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Since CO2 is a kind of nontoxic, non-flammable and biocompatible fluid, introducing CO2 in the PLLA formation process has been regarded as a green way to the manufacture of biological products or medical supplies. However, it is still a challenge to understand the influence of CO2 on the crystal growth behavior of PLLA. Here, we developed an in situ high-pressure observation system, composed of optics, polarization optics and a small angle laser scattering system, to record the growth process of PLLA crystals in a pressurized CO2 environment. It is found that, at a low temperature (near Tg), low pressure CO2 (0.5 MPa in this work) can still induce the formation of numerous micron-sized spherulites of PLLA. Therefore, the introduction of CO2 can significantly enhance the crystallization ability of PLLA and decrease the crystallization temperature, which is helpful in improving the mechanical properties of PLLA products. We also found that a snowflake-shaped crystal was assembled by rhombic lamellae under pressurized CO2. There is a melt accumulation zone surrounding the growth front of the snowflake-shaped crystal, indicating that the growth front nucleation is limited by the pressurized CO2. This melt accumulation zone is quite different from the melt depletion zone existing ahead of the reported dendritic crystal front. Interestingly, in a high-pressure CO2 environment, a kind of bamboo-like branch is formed in a rhythmic growth mode. The repeating unit of the bamboo-like branch is constructed by an asymmetric terrace crystal originated from screw dislocation in the melt accumulation zone. These results demonstrated that CO2 has a remarkable tunability on the polymer crystal morphology.

We established a model of hypothermic hypoxia/reoxygenation injury of fibroblasts, simulated the process of ischemia/reperfusion injury during cardiopulmonary bypass, and studied the effects of cardiac fibroblasts on cardiomyocyte activity, connexin 43 (Cx43), and calmodulin kinase II (CaMKII) expression. Furthermore, the effects of sevoflurane-treated fibroblast culture medium on cardiac activity, Cx43 protein, and CaMKII expression were observed. The results showed that the fibroblast culture medium damaged by hypothermic hypoxia/reoxygenation could reduce the beating frequency of cardiomyocytes, increase the mortality of cardiomyocytes, decrease the relative expression of Cx43, and increase the relative expression of CaMKII. However, sevoflurane containing hypothermic hypoxia/reoxygenation injury fibroblast culture medium can increase the beating frequency of cardiomyocytes, reduce the mortality of cardiomyocytes, increase the relative expression of Cx43 protein, and decrease the relative expression of CaMKII. The results suggest that the antiarrhythmic effects of sevoflurane on the expression of Cx43 and CaMKII are related to fibroblasts.

Author(s): Hu, Chunxiao; Wang, Guilong; Zhou, Difei; Wang, Wei; Qin, Zhong; Wang, Yanjuan; Chen, Jingyu; Liu, Hong; Li, Quan; Huang, Dongxiao

BACKGROUND: Lactic acidosis is often seen in lung transplantation (LTx). Postoperative lactate is frequently associated with poor outcome in postoperative and critically ill patients. Our aim was to evaluate the predictive value of postoperative peak lactate levels within 72 h of LTx for 30-day and late mortality. METHODS: We evaluated patients who underwent LTx from January 2015 to September 2017. All admitted patients were classified according to the peak lactate level (PL) within 72 h of surgery: PL 10 mmol/L (Group 3). We performed logistic regression analysis and used Cox regression models to identify the peak lactate level as a predictive factor for 30-day and late mortality, respectively. RESULTS: Of 255 eligible patients, mean age 55.61±12.16, mean lactate 4.99±2.93 and 80% male, and 40% had hyperlactatemia (PL >5 mmol/L) after LTx. The 30-day mortality rate was 17.9%, 28.9% and 68.8% in the three groups, respectively (P

Although polypropylene (PP) foams fabricated by microcellular injection molding (MIM) have been widely studied and globally applied, it is still a big challenge to achieve lightweight products with high mechanical performance. Herein, the MIM method assisted by a fast cooling design was applied to prepare lightweight bimodal nanoporous PP foams with high toughness. A specific mold with a thin cavity was designed to achieve rapid cooling rate during MIM process, and to further accelerate crystallization and refine crystals, which was verified by visualization results, DSC curves, and WAXD patterns. Thus, nanocellular PP foams were prepared, whose high toughness was presented in tensile testing, especially for bimodal cellular foams, more than 327% higher than that of microcellular foams, and up to 53% higher than that of solid. It is owing to the introduced matrix craze, shear yielding, and larger plastic zone by nanocells and the transformed crack propagation direction by microcells. Therefore, this novel toughening method paves a promising prospect for MIM technology to achieve lightweight and tough products for industrial applications.

Assembling active materials on flexible conductive matrixes for fabricating high-rate, self-supported and durable anodes is essential for the development of high-power flexible lithium-ion batteries. In this study, we report an efficient combinational strategy for producing hybrid composites (TNO@MCF) of Ti

This work aims to predict the thermal conductivity of microcellular and nanocellular thermal insulation foams to explore the correlation between the cellular structure and the thermal insulating properties. Closed-cell foam consisting of cell walls and struts was used as the base geometry for modeling. The mathematical correlations to calculate the thickness of cell walls and the diameter of struts for a given cell size, the void fraction and the volume fraction of polymer located in struts were investigated. Then, a mathematical model for the conductive thermal conductivity including the dependency on the void fraction, the strut fraction and the Knudsen effect for gas was introduced. The radiative thermal conductivity was determined by analyzing the attenuation of radiative energy by absorption and scattering based on Mie's theory together with electromagnetic wave interference, as well as interference of propagating waves and tunneling of the radiative energy by evanescent waves in the cells. The thermal conductivity model was validated by experimental data and used to predict the thermal conductivity of polystyrene (PS) and poly(methyl methacrylate) (PMMA) foams at various cell sizes and volume expansion ratios. It was found that the radiative thermal conductivity plays a crucial role in nanocellular foam. The trade-off between the cell size and cell wall thickness when cell walls become thinner and highly transparent to thermal radiation was demonstrated, leading to the optimal volume expansion ratio at which the thermal conductivities were minimized. Perspectives for the manufacture of high-performance thermal insulation foams are also discussed.

To manufacture entirely biodegradable polylactic acid (PLA) foam with a high expansion ratio and a fine-cell structure, we attempted to design economically viable material recipe as well as the injection foam molding (FIM) process. It is well-known that PLA foam featuring high expansion and fine cells is challenging to achieve on FIM technique due to its intrinsically low melt strength. To overcome the inferior foaming characteristics of PLA in this study, nano-fibrils of polytetrafluoroethylene (PTFE) were added expecting an increase of molecular chain entanglements. Another bio-based biodegradable polymer, polyhydroxyalkanoate (PHA) was also blended with PLA to improve the impact strength of the final foams. High-pressure FIM process combined with mold-opening technique was performed to make highly expanded PLA foams with varied material recipes. A constant amount (0.6 wt%) of supercritical nitrogen was injected into FIM system and uniformly mixed with various polymer compositions. The gas-laden melt was injected into the mold cavity to create the foamed PLA samples. Finally, we could demonstrate that it is clearly feasible to manufacture entirely biodegradable PLA foams having a high expansion ratio and a desirable cellular structure using an advanced FIM process.

International audience; Recently, natural fiber becomes an alternative to the synthetic fiber for the composites used in aerospace, automotive, sports, packaging and so on, due to its inherent characteristics like biodegradablity, renewablity, high-specific strength and specific modulus. However, there are still many challenges in the fabrication of the natural fiber composites, including the poor compatibility between the nonpolar matrix and the polar natural fiber, relatively high-moisture absorption and low-thermal resistance of natural fibers, etc. Moreover, when manufacturing this type composite, the processing conditions, fiber loading and inherent properties of fiber not only affect the mechanical properties, but also cause products defects, such as warpage, volume shrinkage and weld lines, which needs a rapid numerical design for the mold and manufacturing parameters. Therefore, the properties of natural fiber composites have been widely investigated to satisfy the increasing demand in different applications. This paper intends to review the mechanical properties, flammability, durability, foaming behaviors and numerical simulation of injection molding process of natural fiber composites.

Extracorporeal membrane oxygenation (ECMO) is a widely used cardiopulmonary support method that is usually implemented after anesthesia during the period of lung transplantation (LTx). In severe pulmonary arterial hypertension (PAH) patients, however, anesthesia induction is a high-risk phase and can result in severe cardiorespiratory failure. Herein, we describe two severe PAH patients who received ECMO support before anesthesia and whose preoperative evaluations indicated that the risk was too high to safely survive the anesthesia induction period before LTx. The strategy was successful, and in both patients, hemodynamics was stable and no ECMO-related complications occurred.

Poly(ether-block-amide) (PEBA) is an advanced thermoplastic elastomer that has very low material density and excellent resilience over a wide temperature range. High-performance PEBA foams enabled by microcellular foaming show great prospects in sports, safety protection, and medical rehabilitation, yet their preparation is still greatly limited by the unclear processing-structure-property relationships. Herein, microcellular foaming with CO2 as the blowing agent was developed to fabricate high-performance PEBA foams. Foaming temperatures and CO2 pressures were varied to investigate their effects on foam structure, and hence PEBA foams with a tailored cellular structure were achieved. With the structure-tunable PEBA foams, the processing-structure-performance relationships were clarified. It was demonstrated that a higher expansion ratio and larger cell size lead to significantly enhanced resilience and reduced energy loss coefficient. In particular, PEBA foams with an expansion ratio of up to 24.5-fold were prepared, which possess a drop-ball resilience of up to 80 %, obviously superior to current foams. Moreover, the PEBA foams with larger cells exhibit significantly improved cyclic compression stability, and the minimum energy loss coefficient is lower than 15 %. The super-elastic PEBA foams with tailored structure exhibit promising prospects in advanced resilience applications.

Lightweight is of great significance for reducing material and energy consumptions. Microcellular injection molding is an advanced technology for fabricating lightweight plastic structural components, but the deteriorated mechanical performance is a big challenge. In this study, we reported a facile and scalable way to fabricate the lightweight and strong microcellular polypropylene/talcum (PP/talc) component. Both PP/talc microcomposite and PP/talc nanocomposite were prepared by the twin-screw compounding, and the SEM images show a uniform dispersion of talc. The DSC analysis results demonstrate that either the micro or nano talc is very effective in promoting the crystallization of PP. The rheological tests show that both the micro talc and the nano talc lead to obviously enhanced viscoelastic properties of the PP melt, while the effect of the nano talc is much more pronounced than that of the micro talc. Thanks to the enhanced crystallization and improved viscoelastic behavior, both the microcomposite foam and the nanocomposite foam shows much refined cellular structure than the pure PP foam. The PP/talc microcomposite foam shows significantly improved strength but seriously deteriorated toughness, compared with the pure PP foam. In contrast, the PP/talc nanocomposite foam shows simultaneously improved strength, rigidity and toughness. Notably, the tensile toughness and the Gardner impact toughness of the PP/talc nanocomposite foam are dramatically enhanced by 226.1% and 166.2%, respectively. Taking into account the flexible and scalable features of the processing methodology, the lightweight and strong PP/talc nanocomposite foam shows a promising future to replace the solid structural components in many industrial applications such as automotive and consumer electronics.

Treatment of heterocyclic amines featuring fused rings of [1,2,4]triazolo[4,3-b][1,2,4,5]tetrazine with fuming HNO3 /P2 O5 leads to six fully characterized explosives through multiple nitration and reduction or oxidation mechanism. Thus, 4-nitro-N-(3-nitro[1,2,4]triazolo[4,3-b][1,2,4,5]tetrazin-6-yl)-1,2,5-oxadiazol-3-amine (3 b, TTDNF) showed high performance (D=9180 m s-1 , P=36.7 GPa) and low impact sensitivity (IS>40 J) while N-([1,2,4]triazolo[4,3-b][1,2,4,5]tetrazin-6-yl)-3-nitro-1,2,4-oxadiazol-5-amine (4 a, TTNOA) exhibited a potential cast explosive component with low melting point at 88.2 °C and high onset decomposition temperature at 226.2 °C.

Poly(lactic acid) (PLA) is a kind of bio-based and biodegradable polymers. PLA foams with high expansion ratio have great application potential in heat insulation, adsorption and other areas. However, due to its low melt strength and slow crystallization rate, linear PLA has poor foaming ability, so it is hard to prepare PLA foams with high expansion ratio. Although chain branching, blending, and other methods have been utilized to improve PLA's melt strength and foaming ability, they easily destroy PLA's biodegradability, cause chemical pollution, and raise production costs. In this study, a new supercritical fluid foaming process, based on pre-isothermal cold crystallization, was proposed to prepare PLA foams with high expansion ratio. To improve PLA's melt strength and foaming ability, a pre-isothermal treatment was applied to induce sufficient cold crystallization. According to the SEM results, the cold crystallization of PLA becomes more sufficient and the crystal morphology becomes more perfect with the pre-isothermal treating. The DSC and WAXD results confirm that, the pre-isothermal treatment remarkably promotes the PLA's cold crystallization, and endows the PLA sample higher crystallinity and more perfect crystalline structure. Moreover, the high-pressure rheology testing results indicate that the pre-isothermal treatment improves the PLA's melt viscoelasticity significantly. Finally, the foaming results show that the pre-isothermal treatment significantly enhances the PLA's foaming ability. With the pre-isothermal treatment, the PLA's maximum expansion ratio increases from 6.40-fold to 17.7-fold, and the uniformity of cellular structure is also improved obviously. The new process provides a green, flexible, and low-cost way to prepare fully biodegradable PLA foams with high expansion ratio.

Lightweight plastic materials are important for saving resources and energy, reducing environmental pollution, and achieving sustainable development. Foam injection molding is a promising technology for manufacturing lightweight plastic components. However, these plastic components present poor mechanical properties and imperfect surface appearances. Herein, we reported a novel strategy to prepare lightweight and tough polypropylene (PP)/polytetrafluoroethylene (PTFE) nanocomposite parts with defect-free surfaces by combining in situ fibrillation and nanocellular injection molding technologies. The nano-fibrillary PP/PTFE nanocomposite was firstly prepared using an in situ method based on twin-screw compounding. Scanning electron microscopy (SEM), rheological and differential scanning calorimetry (DSC) analysis, combined with online optical microscopy observation, demonstrated the network structure of PTFE nanofibrils and its positive effects on melt strength and promoting crystallization. Using nanofibrillary nanocomposites, we achieved nanocellular foaming, for the first time, using the foam injection molding process. The nanocellular PP/PTFE nanocomposite foam thus obtained significantly enhanced mechanical properties compared to the regular PP foam, and even superior strength and ductility compared to unfoamed PP. In particular, the impact strength of the nanocellular foam was 700% higher than that of the regular foam and 200% higher than that of the unfoamed product. Moreover, unlike regular foam, the nanocellular PP/PTFE nanocomposite foam showed outstanding surface appearance without any silver or swirl marks. More importantly, the whole process was facile, flexible, efficient, and easy to scale-up, and could be easily extended to other materials. The remarkable mechanical performance and surface appearance, combined with the flexible and extendable process, confers nanocellular PP/PTFE nanocomposite foams a promising future in many advanced applications where both lightweight and mechanical integrity are required.

Polyether block amide (PEBA) is a thermoplastic elastomer that offers a unique combination of low density, flexibility, small hysteresis and excellent flex fatigue resistance. Foaming is an effective method to save material, reduce weight, and tune mechanical properties, and thus to broaden the applications of PEBA. Here we report a flexible and scalable strategy to fabricate low-density PEBA foams via mold-opening foam injection molding. PEBA foams with tunable cellular structure were fabricated. The lightweight PEBA foam with a density of 0.17 g/cm3 exhibits super elasticity with an energy loss coefficient less than 25%, a resilience value up to 82%, and a compression set less than 5%. Moreover, it also performs outstanding while anisotropic thermal insulation properties, with an in-plane thermal conductivity of 30 mW·m−1·K−1 and a through-plane thermal conductivity of 50 mW·m−1·K−1. Furthermore, the lightweight PEBA foam also presents excellent acoustic insulation properties in a wide frequency range from 1000 Hz to 4000 Hz. Interestingly, it is found that smaller cell size contributes to enhanced strength, elasticity, and sound insulation. The lightweight, super-elastic, and thermal-sound insulation bio-based PEBA foams with tunable structure show a promising future in many applications such as sportswear, protective materials, and insulation materials.

This paper presented a new core-back chemical foam injection molding (CFIM) method. Different from the conventional method, the new method has a unique secondary filling stage right after core-back operation. By combining core-back and secondary filling, a closed shell composed of dense polymer skins can be created right before melt filling. This closed shell can prevent the gas loss from the melt flow front, and act as the gas counter pressure to reduce cell coalescence and collapse, thus leading to significant improvement of cell structure. The mechanical testing results show that the new technology can produce plastic foam with simultaneously enhanced tensile strength, elastic modulus, and notch impact strength. Moreover, this technology can also improve the surface appearance of the foamed sample. Thus, it shows a promising future in offering lightweight structural components with improved mechanical strength and enhanced surface appearance. Keywords: Core-back, Foam injection molding, Polypropylene, Foam, Chemical blowing agent

In our recent study, it is reported that gas-assisted microcellular injection molding (GAMIM) is a promising method to fabricate plastic foams with good surface quality, high weight reduction, and improved mechanical performance. To clarify the foaming mechanism, the crystallization behaviors of polypropylene in both conventional injection molding (CIM) and gas-assisted injection molding (GAIM) were studied. It is found that GAIM can significantly promote melt crystallization and refine crystals. To explore the improvement mechanism of crystallization, a numerical model was developed to simulate the filling and cooling processes of CIM and GAIM. The simulation results show that the much stronger shear field and the faster cooling rate lead to the refinement of crystals in GAIM. Finally, a crystallization-driven cell nucleation model was proposed to explain the improved foaming behavior of polypropylene in GAMIM. This paper provides a deep understanding of the foaming behavior and hence benefits the foamin...

The demand for microwave absorbing materials with strong absorption capability and wide absorption band is increasing due to serious electromagnetic interference issues and defense stealth technology needs. Here the carbon-coated Fe3O4 (Fe3O4@C) yolk-shell composites were successfully synthesized in a large scale for the application of microwave absorption through an in-situ reduction process from carbon-coated γ-Fe2O3 precursor. The results show that the Fe3O4 nanoparticles are uniformly coated with a thin carbon layer about 10 nm in thickness and a clear void about 1 nm in width between Fe3O4 core and carbon shell are formed due to the volume shrinkage during the reduction treatment. The obtained yolk-shell composites exhibit excellent microwave absorption properties. The absorption bandwidth with RL values exceeding −10 dB is up to 5.4 GHz for the absorber with a thickness of 2.2 mm. The optimal RL can reach up to −45.8 dB at 10.6 GHz for the composite with a thickness of 3.0 mm. The outstanding microwave absorption properties may be attributed to the multiple interfacial polarization, good impedance match and multiple reflections and scattering owing to the unique yolk-shell structures.

The morphology evolution and elimination mechanism of surface bubble marks on microcellular injection-molded parts with dynamic mold temperature control were investigated. It is found that with the increase of mold temperature, the surface bubble marks with morphology of rolling ribbons and uneven gullies formed in low mold temperature conditions gradually evolve into thin and tiny strips and finally disappear. The evolution of surface bubble marks under high mold temperature conditions undergoes a process from generation to disappearance, that is, the melt first forms a surface with originally generated marks; then the bottom melt of the generated marks is continuously pushed out and forms island protuberances, thus gradually dividing and reducing their space and volume; finally, the original marks are eliminated. Escaping from the gap between mold and melt and redissolving into the high-temperature melt are the main ways the gas in the original surface bubble marks disappears.

Polymer foam has become an important thermal insulation material due to its outstanding features, while its fabrication is still very challenging by foaming injection molding technology. Herein, we reported the successful fabrication of low-density branched polypropylene (BPP) foam with an expansion ratio of up to 25-fold and fine cellular structures using mold-opening foam injection molding (MOFIM) technology. To improve foaming ability, polytetrafluoroethylene (PTFE) nanofiber reinforced BPP composite was prepared in an in-situ way through a simple twin-screw blending technology. The DSC results show that PTFE nanofibers can promote crystallization of BPP effectively, while the rheological measurements demonstrate that PTFE fibers can improve the viscoelastic behavior of BPP. Furthermore, the MOFIM experimental results show that the cell size is reduced by one order of magnitude while the cell density is increased by four orders of magnitude. Interestingly, PTFE nanofibers endow BPP/PTFE foams a unique cell wall structure with plenty of micro-holes and micro/nano fibrils. Moreover, BPP/PTFE foams show markedly improved thermal insulation and compressive mechanical performance with a thermal conductivity of as low as 32.4 mW·m−1·K−1. Thus, this unique low-density BPP/PTFE foam shows a promising future in high-performance thermal insulation applications, particularly considering the used scalable, versatile, facile and cost-saving processing technology.

Lipases are scarcely exploited as feed enzymes in hydrolysis of lipids for increasing energy supply and improving nutrient use efficiency. In this work, we performed homologous overexpression, in vitro characterization and in vivo assessment of a lipase from the yeast Yarrowia lipolytica for feed purpose. Simultaneously, a large amount of yeast cell biomass was produced, for use as single cell protein, a potential protein-rich feed resource. Three kinds of low cost agro-industrial wastes were tested as substrates for simultaneous production of lipase and single cell protein (SCP) as feed additives: sugarcane molasses, waste cooking oil and crude glycerol from biodiesel production. Sugarcane molasses appeared as the most effective cheap medium, allowing production of 16420 U/ml of lipase and 151.2 g/L of single cell protein at 10 liter fermentation scale. In vitro characterization by mimicking a gastro-intestinal environment and determination of essential amino acids of the SCP, and in vivo oral feeding test on fish all revealed that lipase, SCP and their combination were excellent feed additives. Such simultaneous production of this lipase and SCP could address two main concerns of feed industry, poor utilization of lipid and shortage of protein resource at the same time.

In this study, we used a high-pressure foam injection molding process to fabricate microcellular high-impact polystyrene (HIPS) foams with a tailored cellular structure. The process is cost-effective, highly efficient and flexible, and can be easily scaled up to complex components. The cellular structure of HIPS foam can be tuned over a wide range by manipulating packing time, cooling time, mold temperature, and mold-opening distance. Microcellular HIPS foam with a weight reduction of up to 60% was prepared, which possesses a low thermal conductivity of 60 mW m−1 K−1 and an ultra-low dielectric constant of 1.25. Both the thermal conductivity and the dielectric constant can be tailored by regulating the expansion ratio of HIPS foam. Mathematical models based on the mixing rule were developed to clarify the dependence of thermal conductivity and dielectric constant on the cellular structure of the foam. The outstanding thermally and electrically insulating properties of HIPS foams come from a large amount of air in the microcellular structure. These lightweight, thermally insulating, and ultralow dielectric microcellular HIPS foams hold great promise as an ultra-efficient insulating material for future use in many applications such as microelectronics and microelectromechanical systems (MEMSs).

High-performance EMI shielding materials with renewable characteristics are needed to address the issue of electromagnetic radiation pollution. The use of traditional metal-based EMI shielding materials is limited by their high density, corrosiveness, and expensive processing costs. At the same time, using regular fossil-fuel-driven conductive polymer composite-based EMI shielding materials creates environmental pollution, exacerbates resource consumption, and offers poor electromagnetic shielding effectiveness. Moreover, most of the processing methods used for conductive polymer composite-based EMI shielding materials are focused on a batch-scale process, which cannot easily be scaled up. We studied a sustainable foam injection molding-based method to efficiently fabricate renewable microcellular PLA/graphite nanocomposite foams, with improved mechanical and electrical properties for ultra-efficient EMI shielding applications. A microcellular PLA/graphite nanocomposite foam, with a density of 0.7 g cm−3 and a thickness of 2.0 mm, exhibits an outstanding EMI shielding performance with a total electromagnetic interference shielding effectiveness (EMI SE) of up to 45 dB. More importantly, thanks to the reduced reflection, which resulted from the strong thin-film interference effect, this lightweight porous nanocomposite foam has an absorption-dominated EMI shielding feature with a radiation energy reflection of less than 15%. The nanographite reorientation, which resulted from foaming, led to the microcellular PLA/graphite nanocomposite foam's electrical conductivity being dramatically increased by almost six orders of magnitude, in relation to the unfoamed sample. Furthermore, the microcellular PLA/graphite nanocomposite foam also exhibited outstanding mechanical properties. These were characterized by a strong specific strength and modulus, and super-ductile fracture behavior. Thus, this lightweight sustainable nanocomposite foam demonstrated great promise as an ultra-efficient EMI shielding material for future use in many applications such as aerospace and electronics.

Rapid heat cycle molding (RHCM) is an advanced injection molding technology for producing spraying-free plastic products with excellent appearance. Rapid mold heating and cooling is the key technique of RHCM. Despite widely used in practice, the regular rapid mold heating and cooling methods still have some obvious defects. Thus, the authors developed a new rapid mold heating and cooling method characterized by electric heating and annular cooling, and this study experimentally investigated its temperature and pressure responses in the heating and cooling periods. The results show that the tool surface temperature increases almost linearly with the heating time after a short response time. The larger the heating power or the smaller the distance from heater to tool surface, the faster the heating rate. Introducing air bubbles into working fluid can remarkably reduce the pressure growth of working fluid without affecting the heating rate. In the investigated range of flow rate, the cooling rate firstly increases significantly with the flow rate, and then reaches a plateau, while the running pressure of working fluid increases linearly with the flow rate in the whole range. The optimum flow rate is around 6.0 L/min corresponding to the Reynolds number of 6700. The heat transfer coefficient in cooling period increases sharply at the initial stage, and then reduces gradually, and finally reaches a plateau. The larger the Reynolds number the higher the heat transfer coefficient. In particular, the heat transfer coefficient and the Reynolds number show a linear relationship on the double logarithm scale. Finally, a mathematical model was developed for predicting and controlling the temperature fluctuation range of tool surface. Thus, this study can benefit the industrial application of the new rapid heating and cooling method.

A new family of energetic ionic salts containing a 1,2,4-oxadiazole ring and an amino or triazene linkage were synthesized by the oxidation of 3-nitro-5-amino-1,2,4-oxadiazole (NOA) with sodium dichloroisocyanurate (SDCI) affording sodium bis(3-nitro-1,2,4-oxadiazol-5-yl)amide (2) and sodium 1,3-bis(3-nitro-1,2,4-oxadiazol-5-yl)triaz-2-en-1-ide (3) followed by cation metathesis. Their molecular structures were fully characterized by 1H and 13C NMR, MS and IR spectroscopy, while three ionic salts 4, 5 and 7 along with two sodium salt precursors 2 and 3 were confirmed by single-crystal X-ray diffraction. Differential scanning calorimetry (DSC) was employed to investigate the thermal stability of these ionic salts, revealing moderate onset decomposition temperatures ranging from 166 °C to 249 °C. By using a fall hammer test, most salts were found to exhibit low impact sensitivities. Guanidinium bis(3-nitro-1,2,4-oxadiazol-5-yl)amide (4) exhibits good performance with acceptable detonation properties (D: 8351 m s−1, P: 29.0 GPa), good stability (Td: 241 °C, onset) and low impact sensitivity (IS > 40 J).

In this work, we report an anomalous phenomenon on superelastic cycling of NiTi shape memory alloys when deforming at the temperature close to the border of superelastic window. New unexpected effects are found-(i) critical stress for inducing martensite transformation during the second loading cycle is higher than that of the first cycle; ( ii ) the plateau stress of the second cycle decreases to the original level when the strain overcomes the limit of the first cycle; ( iii ) transition from good superelasticity in the first cycle to fully irreversible strain in the second. We propose that defects generated during the first superelastic cycle close to the border of superelastic window impede following stress-induced martensitic transformations, leading to the increase of critical stress beyond yield stress of the B2 matrix, and thus functional fatigue of NiTi alloys. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Microcellular foaming is an advanced eco-friendly foaming technology with carbon dioxide as blowing agent. Generally, high-pressure supercritical blowing agents is needed to achieve microcellular structure with cell size less than 10 μm, which places high requirements on the foaming equipment and brings safety issues, thereby resulting in high production and maintenance costs. Herein, the stretch-assisted microcellular foaming technology was developed to prepare TPU, TPU/nanographite, and TPU/PMMA foams with significantly refined cellular structure. The results demonstrate that stretch can dramatically promote cell nucleation. For the neat TPU, the cell density can be increased by more than 8 orders of magnitude by applying a linear strain of 50 % in microcellular foaming. Increasing the amount of stretching can continue to refine the cell morphology. Compared with the neat TPU foam, the TPU/nanographite composite foam and the TPU/PMMA composite foam show further refined cellular morphology under the same foaming condition. Surprisingly, with low-pressure (300 psi) gaseous carbon dioxide as blowing agents, microcellular TPU and TPU/nanographite foams, and nanocellular TPU/PMMA foam were achieved by the stretch-assisted microcellular foaming. Furthermore, the modified classical cell nucleation theory by considering the role of elastic distortion energy in cell nucleation was proposed to clarify the cell nucleation behavior in the stretch-assisted microcellular foaming process. According to the theory, the synergistic effect of stretch-induced cell nucleation and heterogeneous phase-induced cell nucleation is the underlying mechanism of the significantly refined cellular morphology.

Natural fiber composites are of great potential for renewability and environmental friendless, but the poor interfacial bonding between the fiber and polymer matrix limits its engineering applications. In the present study, the mechanical strength of the poly (lactic acid) (PLA)/ramie fiber composites were focused. The adhesion ability was investigated by adding the compatilizer triglycidyl isocyanurate (TGIC) or treating the fibers with silane , NaOH or the combination of NaOH and silane. Fourier transform infrared spectroscopy analysis showed that PLA molecular chain was bonded on the fiber surface after treating the fibers or blending with TGIC, resulting in many tore and broke fibers in the fracture surface of the composits. At the same time, the rheological analysis indicated that the viscoelastic response of the composites was improved since the mobility of the PLA molecular chains were restricted in composites. In addition, the tensile and flexural strengths of the composites were significantly improved by the fiber surface treatment and blending with TGIC. Especially, the introduction of untreated fibers and TGIC in PLA increased the tensile and flexural strengths by 49.8% and 46.5%, respectively.

Potassium-ion batteries (PIBs) have aroused enormous interest from researchers for future electrochemical energy storage due to the low cost and abundant reserve of potassium resource. Although hard carbon materials are regarded as promising candidates for PIBs anodes, it is still a great challenge to achieve a fast and stable charging/discharging process owing to the sluggish kinetics of large-radius potassium ions. Herein, a nitrogen/oxygen co-doped bi-continuous nanoporous carbon scaffold (denoted as BNCS) anode is successfully fabricated using low-cost polyacrylonitrile as precursor through a supercritical CO2 foaming and pyrolysis method without any post-treatment. As an anode material for PIBs, the BNCS delivers a high reversible specific capacity (325 mA h g−1 at 0.1 A g−1 after 300 cycles), excellent rate performance (118 mA h g−1 at 10 A g−1) and ultra-stable cyclability (184 mA h g−1 at 1 A g−1 after 5000 cycles). The attractive electrochemical performances can be ascribed to the synergic contribution from hierarchically interconnected micro-meso-macroporous structure and nitrogen/oxygen co-doping. This template-free and scalable method provides a promising nanoporous carbon strategy for preparing high-performance PIBs anode materials.

Hard carbon materials with rational heteroatom doping and nanostructure are potential candidates for potassium-ion batteries (PIBs) anodes and arouse enormous interest from researchers. However, the application of hard carbon anodes still suffers from many obstacles of rapid capacity fading, low rate capability, extra procedures for introducing heteroatom doping and environmentally unfriendly template-removal process. Herein, nitrogen-doped carbon nanofoams (denoted as N-CNFs), which are fabricated through CO2 aided two-step foaming and pyrolysis of commercially available polyacrylonitrile, are demonstrated as high-performance PIBs anodes. The influences of pyrolysis temperature on the physical/chemical properties including porous structure, graphitization degree, nitrogen doping level, as well as electrochemical performances of N-CNFs are revealed by a series of material characterizations and electrochemical measurements. The as-fabricated N-CNF pyrolyzed at 750 °C exhibits the optimal electrochemical performances with a high reversible specific capacity (332 mA h g−1 at 0.1 A g−1 over 100 cycles), excellent rate capability (144 mA h g−1 at 5 A g−1) and great cyclability (195 mA h g−1 at 1 A g−1 over 2000 cycles). The appealing electrochemical performances benefit from the collaborative contribution of moderate specific surface area, graphitization degree and nitrogen doping level. The results could provide some guidelines for designing nitrogen-doped carbon nanofoams as high-performance anodes for PIBs.

Porous shape memory polymers (SMPs) are attracting people's attention due to their extensive application prospect. Herein, a novel and flexible method to produce bio-friendly polylactic acid (PLA)/polymethyl methacrylate (PMMA) shape memory foam by a two-step CO2 microcellular foaming is proposed. The achieved foams exhibit outstanding shape memory performance, such as a maximum shape fixity ratio of 98 %, a maximum shape recovery ratio of 86 %, and further the recovery ratio remaining more than 75 % even after 10 compression-recovery cycles. The additive PMMA phases uniformly disperse with spherical morphology in nanoscale, and they result in the greatly decreased crystallinity and crystal size of PLA. Meanwhile, the extensive interfaces lead to increased crystal density. In this context, more amorphous molecular chains left in the cell wall act as reversible segments, and more numerous denser crystals act as net points, which together can decrease the resistance in the shape memory process, thus, facilitating the significant promotion of shape memory capability of the as-achieved PLA/PMMA foams. Therefore, it exhibits a promising future to produce environmentally friendly SMPs by a simple, cost-efficient, and clean microcellular foaming technology.