ABSTRACT:The rheological properties and initiation mechanism during the reactions of new catalytic (N-benzylpyrazinium hexafluoroantimonate, BPH) epoxy thermosetting system with increase of BPH concentration have been studied by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), and steady shear measurements. This cationic catalyst system turned out to have an availability as themial latent initiator in the epoxy curing reaction. The dependence of viscosity on processing variables could be explained by structural change owing to the composition dependence of initiation reactions with increasing of BPH concentration. The temperature dependence on the induction time is well described by the Arrhenius expression, and the activation energies (E,) have similar values for various compositions, which indicates that the overall curing mechanisms are nearly same.
A new thermotropic liquid crystalline (TLC) copolyesteramide with a phenylhydroquinone derivative was synthesized by a solution polymerization. The annealing effect of the copolyesteramide was investigated by using differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction. The TLC copolyesteramide turned out to have a low melting temperature and a wide nematic range above the melting temperature. Because it had bulky side groups from the main chain, the formation of a three-dimensional order was hindered but it could only be achieved by a long time annealing. The fast crystallization was not observed but mainly the slow process was involved in the crystallization. The Avrami parameter (n) of the copolyesteramide has very low values because of the slow crystallization. KEY WORDS Thermotropic Liquid Crystalline Copolyesteramide I Nematic Texture I Slow Crystallization Process I Annealing I
ABSTRACT:The crystallization behavior and microstructure of linear low density polyethylene (LLDPE)/modified montmorillonite (20A) composites containing maleic anhydride grafted polyethylene (MA-g-PE) were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscope (TEM). The dispersion of 20A in LLDPE matrix depended on the amount of MA-g-PE. The degree of super cooling reduced when 20A was introduced into LLDPE with MA-g-PE. The Avrami analysis shows that the nonisothermal crystallization process of the LLDPE/20A composites followed the Avrami equation with Avrami exponent value in the range of 2.75-3.97. The activation energies calculated by Kissinger method were 986 kJ/mol for LLDPE, 949 kJ/mol for PE-A5MA0, 1445 kJ/mol for PE-A5MA5, and 1581 kJ/mol for PE-A5MA20. The activity of nucleation of PE-A5MA0 was 0.75 but the values of the composites with MA-g-PE were in the range of 0.37-0.56. These behaviors can be interpreted by the fact that the loading of MA-g-PE in LLDPE/20A composites enhances the dispersion of clay in LLDPE matrix and the good dispersion of 20A affects the degree of super cooling and the nucleation activity of silicate. [DOI 10.1295/polymj.38.250] KEY WORDS Maleic Anhydride / Linear Low Density Polyethylene / Nanocomposite / Crystallization Behavior / Nucleation Activity / Polymer nanocomposites comprise a new class of materials where the particulates are finely dispersed within a matrix. There is much interest, scientifically and technologically, in nanocomposites of polymers with nanoscale layered silicates because these materials offer markedly improved properties as compared to the conventional polymer composites.1-8 Further, these improvements are achieved at very low loadings of the inorganic component.In the case of semicrystalline polymers, it is well known that the crystallization behavior get affected by the presence of particulate additives especially at low concentrations. This feature can affect the overall properties of the nanocomposite but such a few investigations have been reported. 9,10 Nonisothermal crystallization studies on semicrystalline polymers have been widely carried out because of the analogous crystallization condition to that of real processing. Although the analysis for the nonisothermal crystallization process may much more complicated than that for isothermal process, nonisothermal crystallization measurements can provide ample information about the crystalline transition. Since the microstructures of silicate and the linear low density polyethylene (LLDPE) matrix crystallite may have remarkable effects on the physical properties of the LLDPE/silicate nanocomposites, it is meaningful to study the influence of silicate on the crystallization process of LLDPE matrix. This is the reason that the study of the LLDPE/silicate nanocomosite on the crystallization behavior is a topic of interest.Another field of interest with the polymer nanocomposite was that the outstanding properties of the nanocomposit...
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