This study reports for the first time a green process
to fabricate
Lyocell fiber and graphene oxide (GO) based novel cellulose/graphene
oxide nanocomposite (CGN) flexible films for ultraviolet (UV) shielding
applications. A polyethelene glycol (PEG) mediated solvent system
was utilized to make CGN films via solution casting route. To improve
the dispersion of GO sheets in a cellulosic matrix, a reactive interface
was formed in between cellulose and oxygenic functionalized groups
of GO sheets via cross-linking them with epichlorohydrin (ECH). The
addition of GO sheets in cellulose matrix leads to the synergistic
changes, which were observed in the structure and surface morphology
of CGN nanocomposite films. Enhanced dispersion of GO sheets in CGN
films was observed in morphological investigations which is attributed
to the adequate cellulose–GO interaction by hydrogen bonding
and led to significant enhancement in the mechanical and thermal properties.
The tensile strength and Young’s modulus of CGN films with
2 wt % GO loading (CGN2) increased to 89 MPa and 4.3 GPa from 55.6
MPa and 2.1 GPa, respectively, as compared to the neat cellulosic
film. Additionally, the CGN films exhibited remarkable UV shielding
capability which increased with GO loading in a cellulose matrix.
The CGN2 film (2 wt % GO loading) possessed outstanding absorbance
in the wavelength range of 280 to 400 nm and showed almost complete
shielding (∼99%) of UV rays in both the UV-B and the UV-A regions.
Moreover, the ultraviolet protection factor of the CGN2 film demonstrated
more than 80-fold increase compared to that of the neat cellulose
film. The obtained CGN nanocomposite film has a high potential for
applications in the field of UV protection.
We report the electrical, mechanical and electromagnetic interference (EMI) shielding performance of polypropylene random copolymer (PPR)/multi-wall carbon nanotube (MWCNT) nanocomposites enabled via customized fused filament fabrication process. The electro-conductive PPR/MWCNT filament feedstocks were fabricated via shear-induced melt-blending process that allows 3D printing of nanoengineered composites even at higher MWCNT loading (up to 8 wt%). The uniform dispersion of MWCNTs in PPR matrix confirmed via Raman spectroscopy and scanning electron microscopy facilitates better mechanical, electrical and EMI shielding performance. The results furthermore show enhanced shielding properties and higher attenuation for the nanocomposites printed in 90° direction (~ − 37 dB for 8 wt% MWCNT loading). Effective interfacial adhesion between the beads with lesser extent of voids (confirmed via micro-computed tomography) endorsed low transmission loss in nanocomposites printed in 90° direction compared to samples printed in 0° direction. Surface architected structure (frustum shape) reveals higher specific shielding effectiveness (maximum ~ − 40 dBg−1cm3, + 38%) over the plain structure. The realization of excellent shielding effectiveness (~ 99.9% attenuation) of additive manufacturing-enabled PPR/MWCNT nanocomposites demonstrates their potential for lightweight and strong EMI shields.
Graphical Abstract
We have demonstrated noncontact heating of melt electrospun polymer fibers by using radio-frequency (RF) fields which heat carbon nanotube (CNT) receptors inside the fibers. RF radiation is attractive as it allows for noncontact heating of polymers with low concentrations of CNTs. We observed that the heating rate scales with the CNT loading even below the bulk electrical percolation threshold, suggesting that individual CNTs can serve as RF receptors/heat sources. This capability eliminates the requirement for a percolated network of CNTs inside a fiber as a means to enable heating. We also showed that a strong radial temperature gradient will develop within the fibers. For a 2 μm diameter fiber, the temperature of the core is 10−15 °C higher than the surface. Hence, the temperature of the core can surpass the melting temperature inside the fiber without altering the morphology of the fibers (i.e., without fusing between fibers). These electrospun fibers that can be stimulated through RF energy can be used for applications such as plastic electric heaters, hyperthermia treatment, and heatgenerating textiles.
Electrospinning is commonly used for fabrication of polymer fibers. Melt electrospinning, instead of the commonly used solution electrospinning, offers many advantages in generating polymer fibers without using solvents. However, polymer melts have high viscosity which poses major limitations in producing low diameter fibers. Here, melt electrospinning is investigated at elevated temperatures in inert atmosphere to reduce fiber diameters while suppressing thermal degradation. Two types of spinneret configurations, syringe and wire, with two distinct outcomes are studied. In syringe‐based electrospinning, increasing the nozzle temperature from 300 to 360 °C in nitrogen reduced fiber diameter significantly from 33 ± 5 to 10 ± 4 µm. Electrospinning in nitrogen leads to formation of fibers even at a high nozzle temperature of 360 °C, while this temperature leads to thermal degradation when spinning in air. In contrast, increasing the temperature of wire electrospinning setup do not lead to a noticeable reduction in diameter. This is attributed to the viscosity‐dependent flow rate in this method. Increasing the temperature leads to increased flow rates, promoting the formation of thicker fibers, while the increased stretchability promotes the formation of thinner fibers. The results clearly demonstrate advantages of developing polymer microfibers in inert atmosphere to avoid thermal degradation with a temperature‐independent flow control.
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