Feng Chen

A simple and efficient method to prepare graphene by reduction of graphite oxide with sodium hydrosulfite.

Inspired by an ancient reducing method used in textile production, sodium hydrosulfite was used to reduce graphite oxide as an efficient reducing agent in our work. The reduced materials were characterized by x-ray photoelectron spectroscopy, thermogravimetric analysis, wide-angle x-ray scattering, Raman spectroscopy, solid state (13)C NMR spectroscopy and electrical conductivity measurements, respectively. The results showed that graphite oxide can be reduced with sodium hydrosulfite in a few minutes, with a degree of reduction comparable to those achieved with hydrazine. It provides an efficient method to reduce graphite oxide and could be used as a method to prepare novel composites.

Enhanced Epoxy/Silica Composites Mechanical Properties by Introducing Graphene Oxide to the Interface

Controlling the interface interaction of polymer/filler is essential for the fabrication of high-performance polymer composites. In this work, a core-shell structured hybrid (SiO(2)-GO) was prepared and introduced into an epoxy polymer matrix as a new filler. The incorporation of the hybrid optimized the modulus, strength and fracture toughness of the composites simultaneously. The ultrathin GO shells coated on silica surfaces were regarded as the main reason for the enhancement. Located at the silica-epoxy interface, GO served as an unconventional coupling agent of the silica filler, which effectively enhanced the interfacial interaction of the epoxy/SiO(2)-GO composites, and thus greatly improved the mechanical properties of the epoxy resin. We believe this new and effective approach that using GO as a novel fillers surface modifier may open a novel interface design strategy for developing high performance composites.

Preparation of polyester/reduced graphene oxide composites via in situ melt polycondensation and simultaneous thermo-reduction of graphene oxide

The introduction of graphene into a polymer matrix can markedly improve its mechanical properties and electrical conductivity. We report herein a novel strategy to fabricate polyester/reduced graphene oxide composites via simultaneous dispersion and thermo-reduction of graphene oxide (GO) during in situ melt polycondensation. The pristine graphite was first oxidized using a strong oxidant acid to prepare GO, and then GO sheets were dispersed into ethylene glycol (EG), where a homogeneous dispersion of GO in EG was obtained with ultrasonication. Finally polyester/reduced graphene oxide composites were prepared via in situpolymerization of terephthalic acid (PTA) and ethylene glycol containing well dispersed GO. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and sedimentation experiments have been used to characterize the prepared composites. It is demonstrated that poly(ethylene terephthalate) (PET) chains may have been sucessfully grafted onto GO sheets during polymerization, accompanied by the thermo-reduction from GO to graphene. The TGA and XPS results showed that the content of grafted PET polymer was about to 60–80%, which indicates a homogeneous dispersion of GO sheets in the PET matrix, as demonstrated by SEM. Furthermore, a significant improvement in tensile strength and elongation at break of PET has been achieved. Therefore, our work provides a new way for the preparation of polyester/reduced graphene oxide composites and functionalization of graphene.

Fabrication of a transparent superamphiphobic coating with improved stability

We herein provide an effective method to fabricate a transparent superamphiphobic coating with superhydrophobicity and near-superoleophobicity, the finished coating also shows improved stability under various measurements. To do this, a transparent superhydrophobic coating was first prepared with polydimethylsiloxane (PDMS) and hydrophobic silicon dioxide (SiO2) nanoparticles. Then the coating was sintered to degrade the PDMS into SiO2 before it was further oxidized into silanol (Si–OH). Finally, the coating was treated with 1H, 1H, 2H, 2H-Perfluorooctyl-trichlorosilane (PFTS). The PFTS treated coating shows transparency, superhydrophobicity with a water contact angle of 152.7 ± 2.1° and near-superoleophobicity with a diiodomethane contact angle of 140.7 ± 3.2°. The droplets of water and diiodomethane can simultaneously slide off the surface with a sliding angle of less than 6°. Moreover, the PFTS treated coating shows a higher stability than the PDMS/SiO2 coating fabricated by spin coating under various environmental conditions. The PFTS treated coating also shows quite good stability under high temperature environment. The superamphiphobic properties, transparency and improved stability of the PFTS treated coating are systemically discussed and the results show that the finished coating may be appropriate for many outdoor applications.

Superior reinforcement in melt-spun polyethylene/multiwalled carbon nanotube fiber through formation of a shish-kebab structure.

The formation of a shish kebab (SK) structure, where carbon nanotubes (CNTs) serve as shish and polymer lamellae serve as kebab, is particularly interesting and provides a novel way to enhance the polymer-CNT interface. A fine SK structure is achieved through melt spinning. High density polyethylene and pristine CNTs were first compounded in an extruder. The compound was then spun into fibers with different draw ratios with the aid of a capillary rheometer. The crystalline structure and mechanical behavior were characterized by scanning electron microscopy, differential scanning calorimetry, two-dimensional wide-angle X-ray scattering, polarized Raman spectroscopy, and tensile testing. An increase in tensile strength as high as 3 times has been achieved in the fiber. The formation of SKs is considered as the main mechanism responsible for the enhanced interfacial interaction and excellent tensile property.

Toward high performance graphene fibers

Two-dimensional graphene and graphene-based materials have attracted tremendous interest, hence much attention has been drawn to exploring and applying their exceptional characteristics and properties. Integration of graphene sheets into macroscopic fibers is a very important way for their application and has received increasing interest. In this study, neat and macroscopic graphene fibers were continuously spun from graphene oxide (GO) suspensions followed by chemical reduction. By varying wet-spinning conditions, a series of graphene fibers were prepared, then, the structural features, mechanical and electrical performances of the fibers were investigated. We found the orientation of graphene sheets, the interaction between inter-fiber graphene sheets and the defects in the fibers have a pronounced effect on the properties of the fibers. Graphene fibers with excellent mechanical and electrical properties will yield great advances in high-tech applications. These findings provide guidance for the future production of high performance graphene fibers.

Simultaneous reinforcing and toughening of polyurethane via grafting on the surface of microfibrillated cellulose.

In the present work, a series of thermoplastic polyurethane (TPU)/microfibrillated cellulose (MFC) nanocomposites were successfully synthesized via in situ polymerization. TPU was covalently grafted onto the MFC by particular association with the hard segments, as evidenced by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The adequate dispersion and network structure of MFC in the TPU matrix and the strong interfacial interaction through covalent grafting and hydrogen bonding between MFC and TPU resulted in significantly improved mechanical properties and thermostability of the prepared nanocomposites. The tensile strength and elongation-at-break of the nanocomposite containing only 1 wt % MFC were increased by 4.5-fold and 1.8-fold compared with that of neat TPU, respectively. It was also very interesting to find that the glass transition temperature (Tg) of TPU was decreased significantly with the introduction of MFC, indicating potential for low-temperature resistance applications. Most importantly, compared with TPU nanocomposites reinforced with other nanofillers, the TPU/MFC nanocomposites prepared in this work exhibited excellent transparency and higher reinforcing efficiency.

Molecular weight dependence of hybrid shish kebab structure in injection molded bar of polyethylene/inorganic whisker composites.

In our previous work, a hybrid shish kebab structure, with polyethylene (PE) crystal lamellae periodically decorated on the surface of an inorganic whisker (SMCW) and aligned approximately perpendicular to the long axis of the whisker, has been observed in the injection molded bar of PE/SMCW composites. To investigate the effect of the molecular weight of the PE matrix on the formation of the hybrid shish kebab structure and the corresponding physical properties of HDPE/SMCW composites, in this work, three types of PE with different molecular weights were used to prepare the composites. They were first melt blended and then subjected to dynamic packing injection molding (DPIM), in which the prolonged shear was exerted on the melt during the solidification stage. An obvious hybrid shish kebab (HSK) structure, with PE crystal lamellae closely packed on the surface of the SMCW, was found in the samples with a low molecular weight PE (LMW-PE) matrix and a medium molecular weight PE (MMW-PE) matrix. However, in samples with a high molecular weight PE (HMW-PE) matrix, an incomplete HSK structure with PE crystal lamellae loosely decorated on the surface of the SMCW was observed. Furthermore, DSC results indicated that SMCW served as a good nucleating agent only for the composite with a LMW-PE matrix and the nucleation efficiency decreased with increasing PE molecular weight. Correspondingly, the tensile strength of the PE/SMCW composites was significantly improved by adding SMCW for the samples with a LMW-PE or MMW-PE matrix. Especially for samples with a LMW-PE matrix, the tensile strength was remarkably enhanced by the presence of only 1 wt % SMCW. For the composites with a HMW-PE matrix, the addition of SMCW had almost no reinforcing effect on the composites. The molecular weight dependence of the formation of HSK and property enhancement was discussed on the basis of the chain mobility and crystallization capability of the PE matrix.

Enhancing the melt stability of polylactide stereocomplexes using a solid-state cross-linking strategy during a melt-blending process

Stereocomplexation between poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) provides a feasible route for improving the performance of polylactide (PLA), including mechanical strength, thermal stability and hydrolysis resistance. In recent years, several effective methods have been developed to prepare polylactide stereocomplexes (sc-PLA) from commercially available, linear, high-molecular-weight PLLA and PDLA. However, it is still a big challenge to attain pure sc-PLA in the melt-processed products because the prepared sc-PLA has a very poor melt stability, that is the ability to trigger the reformulation of stereocomplex (sc) crystallites after complete melting is significantly depressed, resulting in the formation of mixed homochiral (hc) and sc crystallites. Here we present a facile strategy to fabricate sc-PLA with good melt stability by low-temperature (180 °C) melt-blending of equimolar PLLA and PDLA in the presence of a trace amount (0.1–0.5 wt%) of a cross-linker. During the blending process, sc crystallites form rapidly, followed by a slight cross-linking of PLLA and PDLA chain couples in the mobile amorphous phase, whereas the chain couples in the crystalline phase hardly participate in the cross-linking reaction. The exclusive cross-linking of PLA chains in the amorphous phase not only allows for the introduction of abundant cross-linking points at the ends of the chain couples to prevent them from completely decoupling upon melting but also retains large amounts of long crystallizable PLA segments existing in the initially formed sc crystallites to impart the resulting sc-PLA with an excellent recrystallization ability upon cooling. The formation or reformulation of sc crystallites in the continuous melting and recrystallization process is found to be perfectly reversible, without any trace of hc crystallites.

A promising alternative to conventional polyethylene with poly(propylene carbonate) reinforced by graphene oxide nanosheets

We show an order of magnitude increase in yield strength and Youngs modulus of poly(propylene carbonate) (PPC) by adding a small amount of graphene oxide (GO) nanosheets, accompanied by a dramatic increase of glass transition temperature (Tg). The reinforced tensile properties are comparable to those of conventional polyethylene. This work opens the door to replace conventional polyethylene by PPC.