Nevra Ercan

Isothermal crystallization kinetics of glass fiber and mineral-filled polyamide 6 composites

In this study, isothermal crystallization kinetics of polyamide 6 (PA6) composites reinforced with surface-treated glass fiber (GF) and natural, clay-type mineral (MN) were investigated by differential scanning calorimetry method in the presence and absence of a nucleating agent (NA). Microstructural features of the composites and interfacial interactions between filler and polyamide phases were also quantified by rheological measurements. The kinetic parameters for the isothermal melt-crystallization process of the samples were determined with the Avrami and Lauritzen–Hoffman models. The crystallization activation energies were determined by the Arrhenius method. It was found that the both fillers yielded a significant increase in the storage modulus of PA6. Kinetic calculations showed that the MN has a more pronounced acceleration effect on the crystallization rate of PA6 than the GF. Introduction of a small amount of NA significantly favored the isothermal crystallization rate of GF-reinforced PA6 but did not accelerate that of MN-reinforced one. Based on the results, it has been highlighted that PA6 composites reinforced with surface-treated GFs and including a small amount of clay-like mineral as a cheap and easy-accessible minor filler could yield the best performance for the injection-molded PA6 parts because the GF enhances the mechanical properties and the clay-like mineral accelerates the crystallization rate.

Effects of Halloysite Nanotube on the Mechanical Properties and Nonisothermal Crystallization Kinetics of Poly(Butylene Terephthalate) (PBT)

In this study, poly(butylene terephthalate) (PBT)/halloysite composites having various amounts of halloysite, as a one-dimensional (1D) nanotubular alumina-silicate filler, were prepared by melt processing in a twin screw extruder. Nonisothermal crystallization behaviors of the samples were studied by DSC and XRD methods. The effect of halloysite amount on the nonisothermal melt crystallization kinetics of the PBT was analyzed with various kinetic models, namely the Ozawa, Avrami modified by Jeziorny, and Liu–Mo. Crystallization activation energies of the samples were determined by the Kissinger model. Viscoelastic properties of the samples were studied by DMA tests. By comparing the effect of halloysite amount on the melt crystallization kinetics of PBT, it was found that halloysite increased the crystallization rate of PBT. Crystallization activation energy values of the PBT and composite samples including 2%, 5%, and 10% of halloysite were found to be −341.8, −353.3, −373.6, and −419.6 kJ/mol, respectively. Based on the DMA tests, it was found that halloysite increased the elastic feature of the sample due to polymer-filler interactions.

Comparing of melt blending and solution mixing methods on the physical properties of thermoplastic polyurethane/organoclay nanocomposite films

In this study, microstructural features and physical properties of thermoplastic polyurethane (TPU)/organoclay nanocomposites films prepared via melt blending (MB) and solution mixing (SM) methods were investigated in detail. Amount of organoclay into the composition varied in the range of 2 and 8 wt%. Microstructural properties of samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) methods. It was found that the organoclay layers exhibited better dispersion, exfoliated, and semi-exfoliated structure in the MB samples than the SM counterparts. Viscoelastic properties of samples were also studied by measuring the rheological behaviors of bulk samples in an oscillatory rheometer in the melt state and measuring of the time-dependent nonlinear creep behaviors of film samples in a dynamic mechanical analyzer in the solid state. Gas and water vapor permeability (WVP) values of nanocomposite films were measured. Based on the melt rheology measurements, it was found that the MB samples showed characteristic solid-like behavior and higher improvement in storage modulus at low-frequency region. Creep behaviors of samples were also quantified with the four-element Burger model. It was found that the introducing of organoclay into the composition via MB method yielded more improvement in the creep resistance, gas, and WVP values of films than the SM counterparts, possibly due to the better dispersion of organoclay layers into the TPU structure. Based on the improvement in permeability and mechanical properties of the samples and also SEM and TEM observations, the average aspect ratio value (A f) of organoclay stacks was estimated in the range of 15–20 for the MB samples.

Effects of various polyolefin copolymers on the interfacial interaction, microstructure and physical properties of cyclic olefin copolymer(COC)/graphite composites

In this study, effects of various types of functional polyolefin copolymers (FPOCs), poly(isobutylene-alt-maleic anhydride), poly(maleic anhydride-alt-1-octadecene) and poly(ethylene-graft-maleic anhydride), on the microstructure formation, interfacial interaction and physical properties of cyclic olefin copolymer (COC)/graphite composites were investigated. The COC/graphite composites were prepared in a lab. scale twin screw extruder. Microstructural features of samples were studied in a field emission scanning electron microscopy (FESEM). Viscoelastic properties of samples, obtained from the rheology tests in melt state and the dynamic mechanical analysis in solid state were used to quantify interfacial interactions between the COC and graphite depending on the types of FPOC. The average aspect ratio (Af) values of graphite flakes in the COC phase were determined about 40–65 by SEM observation and image analysis study on the samples prepared with different types of FPOC. Based on the gas permeability measurements, tortuous diffusion model suggested that the Af values of graphite flakes varied between 40 and 80 depending on the amount of graphite. It was shown that the poly(isobutylene-alt-maleic anhydride) copolymer provided relatively higher interfacial interaction between the COC and graphite flakes than the other FPOCs.

Effect of Graphitic Nanosheets on the Physical Properties of Cyclic Olefin Copolymer Composite Films

ABSTRACT In this study, microstructural and physical properties of cyclic olefin copolymer composite films prepared by melt processing method and using of graphitic nanofillers, namely, graphite, graphite oxide, and reduced graphite oxide were investigated. Structural and physical properties of the chemically modified graphites and composite films were characterized by the Fourier transform infrared, X-ray diffractometer, scanning electron microscopy, dynamic mechanical analyzer, and thermogravimetric analyzer methods. It was found that the composite films including reduced graphite oxide exhibited exfoliated structure whereas graphite- and graphite oxide-based films showed intercalated structure. It was also obtained that all composite films showed superior gas barrier performance compared to the cyclic olefin copolymer. GRAPHICAL ABSTRACT