via comparison of activation index. The introduction of GF and T-ZnOw could improve the mechanical properties including tensile strength, elastic modulus, flexural strength, flexural modulus, and impact strength, indicating that the surface modification and compatibilizer could enhance the interfacial interaction of iPP/GF/T-ZnOw composites. Moreover, XRD and differential scanning calorimentryresults show that T-ZnOw as a novel β-nucleating agent could induce the formation of β-crystal and the existence of GF counteracts the formation of β-crystal induced by T-ZnOw. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44217. [ABSTRACT FROM AUTHOR]

Abstract: Isotactic polypropylene (iPP) composites with unmodified and modified tetra-needle-shaped zinc oxide whisker (T-ZnOw) were prepared via melt blending in a twin-screw extruder. The mechanical properties, thermal properties, morphology and crystallization behavior were investigated. The mechanical properties of iPP with T-ZnOw modified by silane based coupling agent were much better than that of iPP with unmodified T-ZnOw. The reason was that the interfacial interaction between T-ZnOw and iPP matrix became stronger when T-ZnOw was modified by coupling agent. Besides, the addition of T-ZnOw improved thermal properties of iPP, including heat deflection temperature and thermal degradation temperature. Furthermore, wide angle X-ray diffraction (WAXD) results showed that T-ZnOw can be used as a novel β-nucleating agent, and the relative content of β-crystal was 0.38 when T-ZnOw content was 5wt.%. iPP/T-ZnOw composites were found to exhibit higher crystallization temperature, smaller spherulites, and faster crystallization rate than those of pure iPP, indicating that T-ZnOw played a role of nucleating agent on the crystallization of iPP and could induce accelerated crystallization. [Copyright &y& Elsevier]

Monomer casting polyamide 6(MCPA6)/toluene 2,4-diisocyanate functionalized multi-walled carbon nanotubes (MWNTs-NCO) nanocomposites were prepared via in situ anionic ring opening polymerization, and the non-isothermal crystallization behavior of the nanocomposites were investigated by differential scanning calorimetry with various cooling rates. The commonly used Avrami, Ozawa, Mo, and Urbanovici-Segal models were employed to analyze the non-isothermal crystallization data and the validity of the models on the process of MCPA6 and its nanocomposites was discussed, where Mo and Urbanovici-Segal models could well describe the non-isothermal crystallization process for the samples. The results revealed that MWNTs could accelerate the crystallization process of MCPA6, attributing to the nucleating effect of the nanofillers. Finally, the effective energy barrier for non-isothermal crystallization was evaluated as a function of the relative crystallinity by applying an isoconversional method. [ABSTRACT FROM AUTHOR]

Abstract: Non-isothermal crystallization kinetics of isotactic polypropylene (iPP) was simulated with the assumption that the non-isothermal crystallization process was composed of some finite isothermal crystallization processes, while each isothermal crystallization process consists of three main steps—induction, nucleation and crystal growth. In the simulation, induction time was taken into account, allowing one to make predictions on the start of the non-isothermal crystallization of iPP; nuclei density was treated as a function of temperature; the Hoffman–Lauritzen theory was employed to describe the spherulite growth rate varied with temperature, and the relative crystallinity was determined by the equation of Kolmogorov. Finally, model prediction was verified by quantitative comparison between the theoretical results with the experimental results. [ABSTRACT FROM AUTHOR]

Poly(ethylene terephthalate) (PET) composites containing carbon fiber (CF) or polymethyl methacrylate (PMMA)-grafted carbon fiber (PMMA-g-CF) were prepared by melt compounding. The rheology, non-isothermal crystallization behavior, and mechanical and thermal properties of pure PET, PET/CF and PET/PMMA-g-CF composites were investigated. The results show that the addition of CF or PMMA-g-CF significantly increases the storage modulus (G′), loss modulus (G″), and complex viscosity (η*) of the composites at low frequency. The Cole-Cole plots confirm that the surface modification of CF leads to a better interaction between the CF and PET, and then decreases the heterogeneity of the polymeric systems, which is confirmed by the SEM observation on the tensile fracture surface of the composites. Non-isothermal crystallization analysis shows that the CF or PMMA-g-CF could serve as nucleation agent to accelerate the crystallization rate of the composites, and the effect of PMMA-g-CF is stronger than that of CF. The result is further confirmed by the analysis of the crystallization activation energy for all composites calculated by the Flynn-Wall-Ozawa method. Moreover, the tensile and impact strength and the thermal stability of the composites are improved by CF, while the incorporation of PMMA-g-CF further enhances the tensile and impact strength and thermal stability. [ABSTRACT FROM AUTHOR]

Abstract: To improve the thermal and mechanical properties of isotactic polypropylene (iPP), iPP/Kevlar fiber (KF)/polyamide 6 (PA6) composites were prepared via the melt-extrusion method on twin-screw extruder. Kevlar fiber was modified with caprolactam using toluenediisocyanate (TDI) as bridge. The microstructure of modified KF was successfully characterized by Fourier transform infrared (FT-IR), X-ray photoelectron spectrometer (XPS) and scanning electron microscopy (SEM), the results showed that KF was bonded with caprolactam and became coarser. Then the modified KF was introduced into iPP, the composites have better mechanical and thermal properties, implying that modification of KF was helpful to improve the interfacial interaction of iPP/KF/PA6 composites. Besides, the crystallization curves indicated that crystallization behavior of PA6 in the composites was homogeneous and fractional. Furthermore, compatibilizer content played an important role in the mechanical and thermal properties of composites. [Copyright &y& Elsevier]