Study on the evaluation and compensating strategy for the wear damage of non-return valve during injection molding process

Injection molding (IM) is one of the most essential forming methods for plastics. However, some potential risks which influence part quality may occur in the molding process. A non-return valve (NRV) is a major component on the screw head whose function is to seal during the injection process to prevent the backflow of the melt. The NRV will wear in this process and cause fluctuations in parameters and quality but the wear states of NRVs cannot be monitored without the disassembly of the injection barrel. In this study, we proposed an optimization method to compensate for the wear damage of the NRVs. The V/P switchover point in each molding cycle was recalculated and output to stabilize the part quality. As a result, the wear damage of the NRV on the current machine was able to be predicted and the part quality could be initially optimized in the condition that the NRV had a degree of wear. The experimental results reveal that our proposed compensation algorithm can monitor the type of wear of NRV online, and at the same time, it can compensate the axial wear of NRV and finally improve the consistency of product weight, which established a fundamental for further research in the future.     

Flame retardant and antibacterial properties of PLA/PHMG-P/APP composites

Poly(lactic acid) (PLA) has evolved into a commodity polymer with numerous applications. However, its high flammability limits its viability as a perfect alternative to petrochemical engineering plastics. In this study, PLA was modified using polyhexamethyleneguanidine phosphate (PHMG-P) and ammonium polyphosphate (APP). The flame retardant performance of PLA/PHMG-P/APP was investigated based on the limiting oxygen index (LOI), vertical burning test (UL-94), thermogravimetric analysis (TGA), cone calorimetry (CC), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Raman Spectrometry. Qualitative and quantitative methods were used to determine the antibacterial properties of PLA composites. The LOI of PLA-10% (P:A = 1:4) was 31.7% and was rated V-0 in the UL-94 V-0 test. The antibacterial properties of the composites reflected the antibacterial effects of PLA-10% (P: A = 1:4) against Escherichia coli and Staphylococcus aureus, with the antibacterial rates reaching 93.41% and 93.26%, respectively. PHMG-P and APP had a synergistic flame-retardant effect and improved the flame retardancy of PLA while exhibiting excellent antibacterial properties.     

Silica islands regulated external Ti-site environment of TS-1 for enhanced performance of 1-hexene epoxidation

Rational regulation of the local environment of Ti-sites in TS-1 harbors tremendous industrial and scientific significance to epoxidation reactions. Herein, we report a facile and environment-friendly strategy to boost catalytic selectivity by covering the Ti-sites on an external surface of TS-1 (ITS-1) without sacrificing activity of internal Ti sites. By a quantitative analysis of d₃-acetonitrile and quinoline-DRIFTS, ¹H MAS NMR and XPS, it is found that the percentage of external Ti-sites decreased from 11% to 6% after depositing surface silica islands. This successfully inhibits ring-opening reaction of 1,2-epoxyhexane on catalyst surface, as demonstrated by slower kinetic decomposition rate of 1,2-epoxyhexane. Compared with conventional TS-1 catalyst, selectivity of 1,2-epoxyhexane over ITS-1 catalyst significantly increased from 83.5% to 98.5% while maintaining high 1-hexene conversion. Furthermore, overmuch surface silica coverage only leads to extremely low conversion (2%) due to inhibition of mass transfer. This work paves the way for rational construction of Ti-containing catalysts for 1-hexene epoxidation.     

Direct and transfer hydrogenation of furfural over MOF-derived Pd-Cu@C catalysts

Owing to the self-reducing ability of palladium acetate in solutions, an ethanol solution containing Pd⁰ particles was prepared and coated in-situ into copper metal–organic framework (Cu-MOF), forming Pd@Cu-MOF in a coated structure. The Pd@Cu-MOF was reduced under N₂ or H₂ to form carbon-coated Pd-Cu@C. The pyrolysis and carbonization of Cu-MOF and the reduction of Cu²⁺ were studied. The Cu-MOF under either N₂ or H₂ was pyrolyzed and carbonized, but the Cu²⁺ reduction mechanisms were different. The high-temperature carbothermic reduction of Cu²⁺ under N₂ produced Cu⁰, but during low-temperature reduction under H₂, the reducing H₂ reduced Cu²⁺ to Cu⁰. Furfural hydrogenation experiments showed that compared with H₂, the Pd-Cu@C prepared under N₂ reduction displayed higher furfural hydrogenation activity. The catalytic activity of Pd-Cu@C prepared from in-situ Pd⁰ coating was higher than the Pd/Cu@C prepared from the impregnation method. With i-propanol as the solvent, the catalytic hydrogenation of furfural under H₂ consisted of direct catalytic hydrogenation with molecular hydrogen as the hydrogen source and catalytic transfer hydrogenation with i-propanol as the hydrogen donor. The catalytic activity of direct catalytic hydrogenation is higher than the catalytic transfer hydrogenation.     

Polydopamine-Assisted Bi-Functional Modification of NiO Anode for Enhanced Lithium-Ion Storage Performance

The blooming requirement of high-performance energy storage systems has aroused the thirst for advanced energy storage materials. As a high capacity anode, however, the application of NiO nanoparticles (NiO NPs) is hindered by intractable issues of dramatic volume change, intrinsic low electronic conductivity, and severe aggregation tendency during lithiation/delithiation. Herein, a polydopamine (PDA) assisted bi-functionalization strategy for fabricating of PDA@NiO-CNT composites for fast and durable lithium storage is reported. In this composite, CNTs intertwine to form a network to ensure sufficient electrolyte infiltration and act as a highly conductive system to motivate fast charge transmission. The strong binding affinity of PDA facilitates bonding between NiO NPs and CNTs, which not only forms uniform and flexible PDA coating but also ensures homogeneous distribution of NiO NPs on CNTs network. Therefore, the bi-functional modified PDA@NiO-CNT electrode possesses high conductivity, alleviates volume change and aggregation of NiO NPs during cycling, achieves a reversible capacity of 1326 mAh g⁻¹ at 100 mA g⁻¹, a rate capability of 215 mAh g⁻¹ at 2000 mA g⁻¹ and a cycling stability with 78% capacity retention after 250 cycles. This bi-functional modification approach manifests its prospective potential for architecting other electrode materials toward high-performance electrochemical devices.     

Fibrous ceramic membrane constructed by mullite whiskers for the treatment of oil-in-water emulsions

Ceramic membranes with high porosity and excellent separation efficiency are necessary for the efficient treatment of large-scale wastewaters. However, the conventional ceramic membranes are usually prepared by particles-packing, which inhibits the advances of separation efficiency because of the low porosity and connectivity. Here, a fibrous ceramic membrane with mullite whiskers-interlocked structure was prepared by gas-solid reaction. The effects of aluminum fluoride (AlF₃) on the formation and growth of mullite whiskers, and then the permeability and selectivity of the ceramic membranes were investigated. With the increase of AlF₃ contents, the mullite phase evolved from needle-like, rod-like to flake-like structure, thus the catalyst accelerated the growth of mullite whiskers in the diameter direction. For the ceramic membrane sintered at 1400°C, the porosity increased from 58% to 76% while the average pore sizes increased from 0.65 to 3.93 μm because of the whisker-constructed structures. For the ceramic membrane sintered at 1450°C, the emulsion flux increased stably from 295 L/(m²·h) to 992 L/(m²·h) with the increase of trans-membrane pressure, and the oil rejection exceeded 98%. Thus, this study provides a feasible strategy for the preparation of ceramic membranes with high porosity and excellent separation performances.     

Microstructure of rapidly-quenched ZrO2-SiO2 glass-ceramics fabricated by container-less aerodynamic levitation technology

In this work, an aerodynamic levitation technology (ALT) was utilized to prepare ZrO₂-SiO₂ glass-ceramics with two different ZrO₂ contents, that is, 35 mol% and 50 mol%. The glass-ceramics were partially melted at ∼2000°C or fully melted at ∼3000°C by ALT, followed by rapid quenching to obtain spherical glass-ceramic beads. The phase compositions and microstructures of the glass-ceramics were characterized. Crystallization of ZrO₂ occurred during the solidification process and ZrO₂ content, processing temperature, and the addition of yttrium (3 mol%) affected the crystalline phase of ZrO₂. No ZrSiO₄ or crystalline SiO₂ were formed during the solidification process and the glass-ceramics were away from thermodynamic equilibrium due to rapid quenching. The glass-ceramics showed a microstructure of irregular-shaped ZrO₂ micro-aggregates embedded in an amorphous SiO₂ matrix, with lamellar twins and lattice defects formed within ZrO₂ crystals. For samples prepared at ∼3000°C, a liquid-liquid phase separation occurred in the melt, which eventually resulted in the formation of large and irregular-shaped ZrO₂ aggregates. In comparison, for samples prepared at ∼2000°C, pre-existed ZrO₂ crystals formed during heating acted as nucleation sites during the cooling process, followed by grain growth to form large ZrO₂ aggregates. Solidification and microstructure formation mechanisms were proposed to elucidate the solidification process during rapid cooling and the microstructure of the glass-ceramics obtained.     

Anodic dissolution of spongy titanium in ethanol solution for preparation of nano-sized TiO2 powder

Nano-sized TiO₂ powder was prepared by electrochemical dissolution of spongy titanium in an ethanol solution following direct hydrolysis of the electrolyte solution. Characterization of the electrochemical product revealed that Ti(OEt)₄ was formed by anodic dissolution of spongy titanium in ethanol solution. X-ray diffraction and transmission electron microscope were, respectively, used to investigate the structure of TiO₂. This study showed that nano-sized TiO₂ prepared by this method has a structural and thermal stability with a narrow size distribution of 5-10 nm. The optimum electrochemical operating conditions established were a temperature of 333-343 K, current density of 400 A m⁻² and faradaic efficiency of 86%. Experiments showed that this process might be recommended as a promising technique for synthesis of nano-sized powder.     

Preparation of hyperbranched polymers by atom transfer radical polymerization

A cheap acrylic AB* monomer, 2‐(2‐chloroacetyloxy)‐isopropyl acrylate (CAIPA), was prepared from 2‐hydroxyisopropyl acrylate with chloroacetyl chloride in the presence of triethylamine. The self‐condensing vinyl polymerization by atom transfer radical polymerization (ATRP), a “living”/controlled radical polymerization, has yielded hyperbranched polymers. All the polymerization products were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR). CAIPA exhibited distinctive polymerization behavior that is similar to a classical step‐growth polymerization in the relationship of molecular weight to polymerization time, especially during the initial stage of the polymerization. However, a significant amount of monomer remained present throughout the polymerization, which is consistent with typical chain polymerization. Also, if a much longer polymerization time was used, the polymer became gel. As a result of the unequal reactivity of group A* and B*, the polymerization is different from an ideal self‐condensing vinyl polymerization: the branch structures of polymers prepared depend dramatically on the ratio of 2,2'‐bipyridyl to CAIPA. Hyperbranched polymers exhibit improved solubility in organic solvent, however, they have lower thermal stability than their linear analogs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2114–2123, 2002