Xingyou Tian

The effects of polydimethylsiloxane on transparent and hydrophobic waterborne polyurethane coatings containing polydimethylsiloxane.

The effects of polydimethylsiloxane (PDMS) on phase separation, optical transmittance and surface properties including surface composition, morphology and wettability of waterborne polyurethane (WPU) containing PDMS were investigated. After the introduction of PDMS into the WPU backbone by polymerization, the large difference in the solubility parameter of the non-polar PDMS segment and the high-polar urethane segments promoted PDMS enrichment at the air-polymer interface and enhanced phase separation, resulting in rough structures. Accordingly, the combination of PDMS enrichment and the rough structures contributed to the high or superhydrophobic surfaces and the highest contact angle with water achieved was 156.5°. The optical transmittance of the highly hydrophobic coatings reached about 78-87% throughout most of the visible light region. Importantly, the highly hydrophobic and transparent properties will greatly broaden the applications of WPU, showing potential for the environmental protection and industrial applications.

Preparation and Properties of Poly(ethylene terephthalate)/Silica Nanocomposites

A kind of poly(ethylene terephthalate) (PET)/Silica nanocomposite (PETS) was synthesized via in situ polymerization using the compatibility between silica nanoparticles and ethylene glycol (EG). Transmission electron microscopy (TEM) micrographs revealed that the silica nanoparticles were well dispersed in the PET matrix, the particle size was about 10 nm with narrow distribution, and there existed strong interaction between the particles and the polymer chains. Differential scanning calorimetry (DSC) results indicated that the thermal properties of PETS with 2 wt% silica (PETS‐2) are different from those of pure PET (PETS‐0). The properties of the as‐spun fibers show that the tenacity and LASE‐5 (load at a specified elongation of 5%) of PETS‐2 were higher than those of PETS‐0, while the heat shrinkage of PETS‐2 was lower than that of PETS‐0. We suggest that the increasing of crystallinity and the strong interface interaction of the nanocomposite caused the fibers of PETS‐2 to not only have higher tenacity and LASE‐5 but also to have lower heat shrinkage.

Room temperature fabrication of an RGO–Fe3O4 composite hydrogel and its excellent wave absorption properties

As a result of their lightweight properties and high dielectric loss, graphene and their composites have attracted great attention for potential applications in wave absorption. Herein, we report room temperature conditions for the synthesis of a 3D composite hydrogel composed of reduced graphene oxide nanosheets and Fe3O4 nanoparticles (RGO–Fe3O4). The experimental results show that the composite has an interconnected 3D porous network with micrometer-sized pores, and that the Fe3O4 nanoparticles with a small size of about 5–10 nm are uniformly dispersed onto the thin graphene nanosheets. The as-prepared RGO–Fe3O4 composite hydrogel shows excellent microwave absorbability compared with previously reported nanocomposites based on graphene and Fe3O4. The obtained composite with a coating layer thickness of only 2.5 mm exhibits a maximum absorption of −47.9 dB at 10.1 GHz. In particular, the product with a coating layer thickness of only 2.0 mm shows a bandwidth of 5.3 GHz (from frequency of 11.3–16.6 GHz) corresponding to reflection loss at −10 dB (90% absorption). Additionally, the fabrication method is simple, low cost and easily done on a large scale. This further confirms that nanoscale Fe3O4 particles on graphene networks give the composite hydrogel the ability to realize practical applications for wave absorption.

Au–Pt alloy nanoparticles site-selectively deposited on CaIn2S4 nanosteps as efficient photocatalysts for hydrogen production

Au–Pt/CaIn2S4 composites were synthesized for the first time using the photoreduction method by which bimetallic Au–Pt alloy nanoparticles were in situ site-selectively photoreduced on the edges of monoclinic CaIn2S4 nanosteps. The Au–Pt alloy nanoparticles as cocatalysts can spatially separate the oxidation and reduction sites and effectively enhance the photocatalytic hydrogen activity of CaIn2S4 under visible light irradiation. When introducing 0.5 wt% Au–Pt alloy nanoparticles, the rate of hydrogen production could reach 107.6 μmol h−1, which was higher than that of CaIn2S4, Au/CaIn2S4 and Pt/CaIn2S4 by a factor of 18.3, 2.37 and 2.4, respectively. The enhanced photocatalytic activity for hydrogen production could be attributed to the low recombination efficiency of the photogenerated charges and surface-plasmon-resonance-induced effect of Au nanoparticles.

Flame-retardant, electrically conductive and antimicrobial multifunctional coating on cotton fabric via layer-by-layer assembly technique

A multifunctional coating composed of polyhexamethylene guanidine phosphate (PHMGP) and potassium alginate-carbon nanotubes (PA-CNTs) was constructed on cotton fabric via a layer-by-layer assembly technique. The growth of the assembly coating was monitored by Fourier transform infrared spectroscopy and the result shows the assembly coating grows approximately linearly with the increase of bilayer number. The electrical conductivity test shows that the assembly coating endows cotton with electrical conductivity, due to the formation of a CNT network on the cotton fabric. The thermo-stability and flame resistance were evaluated by thermo-gravimetric analysis and a vertical flammability test, and the results indicate that the assembly coating promotes char formation, decreases the burning time and eliminates the afterglow during combustion. The antimicrobial assessment suggests that the assembly coating can effectively inhibit the growth of Escherichia coli, and the inhibiting effect increases with the growth of bilayer number. A multifunctional cotton fabric could be produced by the LBL assembly technique, which enlarges its application area.

Relationship between Microstructure and Tensile Properties of PET/Silica Nanocomposite Fibers

The influence of silica nanoparticles on the tensile properties of poly(ethylene terephthalate)(PET) fibers was investigated. The results showed that mechanical properties of PET fibers were improved through nano‐silica incorporation. Two maxima of the modulus‐strain curves of PET/silica nanocomposites (PETS) fibers are always higher than those of pure PET (PET0) fibers. The results of microstructure investigations suggested that the amorphous orientation factor of PETS fibers is higher than that of PET0 fibers. It is suggested that the increase of amorphous orientation factor contributed to the improvement of tensile properties of PET fibers. Considering the difference in modulus‐strain curves of PET0 and PETS fibers, it is believed that the addition of nanoparticles not only improved the amorphous orientation factor but also changed the load units of PET fibers when strained, which also resulted in the improvement of tensile properties.

Synthesis and Thermal Behavior of Silica‐Graft‐Polypropylene Nanocomposites Studied by Step‐Scan DSC and TGA

Silica graft poly(propylene) (silica‐g‐PP) nanocomposites were successfully prepared by radical grafting copolymerization and ring‐opening reaction. Their thermal properties were studied by step‐scan differential scanning calorimetry (SDSC) and thermogravimetric analysis (TGA). The exothermic peaks in the IsoK baseline (Cp,IsoK, nonreversing signal) of SDSC reveal that PP and silica‐g‐PP nanocomposites undergo melting‐recrystallization‐remelting during heating. The peak temperatures of recrystallization and remelting shift upward with the existence of nanoparticles in the PP matrix. The thermal degradation kinetics of silica‐g‐PP nanocomposites were investigated using nonisothermal TGA and the Flynn‐Wall‐Ozawa method. The results indicate that the thermal stability was significantly improved with increasing silica content, mainly because of the physical‐chemical adsorption of the volatile degradation products on the nanoparticles that delays their volatilization during decomposition, and the covalent interaction between nanoparticles and PP chains, which will also reduce the breakage of PP backbone chains.

Isothermal Crystallization and Subsequent Melting Behavior of Poly(ethylene terephthalate)/Silica Nanocomposites

The crystallization process of poly(ethylene terephthalate)/silica nanocomposites were investigated by differential scanning calorimetry (DSC) and then analyzed using the Avrami method. The results indicated that the crystallization of pure poly(ethylene terephthalate) (PET) was fitted for thermal nucleation and three‐dimensional spherical growth throughout the whole process, whereas the crystallization of PET/silica nanocomposites exhibits two stages. The first stage corresponds to athermal nucleation and three‐dimensional spherical growth, and the second stage corresponds to recrystallization caused by the earlier spherulites impingement. The crystallization rate increases remarkably and the activation energies decrease considerably when silica nanoparticles are added. The subsequent melting behavior of the crystallized samples shows that the melting point (T m) of nanocomposites is higher than that of pure PET, which might be caused by two factors: (1) The higher melting point might be due to some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; (2) it might also be the case that more perfect crystals can be formed due to the higher crystallization temperatures and lower activation energies of PET/silica nanocomposites.

Isothermal Crystallization Kinetics and Melting Behavior of Poly(ethylene terephthalate)/Attapulgite Nanocomposites Studied by Step-scan DSC

The crystallization kinetics of poly(ethylene terephthalate)/attapulgite (AT) nanocomposites and their melting behaviors after isothermal crystallization from the melt were investigated by DSC and analyzed using the Avrami method. The isothermal crystallization kinetics showed that the addition of AT increased both the crystallization rate and the isothermal Avrami exponent of PET. Step-scan differential scanning calorimetry was used to study the influence of AT on the crystallization and subsequent melting behavior in conjunction with conventional DSC. The results revealed that PET and PET/AT nanocomposites experience multiple melting and secondary crystallization processes during heating. The melting behaviors of PET and PET/AT nanocomposites varied in accordance with the crystallization temperature and shifted to higher temperature with the increase of AT content and isothermal crystallization temperature. The main effect of AT nanoparticles on the crystallization of PET was to improve the perfection of PET crystals and weaken its recrystallization behavior.

Non-Isothermal Crystallization Kinetics of Poly(Butylene Terephthalate)/Silica Nanocomposites

Poly(butylene terephthalate)/silica nanocomposites were prepared by in situ polymerization of terephthalic acid, 1,4-butanediol and silica. Transmission electron microscopy (TEM) was used to examine the quality of the dispersion of silica in the PBT matrix. The non-isothermal crystallization behavior of pure PBT and its nanocomposites was studied by differential scanning calorimetry (DSC). The results show that the crystallization peak temperatures of PBT/silica nanocomposites are higher than that of pure PBT at a given cooling rate. The values of halftime of crystallization indicate that silica could act as a heterogeneous nucleating agent in PBT crystallization and lead to an acceleration of crystallization. The non-isothermal crystallization data were analyzed with the Avrami, Ozawa, and Mo et al. models. The non-isothermal crystallization process of pure PBT and PBT/silica nanocomposites can be best described by the model developed by Mo et al. According to the Kissinger equation, the activation energies were found to be −217.1, −226.4, −259.2, and −260.2 kJ/mol for pure PBT and PBT/silica nanocomposites with silica weight content of 1, 3 and 5 wt%, respectively.