Preparing flame-retardant polyamide 66 (PA66) fibers through melt spinning remains one of the biggest challenges nowadays. In this work, dipentaerythritol (Di-PE), an eco-friendly flame retardant, ...was blended into PA66 to prepare PA66/Di-PE composites and fibers. It was confirmed that Di-PE could significantly improve the flame-retardant properties of PA66 by blocking the terminal carboxyl groups, which was conducive to the formation of a continuous and compact char layer and the reduced production of combustible gas. The combustion results of the composites showed that the limiting oxygen index (LOI) increased from 23.5% to 29.4%, and underwriter laboratories 94 (UL-94) passed the V-0 grade. The peak of heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) decreased by 47.3%, 47.8%, and 44.8%, respectively, for the PA66/6 wt% Di-PE composite compared to those recorded for pure PA66. More importantly, the PA66/Di-PE composites possessed excellent spinnability. The prepared fibers still had good mechanical properties (tensile strength: 5.7 ± 0.2 cN/dtex), while maintaining good flame-retardant properties (LOI: 28.6%). This study provides an outstanding industrial production strategy for fabricating flame-retardant PA66 plastics and fibers.
By considering the joint effects of the Kelvin–Helmholtz (KH) and Rayleigh–Taylor (RT) instabilities, this paper presents an interpretation of the wavy patterns that occur in explosive welding. It is ...assumed that the elasticity of the material at the interface effectively determines the wavelength, because explosive welding is basically a solid-state welding process. To this end, an analytical model of elastic hydrodynamic instabilities is proposed, and the most unstable mode is selected in the solid phase. Similar approaches have been widely used to study the interfacial behavior of solid metals in high-energy-density physics. By comparing the experimental and theoretical results, it is concluded that thermal softening, which significantly reduces the shear modulus, is necessary and sufficient for successful welding. The thermal softening is verified by theoretical analysis of the increase in temperature due to the impacting and sliding of the flyer and base plates, and some experimental observations are qualitatively validated. In summary, the combined effect of the KH and RT instabilities in solids determines the wavy morphology, and our theoretical results are in good qualitative agreement with experimental and numerical observations.
High-molecular weight nylon 66/modified clay (Mclay) nanocomposites with a low apparent viscosity were prepared by in-situ polymerization and post solid-state polycondensation. Thermogravimetric ...analysis and X-ray diffraction patterns of the Mclay revealed that cetyltrimethyl ammonium bromide successfully inserted into the interlayers of the clay. Scanning electron microscope images of the cross sections showed that the Mclay was well-dispersed in the nylon 66 matrix. The effects of clay on the mechanical, rheological, and thermal properties of the nanocomposites were investigated using an Instron 5969 machine, a capillary rheometer, and a differential scanning calorimeter. The results indicated that the incorporation of a very small amount of Mclay considerably decreased the shear viscosity of the nanocomposites and increased the melt index, acting as a viscosity reducer. More importantly, the mechanical properties and spinnability of the nylon 66/Mclay nanocomposites were not affected by the viscosity reducer.
•The fifth-order characteristic-wise WENO numerical method was applied to the hyper-elastic Eulerian equations.•A friction model was proposed in Eulerian frame work to obtain the interfacial status ...for shear impact problems.•A slip factor was introduced to govern the partition of kinetic energy and strain energy in multi-material interactions.
A friction model for hyper-elastic solid materials was proposed for the simulation of complex shear impacts in a Eulerian framework. The interfacial status of multi-material interactions was obtained in Harten, Lax, and van Leer discontinuity (HLLD) Riemann solver. The inverse deformation gradient tensor was utilized in governing equations to describe the shape change of hyper-elastic solid materials. The level set method (LSM) was used to identify multiple materials in computational domain and the interface boundary condition was applied using the real ghost fluid method (RGFM). A uniform eigensystem of hyperbolic equations was derived using the fifth-order characteristic-wise weighted essentially non-oscillatory (WENO) scheme. Six numerical tests of one-dimensional problems were used to illustrate the robustness of the 5th order WENO scheme. The proposed friction model was evaluated for impact cases in both one and two dimensions with three-dimensional components. The redistribution of strain and kinetic energy during solid-solid interactions was represented using the proposed friction model, while both ‘slip’ and ‘stick’ interface showed unphysical approximations. We believe that the friction interface model completes the theory of multi-material interaction and provide a more appropriate way to model the complex dynamic behavior in Eulerian framework for solid materials.
The biomass and productivity of Schima superba-Castanopsis carlesii forests in Tiantong, Zhejiang Province, were determined using overlapping quadrants and stem analyses. The total community biomass ...was (225.3+/-30.1) t hm(-2), of which the aboveground parts accounted for 72.0% and the underground parts accounted for 28.0%. About 87.2% of biomass existed in the tree layer. The resprouting biomass was small, of which over 95.0% occurred in the shrub layer. The productivity of the aboveground parts of the community was (386.8+/-98.9) g m(-2)a(-1), in which more than 96.0% was present at the tree level. The trunk's contribution to productivity was the greatest, while that of leaves was the smallest. In China, the community biomass of subtropical evergreen broadleaved forests differs significantly with the age of the forest. The community biomass of the 52-year-old S. superba-C. carlesii forests in this study was lower than the average biomass of subtropical evergreen broadleaved forests in China, and was lower than the biomass of other subtropical evergreen broadleaved forests elsewhere in the world. Moreover, its productivity was lower than the model estimate, indicating that without disturbance, this community has great developmental potential in terms of community biomass and productivity.
The pulsation and jet of underwater explosion bubble heavily affected by the boundary conditions. To explore the pulsation behavior and jet load of underwater explosion bubble near a damaged double ...structure, some double plates with circular hole were designed. The electric spark-generated bubble was employed to act as the underwater explosion bubble, and the experiment research on bubble pulsation and jet below the double plate with circular hole was carried out. The bubble pulsation and jet process were recorded by a high-speed camera, and the bubble jet load was measured by a wall pressure sensor. The results show that with the growth of the standoff distance, the bubble jet changes from the type I “gas-liquid two-phase jet” to the type II “gas-liquid two-phase jet”, and finally into the water jet. The load of the type I “gas-liquid two-phase jet” are characterized with high peak pressure with short duration in the initial pressure stage, and low pressure with long duration in the standing pressure stage. Whereas the type II “gas-liquid two-phase jet” feature high peak pressure with short duration in the initial pressure stage without standing pressure stage.
•The difference between the bubble pulsation characteristics near the double plate with a hole and the free field bubble is found and analyzed.•A new bubble load type of “gas-liquid two-phase jet” is found by highspeed camera and wall pressure sensor.•A thorough analysis was conducted on the load characteristic and formation mechanism of “gas-liquid two-phase jet”.
The thermal decomposition behavior of HBT was studied by TG-DSC thermal analysis method. The decomposition products of HBT were analyzed. TGA curves and differential thermal curves of HBT were ...measured in different heating rates. The activation energy and pre-exponential factor of HBT was separately calculated by Ozawa equation and Kissinger equation. Thermal decomposition Mechanism of HBT were derived by Ozawa equation and its possible mechanism function was got. The differential thermal curves of HBT prepared by different dispersants were measured and the kinetic parameters were obtained. These kinetic parameters are in good agreement. The test values of the HBT dispersed with acetone have a higher accuracy, so the activation energy calculated is more meaningful.
To reveal the combustion and explosion characteristics of RP-3 aviation kerosene, a three-step simplified mechanism involving CO-CO2, H2-H2O equilibrium was constructed. Using a general program based ...on Cantera and genetic algorithms, the reaction rate parameters were optimized under given conditions, and a relationship between reaction rate parameters and fuel equivalence ratio was developed. The optimized mechanism was compared with multiple flame parameters under multiple operating conditions of RP-3 aviation kerosene. The results showed that the laminar flame speed and adiabatic flame temperature of the three-step simplified mechanism were in good agreement with the experimental data of RP-3 aviation kerosene within the temperature range of 300 ∼ 600 K and pressure range of 1–5 atm, with an error of less than 10 %. The optimized mechanism corrected using a correction function is in good agreement with experimental and numerical results under multiple conditions, verifying the rationality of the simplified program and the accuracy of the three-step simplified mechanism. For practical engineering issues, RP-3 aviation kerosene explosion experiments were conducted, and the pressure and flame data were analyzed and compared. The results indicated that the three-step simplified mechanism had satisfactory calculation time scales and numerical simulation feasibility.
•A reactive S- & P-containing flame retardant (PDDDS) was designed and synthesized.•The LOI of PA66 with 2% PDDDS increased to 31.6% from 22.7%.•The PHRR, THR, and TSP of PA66-2%PDDDS were depressed ...by 47%, 45.7% and 65.1%, respectively.•PA66-PDDDS has excellent flame retardant both in gas phase and condensed phase.
A sulfur- and phosphorus-containing flame retardant monomer phosphonic diamide, P-phenyl-N, N′-bis(p-sulfanilylphenyl) (PDDDS) was designed, synthesized, and incorporated into polyamide 66 (PA66) through polycondensation to suppress smoke generation upon combustion and achieve satisfactory mechanical properties, a good UL-94 rating (V-0), and a high limiting oxygen index (31.6%). The increased flame retardancy of the PA66-PDDDS copolymer was ascribed to its decomposition into (i) gas-phase P–O and SO2 species scavenging free radicals such as H• and OH• and (ii) condensed-phase products catalyzing the dehydration of PA66 to form char layer. Thus, our work presents a strategy for improving the fire safety of PA66 to significantly expand its practical application value.
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