Table of Content

25 August 2022, Volume 50 Issue 8

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2022, 50(8):  0-0. 

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Food Science & Technology

Preparation of Pineapple Peel Cellulose Nanocrystals and Their Environment Stability in Pickering Emulsions



HUANG Huihua, TANG Lu, LIU Yushan, et al

2022, 50(8):  1-11.  doi:10.12141/j.issn.1000-565X.210521

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In recent years, with the gradual increase of pineapple sales, the resource waste problem of pineapple peel needs to be urgently solved. Pineapple peel residue is rich in insoluble cellulose, which provides a possibility for the derivative development of cellulose extracted from pineapple peel residue. In order to discuss the potential in the preparation and application of pineapple peel cellulose nanocrystals (PCNCs), this paper prepared pineapple peel residue cellulose nanocrystals PPeNc and PTNc by sulfuric acid hydrolysis and 2,2,6,6-tetramethylpiperidine oxide (TEMPO) oxidation, respectively, and applied them to the Pickering emulsion (made into PPeNc-P and PTNc-P) for the environmental stability study. Fourier transform infrared spectroscopy, X-ray diffraction and thermal gravimetric analysis show that both PPeNc and PTNc retain the original structure of cellulose, but the crystallinity and thermal stability of PTNc are lower than those of PPeNc. Atomic force microscopy show that the aspect ratio of PTNc is as high as 54.11. As compared with PPeNc, PTNc exhibits higher aspect ratio and longer diameter. Furthermore, it is found that the stability of PTNc-P is better than that of PPeNc-P in the range of pH = 2 ~ 12, and the ionic strength is below 70 mmol/L or the oil-water ratio is below 5∶5. The storage experiment shows that the storage period of PPeNc-P is within 70 days, while PTNc-P can be stored stably for more than five months. The research results in this paper indicate that PCNCs prepared by TEMPO oxidation show greater potential in stabilizing Pickering emulsion, which provides a theoretical basis for the storage and further application of PTNc in Pickering emulsion. It is conducive to realizing the high-value utilization of pineapple peel residue.

Influence of Heat-Moisture Treatment on Physicochemical Properties of Potato Starch Ghost



GAO Qunyu, LIU Qiang, DONG Shiting

2022, 50(8):  12-20.  doi:10.12141/j.issn.1000-565X.220001

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Starch Ghost is an insoluble hollow sac structure that remains in GSD (Gelatinized Starch Dispersions) after starch gelatinization, named for its shape like “ghost”. Controlling the content and properties of Ghost can regulate such physicochemical properties of GSD as digestibility, electrical conductivity, viscoelasticity, etc. To further understand the effect of modified starch Ghost on the performance of starch-based products and provide a reference for its application, this paper used waxy and native potato starch with low pasting temperature and high expansion as research objects to prepare potato starch Ghost by optimizing Brabender parameters, and the influence of heat-moisture treatment temperature on the preparation and properties of two kinds of potato starch Ghost was discussed. The results show that the SEM images of heat-moisture treatment native and waxy potato starch Ghost are mostly cyst-like and thick, with swelling degrees of 1.23 ~ 2.71 and 1.58 ~ 2.78, particle sizes of 15.2 ~ 51.3 μm and 21.5 ~ 81.0 μm, and RS contents of 90.7% ~ 98.4% and 90.4% ~ 98.4%, respectively. The heat-moisture treatment increases the onset temperature but reduces the expansion volume of potato starch, and enhances the interaction between starch molecules, which leads to the decrease of the average particle size and rapid digestion starch (RDS) content of potato starch Ghost, but the content of amylose, relative crystallinity, resistant starch (RS) and the inte-grity of potato starch Ghost are increased. With the increase of heat-moisture treatment temperature, the average particle size and RDS content of potato starch Ghost show a decreasing trend, while the relative crystallinity and RS content show an increasing trend. The integrity of potato starch Ghost increases with the increase of heat-moisture treatment temperature, and the two kinds of potato starch Ghost prepared after 110 ℃ heat-moisture treatment can maintain a good hollow sac structure. By enhancing the connections between amylose and amylopectin, amylose and lipid, and amylopectin and amylopectin in starch granules, the heat-moisture treatment can significantly improve the integrity and stability of native and waxy potato starch Ghost. By controlling the conditions of heat-moisture treatment, the structure of starch Ghost can be regulated, so as to accurately produce products containing Ghost. These results have certain guiding significance for the application of heat-moisture treatment starch.

Culture Medium Optimization and Probiotic Characteristics Evaluation of Lactobacillus rhamnosus LR-ZB1107-01



XU Xilin, ZHAO Sibo, ZHENG Liuqing, et al

2022, 50(8):  21-29.  doi:10.12141/j.issn.1000-565X.200437

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In order to increase the number of organisms per unit volume of fermentation broth and provide a basis for the development and application of Lactobacillus rhamnosus ZB1107-01 (LR-ZB1107-01) obtained in the early stage of the study, which is well tolerated by simulated gastrointestinal tract, this paper initially performs medium optimization and probiotic properties investigation of the strain. First, the growth curve of strain LR-ZB1107-01 in MRS medium was measured to clarify its growth pattern in liquid medium. Next, the number of viable bacteria in the fermentation broth of strain LR-ZB1107-01 was used as the detection index, and different kinds of nitrogen sources, carbon sources and growth factors were examined unilaterally to determine the optimal medium components, and response surface tests were conducted to optimize the medium ratios and select the best medium. Finally, the in vitro safety of the nitro reductase activity and amino decarboxylase activity was evaluated. The results show that the viable bacteria count concentration can reach 8.56×10⁸ CFU/mL, if three nutrients and contents that significantly affected the viable bacteria count are changed as follows: the addition of D-isoascorbic acid at 0.02%, magnesium sulfate at 0.12% and peptone at 3%, based on the glucose content of MRS medium at 2% and combined with the optimized culture conditions. The viable bacteria count is about 10.7 times higher than that in MRS medium. The in vitro safety evaluation results indicate that LR-ZB1107-01 is negative for both nitroreductase and amino acid decarboxylase, suggesting that the strain has a certain safety profile. This achievement has a certain guiding effect on the industrial production of probiotic strains and the subsequent development of products.

Antitumor Activity of Ferulic Acid and Its Colonic Metabolites



ZHENG Bisheng, YANG Wenhan, XU Qiuxiong, et al

2022, 50(8):  30-40.  doi:10.12141/j.issn.1000-565X.220113

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Ferulic acid (FA) is a common dietary polyphenol which is widely found in plant tissues. It has various biological activities such as antioxidant, anti-inflammatory, antithrombotic, and hypoglycemic. Due to the biological activities of dietary polyphenols largely depend on their digestion and absorption in vivo, studies on the intestinal metabolites of dietary polyphenols have gradually attracted researchers’ interest in recent years. Ferulic acid cannot be absorbed in the stomach and small intestine, but it can be converted into a series of hydroxyphenylpropionic acid compounds under the action of colonic esterases. This study selected three main colonic metabolites of FA, namely, 3-(3,4-dihydroxyphenyl) propionic acid (3,4diOHPPA), 3-(3-hydroxyphenyl) propionic acid (3OHPPA) and 3-phenylpropionic acid (PPA), to evaluate their antioxidant and antitumor activities. The results show that the antioxidant activity of metabolite 3,4diOHPPA is superior to that of FA and metabolites 3OHPPA and 3PPA. FA and its three metabolites can significantly inhibit the proliferation of HepG2 with EC50 values of 1.82 mmol/L (FA), 0.74 mmol/L (3,4diOHPPA), 7.77 mmol/L (3PPA) and 4.52 mmol/L (3PPA), respectively. Cell-cycle experiments show that FA and its three metabolites can regulate HepG2 cell cycle progression in an orderly manner, blocking the cell cycle in G2 or S phase. FA and its three metabolites can also induce apoptosis of HepG2 in a dose-dependent manner. Among them, FA and 3,4diOHPPA can increase the total apoptosis rate of HepG2 cells to 15.47% and 71.84% (4.23% for the control). After a pretreatment for 24 h, FA exerts its antiproliferative effects by upregulating Bax, p53 genes and downregulating CDK-2, CDK-4 genes; 3,4diOHPPA inhibits the proliferation of HepG2 by upregulating Bax, caspase-3 genes and downregulating CDK-2, CDK-4 genes. All these findings show that the anti-oxidative and anti-HepG2 cell proliferation ability of the metabolite 3,4diOHPPA is superior to that of FA. This research provides theoretical support for the antitumor activity of FA and its colonic metabolites, revealing the health benefits of FA intestinal metabolites.

Effect of Caffeic Acid/Chlorogenic Acid on Digestion and Retrogradation Properties of Chestnut Starch Under Heat-Moisture Treatment



CHEN Jin, HE Dawei, CHEN Ling

2022, 50(8):  41-48.  doi:10.12141/j.issn.1000-565X.210527

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Chinese chestnut is a Chinese characteristic economic forest fruit, and its planting area and output in China ranked in the world’s top. It is favored by consumers as one of the most important snack foods and food supplements. However, the content of starch in chestnut is relatively high. After processing, the content of fast-digested starch is significantly increased, which can easily lead to blood glucose disorder and can increase the risk of chronic metabolic diseases such as type 2 diabetes and obesity. In addition, chestnut starch is easy to suffer retrogradation during storage, which affects the processing quality of chestnut food. Therefore, to improve the nutritional function and processing quality of chestnut-based products, chestnut starch was modified by heat-moisture treatment (HMT) together with the composition of polyphenols. The effects of structure of caffeic acid (CCA)/chlorogenic acid (CGA) on the multi-scale structure, digestion and retrogradation performance of chestnut starch-polyphenol complexes were studied by modern analytical technologies. The results show that the addition of CCA/CGA during HMT can significantly reduce the digestibility of chestnut starch. And the content of anti-enzymatic components of chestnut starch, HMT treated chestnut starch, starch-CGA complex and starch-CCA complex are 15.53%, 17.77%, 19.72% and 22.73%, respectively. Moreover, as compared with CGA, small molecular volume of CCA is more likely to form anti-enzymatic hydrolysis structure domains (short-range ordered structures and V-type crystalline structures) with chestnut starch. Low temperature storage for 7 days can promote the retrogradation of chestnut starch granules and its polyphenol complexes. During the retrogradation process, the aggregation and re-arrangement of starch molecular chains will promote the formation of more ordered short-range ordered structures and crystalline structures, but the whole retrogradation is not obvious.As compared with HMT treated chestnut starch, the addition of polyphenols can hinder the aggregation and rearrangement of starch molecular chains to form long-range ordered crystalline structures, therefore inhibiting the retrogradation of starch granules and improving their storage stability. Overall, as compared with CGA, the addition of CCA can endow chestnut starch with great anti-digestion and anti-retrogradation performance, thus providing a new way and technical support for creating high quality and healthy chestnut starch food.

Mechanical Engineering

Study on Cutting Forces and Machining Performance in Turning Stainless Steel with Variable-Length Restricted Contact Tool



PANG Xueqin, DENG Wenjun, LI Songqing

2022, 50(8):  49-61.  doi:10.12141/j.issn.1000-565X.210741

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As a typical difficult-to-machine material, AISI 316L austenitic stainless steel has the problems of low machining efficiency and large thermo-mechanical load during machining. The present methods to improve the machining performance of stainless steel such as adopting lubrication, designing tool surface structure, etc., all exist obvious defects. For example, the extensive use of cutting fluid is detrimental to the environment and human health, and tool wear will be aggravated if the tool surface structure is designed unreasonably. Given that the existing methods fail to well deal with the problems like large thermo-mechanical load during machining austenitic stainless steel, a new restricted contact tool with variable contact length was designed aiming at machining AISI 316L auste-nitic stainless steel. Compared with traditional restricted contact tools, the new tool is superior in reducing cutting force and friction coefficient. This paper first developed a semi-analytical model for turning to predict cutting forces for inconstant restricted contact length based on the non-equidistant shear zone model and the principles of unified cutting mechanics. Then, the conventional and variable-length restricted contact pattern (rectangular and trapezoidal restricted contact pattern) was fabricated on the rake surface of uncoated cemented carbide by the W-EDM and micro-EDM process. Subsequently, extensive experiments were performed to validate the proposed model. Results show that the cutting forces predicted by the proposed semi-analytical model are in good agreement with the experimental values. As compared with conventional restricted contact tools, the developed restricted contact tool can significantly reduce cutting forces. Furthermore, the influences of conventional and developed restricted contact tools on cutting performance were compared and analyzed under dry machining conditions. The restricted contact tool developed in this paper can effectively decrease the cutting temperature and tool wear. This study can provide a basis for designing the cutting tools in machining difficult-to-cut materials.

Fatigue Life Evaluation of Excavator Working Device Based on Equivalent Structural Stress Method



CAO Leilei, WANG Liutao, WANG Yan, et al

2022, 50(8):  62-70.  doi:10.12141/j.issn.1000-565X.210689

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The working device of the excavator is a large welded structure, which is prone to damage at the weld due to various complex loads during the operation, and its fatigue strength is directly related to the service life and performance of the whole machine. In order to evaluate the fatigue life of its welds more effectively, an evaluation method of weld fatigue life of excavator working device was proposed based on the equivalent stress method in this paper. That is, based on the node force and node moment on the welding line, the structural stress that is not sensitive to the grid is calculated. The fatigue life is evaluated by the fatigue cumulative damage criterion and the main S-N curve of welded joints, which can unify with different joint types, plate thicknesses, and loading modes. By building the finite element models with detail information of the welding seam for the boom and bucket, the fatigue damage assessment was carried out for six key welds on the boom and the bucket by the equivalent structural stress method. The fatigue assessment accuracy of the boom and the bucket is comparatively studied with the fatigue experiment results in this study, the results indicate that the deviations obtained through the nominal stress method are 9.2% and 14.2%, and they reach to 24.4% and 23.4% by employing the hot spot stress method and decrease to 6.6% and 9.5% in the approach with equivalent structural stress analysis. Therefore, compared with the nominal stress method and the hot spot stress method, the evaluation results of the equivalent structural stress method are the closest to the fatigue test results. The evaluation results of the nominal stress method tend to be bold, while the evaluation results of the hot spot stress method tend to be conservative, which means that the equivalent structural stress method is very effective and reliable for the fatigue life assessment of excavator working device. The proposed method can provide ideas for the fatigue life assessment of other welded structures.

Deep Learning-Based Prediction of Contact Force in the Process of Shoveling Up Glass Subtrate



HOU Liwei, WANG Hengsheng, ZOU Haoran

2022, 50(8):  71-81.  doi:10.12141/j.issn.1000-565X.210698

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In view of the problem of insufficient characterization ability and poor versatility of action force modeling methods in existing robot contact operation tasks, this paper studied on the modeling methods of complex contact dynamics by taking the actual production process of glass substrate shoveling as an example. Considering the fact that the forces during the glass substrate shoveling are affected by the contact dynamics of multiple interfaces, exhibiting the multimodal, nonlinear, and non-stationarity properties, this paper proposed a method for the prediction of the contact force by integrating physical prior knowledge in different forms in the design and training process of deep learning models. According to the stress characteristics of the glass substrate’s shoveling up process, a deep learning model structure combining multi-scale convolutional kernel, attention mechanism and long and short-term memory network was proposed; the kinetic parameter randomization method and the contact force compensation measures based on material mechanics and fracture mechanics were proposed to make the simulation training data more robust to reflect the real contact situation; based on the mean square error loss function, the additional loss function was introduced for network training for the unreasonable physical “penetration” behavior. The experimental results show that the proposed model can accurately predict the horizontal and vertical forces with the root mean square error of 0.286 in the single-step prediction, and the multi-step prediction results are also good enough to meet the application requirements. The prediction performance of the model is superior to the existing mainstream models. The ablation experiment shows that the excellent prediction performance of the model proposed is the result of the joint contribution of the local feature extraction module, the attention mechanism module and the temporal feature extraction module. At the same time, the improved loss function improves the stability of the model training. Our method can be used in similar applications for the prediction of robotic contact force with the environment.

Transmission Performance Analysis and Optimization Design of Grasping Module of Steel Arch Looping Mechanism



HE Yuanfu, XIA Yimin, LI Shenyuan, et al

2022, 50(8):  82-91.  doi:10.12141/j.issn.1000-565X.210534

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At present, the installation of steel arch during the construction of tunnel boring machine (TBM) is completed by manual operation, and the working environment is very harsh, thus leads to the problems of low support efficiency, high labor intensity and high construction risk. Therefore, the authors and their team had designed a steel arch rapid-looping installation mechanism to replace manual operation. As the core part of the looping installation mechanism that directly contacts with the steel arch, the grasping module demands sufficient transmission performance to meet the requirements of clamping operation. Based on the screw theory, the paper established a kinema-tics model of the grasping module, and deduced the virtual coefficient between the input screw and the output screw. Then, the transmission performance of the grasping module was obtained and its transmission index was proposed. On this basis, the size parameter optimization model of grasping module was established. According to the actual grasping requirements of the steel arch looping parts, the optimization results of each size parameter were obtained as follows: the initial included angle between the jaw and the connecting rod is α = 88°, the initial position of the guide rod is l_FJ = 170 mm, and the movement range of the guide rod is 0 ~ 63 mm. Using ADAMS software to analyze the posture change process of the grasping module from clamping to opening, it comes to the conclusion that, the distance between the ends of the jaws gradually increases from 50.0 mm to 234.6 mm, which meets the requirements of grasping space; the output torque increases first and then decreases. When the jaw is fully opened, the minimum torque is 21.23 N·m, which meets the output torque demand. Finally, the steel arch looping installation experiment shows that, the difference between the measured values and the calculated model is only 4.5 mm, which proves the correctness of the model; the whole looping installation time of the steel arch is 8.6 min. As compared with the traditional manual operation, the operation efficiency of the steel arch looping mechanism is improved by 20% ~ 70%.

Environmental Science & Technology

Experimental Study on Thermal Drying Characteristics and Pollutant Discharge Law of Municipal Sludge



LIAO Yanfen, QIU Mengze, CHEN Shunkai, et al

2022, 50(8):  92-101.  doi:10.12141/j.issn.1000-565X.210726

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With the development of China’s economy and the acceleration of the urbanization process, the amount of municipal sludge has increased sharply. Sludge treatment and disposal has become an urgent problem to be solved. By taking the sludge from a sewage treatment plant as the research object, this paper studied its thermal drying characteristics and pollutant discharge law. In the study, the thermal weight loss experiment was carried out at seven sets of temperatures at 100 ~ 250 ℃ equidistantly with homemade equipment, and the drying properties were characterized by the drying rate and the dehydration rate. It is found that the best temperature for drying is 200 ℃. Moreover, the gaseous pollutants were measured online with a flue gas analyzer. It is found that, besides NH₃ and H₂S, the gaseous pollutants also contain acid gases such as NO, SO₂ and HCl, as well as hydrocarbon components such as CO, CO₂, H₂, C₂H₆ and C₂H₄. The experiment also finds that the temperature being controlled below 200 ℃ is beneficial to inhibit the release of gaseous pollutants. Under the experimental conditions, the drying condensate is high-concentration organic wastewater, the pH values are concentrated in the range of 8.88 ~ 9.17 at 125 ~ 250 ℃, forming a buffer system; the COD increases as the temperature increases, and is up to 16 000.0 mg/L under the experimental conditions. Through the basic fuel characteristics test results of the dried sludge, it can be found that the carbon content and calorific value at 125 ~ 275 ℃ decrease with the increase of temperature, but at 300 ℃, due to the conditions of low-temperature carbonization, both the carbon content and calorific value increase. This provides ideas for the energy conversion of sludge. Combining SEM, BET and other methods to characterize the sludge, it finds that temperature increase can increase the microporous structure of the dried sludge, the structure of sludge becomes loose, so that the sludge can be used as a low-grade adsorbent or building material. The results in this paper provide a new idea for sludge resource utilization.

Effect Factors and Generation Pathway of Iodoacetic Acid from Tryptophan During UV Irradiation Combined with Chlorine Disinfection



YANG Yulong, FEI Weicheng, JI Jingxuan, et al

2022, 50(8):  102-108.  doi:10.12141/j.issn.1000-565X.210345

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Amino acid is a common nitrogenous compound in water. Iodine disinfection by-products could be produced in the process of tryptophan chlorination disinfection in present of I^-. To investigate the generation and mechanism of iodoacetic acid from amino acid during the use of UV and chlorine for disinfection, this paper selected a typical iodoacetic acid, namely, tryptophan, and developed a generation kinetic model. In the investigation, first, the influences of different factors including UV irradiation time, chlorine dosage, pH value, Br^- content, and I^- content on the generation of iodoacetic acid were explored, and the generation pathway of iodoacetic acid was further analyzed. The results show that the generation process of iodoacetic acid fits the pseudo first-order reaction kinetic model, with a generation rate constant k of 0.17 h^-1. UV irradiation time, chlorine dosage, pH value, Br^- content, and I^- content all exert big influence on the generation process of iodoacetic acid. UV irradiation time promotes the generation of iodoacetic acid, and the yield of iodoacetic acid increases with the increase of UV irradiation time. When the pH value is in the range of 6 ~ 8, the yield of iodoacetic acid increases with the pH value. The generation of iodoacetic acid exhibits a firstly increase and then decrease trend with the increase in chlorine. When the ration of the concentrations of tryptophan and chlorine dosage is 1∶2, the production of IAA reaches the highest (15.30 μg/L). The paper also established an equation describing the relationship among Br^- content, I^- content and iodoacetic acid yield. It is found that Br^- has a negative correlation to the generation of iodoacetic acid, while I^- content has a greater positive one. In addition, four products including butanoic acid anhydride and isovaleric anhydride were detected using LC-MS-MS and GC-MS. It is speculated that the generation path of iodoacetic acid is that C₁₂H₁₇NO₃ is firstly produced from tryptophan through the action of UV photohydrolysis and hydroxyl radicals, and then isovaleric acid and butyrate acid are generated sequentially under the oxidation of HOCl and HOI, and finally iodoacetic acid is generated.

Test of Various Plasticizers in Groundwater by Using SPME-GC-MS



XU Ruijie, CHEN Kefu, ZHAO Weihong, et al

2022, 50(8):  109-118.  doi:10.12141/j.issn.1000-565X.210494

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The pollution problem of plasticizers in water has attracted more and more attention, and the research on their testing methods is also increasing, but the research on testing different types of plasticizers at the same time is relatively rare. And most of these studies use headspace solid phase microextraction, which is difficult to ensure good extraction efficiency and low detection limit. Therefore, this paper developed a SPME-GC-MS method to test 11 plasticizers included in two types in groundwater by using immersion solid phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). This method used 65 μm DVB/PDMS fiber, and the extraction was carried out at 80 ℃ for 50 min with a constant stirring speed of 1 000 r/min. The fiber was introduced into GC injector port, the extract was desorbed at 270 ℃ for 2.5 min and then detected by GC-MS. Qualitative analysis was performed by using retention time and characteristic ion, and quantitative by internal standard method. The results show that the linearity of 11 plasticizers is good in the range of 0.1 ~ 2.0 μg/L and the correlation coefficients are greater than 0.996; the detection limit is 0.03 ~ 0.06 μg/L; the recovery is 60.9% ~ 128.0%; and the relative standard deviation (RSD) is 6.68% ~ 19.00%. The proposed method is simple, reliable and sensitive, and it’s suitable for the determination of phthalate esters and adipate esters in groundwater. Moreover, aiming at the blank interference in plasticizer analysis, this paper conducted an in-depth study on this difficulty for the first time, carried out a detailed analysis from various aspects such as reagents, consumables and instrument maintenance, and proposed practical and operable solutions, which can effectively reduce the blank interference of plasticizers in the analysis process and further ensure the reliability of the analysis results.

Materials Science & Technology

Preparation of PEO-Based Solid Polymer Electrolyte Membranes via Solvent-Free Melting and Properties of the Product



ZHANG Guizhen LIU Yang YAN Mingbao

2022, 50(8):  119-127.  doi:10.12141/j.issn.1000-565X.210805

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With the advancement of science and technology, various intelligent electronic devices, electric vehicles and grid systems have grown rapidly, and people have a growing demand for high energy density and rechargeable battery systems. In the past few decades, the development of lithium-ion batteries has made great progress. Lithium-ion batteries consisting of positive and negative electrodes, electrolytes and separators has the danger of volatile and leakage, leading to short circuit, fire, explosion and other safety accidents. The emergence of solid electrolytes has largely eliminated this safety hazard. The solid-state electrolyte can not only separate the positive and negative electrodes in the battery to prevent internal short circuits, but also act as an ion conductor to achieve the dual role of lithium ion transfer between positive and negative active substances. The solid-state electrolyte has become one of the research hotspots in the field of new energy. At present, the preparation methods of solid electrolyte membranes mainly include organic solvent casting/coating or hot molding. Organic solvents used by these methods are not friendly to the environment and these methods have disadvantages like high manufacturing cost and low production efficiency. To solve this problem, this paper proposed a new method for preparing PEO-based composite solid electrolyte membrane based on tensile stress and solvent-free melting, characterized the crystalline morpho-logy and microscopic morphology of the electrolyte membrane by SEM and XRD, and characterized the thermal properties of the membrane by DSC and FT-IR. The electrochemical performance of the membrane was characte-rized by linear sweep voltammetry and conductivity test. The results show that, as compared with simple mechanical mixing, the PEO/LiTFSI/PVDF composite solid electrolyte membrane prepared based on tensile stress and solvent-free melting has better lithium salt dispersibility. Ionic conductivity test shows that, even the proposed method does not use organic solvents, it is still comparable to the ionic conductivity of electrolyte membranes prepared by the solution method. When the content of PVDF-HFP is 30%, the ionic conductivity of the PEO-based solid polymer electrolyte membrane at 60 ℃ reaches 2.07×10^-4 S/cm, and the electrochemical stability window is 5.0 V.

Analysis of Arc Characteristics in Oxide Active TIG Welding Based on Spectroscopy Diagnosis



LI Chunkai, DING Bin, SHI Yu, et al

2022, 50(8):  128-135.  doi:10.12141/j.issn.1000-565X.210699

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As a new welding method, active tungsten argon arc welding (A-TIG welding), which increases weld pe-netration and improves welding efficiency by coating active agent on the surface of base metal, has been widely used in actual production. As one of the most common active flux formulations in A-TIG welding, oxide’s influence mechanism for arc behavior is still in debate. In order to clarify the influence mechanism of oxide on the arc beha-vior of TIG welding, a synchronous acquisition system of arc morphology and arc spatial spectrum was established. The spectral line distribution and arc morphology characteristics of active agent particles, argon, iron and other charged particles in the arc spatial space under the action of oxide were studied, and the arc electron temperature in different regions was calculated based on Boltzmann mapping method. It is found that the relative intensity of Ar Ⅱspectral lines in the arc space decreases gradually with the increase of the distance from the cathode region. This is because the closer the arc is to the cathode region, the more concentrated the arc energy density is, the more favo-rable it is to promote the ionization of Ar atoms. SiO₂ and B₂O₃ can promote the ionization of Ar particles, while TiO₂ can inhibit the ionization of Ar particles. The distribution law of the relative intensity of Fe Ⅱ spectral lines in the axial direction is opposite to that of Ar Ⅱ spectral lines. The relative intensity of the spectral lines gradually decreases from the vicinity of the anode region to the vicinity of the cathode region. This is because the closer it is to the surface of the molten pool (near the anode region), the higher the concentration of iron vapor evaporated into the arc space is and the more obvious the ionization is. The introduction of three kinds of oxide active agents can reduce the relative intensity of Fe Ⅱ spectral lines. In the arc space coated with TiO₂ active agent, no obvious Ti Ⅰcharacteristic line and arc contraction phenomenon were detected, and the arc temperature field did not change significantly, which means that the influence of TiO₂ active agent on the arc behavior is very weak. The characteristic spectral lines of Si Ⅰ and B Ⅰ were detected in the arc space coated with SiO₂ and B₂O₃ active agents, and the two active agents can cause arc contraction, but the arc contraction has no obvious effect on the arc temperature field.

Influence of Solution Temperature on Microstructure and Mechanical Property of GH4099 Alloy



TAN Haibing, LI Shu, WANG Jing, et al

2022, 50(8):  136-143.  doi:10.12141/j.issn.1000-565X.210704

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In order to study the effect of solution temperature on the microstructure and properties of GH4099 alloy ring forgings, a heat treatment test was designed with solution treatment temperature of 1 080, 1 100 and 1 120 ℃, holding time of 1 h and aging treatment system was 900 ℃ and the holding time was 5 h. Then, the microstructure analysis and mechanical properties test were carried out. The effect of solution temperature on the microstructure and properties of GH4099 alloy ring forgings was investigated by SEM, EPMA, JMatPro software and mechanical experiment detection. The results show that, after the solid solution treatment at 1 080, 1 100 and 1 120 ℃, the average size of the γ′phase is 47.3, 48.5 and 49.3 nm, respectively, and the volume fraction is 30.1%, 31.0% and 29.9%, respectively. It can be seen that the solid solution temperature has little effect on the size, content and distribution of γ′phase. With the increase of solution temperature, the hardness of the alloy decreases. The granular M₂₃C₆ carbide in the crystal gradually dissolved with the rise of solid solution temperature. When the temperature reached 1 120 ℃, the M₂₃C₆ in the crystal almost completely dissolved. The fine and uniform grain can be obtained below 1 100 ℃; when the temperature is above 1 100 ℃, the grain size grows obviously, and the M₂₃C₆ carbide precipitate in a chain shape at the grain boundary after aging, which makes the grain boundary change from flat to curved. The curved grain boundary can effectively improve the rupture life of the alloy. The grain structure near the fracture of the durable specimens is elongated, and there are a lot of voids at the grain boundaries, which indicates that intragranular fracture is the main mechanism of crack initiation and propagation in the alloy. In addition, uneven internal texture and mixed crystal phenomenon occur in the alloy when solution treatment temperature is 1 120 ℃. Therefore, the best solution treatment temperature for GH4099 alloy ring forgings is 1 100 ℃.

Influence of Pulse Vibration Frequency on Structure and Properties of UHMWPE Molded by Pulse Vibration Molding



HU Songxi, FENG Yanhong, YIN Xiaochun, et al

2022, 50(8):  144-154.  doi:10.12141/j.issn.1000-565X.210672

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The existing static molding methods of ultra-high molecular weight polyethylene (UHMWPE) generally have the problems of long forming cycle, high energy consumption, easy thermal decomposition and so on, and the primary phase characteristic structure of their products has been completely eliminated, leading to failure in keeping good mechanical properties and excellent wear resistance at the same time. Therefore, UHMWPE products (PVM-UHMWPE) were prepared efficiently at low temperature by pulse vibration molding (PVM) technology in this paper, and the influence of pulse vibration frequency during molten hot pressing stage on structure and properties of UHMWPE products were studied. The results show that PVM can promote the interfacial fusion of particles at low molding temperature by friction between UHMWPE particles, and effectively preserve the structure characteristics of high regularity and crystallinity of nascent phase to increase the crystallinity and lamellae thickness. With the increase of pulse vibration frequency during molten hot pressing stage, the effect of pulse vibration increases, and this can improve the quality of particles interface consolidation. The yield strength, tensile modulus, break strength and work to failure of PVM-UHMWPE are all improved. However, when the frequency exceeds 3.0 Hz, the damage degree of such structure characteristics as high regularity and crystallinity of UHMWPE is aggravated by the effect of pulse vibration, and the overall crystallinity and melting temperature are reduced, resulting in the decrease of tensile modulus without further improving fracture toughness. As compared with sample CM-210 ℃-60 min with double molding cycle and 40 ℃ higher molding temperature, yield strength and tensile modulus of PVM-UHMWPE with a molding temperature of 170 ℃ and a pulsation frequency of 3.0 Hz (PVM-170 ℃-3.0 Hz) is improved by about 9% and 23%, respectively, and wear rate and wear index decrease by about 24% and 22%, respectively. That is, as compared with sample CM-210 ℃-60 min, sample PVM-170 ℃-3.0 Hz has higher mechanical strength and be-tter wear resistance.