Morphological Study and Dielectric Behavior of Nonisothermally Crystallized Poly(ethylene naphthalate) Nanocomposites as a Function of Graphene Content

Morphological evolution and dielectric properties of poly(ethylene naphthalate)- (PEN-) graphene nanocomposites nonisothermally crystallized have been investigated. PEN-graphene nanocomposites containing 0.01, 0.025, 0.05, 0.075, and 0.1 wt% of graphene were prepared by melt blending in a mini twin screw extruder. The results showed that graphene exhibited a superior influence on morphological and conformational structure of PEN during nonisothermal crystallization at low graphene contents. Crystallization temperature (Tc) was found to be increased up to 18°C supporting the high nucleating activity of graphene layers. Wide angle X-ray diffraction (WAXD) and Fourier Transform Infrared Spectroscopy (FTIR) indicated that graphene modifies the conformation of PEN chains promoting crystallinity and favoring the evolution from α to β crystalline form with homogeneous lamellar thickness. It may be attributed to the structural similarity between naphthalene rings and graphene structure and to π-π interactions during nucleation. Dielectric behavior was found to be a function of graphene content where the nanocomposites changed from dielectric to low conducting material when passing from 0.075 to 0.1 wt% of graphene content. This phenomenon permits having a wide range of properties to fit a wide variety of applications required to store electrical energy of low voltage

Nanocomposite and biodegradable polymers applied to technical textiles

Based on the results of research papers reflected in the scientific literature, the main examples, methods and perspectives for the development of technical textiles are considered. The focus of this work is to concentrate the results obtained for different textile applications (technical textiles) through the use of biodegradable polymers modified and improved with nanoparticles. The techniques for obtaining polymeric nanocomposites, finishing processes, type and structure of textiles are specified. In general, key aspects are identified for a better understanding of the technical challenges and physicochemical effects of the fibersCon base en los resultados de trabajos de investigación reflejados en la literatura científica, se consideran los principales ejemplos, métodos y perspectivas para el desarrollo de textiles técnicos. El enfoque de este trabajo consiste en concentrar los resultados obtenidos para diferentes aplicaciones textiles (textiles técnicos) mediante el uso de polímeros biodegradables modificados y mejorados con nanopartículas. Se especifican las técnicas para obtención de nanocompuestos poliméricos, procesos de acabado, tipo y estructura de textiles. En general, se identifican aspectos clave para una mejor comprensión de los retos técnicos y efectos fisicoquímicos de las fibra

Chain-folding and overall molecular conformation in a novel amphiphilic starlike macromolecule

The crystallization and self-assembly behavior of an amphiphilic starlike macromolecule (ASM) with a lipophilic core and four poly(ethylene oxide) (PEO) arms (Mn = 2000 g/mol) were characterized by synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction at different crystallization temperatures (Tc). The overall d-spacing of the alternating amorphous core and crystalline PEO lamellae almost doubled from 11.4 nm for samples quenched into liquid nitrogen to 21.0 nm for Tc = 42 °C, indicating gradual transitions from nearly once-folded to fractionally folded and finally to extended chain crystals with increasing the Tc. On the basis of SAXS, transmission electron microscopy, and computer simulation results, it was suggested that the lamellae contained an interdigitated, single-layered PEO crystal, and an amorphous layer consisted of a double-layered lipophilic core and amorphous PEO. A folded (four PEO arms at one side of the core) rather than an extended (two PEO arms on each side of the core) overall molecular conformation (OMC) of the ASM was deduced in the solid state. These results implied that chain-folding and OMC of the ASM closely depended on its star-block-like architecture

Metamaterial Behavior of Polymer Nanocomposites Based on Polypropylene/Multi-Walled Carbon Nanotubes Fabricated by Means of Ultrasound-Assisted Extrusion

Metamaterial behavior of polymer nanocomposites (NCs) based on isotactic polypropylene (iPP) and multi-walled carbon nanotubes (MWCNTs) was investigated based on the observation of a negative dielectric constant (ε′). It is demonstrated that as the dielectric constant switches from negative to positive, the plasma frequency (ωp) depends strongly on the ultrasound-assisted fabrication method, as well as on the melt flow index of the iPP. NCs were fabricated using ultrasound-assisted extrusion methods with 10 wt % loadings of MWCNTs in iPPs with different melt flow indices (MFI). AC electrical conductivity (σ(AC)) as a function of frequency was determined to complement the electrical classification of the NCs, which were previously designated as insulating (I), static-dissipative (SD), and conductive (C) materials. It was found that the SD and C materials can also be classified as metamaterials (M). This type of behavior emerges from the negative dielectric constant observed at low frequencies although, at certain frequencies, the dielectric constant becomes positive. Our method of fabrication allows for the preparation of metamaterials with tunable ωp. iPP pure samples show only positive dielectric constants. Electrical conductivity increases in all cases with the addition of MWCNTs with the largest increases observed for samples with the highest MFI. A relationship between MFI and the fabrication method, with respect to electrical properties, is reported