High-density polyethylene/Mg2Al-layered double hydroxide nanocomposites with different ethylene-acrylic acid random copolymer/Mg2Al-layered double hydroxide master batches were prepared by melt-mixing. The effect of the ethylene-acrylic acid random copolymer melt index on the exfoliated/intercalated nanocomposite structures was investigated by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. The crystallization behavior and thermal property of the nanocomposites were determined via differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis and cone calorimetry. The Mg2Al-layered double hydroxide layers were well-dispersed at the nanometer level, providing direct evidence of the formation of intercalated/exfoliated nanocomposites, as well as the important effect of ethylene-acrylic acid random copolymer melt index on these structures and their properties. Lower ethylene-acrylic acid random copolymer melt index resulted in higher exfoliation and better dispersion of layered double hydroxide in the high-density polyethylene matrix. Reductions in the heat release rate, total heat release and the carbonic oxide and carbon dioxide production of the nanocomposites were also observed. These phenomena led to higher thermal stability and changes in the storage modulus, tan δ and loss modulus of the nanocomposites, as well as improvement in the heterogeneous nucleation effect of layered double hydroxide on high-density polyethylene.
Three-tier high-strength prestressed combination concave dies are designed to manifacture highpower corn combine harvester engine piston heads. This design integrates the advantages of traditional casting or hot die forging and warm extrusion. The following key parameters, viz radial dimensions of each mating layer, axial bonding and radial contact interaction, are obtained by theoretical calculation. Nonlinear analysis of the contact interaction was carried out, and the die contact condition was studied at no-load and full-load. Based on the Archard wear theory, thermomechanical bonding was studied in operation of the die. Through numerical simulation of the die wear in each operation cycle, the univariate linear regression equation of the die service life was derived, and the reliability of this equation was verified. The results show that the die contact is both stable and reliable if the radial contact interaction of the inner and outer layers is d 2 = 1.9716 mm and d 3 = 1.3870 mm, respectively. With the nitriding layer thickness of 0.24 mm, the extrusion die service life in the production of piston heads corresponds to 6357 pieces.
In this work, the effect of calcium sulfate whisker (CSW) and ultrasonicallymodified CSW (UCSW) on the crystal structure and isothermal crystallization of isotactic polypropylene (iPP) is studied by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarized optical microscopy (POM). UCSW obviously increases heterogeneous nucleation. The isothermal crystallization kinetics of pure iPP, iPP/CSW, and iPP/UCSW composites are analyzed by the Avrami method. Although the Avrami exponent (n) of these samples only changed slightly, the half crystallization time (t 1/2 ) indicates that CSW and UCSW decrease the overall crystallization time and increase the crystallization rate (R c ). POM results show that most crystals are β-iPP shaped and the spherulite size decreases significantly with the addition of UCSW. The apparent equilibrium temperature of iPP/UCSW composites is lower than that of pure iPP and iPP/CSW composites. The values of β-iPP fold surface free energy (σ e ) and the nucleation parameter (K g ) are much lower than that of α-iPP for these iPP composites. The content of β-crystal in iPP composites increases due to the addition of UCSW.
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