ABSTRACT
A notable application of polymeric nanocomposites is the design of water vapor permeable (WVP) membranes. "Breathable" membranes can be created by the incorporation of micro/nanofillers, such as CaCO3, that interrupt the continuity of the polymeric phase and when subjected to additional uniaxial or biaxial stretching this process leads to the formation of micro/nanoporous structures. Among the candidate nanofillers, carbon nanotubes (CNTs) have demonstrated excellent intrinsic WVP properties. In this study, chemically modified MWCNTs with oligo olefin-type groups (MWCNT-g-PP) are incorporated by melt processes into a PP matrix; a ß-nucleating agent (ß-ΝA) is also added. The crystallization behavior of the nanocomposite films is evaluated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The WVP performance of the films is assessed via the "wet" cup method. The nanohybrid systems, incorporating both MWCNT-g-PP and ß-NA, exhibit enhanced WVP compared to films containing only MWCNT-g-PP or ß-NA. This improvement can be attributed to the significant increase in the growth of α-type crystals taking place at the edges of the CNTs. This increased crystal growth exerts a form of stress on the metastable ß-phase, thereby expanding the initial microporosity. In parallel, the coexistence of the inherently water vapor-permeable CNTs, further enhances the water vapor permeability reaching a specific water vapor transmission rate (Sp.WVTR) of 5500 µm.g/m2.day in the hybrid composite compared to 1000 µm.g/m2.day in neat PP. Notably, the functionalized MWCNT-g-PP used as nanofiller in the preparation of the "breathable" PP films demonstrated no noteworthy cytotoxicity levels within the low concentration range used, an important factor in terms of sustainability.
ABSTRACT
Polymer matrix nanocomposites are widely studied because of the versatility of their physical and mechanical properties. When these properties are present simultaneously, responding at relative stimuli, multifunctional performance is achieved. In this study, hybrid nanocomposites of SrFe12O19 and BaTiO3 ceramic particles dispersed in an epoxy resin matrix were fabricated and characterized. The content of SrFe12O19 was varying, while the amount of BaTiO3 was kept constant. The successful fabrication of the nanocomposites and the fine dispersion of the ceramic particles was verified via the morphological and structural characterization carried out with X-ray Diffraction patterns and Scanning Electron Microscopy images. Dielectric response and related relaxation phenomena were studied by means of Broadband Dielectric Spectroscopy. Dielectric permittivity augments with filler content, while the recorded relaxations, with descending relaxation time, are: (i) interfacial polarization, (ii) glass-to-rubber transition, (iii) intermediate dipolar effect, and (iv) re-orientation of polar-side groups of the main polymer chain. SrFe12O19 nanoparticles induce magnetic properties to the nanocomposites, which alter with the magnetic filler content. Static and dynamic mechanical response improves with filler content. Thermogravimetric analysis shown that ceramic particles are beneficial to the nanocomposites' thermal stability. Glass transition temperature, determined via Differential Scanning Calorimetry, was found to slightly vary with filler content, in accordance with the results from dynamic mechanical and dielectric analysis, indicating the effect of interactions occurring between the constituents. Examined systems are suitable for energy storing/retrieving.
ABSTRACT
The global trend in restrictions on pollutant emissions requires the use of catalytic converters in the automotive industry. Noble metals belonging to the platinum group metals (PGMs, platinum, palladium, and rhodium) are currently used for autocatalysts. However, recent efforts focus on the development of new catalytic converters that combine high activity and reduced cost, attracting the interest of the automotive industry. Among them, the partial substitution of PGMs by abundant non-PGMs (transition metals such as copper) seems to be a promising alternative. The PROMETHEUS catalyst (PROM100) is a polymetallic nanosized copper-based catalyst for automotives prepared by a wet impregnation method, using as a carrier an inorganic mixed oxide (CeO2-ZrO2) exhibiting elevated oxygen storage capacity. On the other hand, catalyst deactivation or ageing is defined as the process in which the structure and state of the catalyst change, leading to the loss of the catalyst's active sites with a subsequent decrease in the catalyst's performance, significantly affecting the emissions of the catalyst. The main scope of this research is to investigate in detail the effect of ageing on this low-cost, effective catalyst. To that end, a detailed characterization has been performed with a train of methods, such as SEM, Raman, XRD, XRF, BET and XPS, to both ceria-zirconia mixed inorganic oxide support (CZ-fresh and -aged) and to the copper-based catalyst (PROM100-fresh and -aged), revealing the impact of ageing on catalytic efficiency. It was found that ageing affects the Ce-Zr mixed oxide structure by initiating the formation of distinct ZrO2 and CeO2 structures monitored by Raman and XRD. In addition, it crucially affects the morphology of the sample by reducing the surface area by a factor of nearly two orders of magnitude and increasing particle size as indicated by BET and SEM due to sintering. Finally, the Pd concentration was found to be considerably reduced from the material's surface as suggested by XPS data. The above-mentioned alterations observed after ageing increased the light-off temperatures by more than 175 °C, compared to the fresh sample, without affecting the overall efficiency of the catalyst for CO and CH4 oxidation reactions. Metal particle and CeZr carrier sintering, washcoat loss as well as partial metal encapsulation by Cu and/or CeZrO4 are identified as the main causes for the deactivation after hydrothermal ageing.
ABSTRACT
In this study, hybrid nanocomposites consisting of Fe3O4/BaTiO3/epoxy resin were prepared with varying amounts of filer content. Structural and morphological characterization, conducted via X-Ray Diffraction patterns and Scanning Electron Microscopy images, revealed the successful fabrication of composites and fine dispersion of inclusions. Thermomechanical properties are studied via Differential Scanning Calorimetry, Thermogravimetric Analysis, Dynamic Mechanical Analysis and static mechanical tests. Hybrid composites exhibit enhanced thermal stability and improved mechanical response. Indicatively, Young's modulus, tensile strength and fracture toughness increase from 1.26 GPa, 22.25 MPa, and 3.03 kJ/m3 for the neat epoxy to 1.39 GPa, 45.73 MPa, and 41.08 kJ/m3 for the composites with 20 or 15 parts per hundred resin per mass (phr) of Fe3O4, respectively. Electrical behavior is investigated via Broadband Dielectric Spectroscopy and ac conductivity measurements. The real part of dielectric permittivity reaches the value of 11.11 at 30 °C for the composite with 40 phr of Fe3O4. The ability to store and retrieve electric energy on the nanocomposites is examined with the following parameters: the filler content and the applied voltage under dc conditions. Retrieved energy reaches 79.23% of the stored one, for the system with 15 phr of Fe3O4. Magnetic response is studied via a Vibrating Sample Magnetometer. Magnetic saturation, for the system with the highest magnetic filler content, obtains the value of 25.38 Am2/kg, while pure magnetic powder attains the value of 86.75 Am2/kg. Finally, the multifunctional performance of the nanocomposites is assessed regarding all the exerted stimuli and the optimum behavior is discussed.
ABSTRACT
Polymeric composites constitute an appealing class of materials with applications in various fields. Spin crossover (SCO) coordination complexes are switchable materials with potential use in data storage and sensors. Their incorporation into polymers can be considered an effective method for their wider practical application. In this study, Fe(II) SCO/polylactic acid hybrid polymeric composites have been prepared by film casting. The mononuclear coordination complex [Fe{N(CN)2}2(abpt)2] was incorporated into polylactic acid. The morphological, structural and thermoanalytical characterization of the composite films were performed via scanning electron microscopy (SEM), attenuated total reflectance (ATR/FTIR), Raman spectroscopy and differential scanning calorimetry (DSC). In addition, the migration release study (MRS) of the SCO compound from the polymeric matrix into the food simulant 50% v/v water/ethanol solution was also examined via UV/Vis absorption. Of particular interest was the investigation of the SCO behavior of the coordination complex after its incorporation into the polymer matrix; it was accomplished by temperature-dependent micro-Raman spectroscopy. The described attempt could be considered a preparatory step toward the development of SCO-based temperature sensors integrated into food packaging materials.
