Zhongbin Xu

Synergistic effect of carbon nanotube and clay for improving the flame retardancy of ABS resin

Synergistic effect between multi-walled carbon nanotubes (MWNTs) and clay on improving the flame retardancy of acrylonitrile–butadiene–styrene (ABS) resin was studied. Flammability properties measured by a cone calorimeter revealed that incorporation of clay and MWNTs into ABS resin significantly reduced the peak heat release rate (PHRR) and slowed down the whole combustion process compared to the individually filled system based on clay or MWNTs. The flame retardancy of the ABS/clay/MWNTs nanocomposites was strongly affected by the formation of a network structure. Linear viscoelastic properties of the ABS nanocomposites showed that the coexistence of clay and MWNTs can enhance the network structure which can hinder the movement of polymer chains and improve flame retardancy. From transmission electron microscope analysis, MWNTs were shortened after combustion and there was no significant change in their diameters. For chars of ABS/clay/MWNTs nanocomposites, some MWNTs ran across between clay layers, indicating a strong interaction existed between clay and MWNTs. The existence of clay enhanced the graphitization degree of MWNTs during combustion. Clay can assist the elimination of dislocations and defects and the rearrangement of crystallites. Al2O3, one of the components of clay, acts as the catalyst of graphitization.

Thermal Stability and Flame Retardancy of Rigid Polyurethane Foams/Organoclay Nanocomposites

The thermal stability and flame retardancy of a new kind of rigid polyurethane (PU) foams/organoclay nanocomposites developed by our research group were investigated by using thermogravimetry analysis (TGA) and cone calorimeter test. Results indicate that compared with pure PU foams, rigid PU foams/organoclay composites show significantly enhanced thermal stability and flame retardancy. The reasons leading to the results were discussed in detail by relating with the morphology of the composites. The discussion suggests that the enhancement degree of thermal stability and flame retardancy of composites compared with that of PU foams coincides well with the sequences of gallery spacing of organoclay in the PU matrix.

Electric Conductivity and Thermorheology Properties of Polyacrylonitrile/Nylon6 Composites Filled with Carbon Black

The electric conductive polymer composites, which were made of carbon black particles through dispersing in mixtures of polyacrylonitrile (PAN)/nylon6 (PA6), were prepared in a Haake Thermo-mixer. The morphology, conductivity, thermorheology properties and their relationships were studied. Microphase separations and partial miscibility were confirmed when a small mass of PAN was introduced into PA6/CB composites. A part of CB particles could be attracted by PAN, and transferred to the interface of PA6 and PAN, leading to an increase of electric conductivity. Results also indicated that the introduction of PAN in the PA6/CB composite improved its elastic modulus as well as the thermal stability of its electric conductivity.

A mathematical model of mixing enhancement in microfluidic channel with a constriction under periodic electro-osmotic flow

A microfluidic channel with a constriction produced poor mixing conditions under periodic electro-osmotic flow. However, the mixing performance may be enhanced significantly by altering other parameters. Numerical simulations are used to investigate the effect of the direct current electric field (EDC), phase difference (ϕ), and length of constriction (L). A mathematical model, based on the structural features of the Lagrange function rather than its application, is proposed to establish a relationship between the mixing performance and these three parameters. The feasibility analysis has been carried out, and the results are verified by the data from simulation and experiment.

Effect of oscillatory shear on the mechanical properties and crystalline morphology of linear low density polyethylene

In this study, effects of oscillatory shear with different frequencies (0–2.5 Hz) and amplitudes (0–20 mm) on the mechanical properties and crystalline morphology of linear low density polyethylene (LLDPE) were investigated. It was found that the mechanical properties of LLDPE are improved because of the more perfect crystalline structure when LLDPE crystallizes under low-frequency and small-amplitude (0.2 Hz/4 mm) oscillatory shear. The mechanical properties can be further improved by increasing either the frequency or the amplitude of oscillatory shear. The Young’s modulus and tensile strength of LLDPE are improved by 27% and 20%, respectively, when the frequency is increased to 2.5 Hz and the amplitude is maintained at 4 mm; while the Young’s modulus and tensile strength are improved by 49% and 47%, respectively, when the amplitude is increased to 20 mm and the frequency is remained as 0.2 Hz. The crystallinity and microstructure of LLDPE under different oscillatory shear conditions were investigated by using differential scanning calorimetry, wide angle X-ray diffraction and scanning electron microscopy to shed light on the mechanism for the improvement of mechanical properties.

Analysis of Pressure Pulsation Induced by Rotor-Stator Interaction in Nuclear Reactor Coolant Pump

The internal flow of reactor coolant pump (RCP) is much more complex than the flow of a general mixed-flow pump due to high temperature, high pressure, and large flow rate. The pressure pulsation that is induced by rotor-stator interaction (RSI) has significant effects on the performance of pump; therefore, it is necessary to figure out the distribution and propagation characteristics of pressure pulsation in the pump. The study uses CFD method to calculate the behavior of the flow. Results show that the amplitudes of pressure pulsation get the maximum between the rotor and stator, and the dissipation rate of pressure pulsation in impellers passage is larger than that in guide vanes passage. The behavior is associated with the frequency of pressure wave in different regions. The flow rate distribution is influenced by the operating conditions. The study finds that, at nominal flow, the flow rate distribution in guide vanes is relatively uniform and the pressure pulsation amplitude is the smallest. Besides, the vortex shedding or backflow from the impeller blade exit has the same frequency as pressure pulsation but there are phase differences, and it has been confirmed that the absolute value of phase differences reflects the vorticity intensity.

Determination of hydrogen peroxide using novel test strips based on plastic microcapillary film

This work proposes a novel method for the semi-quantitative determination of hydrogen peroxide (H2O2) in routine applications. Potassium iodide (KI) and starch are adopted as chromogenic reagents, while microcapillary films (MCFs) are employed as the reaction platform. An innovative loading method, including filling, gelatinization, and freeze-drying of reagents, is established to create a solid porous medium inside the MCF matrix for immobilizing the reagents. The porous medium has sufficient specific surface area and rapid rehydration for reaction detection. To verify the feasibility of this new method, two kinds of test strips were fabricated in the present investigation: a colorimetric strip and four-section grading test strip. Results showed that the standard colorimetric strip could detect H2O2 residue with concentrations of 0.02–0.1 wt% with a testing time of 120 s. Meanwhile, using the four-section grading test strip, the H2O2 residue concentration was determined simply by counting the number of colored sections with the naked eye. H2O2 concentrations of 0–0.12 wt% were divided into five grades by the grading test strips, with a testing time of 45 s. Compared with traditional colorimetric methods, this grading method provides a more intuitive and understandable result for users. Furthermore, it provides a new way to involve people suffering from color weakness or blindness in the relevant research community.

Influence of Phase Dispersant on the Cocross-Linking of Polyvinyl Chloride with Low Density Polyethylene

The cocross-linking of polyvinyl chloride (PVC) and low density polyethylene (LDPE) was studied by THF extraction, FTIR, and Dynamic rheological analysis. It is found that dicumyl peroxide (DCP) could neither induce the cross-linking of PVC itself nor cause PVC chains to cocross-link with LDPE. Butadiene rubber (BR), as a solid phase dispersant (SPD) can not give a hand to the cocross-linking. However, NBR, both as a compatibilizer and SPD, can induce PVC to be crosslinked or cocross-linked with LDPE initiated by DCP. The composite cross-linking agent that consists of DCP, triallyl isocyanurate (TAIC), and magnesium oxide (MgO) is easy to induce PVC to cross-link itself or cocross-link with LDPE.

Creating monodispersed droplets with electrowetting-on-dielectric step emulsification

Monodisperse droplets are important in drug screening, and cell-based and biochemical research. However, conventional methods for creating droplets, such as co-flow, T-junction and flow-focusing, have poor monodispersity because of fluctuations in the flow rate. Because step emulsification is based on the principle of Laplace pressure, it is insensitive to the flow rate and yields a constant and high monodispersity. In the present study, we combine electrowetting and step emulsification to reduce the negative influence of flow-rate fluctuations and to prepare highly monodisperse droplets. We demonstrate that the flow rate and voltage applied to the droplets can independently influence the droplet size. This method has great potential in chip-based bioanalysis and cell-based studies where highly monodisperse droplets are needed.Monodisperse droplets are important in drug screening, and cell-based and biochemical research. However, conventional methods for creating droplets, such as co-flow, T-junction and flow-focusing, have poor monodispersity because of fluctuations in the flow rate. Because step emulsification is based on the principle of Laplace pressure, it is insensitive to the flow rate and yields a constant and high monodispersity. In the present study, we combine electrowetting and step emulsification to reduce the negative influence of flow-rate fluctuations and to prepare highly monodisperse droplets. We demonstrate that the flow rate and voltage applied to the droplets can independently influence the droplet size. This method has great potential in chip-based bioanalysis and cell-based studies where highly monodisperse droplets are needed.

Online Research on Plasticizing Process of Starch Under Superimposed Vibration Field

ABSTRACT A novel testing machine, integrating plastic vibration processing with molding, based on a multipass rheometer, was used to investigate the effect of the complex force field on plasticization of taro and wheat thermoplastic starch (TPS) melts. Various kinds of continuous vibration fields could be tested by controlling the movement of pistons. A superimposed vibration field, combining the effects of vibration and shear, was obtained by adding a high-frequency low-amplitude oscillation on a low-frequency high-amplitude oscillation. The rheological properties of starch were directly monitored during and after the plasticization process without removing the starch melts out of the testing machine. The apparent viscosity of the TPS melts were obtained for different high-frequency oscillation conditions by monitoring the pressure difference in the cavity. The plasticization preparation time was used to characterize the benefit provided by the superimposed vibration field. The results showed the decrease of the percentage of the average plasticizing preparation time for taro starch was 3.4%, while that for wheat starch was 1.6% compared to single, low-frequency, high-amplitude oscillation. Comparison of the plasticizing preparation time under different vibration frequencies showed that the plasticization was promoted by applying the superposed vibration field, and the effective degree was related to the vibration frequency and starch type. Both TPS exhibited shear-thinning behavior after the plasticization, and samples of both types of starch which were plasticized under higher vibration frequency presented lower apparent viscosities at certain shear rates.