Haihui Liu

Fabrication and characterization of polyamide 6-functionalized graphene nanocomposite fiber

Graphene oxide was prepared by the Hummers’ method and then functionalized with 4-substituted benzoic acid via “direct Friedel–Crafts” acylation in a mild reaction medium of polyphosphoric acid/phosphorous pentoxide (P2O5). Raman spectroscopy, differential scanning calorimetry, thermo-gravimetric analysis, and transmission electron microscopy were used to characterize the resultant structure. The results show that 4-substituted benzoic acid functionalized graphene (FG) sheets were achieved without pretreatment of oxidation. Polycaprolactam (PA6)-FG composites were prepared by in situ polymerization of ε-caprolactam in the presence of FG. Nanocomposite fiber with 0.01–0.5xa0wt% content of FG was prepared with a piston spinning machine and hot-roller drawing machine. A significant enhancement of mechanical properties of the PA6-FG composites’ fiber is obtained at low graphene loading; that is, a 29xa0% improvement of tensile strength and a three times increase of Young’s modulus are achieved at a graphene loading of only 0.1xa0wt%. The “graft-from” methodologies pave the way to prepare graphene-based nanocomposites of condensation polymers with promising performance and functionality.

Graphene and carbon nanotubes for the synergistic reinforcement of polyamide 6 fibers

Poly(styrene-maleic anhydride) functionalized graphene (FG) and functionalized carbon nanotubes (FCNTs) were fabricated using in situ polymerization. The FG and FCNTs were used in the in situ ring-opening polymerization of ε-caprolactam to form polyamide 6 (PA6)/FG/FCNTs composites. Both PA6 and the composite fibers were melt-spun in a piston spinning machine. The structure and properties of the composites and the fibers were characterized. The experimental results demonstrate that the mixture of graphene and carbon nanotubes exhibits good dispersion in a PA6 matrix. No obvious aggregation of graphene or CNTs was observed inside the composite fibers. The mechanical properties of PA6 are improved by inserting FG/FCNTs into the composite fibers, in particular, the tensile strength of composite fiber containing FG (0.2xa0wt%)/FCNTs (0.3xa0wt%) is 2.4 times that of pure PA6, and Young’s modulus is 132xa0% higher than that of the control. The crystallinity of the composite fibers is also enhanced. With the improvement of the tensile strength and Young’s modulus of PA6, its application will be expanded.

Thermoelectric behavior of PEDOT:PSS/CNT/graphene composites

Abstract Hybrids of poly(3,4-ethylenedioxythiophene) (PEDOT):poly(4-styrene sulfonate) (PSS)/multi-walled carbon nanotube (MWCNT)/graphene (P/M/G), which have high electrical conductivity and low thermal conductivity, were successfully prepared in aqueous solution through in situ polymerization of 3,4-ethylenedioxythiophene (EDOT) monomers in the presence of poly(sodium 4-styrene sulfonate) (PSSNa). Meanwhile, the composites were characterized by Raman spectroscopy, infrared (IR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy. Thermoelectric properties of the samples were measured at room temperature and 50°C. Compared with pristine PEDOT:PSS (P), PEDOT:PSS/MWCNT (P/M) and PEDOT:PSS/graphene (P/G), the power factor of P/M/G composites was significantly improved, whatever the temperature. It increased from 0.061 μW/mK2 to 0.105 μW/mK2 at room temperature and from 0.070 μW/mK2 to 0.142 μW/mK2 at 50°C, meaning 72% and 103% enhancement, respectively. The increased power factor is attributed to the synergic effects of MWCNT and graphene, a hybrid structure with excellent electronic coupling and more electric channels.

Facile preparation and thermoelectric properties of PEDOT nanowires/Bi2Te3 nanocomposites

Poly (3,4-ethylenedioxythiophene) nanowires (PEDOT NWs) with high electric conductivity were synthesized by a facile self-assembled micellar soft-template method. And then, Bi2Te3 powders and Bi2Te3 nanowires (Bi2Te3 NWs) were added as inorganic filler to form the PEDOT NWs/inorganic nanocomposite films by a simple and convenient vacuum filtration method. The thermoelectric (TE) properties of the flexible films were characterized. PEDOT NWs film exhibited the high σ value of 249.5xa0S cm−1 and does not require any treatment at room temperature. By incorporating both Bi2Te3 powders and Bi2Te3 NWs into these PEDOT NWs, the power factor of the polymer/inorganic composite materials is enhanced. The resulting PEDOT NWs/Bi2Te3 powders nanocomposite film exhibited a high power factor of 7.49 µW m−1 K−2 compared to that of 2.54 µW m−1 K−2 in PEDOT NWs. A maximum power factor of 9.06 µW m−1 K−2 is obtained from the PEDOT NWs/Bi2Te3 NWs composite film containing 10xa0wt% Bi2Te3 NWs at room temperature, which is about 3 of times that of the pure PEDOT NWs film. These composites provide a promising route to flexible and high-performance thermoelectric materials.

Biodegradable Transparent Substrate Based on Edible Starch–Chitosan Embedded with Nature-Inspired Three-Dimensionally Interconnected Conductive Nanocomposites for Wearable Green Electronics

Electronic waste (E-waste) contain large environmental contaminants such as toxic heavy metals and hazardous chemicals. These contaminants would migrate into drinking water or food chains and pose a serious threat to environment and human health. Biodegradable green electronics has great potential to address the issue of E-waste. Here, we report on a novel biodegradable and flexible transparent electrode, integrating three-dimensionally (3D) interconnected conductive nanocomposites into edible starch-chitosan-based substrates. Starch and chitosan are extracted from abundant and inexpensive potato and crab shells, respectively. Nacre-inspired interface designs are introduced to construct a 3D interconnected single wall carbon nanotube (SCNT)-pristine graphene (PG)-conductive polymer network architecture. The inorganic one-dimensional SCNT and two-dimensional PG sheets are tightly cross-linked together at the junction interface by long organic conductive poly(3,4-ethylenedioxythiophene) (PEDOT) chains. The formation of a 3D continuous SCNT-PG-PEDOT conductive network leads to not only a low sheet resistance but also a superior flexibility. The flexible transparent electrode possesses an excellent optoelectronic performance: typically, a sheet resistance of 46 Ω/sq with a transmittance of 83.5% at a typical wavelength of 550 nm. The sheet resistance of the electrode slightly increased less than 3% even after hundreds of bending cycles. The lightweight flexible and biocompatible transparent electrode could conform to skin topography or any other arbitrary surface naturally. The edible starch-chitosan substrate-based transparent electrodes could be biodegraded in lysozyme solution rapidly at room temperature without producing any toxic residues. SCNT-PG-PEDOT can be recycled via a membrane process for further fabrication of conductive and reinforcement composites. This high-performance biodegradable transparent electrode is a promising material for next-generation wearable green optoelectronics, transient electronics, and edible electronics.

Solid biopolymer electrolytes came from renewable biopolymer

Solid polymer electrolytes (SPEs) have attracted many attentions as solid state ionic conductors, because of their advantages such as high energy density, electrochemical stability, and easy processing. SPEs obtained from starch have attracted many attentions in recent years because of its abundant, renewable, low price, biodegradable and biocompatible. In addition, the efficient utilization of biodegradable polymers came from renewable sources is becoming increasingly important due to diminishing resources of fossil fuels as well as white pollution caused by undegradable plastics based on petroleum. So N, N-dimethylacetamide (DMAc) with certain concentration ranges of lithium chloride (LiCl) is used as plasticizers of cornstarch. Li+ can complexes with the carbonyl atoms of DMAc molecules to produce a macro-cation and leave the Cl- free to hydrogen bond with the hydroxyl or carbonyl of starch. This competitive hydrogen bond formation serves to disrupt the intra- and intermolecular hydrogen bonding existed in starch. Therefore, melt extrusion process conditions are used to prepare conductive thermoplastic starch (TPS). The improvements of LiCl concentration increase the water absorption and conductance of TPS. The conductance of TPS containing 0.14 mol LiCl achieve to 10-0.5 S cm-1 with 18 wt% water content.