Volume 41, Issue 1

A solid fluorescence sensor composed of g-C 3 N 4 nanosheets and chitosan solid film was fabricated by electrostatic interaction. The g-C 3 N 4 nanosheet/chitosan solid film showed selectivity and sensitivity to Cu 2+ which was higher than that of other metal ions in common use. Cu 2+ ions were found to efficiently bind and quench the fluorescence of the g-C 3 N 4 nanosheet/chitosan solid film. The absorption band of the g-C 3 N 4 nanosheet/chitosan solid film was at 240 nm in the presence of Cu 2+ , and the maximum emission peak was at 380 nm. Copper ion concentrations were between 0 and 3.1 × 10 −5  mol/L at pH 7, the detection limit is 5 nM, compared with previous reports, it was much lower than before. Good linear relationships existed between the metal ion concentration and fluorescence intensity of g-C 3 N 4 nanosheets in the quenching and recovering processes. This is the first study to report on the detection of Cu 2+ by utilizing g-C 3 N 4 nanosheet/chitosan composite film. The as-prepared films were conveniently prepared, easy to operate, and recyclable, as well as sensitive and selective to detect Cu 2+ in water. All these features indicate the sensor’s potential application in disease diagnosis.

This work presents the chemical modification of Spanish broom flour (SBF), and the study of SBF loading and surface treatment on the performances of polypropylene (PP) biocomposites. In order to enhance the interfacial interactions between the PP matrix and the SBF, two types of chemical treatments were used: 2 wt% of sodium hydroxide (NaOH) for different times (8, 24 and 48 h) and 5 wt% of vinyltrimethoxysilane (VTMS), respectively. Different techniques for characterization such as the melting flow index (MFI), X-ray diffraction, transient plane source (TPS) and water absorption were used. The experiment results showed a decrease of the MFI with increasing of modified SBF content, independently of the type of the chemical treatment. Moreover, this decrease became significant in the biocomposites containing SBF-VTMS. The X-ray patterns showed that surface treatment of SBF could improve their crystallinity and crystallite sizes. The TPS measurements illustrates that the thermal conductivity of the biocomposites decreases with 10 wt% of modified SBF loading. Higher content than 20 wt% of SBF, improved the thermal conductivity of the biocomposites. Meanwhile, the lowest values were found when the VTMS is used. Besides, it was accompanied by a decrease in absorptivity due to the better interfacial adhesion SBF-PP.

Dielectric behavior in paracrystalline poly(vinyl trifluoroacetate) was investigated from the viewpoint of ferroelectricity. This polymer has a large CF3 dipole moment (2.3 Debye) and structural defects due to the atactic sequence in its chain conformation. It is possible to rotate the dipoles in paracrystals with defects under high electric field. The dielectric behavior was measured from 20 to 200 °C. A large dielectric constant and dielectric relaxation strength (Δε = 17 at 110 °C) were observed in the α-relaxation region. Corona poling on the samples was carried out at DC field 80 MV/m and 80 °C. Ferroelectric D–E hysteresis loop was observed under high electric field, and the remanent polarization and coercive field at 40 °C were 15 mC/m 2 and 155 MV/m, respectively. Pyroelectric response and thermally stimulated current were measured from the current through the electrode irradiated by a pulsed semiconductor laser. A pyroelectric constant of about 6 μC/m 2 K was observed, which was stable up to near the poling temperature. The ferroelectricity in poly(vinyltrifluoroacetate) stems from the rotation of molecular chains in its paracrystals and orientation of the CF2 dipoles. Poly(vinyltrifluoroacetate) dielectrics can be used for capacitors with high power density, artificial skins, muscles and other flexible electronics.

The actual replacement of traditional metallic components with plastic-based materials in the marine sector is currently extremely limited, mainly due to mechanical requirements and flammability issues. In this work, a fiberglass-reinforced polyamide 6,6 matrix, loaded with innovative flame retardants based on nanosized organoclays has been evaluated as a replacement for aluminum in a marine engine cover. Experimental data were acquired to assess the mechanical performances and flammability properties of this novel polymer nanocomposite in comparison with those of a commercial sample based on the same polymeric matrix loaded with traditional flame retardants. The results showed that then use of nanoclays in place of standard flame retardants increased the mechanical properties of the polymer nanocomposite at all tested temperatures (22% of modulus increase at 20 °C, 93% at 110 °C), concomitantly meeting the minimum nonflammability requirements (self-extinguishing, without dropping of flammable material).

A novel functionalized tannin-chitosan bentonite composite (TCBC) was successfully synthesized. The formation of the composite was confirmed by the X-ray diffraction (XRD) patterns and Fourier transform infrared spectroscopy (FT-IR) analysis. The pH pzc of TCBC was 3.38. The influences such as pH, dosage of TCBC, temperature and initial Cr(VI) concentration on adsorption capacity were investigated. The experimental data indicated that the almost saturated adsorption of the TCBC towards Cr(VI) in 100 min. The maximum adsorption capacity was 262.08 mg/g at 333 K with initial pH = 2.5. The adsorption kinetics of Cr(VI) on TCBC followed the pseudo-second-order kinetics model. The isothermal data were well described by the models of Langmuir, Freundlich and Temkin. The results revealed that the adsorption of Cr(VI) on TCBC existed comprehensive effects and mainly belong to the chemisorption. The TCBC could keep good performances ( q e  = 192.17 mg/g) in five runs, 1 M NaOH was used as eluent for desorption, which showed a high desorption efficiency. Studies showed TCBC prepared with low cost and green raw materials, and simple green preparation technology had high adsorption capacity, good reusability and acidic tolerance. By exploring the Cr(VI)-Cr(III) hybrid system, part of Cr(VI) was reduced to Cr(III) and adsorbed by TCBC. The optimal adsorption pH of Cr(III) was 5.0.

The main objective of the present work was to develop intumescent fire-retardant coating (IFRC) for wood based on modified natural rubber (NR). A newly modified form of NR, namely graft copolymers of NR and poly(methacrylic acid) (PMAA), NR-g-PMAA, was first synthesized by a solution polymerization technique. The IFRC was then prepared by compounding the synthesized NR-g-PMAA with a curing agent and an intumescent additive to form a compound coating. Cross-linking of the NR-g-PMAA coating was achieved by reactions with polyisocyanate based on hexamethylene diisocyanate (poly‐HDI) under ambient conditions. Interactions of NR-g-PMAA with poly‐HDI were also studied using X-ray photoelectron spectroscopy. Expandable graphite (EG) was employed as intumescent filler in the present study. The thermal stability of the NR-g-PMAA coating films was first studied by thermogravimetric analysis. The fire-retardant properties of wood, with or without the NR-g-PMAA coating, were then examined using the limiting oxygen index and cone calorimetry test. The flammability tests indicate that the flame-retardant properties of wood were greatly improved by treatment with the NR-g-PMAA-based IFRC. Hence, it can be stated that this new form of modified NR has shown to possess potential application in the IFRC when used in combination with EG.

Ionic hydrogels with great water absorption capacity generally display poor mechanical strength that limits their use and narrows down their application areas. In this study, the new ionic hydrogel composed of poly (3-methacrylamido propyl trimethyl ammonium chloride) crosslinked with N , N -methylenebisacrylamide and sulphate ions was synthesized to obtain the hydrogel formulation which exhibits both huge swelling capacity and high mechanical stability, simultaneously. The successively synthesized gels with this strategy achieved a swelling capacity of 270 g/g and a modulus increased up to 20.43 kPa, indicating that they have a great potential to use in applications in which the both properties are required. The gels carrying a great number of cationic sites were also found to have a high affinity to phosphate ions, attaining an sorption value of 370 mg/g gel and to exhibit pseudo-second-order kinetic and Langmuir sorption isotherm models. The obtained results revealed that the new pMAPTAC gels have good potential for both phosphate sorption and high water uptake capacity without losing structural integrity owing to their enhanced mechanical strength.

A triple interpenetrating polymer network (IPN) with dual responses to temperature and pH was constructed based on chemical crosslinking and electrostatic interaction. In this IPN, CaCO 3 microspheres were used as the kernel and PNIPAAM/sodium alginate microcapsules were prepared by the inverse emulsion polymerization method. Research results demonstrated that CaCO 3 kernels were decomposed into Ca 2+ and CO 2 at pH 1.2. Such decomposition facilitated the formation of triple IPN of Ca 2+ crosslinking. Moreover, microcapsules were expanded by tension of CO 2 and the volume increased to 3.55 × 10 5 times that of the original microcapsules, with capsules remaining an intact morphology. These microcapsules loading doxorubicin hydrochloride (DOX) stability and responses to environment were investigated. No drug overflow was observed at pH 7.4, indicating the high stability of microcapsules. However, DOX was released gradually in the simulated human stomach acid with a weak solution of hydrochloric acid (pH 1.2, 37 °C). This showed that the prepared microcapsules were feasible for drug-loaded capsules and the controlled drug release behavior could relieve side effects of drugs to human body. Moreover, it will help to increase the drug utilization and realize accurate treatment.

A single cell of direct methanol fuel cell (DMFC) typically delivers an electrical potential between 0.5 and 1 V; thus DMFCs are assembled in parallel to meet power demands (1–5 kW). Bipolar plates (BPs) are the primary components connecting a single cell to the adjacent cells so that they provide optimum electrical conductivity. The objective of this research is to reduce the volume resistance of BPs made from a polypropylene/carbon composite by utilizing a metal insert technique. A major obstacle when it comes to molding composite plates inserted by a thin metal sheet is the delamination of material layers after the cooling process. The delamination issue is due to different surface polarities between metal and polypropylene-composite surfaces. One of the strategies to solve this issue is to modify the surface of one layer for creating similarity of the surface polarity. A metal sheet surface was coated with graphene using a cold spraying technique to enhance adhesion ability. The suitable spraying conditions were determined by experimenting with varying temperature, pressure, graphene quantity and graphene types. The effectiveness of surface modification by the graphene spraying technique was assessed by a surface morphology observation, an electrical conductivity measurement and DMFC performance tests. Results were interesting, they indicated that when DMFC was assembled with silver sheet, inserted BPs provided 25.13 mW/cm 2 of power density, 3,350.7 mWh of generated energy and 67% of efficiency. This highlights that the performance of a BP prototype is superior to the performance of a commercial composite bipolar plate.