The dual role of phosphonium- and
imidazolium-based ionic liquids
(ILs) combined with FeCl4 counteranions as hardeners for
epoxy resin (ER) and additives for improving the microwave-absorbing
properties was investigated. The influence of the chemical nature
of the cation on the curing process of ER was evaluated by rheometric
and differential scanning calorimetry (DSC) analysis. No significant
curing process was observed for the ER-based systems until 7 days
of storage at room temperature. DSC analysis under the dynamic mode
was carried out at different heating rates to evaluate the best curing
protocol and the kinetic parameters. Phosphonium-based ILs promoted
faster curing rate and lower activation energy of the epoxy system,
higher cross-link density observed by dynamic mechanical analysis,
and better thermal stability. Moreover, ER cured with phosphonium
ILs presented good microwave-absorbing properties, with minimum reflection
loss values of −13.5 dB (at 9.5 GHz) and −11.5 dB (at
14.5 GHz), corresponding to more than 90% of electromagnetic attenuation.
These results indicate that ER cured with these magnetic ILs can be
used as promising microwave-absorbing materials in both X-band (8–12
GHz) and Ku-band (12–18 GHz).
In this work, immiscible poly(lactic acid) (PLA)/poly(ethylene vinyl acetate) (EVA) composites with 1 phr of multi-walled carbon nanotube (CNT) and different concentration of protonic-based imidazolium ionic liquid (mimbSO 3 H•Cl) were prepared. The protonic ionic liquid (IL) was able to act as dispersing agent for CNT and as compatibilizing agent for the PLA/EVA blend. The multicomponent nanocomposites from the mixture of PLA and EVA containing CNT functionalized with ionic liquid, IL (CNT/ILSO 3 H) were characterized by mechanical and dynamic-mechanical (DMA) tests, electrical conductivity analyses, differential scanning calorimetry (DSC), X-ray diffraction analysis and rheological measurements, as well as chromatographic gel permeation (GPC), and scanning electron microscopy (SEM). The non-covalent functionalization CNT resulted in composites with outstanding electrical and dielectric properties. The high dispersion of CNT promoted by the IL resulted in the formation of a physical networked structure, which was responsible for the higher electrical conductivity and higher melt viscosity. The crystallization process of PLA phase was improved with the presence of CNT/ILSO 3 H. The degradation process during the transesterification reaction did not significantly affect the mechanical properties. The present work highlights the dual role of the IL as compatibilizing and dispersing agent and opens new perspectives for developing new conducting systems with low percolation threshold based on the good dispersion of CNT and the confinement of the filler within a phase of a multiphasic polymeric system.
Poly(vinylidene fluoride) (PVDF) based composites loaded with 3 wt% of carbon black (CB), graphite (GF), and the hybrid CB/GF (1.5/1.5 wt%) were prepared by melt mixing and tested as microwave absorbing material at X-band frequencies (8-12 GHz). The materials were processed and pressed at 220 C into plates of 20 × 20 × 0.1 cm 3. Dielectric and magnetic properties were evaluated using the wave-guide accessory to simulate the reflectivity of singlelayered PVDF composites through impedance matching behavior. The best absorbing properties were achieved with the composite loaded with the CB/GF hybrid material, whose maximum of radiation attenuation of −33 dB at 9.3 GHz was predicted with 4 mm thickness. Afterwards, the reflectivity of sandwiched structures (20 × 20 cm 2 in size) with one-layer honeycomb core sandwiched by two plates of PVDF composites was measured. The PVDF/HBhoneycomb-PVDF/HB structure reached reflection loss = −12 dB (E a = 94%) on a broadband frequency. CB/GF hybrid material in PVDF composites has a promising future as a lightweight and cost-effective microwave absorbing materials for both telecommunication and stealth technology.
Poly(vinylidene fluoride-co-hexafluoropropylene)/polyaniline (PVDF-co-HFP/ PAni) conductive blends were prepared by two methodologies involving the in situ polymerization in two different media and dry blending approach using ball milling. Dodecylbenzenesulfonic acid (DBSA) was used both as surfactant and as protonating agent in PAni synthesis. X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis) spectroscopy, and thermogravimetric analysis were used for characterizing the blends. PAni and PVDF/PAni prepared by in situ polymerization in H 2 O/toluene medium exhibited superior electrical conductivity, higher thermal stability and significantly higher electromagnetic interference shielding effectiveness (EMI SE) than those prepared in H 2 O/dimethylformamide (DMF) medium. PVDF/PAni with high-PAni content (>40%) prepared by the dry blend approach presented higher conductivity and EMI SE than those prepared by in situ polymerization.
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