However, tools are severely worn during processing, considerably shortening their lifespan. In this study, we prepared a series of cemented carbide-coated tools and evaluated their coating properties in cutting tests. Among all tested coatings, PVD coating made of AlCrN (AC) presented with the best surface integrity and mechanical properties, achieving the best comprehensive performance in the coating test. The AC-coated tool also exhibited the best cutting performance at a low speed of 120 m/min, corresponding to a 60% longer cutting life and the lowest workpiece surface roughness relative to other coated tools. In the cutting test at a high speed of 350 m/min, the CVD double-layer coated tool (MT) with a TiCN inner layer of and an Al CGI and gray cast iron (GCI) are two types of cast iron made with different forms of graphite in cast iron ,2. CompaThe cutting tool is one of the most important factors with respect to the cutting process of CGI . In the 40Al60N-coated tools with coating thicknesses of 5 μm, 11 μm and 17 μm, respectively, and found that the coating with the thickness of 11 μm resulted in the best cutting performance, improving the coating quality and tool life by about 35%. Duchosal A et al. [In the current production processes, tool coating is widely used, which can effectively improve the hardness and strength of the tool, in addition to improving the heat resistance and wear resistance of the tool so as to improve its service life. Tooptong S  conducteA et al.  comparedA et al.  accurateScholars have carried out a number of studies on tool materials, tool coatings and coating characteristics, which are of considerable scientific research value. However, most of these experiments were conducted under laboratory conditions, which differ from real-world conditions, meaning that the obtained results can only be used for reference and lack practical guiding value.In this study, a series of coated tools was prepared by physical and chemical deposition methods, and tested under realistic conditions. We analyzed the morphology, thickness, mechanical properties and other characteristics of the prepared coatings and conduced cutting experiments according under realistic processing conditions to determine the most suitable coating for CGI cutting applications in order to establish a guiding scheme for actual processing work.In this study, a YG6 cemented carbide tool  was used to processing CGI, which is mainly composed of tungsten carbide (WC) and cobalt (Co) binder. The name YG6 indicates that Co comprises approximately 6% of the total tool volume. The physical properties of the tool are shown in The coatings were deposited on the cemented carbide substate of an SCMT09T308 tool with a rake angle of 15° and a clearance angle of 7°. TM-EVO 15, Shanghai, China) and an energy-dispersive X-ray spectroscope  to measure the coating thickness and composition. Because of coatings were thin, in order to reduce the influence of the cemented carbide substrate under the coating on the test results, the indentation depth of the nano indenter must be less than 1/10 of the coating thickness to ensure accurate measurement.In the test of coating thickness and composition, the coated tool was cut by wire cutting; then, the cut surface was polished. After polishing, the surface was placed into a scanning electron microscope . The loading force was 10 N, and the pressure holding time was 5 s. Measurements were conducted on the same coating deposited on the surface of the cemented carbide block with the same material. The size of the cemented carbide block was 20 mm × 20 mm × 5 mm. The test was repeated 10 times for a single sample, and the average value was reported to ensure the reliability of the data.NF) was applied to the scratch needle, and the needle tip was uniformly scratched across the coating surface until the coating broke. The critical load (cL) was determined by detecting the real-time morphology of the scratch and the coating. Lc1. When the coating began to peel off near the scratch, the load was denoted as Lc2. When the load increased further and the coating spared off in a large area, the load denoted as Lc3. In this study, Lc2 was selected to characterize the binding force of the coating, and Lc3 was selected to characterize the membrane breaking force of the coating. In this test, a scratch tester  Trading Co., Ltd., Shanghai, China) was used, with a load range of 1–120 N, a load increase speed of 238 N/min, a scratch distance of 5 mm and a moving speed of 10 mm/min.Adhesion strength an important index of the mechanical properties of coatings, as this factor directly affects the service life and reliability of the coating. The scratch method is the most commonly used technique to characterize the adhesion strength of coatings. A schematic diagram of the scratch test is shown in The Rut450 CGI model was used in this turning test. A crystal phase diagram of the material is shown in A CNC lathe (BAOJI SK50P) was used in a dry cutting experiment to evaluate the cutting performance of the coated tools. According to the processing procedures, coated and uncoated tools were used to cut CGI at 120 m/min (low speed) and 350 m/min (high speed) with a feed rate of 0.14 mm/r and a cutting depth of 0.1 mm. The cutting performance of the coated tools was judged according to three factors: the machined surface roughness, the effective cutting life of the tool and tool flank wear. Surface roughness (Ra) was measured using handheld surface roughness meter  Co., Ltd., Suzhou, China); the average roughness value of eight measured machined surfaces was taken as the surface roughness value of the machined workpiece.Coating morphology is an important indicator of the superiority of reactive coatings, which can affect the adhesion between surface coatings and substrates. For some PVD coatings, a small number of particles and holes appeared on the surface of the prepared coating, which may have been caused by molten metal droplets when the PVD coating was deposited from the cathode target to the cemented carbide substrate surface. Surface morphology images of the tested coatings are shown in 2O3 coating (about 6 μm); this structure improved the hardness of the tool, providing improved lubricity. AC, GH and HS coatings have a similar composition, all containing AlCrN. The FN coating was contained AlTiN. The CM coating contained AlSiN. The HD coating contained AlTiN-TiCrSiN. The Al2O3 layer formed in these coatings can effectively improve the high-temperature life of the tool, making it suitable for dry or semidry cutting. The hardness and oxidation resistance of the coating can be adjusted by changing the aluminum content and coating structure. For example, the oxidation resistance of the coating can be improved by increasing the aluminum content and adopting a nanostructure or microalloying.The thickness and composition of the coatings considerably influence the equivalent stress of the tool, thus affecting tool wear during cutting. Images of the thickness and composition of thicker MT coating and thinner AC coating are shown in H is the hardness of the material, maxP is the maximum load during loading and A is the projected area of the indentation.According to the obtained loading and unloading curve, the hardness of the material could be obtained using the following formula:E is the elastic modulus of the tested coating, γ is the Poisson’s ratio of the tested coating, S is the slope of the upper end of the unloading curve.The elastic modulus is generally used to express the toughness of the coating. The elastic modulus of the coating can be calculated using the following formula:A) is generally calculated using the following empirical formula:h is the indentation depth of the indenter, and ε = 0.72). maxP, S can be obtained from the loading-unloading curve (H) and elastic modulus (E) of the coating can be calculated.The indentation projection area  of different kinds of coatings are shown in E) of different kinds of coatings are shown in Ensuring a high surface hardness of the coating is one of the best ways to improve the tool life. Generally speaking, under constant conditions, the higher the hardness of the material or surface, the longer the service life of the tool ,27. The 3/E*2 value of the coating are positively correlated with the plastic deformation and fracture tension [γ is Poisson’s ratio. The H/E* value of the coatings after calculation are shown in 3/E*2 value of the coatings after calculation are shown in 3/E*2 value of CM were 0.1238 and 0.6439, indicating that this coating exhibited the best bearing performance and fracture toughness, respectively. The ratios of the MT coating were 0.1213 and 0.5014, which were second only to CM coating. The H/E* and H3/E*2 ratios of the AC coating were 0.0967 and 0.3131, respectively, which were the lowest among all tested coatings.In addition to the hardness and elastic modulus of the coating, the H/E* value and H tension ,29; E*=ELc2) and membrane breaking force (Lc3) of each coating are shown in 2O3 coating on the surface, the binding force and membrane breaking force of the coating were both higher than 120 N. The AC coating was the thickest PVD coating, with a membrane breaking force of more than 120 N and a binding force of 100.92 N—the highest among all tested coatings. For FN coating, the membrane breaking force was more than 120 N, but its binding force was 88.38 N, slightly lower than that of the AC coating. For the CM, GH and HS coatings, the binding force and membrane breaking force values were roughly equal, at approximately 80 N and 87–91 N, respectively. The binding force and membrane breaking force of the HD coating were 62.97 N and 86.71 N, respectively—the lowest of all tested coatings.The scratch test results of the coatings are shown in The cutting experiment was carried out under actual factory processing conditions. During actual production and processing, in order to achieve the highest economic benefits under the premise of ensuring the product quality, the product quality judgment standard is the processed surface roughness. The cutting tool with the highest cutting life at the same price is therefore considered to have the highest economic benefit when the surface roughness of the machined workpiece reaches the standard. According to the processing procedures, tests were conducted at a low speed (120 m/min) and at a high speed (350 m/min). Machined surface roughness and flank wear are important parameters to evaluate tool wear. In this test, when the processed surface roughness (Ra) is higher than 1.6 μm under the high-speed condition and higher than 2.0 μm under the low-speed condition, the tool is considered to satisfy the wear and scrap standard, and the cutting length is recorded at this time.The surface roughness of the machined surface at low speed is shown in The flank face wear values of different surface-coated tools are shown in According to the above results, when different coated tools were used to cut compacted graphite iron at low speed, when the cutting length reached about 1700 m, there was an obvious gap in both the workpiece surface roughness and the tool flank wear, which may indicate that a 1700 m cutting length of cemented carbide coated tools is a turning point when gaps between different coating types are evident when machining compacted graphite iron. The flank wear results of the coated tools after cutting about 1700 m are shown in In summary, the AC coating exhibited the best machined surface roughness and the longer processing life among all tested coatings during low-speed processing of CGI. Huang J  studied The surface roughness of the machined surface at high speed (350 m/min) is shown in The flank wear values after cutting with different coatings are shown in The flank wear of the coated tools after cutting for 1000 m at 350 m/min is shown in 3/E*2 values of the MT coating were higher, indicating that the MT coating is more resistant to deformation and fracture. According the information presented in In summary, under the high-speed condition, the growth trend of tool flank wear and surface roughness is basically the same, and the tool surface coating can effectively reduce tool wear and improve the surface quality after machining. The MT coating achieved the best workpiece surface roughness, the lowest tool wear and the longest tool life, making it the most suitable coating for processing of CGI among tested coatings. And The HS coating is not suitable for processing of CGI. Therefore, we speculate that during the high-speed machining process, owing to the small feed and short cutting depth, the cutting force is considerably reduced, with a more intense interaction between the tool and the workpiece, making the tool more prone to damage. The H/E* and H(1)3/E*2 values, indicating the low coating hardness and toughness. Compared with the CVD coating, its denser PVD surface coating can resulted in a better resistance at low speed. Compared with other PVD coatings, the lower hardness and toughness of the coating can make it wear less during low-speed machining.The AC coating was the best tool coating for machining of CGI at a low speed of 120 m/min. In the low-speed cutting experiment, with increased cutting length, the surface roughness value of most coatings exceeded 2 μm when the cutting length reached 1250 m. However, when cutting length exceeded 2000 m, the surface roughness value of the AC-coated tool did not exceed 2 μm, with a 60% longer cutting life than other coated tools, achieving the best cutting performance among all tested coatings. The AC coating was an AlCrN series PVD coating, with low coating hardness, low elastic modulus and the lowest H/E* and H(2)2O3 with a thickness of about 6 μm. It had relatively low hardness and the lowest elastic modulus of all tested coatings. However, the H/E* and H3/E*2 values of the MT coating were high, which proved that the coating had high toughness and wear resistance. As a CVD coating, the MT coating had a high bonding strength and high toughness and wear resistance, indicating that it can better protect the tool than other coatings under the intense action of high speed.The MT coating was the best tool coating for machining of CGI at a high speed of 350 m/min. In the high-speed cutting experiment, the flank wear of the MT-coated tool increased slowly with increased cutting length. When the machined surface roughness was close to 1.6 μm, the flank wear value was about 218.57 μm, and when the cutting distance exceeded 2250 m, the surface roughness exceeded 1.6 μm. Its cutting life exceeded that of other coatings by at least 70%. The MT coating was a CVD coating; the inner layer was TiCN with a thickness of about 9 μm, and the outer layer was AlIn this study, seven PVD- and CVD-coated tools were prepared, and the properties of their coating were tested under actual CGI processing conditions. Then, the corresponding cemented carbide-coated tools were evaluated in cutting experiments under low-speed and high-speed conditions. The main conclusions of this study are as follows:


The main aging reaction of curing agent was decomposition. Compared with the aging reactions of binder, the energy barriers of curing agent are higher (196.6–282.7 kJ·mol−1) and the reaction is more difficult to occur. By comparing the energy barriers and rate constants of different reactions, it is found that the aging of NEPE propellant matrix can be divided into two stages. In the first stage, the propellant matrix mainly undergoes H abstraction and oxidation reaction, and as the reaction proceeds, the products crosslink to form -O-O-, -C-C-, and -C-O-C- bonds. At this time, the long chain molecules of the propellant matrix crosslink, and the molecular weight increases. This stage corresponds to the rising stage of mechanical properties in the aging process of the propellant. In the second stage, the propellant matrix mainly undergoes decomposition and nitration, resulting in degradation, the reduction of molecular weights, and the appearance of holes and microcracks in the matrix. This stage corresponds to the decline of mechanical properties in the aging process of the propellant. The above simulation results are in good agreement with the aging experimental phenomena, revealing the microscopic mechanism of the changes in the macroscopic properties of NEPE propellant during the aging process, and providing a theoretical basis for the related research on the aging properties and anti-aging technology of NEPE propellant.Polyethylene glycols (PEG) and toluene diisocyanate (TDI) are often used as the main components of binders and curing agents in solid propellants, and their aging is an important issue in the storage and use of propellants. To study the aging behavior and aging mechanism of nitrate ester plasticized polyether propellant (NEPE) matrix during storage, the transition states of aging reactions of binder and curing agent were optimized at the (U)B3LYP/6-311G level of theory, and the rate coefficients over the temperature range of 298–1000 K were calculated by CVT theory. The results showed that there were five kinds of aging reactions for binder, which included decomposition, nitration, H abstraction, oxidation, and crosslinking reactions. Among them, theenergy barriers of oxidation and H abstraction reactions were relatively low (79.3–91.2 kJ·mol Polyethylene glycol (PEG) is often used as the main component of nitrate ester plasticized polyether propellant (NEPE) matrix together with curing agents, such as toluene diisocyanate (TDI) and isophorone diisocyanate (IPDI), because of its good physical and chemical stability, high enthalpy of formation, and gas generation. During the storage of propellant, the weak points, such as -C-O-C- and C-N bonds, in the chemical structure of the binder and curing agent are prone to undergo chemical changes under the action of environmental factors (heat and oxygen), which, in turn, affect the aging performance of the solid propellant . Thus, i2 with PEG using molecular simulation software. Based on density functional theory (DFT), Pei et al. [At present, much literature has reported the aging behavior of NEPE propellant matrix. The results of thermal decomposition of a NEPE propellant matrix shows that a series of reactions, such as chain breaking and oxidation, will occur between binder and curing agent during thermal degradation, generating products, such as olefins, alcohols, aldehydes, and ketones, and releasing a large amount of gas ,4,5,6,7.i et al.  have cali et al.  have calWith the goal to explore the aging behavior of NEPE propellant matrix and reveal the reaction mechanisms and types of chemical reactions that occur between binder and curing agent during the matrix aging process, in this study, density functional theory (DFT) was used to study PEG and TDI at the 6-311G level. First, molecular simulations of aging reaction types and mechanisms of PEG and a simplified molecular model of PEG-TDI were carried out and the energy barriers and rate constants of each aging reaction further were calculated. Finally, the energy barriers and rate constants of different aging reactions were compared and analyzed to obtain the reaction process and mechanism of the matrix during the aging process of NEPE propellant storage.n is 2 has been found to best represent the aging state of PEG molecules with different degrees of polymerization. Therefore, to save computing power, the PEG model with a polymerization degree of 2 was chosen here as the object of study for the binder aging reaction. Sun et al. [n at 2) at the 6-311G level, including decomposition, nitration, oxidation, H abstraction, and crosslinking reactions.According to the calculation results of the dissociation energy required for the reaction of PEG molecules with different degrees of polymerization by Pei et al. , the degn et al. ,24 have TS1 is the transition state of the decomposition reaction of PEG . As the reaction continued, the H12 atom moved closer to O19 and the bond lengths of H12-O18 and H12-O19 bonds changed from 0.98 and 1.99 in IM1 to 1.06 and 1.34 Å in TS6, respectively. When reaction 4-1 is completed, peroxide P9 was generated, and because of the unstable peroxygen bond in P9, it easily decomposed into alkoxy radicals (·OR) and hydroxyl radicals (·OH) under the action of environmental factors. From the results of energy barrier calculations, the energy barrier required for the occurrence of R4-1 was seen to be larger than that required for the occurrence of R4-2. This indicated that most of the products would exist in the form of P9 and its products during the PEG oxidation reaction. The energy of the intermediate product (IM1) and product (P9) in this reaction were lower by 53.0 and 167.1 kJ·mol−1, respectively, compared to reactants, indicating that the oxidation reaction was exothermic.From the results of transition state calculations, the oxidation was seen to proceed in two steps. At the beginning of the reaction, the H atom in PEG was attracted by OZhao et al. ,17 have The products of the H abstraction and oxidation reactions contain alkyl and alkoxy radicals, respectively. With increased radical concentration, alkyl and alkoxy radicals can combine in a manner without potential energy barriers to form conformationally stable and low energy -C-C- bonds, -O-O-, and -C-O-C- structures , i.e., c2 and O2 to produce active radicals such as alkyl (R·) and alkoxy (RO·); in the chain propagation stage, the unstable active radicals can react with PEG and O2 rapidly to generate new free radicals, leading to the increasing concentration of free radicals in the matrix; in the chain termination stage, the free radicals are combined together in a potential barrier free manner to form macromolecular peroxides, which leads to the crosslinking reaction. As the concentration of free radicals in the matrix continuously decreases, the chain reaction ends.According to the reaction mechanism of H abstraction, oxidation, and crosslinking reactions of binder, it can be found that the reaction process of these three reactions follows the radical chain reaction mechanism consisting of chain initiation, chain propagation, and chain termination. The whole chain reaction process is shown in Since the reaction rate of free radical chain reaction mainly depends on the concentration of active free radicals in the reaction process, the aging reaction of propellant matrix be effectively delayed by preventing the generation of free radicals.2) gas during the aging process. To investigate the reaction types and mechanism of the aging reaction of PT molecules, the bond-dissociation energy of the characteristic chemical bonds in PT molecules was first calculated. The calculated BDE of different bonds in PT molecules are shown in TDI is often used as a curing agent to react with PEG prepolymer to generate PEG-TDI (PT) structures. The aging types of PEG have been calculated and analyzed in From the results of C-N dissociation energy calculations, the bond dissociation energy of the C(Ph)-N bond (C-N bond formed by N connected with C on benzene ring) at the ortho-position was seen to be slightly smaller than that of the bond dissociation energy at the para-position. The dissociation energy of the C(Ph)-N bond (Ⅰ) in the PT molecule had a value which was significantly larger than the dissociation energy of C-N (Ⅰ′) formed by N and C attached to O, indicating that the phenyl ring was conducive to stability of the binder-curing agent structure. From the results of C-O dissociation energy calculations, the C-O bond of Ⅱ was seen to have the smallest bond dissociation energy, which predicted that the chemical bond was easily broken and decomposed during the PT aging process. The results of dissociation energy calculations suggested that homolysis of C-N and C-O bonds in the PT molecule was the main cause of the PT aging reaction. At the level of 6-311G, the main aging reactions of the PT structure were calculated to be decomposition reactions and there existed three reaction pathways. The reaction pathways corresponding to these reactions are shown in The schematic energy diagram for the decomposition reaction of PT was obtained from molecular simulation . IRC cur2. Eventually RNHC(O)O·, RNH·, and other unstable radicals might continue to react with other radicals and active components in the aging process to produce alcohols and benzidine. Among the three reactions, the PT structures in R6-2 and R6-3 both underwent degradation and, although the amino radicals generated in R6-1 still maintained the NH group after recombination with alkyl radicals, the results showed that hydrogen bonds related to NH were easily dissociated at 40–100 °C [2 in NEPE matrix, destroyed the curing network of NEPE propellant matrix, which led to the continuous decline of the mechanical properties of propellant with increased aging time [−1 lower than that of the reactants, respectively, indicating that R6-1 and R6-2 were exothermic reactions. The energy of the products of R6-3 was 41.2 kJ·mol−1 higher than that of the reactants, indicating that R6-3 was an endothermic reaction and its decomposition to PEG and TDI is less likely to occur under normal atmospheric temperature.From the results of transition state calculations, the aging reaction process of PT was seen to be able to be divided into three main stages. First, the C-O bond with the smallest bond dissociation energy in the PT molecule was the first to break to form free radicals. Then, C(O)-N breaks to generate free radicals RNH· and CO0–100 °C ,35,36. Ting time ,37. FromTo further reveal the aging behavior and mechanism of the matrix in NEPE propellant storage, the energy barriers and rate constants in the range of 298–1000 K of reactions R1–R6-3 were calculated. The rate constants, fitted parameters of the rate coefficients, and energy barriers for different reactions are shown in −1, which were much smaller than those required for decomposition and nitration reactions (250.6–279.3 kJ·mol−1), indicating that H abstraction and oxidation reactions were more likely to occur than decomposition and nitration reactions. The decomposition of plasticizers and oxidizers in NEPE propellants had a strong influence on the binder aging reaction. The H abstraction and oxidation reactions initiated by decomposition products from plasticizers and oxidizers were the main types of reactions that occurred in propellant binders. As aging time increased, crosslinking reactions without potential energy barriers (R5-1 to R5-3) occurred between the products of H abstraction and oxidation reactions. This was also the main reason for the slightly increased trend for the maximum tensile strength of NEPE propellant in the middle of aging [The reaction rate constants of different reactions increased with increased reaction temperature . For eacof aging ,36. For The molecular structures required for the simulation were constructed in GaussView, and different molecular structures were optimized at the B3LYP/6-311G level, so that the molecular models with the lowest energy were obtained after frequency analysis to confirm that there was no imaginary frequency (IF). Then, the transition state (TS) involved in the reaction was calculated at the same level, and the intrinsic reaction coordinate (IRC) of the transition state was simulated to ensure the authenticity of the transition state in the reaction. Quantum chemical simulations were all calculated using the Gaussian program. The structural formulae of PEG and TDI are shown in CVTk was calculated using the variational transition state theory of the CVT method. The calculation method of CVTk is represented by Formula (1): σ is the degeneracy of the reaction path and its value is the ratio of the number of rotational symmetries of the reactants to the transition state; Bk is Boltzmann’s constant, J·K−1; T is the temperature; h is Planck’s constant, 6.626 × 10−34 J·s; GTQ and R(T)Q are the partition functions of the transition state and the reactants at the reaction coordinate(s) at the temperature T, respectively; EMPV is the value of potential energy along the minimum energy path. Rate constants were all calculated using the Kisthelp software.The reaction rate constant (1)2 and O2 had lower energy barrier and faster reaction rate, which were the main reactions for aging of binder. The bond energy of C-O in the binder molecule was high and, thus, more difficult for homolytic reactions to occur, resulting in a higher reaction energy barrier and slower reaction rate for decomposition and nitration reactions. This was a secondary aging reaction mode for the binder. As the H abstraction and oxidation products contained alkyl and alkoxy radicals, respectively, their products could not exist stably and were prone to crosslinking reactions without potential barriers and driven by electronic effects, which increased the molecular weight of the binder and formed a network structure.The results of transition state calculations of aging reactions of NEPE propellant binder showed that the reactions could be divided into five types: decomposition, nitration, H abstraction, oxidation, and crosslinking reactions. Among them, H abstraction and oxidation reactions under the action of NO(2)2 released at the same time. All three curing agent aging reactions damaged the long chain structure of the matrix to some extent and caused the gradual appearance of local holes and microcracks in the matrix. Compared with the binder aging reactions, the three curing agent reactions had higher energy barriers and, thus, were more difficult to react.For NEPE propellant curing agent aging reactions, transition state calculations showed that the main cause of curing agent aging was C(O)-N and C-O breakage and, after homolysis, active free radicals (NHC(O)O· and RNH·) and alcohols generated, and CO(3)2 and O2, and active radicals generated by H abstraction and oxidation reactions easily combined with each other to produce crosslinking reactions, resulting in a sharp increase in binder molecular weight and an upward trend in the maximum tensile strength. This aging process mainly occurred in the middle stage of propellant aging, when most of the antioxidants had been consumed and the products of plasticizers and oxidizers started to gather in large quantities. In the second stage, the decomposition reaction of binder and curing agent occurred, which, on one hand, destroyed the curing network and crosslinking network of the matrix, and on the other hand, CO2 released by the decomposition reaction caused a porous structure and holes in the matrix during the process of diffusion and aggregation in the matrix. Under the joint action of both factors, the mechanical properties of NEPE propellant matrix showed a significant decline in the late aging stage.Calculations of the energy barriers and rate constants of different aging reactions of NEPE propellant matrix showed that the aging of the matrix could be divided into two stages: in the first stage, H abstraction and oxidation reactions of long chain binder molecules occurred under the action of NO2 gas released and reasonably adjusting storage conditions to delay the second stage of matrix aging. In following research, it is necessary to conduct relevant experiments to investigate the connection between the amount of CO2 gas release and the trends of matrix mechanical property decline during the aging process and to establish a more convenient and efficient means for monitoring matrix aging.To summarize, the future aging protection of the NEPE propellant matrix can be carried out in two ways: on one hand, through the design and addition of new antioxidants and stabilizers to reduce the impact of plasticizers and oxidizers on matrix aging, thus eliminating the formations of active free radicals in the product and delaying the first stage of matrix aging; on the other hand, the decomposition rate of the matrix could be minimized by monitoring the amount of CO


The WHO has approved the use of several vaccines during the COVID-19 pandemic; experience over the last 2 years has indicated that dose demand can only be covered using more than one design. Therefore, having scientific evidence of the performance of the different vaccines applied in a country is highly relevant. In Mexico, 5 vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were used, allowing a cohort study to analyze the generation of anti-S1/S2 IgG antibodies and anti-RBD antibodies with neutralizing activity at 0, 21, 90, and 180 days after vaccination. Five groups of participants were formed on the basis of the type of vaccine received and were divided on the basis of whether they previously had or did not have COVID-19. After completing the vaccination schedule, the seroprevalence was 95.5, 97.5, 81.0, 95.2, and 90.0% . Among the participants without COVID-19 prior to vaccination, the largest amount of antibodies in the 90-day period was observed in the BNT162b2 group, and the amount of antibodies in the Sputnik V group decreased the least over time. Even though the percentages of seroconversion obtained in this study were lower than those currently reported in other parts of the world, the tested vaccines are able, in most cases, to induce a good production of IgG antibodies anti-S1/S2 and neutralizing capacity. The fact that there are people who have not produced antibodies during the study leaves open some questions that must be investigated to avoid the appearance of serious cases of COVID-19.IMPORTANCE Since the start of the vaccination programs against COVID-19 in 2020, it was evident that due to global shortages, the demand for the dose required in Mexico could only be covered by acquiring different vaccines. Therefore, determining the effectiveness of these and the longevity of acquired immunity is extremely important in a scenario where SARS-CoV-2 circulation becomes endemic and booster doses are required periodically. Our data reveal significant differences both in the generation of antibodies as well as in their longevity for the vaccines applied in the country but suggest that, in general, the Mexican population can reach a high capacity to neutralize the virus, therefore, regarding less the variant for which they were designed. The rapid and uncontrollable spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections that has occurred in the world over the last 2 years generated an unprecedented urgency for the development of tools to mitigate the number of infections. As of October 2022, more than 624 million confirmed cases have been recorded, and more than 6.5 million lives have been lost ; furtherin vitro  the amount of IgG antibodies produced targeting the spike protein; (ii) the neutralization capacity of the antibodies produced targeting the RBD; and (iii) the production and decay rates of these antibodies at 0, 21, 90, and 180 days postvaccination to know the best vaccine options for the Mexican population.During the recruitment process, the participants responded to a questionnaire designed to collect personal and general health status data. This information allowed us to determine that 30.8% of the participants who denied having been in contact with SARS-CoV-2 had asymptomatic infections. In total, the percentage of participants who had previously had COVID-19 was 44.5%. Other relevant data were also collected, such as the percentage of different comorbidities among the participants, sex, and average age .Analyzing those participants who presented antibodies in the first sample, that is, participants who had COVID-19 before their first immunization, in the group who presented symptomatic disease, on average, the anti-S1/S2 IgG levels and the neutralizing capacity of anti-RBD antibodies were significantly higher than those in the asymptomatic group. Compared to the participants with COVID-19 prior to vaccination, whether symptomatic or asymptomatic, participants who had not had COVID-19 prior to vaccination had significantly lower IgG antibody levels and a lower neutralizing capacity across the 4 samples collected .P < 0.05). However, this difference ceased to be significant when the participants had a second contact with the antigen , women produced more anti-S1/S2 IgG antibodies than did men in the group with and without COVID-19 prior to vaccination (P < 0.05).For anti-RBD neutralizing antibodies, women also showed a higher inhibition rate than did men at first contact with the antigen; however, this difference was only observed in participants without COVID-19 prior to vaccination  were identified. At day 90, when it was possible to analyze the effectiveness of the complete two-dose schedule, seronegativity was 4.5% in the BNT162b2 group, 2.5% in the AZD1222 group, 4.8% in the Sputnik V group, and 10.0% in the CoronaVac group. With the intention of identifying some aspect in common among these participants, in In general, there were also participants for whom seroconversion was observed after the first dose, although with a low amount of anti-S1/S2 IgG antibodies or a low neutralizing capacity, subsequently returning to values considered seronegative in the following measurements.Regarding the amount of anti-S1/S2 antibodies, extreme values detected by the interquartile method (IQR) were excluded (Data File S1), and some were analyzed individually . The difAt 21 days after the administration of the first dose, in participants without COVID-19 prior to vaccination, CoronaVac induced the lowest production of IgG antibodies , followed by AZD1222 , Sputnik V , Convidecia , and BNT162b2, with the latter generating the highest titers  . In partAt 90 days, the CoronaVac group continued to have the lowest amount of IgG  and 3G. P < 0.05), and participants in the Convidecia group presented the lowest at 180 days .In general, regarding neutralizing antibodies, the results were very similar to those observed for IgG production , with soTo determine if the amount of total IgG antibodies produced by the different vaccines has any impact on the observed neutralizing capacity or if this can occur independently of the amount of anti-S1/S2 IgG present, a correlation analysis was performed. The graphs generated from this analysis show a positive logarithmic correlation between these antibodies (IgG × RBD)  and 6. TAt 21 days, in the group vaccinated with BNT162b2, the IgG × RBD ratio was weaker than that in the groups that received other vaccines; in this group, there was a greater dispersion of the points due to high levels of neutralization .In general, at 90 days, the curves shifted to the right, indicating an increase in both anti-S1/S2 IgG antibodies and neutralizing antibodies (quadrant II). This phenomenon occurred in all groups, except for the groups vaccinated with Convidecia and CoronaVac  and 5E.By the end of the study, only those vaccinated with BNT162b2 were in quadrants I and II. The other participants, mainly those vaccinated with Convidecia, also occupied quadrant III.In the group with COVID-19 prior to vaccination , the logAfter the administration of the first dose (21 days), participants with COVID-19 prior to vaccination were in quadrant II. Interestingly, in the BNT162b2 and Sputnik V groups, points were observed in quadrant IV, indicating a low neutralizing capacity of the antibodies generated.For the group without COVID-19 prior to vaccination, for those who received BNT162b2, Sputnik V, and AZD1222, the levels of anti-S1/S2 IgG antibodies increased gradually until peaking at 90 days (2 doses), with means of 331.3, 271.5, and 230.6 AU/mL, respectively. With a cutoff at 180 days, the largest decrease was observed for participants in the AZD1222 group (58.9%), followed by those in the BNT162b2 (38.5%) and Sputnik V (8.1%) groups. For the participants immunized with Convidecia and with CoronaVac, the amount of IgG antibodies at 90 days was much lower than that in participants immunized with the other 3 vaccines; however, after 90 days, a considerable increase of 111.6 and 379.7%, respectively, was observed, possibly due to infection after vaccination because this increase coincides with the increase in cases of COVID-19 in the country . RegardiIn the group with COVID-19 prior to vaccination, for both anti-S1/S2 IgG antibodies and the neutralizing capacity, for all vaccines, a rapid increase was observed after the administration of the first dose, peaking and remaining high until the end of the study. The only exception, as seen in Because the National Vaccination Program in Mexico administered vaccines on the basis of age, the participants in each vaccine group belonged to different age groups . With thAs seen in One of the main challenges that health systems will have to face in the short term will be to select from the wide range of vaccines against COVID-19 that are currently on the market. Either with the intention of planning for third or fourth doses (boosters) or in the plausible scenario in which vaccination against COVID-19 becomes an annual immunization, knowing the longevity and capacity of the neutralization of antibodies generated by the different vaccines within a specific population is highly relevant information for decision making.This study analyzed 5 vaccines used in the Mexican population, evaluating the amount of IgG antibodies produced against the spike protein and the neutralizing capacity of the anti-RBD antibodies produced, with a 6-month follow-up with time points at 0, 21, 90, and 180 days postvaccination.The study design allowed determining, through laboratory techniques, whether the participants had already been exposed to the virus at the time of receiving the first dose. Additionally, the applied questionnaire allowed us to determine the true percentage of asymptomatic participants (30.8%), but also, and more importantly, it allowed us to separately analyze the results, considering those participants with hybrid immunity (COVID-19 prior to vaccination plus vaccine) and participants with immunity only due to the vaccine. This approach solves the bias present in other studies , 21, in At the beginning of the study, the cohort showed a seroconversion rate by natural infection with SARS-CoV-2 of 44.5% (May 2021), which is 11% higher than that reported by Muñoz-Medina et al.  from DecAfter administration of the 2nd dose, the seroconversion rates for participants in the BNT162b2, AZD1222, Sputnik V, and CoronaVac groups were greater than 90% at the end of the evaluation period (180 days after the first dose); in contrast, there was a significantly lower seroconversion in those vaccinated with Convidecia (61.2%). The use of this vaccine has been controversial because at the time of its administration in Mexico (May and June 2021), it was not approved by the FDA (recently approved by the WHO on 19 May 2022) ; howeverIn all vaccine groups, there were participants for whom seroconversion did not occur during the 180 days of follow-up. For participants in the Convidecia and CoronaVac groups, seronegativity after the complete vaccination schedule  exceeded the range of 1 to 9% reported by other authors , 28.There are reports of risk factors associated with the persistence of seronegativity after vaccination and/or natural infection, ranging from those related to the evolution of the infection, as for those who are asymptomatic or with mild symptoms, up to a body mass index equal to or greater than 30 ; howeverIn a more detailed analysis of the differences in the generation of anti-S1/S2 and RBD antibodies, in participants with and without comorbidities  and in the group without previous COVID-19, there were no significant differences in terms of the anti-S1/S2 IgG antibody response nor in the percentage of inhibition in any of the comorbidities analyzed. However, in the group with previous COVID-19, the people who suffered from arterial hypertension had a higher average of antibodies compared to those who did not suffer from it, a difference that appeared in the first shots and that was no longer significant at 180 days of follow-up.Lastly, although to a lesser degree, aspects related to the test kits, the vaccine batch administered, the cold chain, and even the administration technique  must be Because other studies have confirmed the existence of a direct relationship between high titers of IgG antibodies and decreased severity or reinfection , it may One variable that can affect the protection provided by vaccines is circulating viral variants. Figure S2 in the supplemental material shows variant of concern (VOC) circulation during the study period, in the area where the samples were obtained. Our data only shows the percentage of neutralizing antibodies versus RBD but not the neutralizing activity against the different variants. A limitation of our study was not performing neutralization assays against the different variants. Besides, since a large part of the Mexican population was not yet vaccinated during the study period, it is difficult to know if the waves occurred due to the lack of effectiveness of the vaccines used or due to the unvaccinated population.In a study carried out by Bednarski et al., a reduction in neutralization was observed by Delta and Omicron variants measure by plaque neutralization assays. Even so, although many cases occurred in people vaccinated during the third (Delta) and fourth waves (Omicron BA.1 and BA.2), these cases were generally milder and produced significantly fewer deaths, which indicates that even with the reduction of the neutralizing activity, the applied vaccines limited the evolution to severe stages of the disease .In general, regardless of the biological drug administered, the participants who had been infected before receiving the vaccine had more IgG antibodies and antibodies with neutralizing activity. Even within this same group, those who presented symptoms still had a significantly higher number of antibodies than did asymptomatic individuals. This phenomenon has been widely observed previously , indicatRegarding the relationship between the production of antibodies between the sexes, to date, there is still controversy regarding whether women are more immunologically reactive than men, either by natural infection or vaccination . In our When analyzing the general behavior of each vaccine in participants without COVID-19 prior to vaccination, the following 2 profiles of antibody generation can be identified. The first, in which BNT162b2, AZD1222, and Sputnik V are included, is a rapid increase in IgG antibodies accompanied by the presence of antibodies with neutralizing activity, peaking at 90 days and decreasing by 180 days; and the second, which includes Convidecia and CoronaVac, is the generation and maintenance of low levels of antibodies and neutralizing activity, even after completing the vaccination schedule , with a considerable increase at 180 days.Regarding the first profile, there was an increase in antibody production at 90 days due to the administration of the second dose and possible infections caused by the Delta variant wave present at that time. At 180 days, the Delta wave did not appear to trigger a response; therefore, the observed decrease in antibodies was expected . This isIn addition, with our results, we were able to corroborate that compared to the adenoviral platform, BNT162b2 produces a larger amount of antibodies , and in turn, Sputnik V was shown to induce a greater amount of antibodies than was AZD1222. The rapid decrease in antibodies that was observed in the participants who received AZD1222 was also reported in other studies , 39. SpuRegarding the second profile, the increase in antibodies that occurred after receiving the complete vaccination schedule in the participants of Convidecia and CoronaVac can only be explained by an infection caused by the Delta and Omicron waves, respectively.Regarding CoronaVac, the antibody profile generated in the participants without COVID-19 prior to vaccination contrasted strongly with that generated in the participants with COVID-19 prior to vaccination; this result is interesting because the 2 groups were equally exposed to infection during the Omicron wave. Only in the first case did the antibodies increase, which would indicate that in only the participants who had new contact with the antigen or in only those in that group was the infection successful. This could be due to the low neutralizing capacity of the antibodies generated thus far in the participants without COVID-19 prior to infection (62.4%) compared to that in those with hybrid immunity (94.5%) as reported by Zhao et al. . However“Hybrid immunity,” as vaccination after natural infection by SARS-CoV-2 has been called, has been shown to strengthen and prolong the humoral immune response against SARS-CoV-2  because The correlation analysis between the amount of IgG produced and the neutralization capacity showed that, contrary to what was expected, these follow a logarithmic relationship and not a linear relationship, which means that, even at the point where a person produces few anti-S1/S2 IgG antibodies, there will not necessarily be a low capacity to neutralize the virus. A clear example that even with a low amount of anti-S1/S2 IgG antibodies, high levels of neutralization can be achieved, is what is observed in the group vaccinated with BNT162b2 after the first immunization. In this group, the logarithmic ratio was lower than that in the groups vaccinated with other brands because more people reached high levels of neutralization despite the low amount of anti-S1/S2 IgG antibodies they produced in general.This finding becomes relevant to the interpretation of other works in which population immunity is measured based on kits directed against protein S and not specifically on the ability to neutralize the virus .Finally, like other studies on this topic, ours also has limitations. The first and most important was that due to economic reasons, it was not possible to determine antibodies against protein N in all groups, so we could not identify the participants who had a postvaccination infection. This generated uncertainty about the production kinetics and longevity of the antibodies, since the reported trends may include biases derived from the exposure of the participants to SARS-CoV-2 during the peaks of infection in Mexico and the appearance of new variants.Another limitation was that, although we detected a high production of antibodies derived from vaccination with the biologics studied, with our data it is not possible to determine whether the circulating variants of SARS-CoV-2 escape the immune response generated in the vaccinated population. And finally, the dropout of certain participants during the study reduced the number of samples analyzed at each follow-up, which directly affected the statistical power of the observed differences and correlations.In conclusion, our results showed that, from the first immunization, the analyzed vaccines caused different levels of seroconversion in the population (without previous infection), whose percentages varied from 54.2 to 87.8%, with CoronaVac being the vaccine with the lowest and BNT162b2 with the highest percentage of seroconversion. Since everything indicates that SARS-CoV-2 will become a seasonal virus, BNT162b2 should be the vaccine of choice for the first immunization. After the second immunization, all of the vaccines caused seroconversion levels above 90% . Despite the fact that the seroconversion percentages obtained in this study were lower than those reported in other parts of the world, given the current global scenario, where a good part of the population has already had a natural SARS-CoV-2 infection, the application of any of the biologicals analyzed in this study manages, in most cases, to induce a good production of anti-S1/S2 and neutralizing IgG antibodies, so they could be an option as a booster dose, as long as care is taken to ensure compatibility with the biological applied initially.The fact that there is a percentage of the population in which there was no production of antibodies during the 180 days of the study leaves open some questions about the effectiveness of the vaccines themselves, the protection generated by the cellular immune response, the form of application, the cold network used to store them, and the associated human factor. All of these factors must be taken care of and investigated to avoid the appearance of serious cases of COVID-19.With the intention of evaluating the humoral immune response generated by the administration of 5 different vaccines against COVID-19 approved in Mexico, a prospective cohort study was conducted; participants were recruited in some of the mass vaccination centers located in the State of Mexico (Mexico). The candidates were divided into 5 groups on the basis of the vaccine that they received, with 171 receiving BNT162b2 , 209 receiving AZD1222 , 203 receiving Convidecia , 179 receiving Sputnik V , and 214 receiving CoronaVac  .The follow-up for all groups was the same and consisted of obtaining 4 samples of peripheral blood, starting on the day of administration of the first dose, with the purpose of dividing the participants on the basis of the occurrence or not of a previous infection, and subsequently at 21, 90, and 180 days. For each sample, chemiluminescence immunoassay (CLIA) was performed to assess the levels of anti-S1/S2 IgG antibodies, and a neutralization enzyme-linked immunosorbent assay (ELISA) was used to measure the neutralizing capacity of the anti-RBD antibodies.The study was registered for evaluation by the IMSS National Scientific Research Committee (registration number R-2022-785-037) and was carried out in accordance with the Declaration of Helsinki. At the beginning of the study, all participants signed informed consent forms and completed a questionnaire regarding personal data and their general health status.Blood samples were obtained in 5-mL BD Vacutainer tubes with separator gel. After collection, all samples were centrifuged  and sent, under refrigeration conditions, to the Central Epidemiology Laboratory (LCE) of the IMSS through institutional mail and triple-packaged as a category B biological substance (UN 3373) following the recommendations of the International Air Transport Association (IATA) .The detection of IgG antibodies was performed using 200 μL of serum and a LIAISON SARS-CoV-2 S1/S2 IgG kit  ; the tesThe neutralizing activity of the anti-RBD antibodies was assessed using an ELISA SARS-CoV-2 surrogate virus neutralization test kit  . The kit2 and Kruskal-Wallis tests were used to compare categorical variables. To cross the factors with the dependent numerical variables, one-way analysis of variance (ANOVA), multifactorial analysis, multivariate analysis of variance (MANOVA), analysis of covariance (ANCOVA), multivariate analysis of covariance (MANCOVA), or the Mann-Whitney U test was used as appropriate. Correlation analyses were performed using the Pearson or Spearman test. Values of P < 0.05 were considered significant. IBM SPSS Statistics 24.0 was used for the analyses.Descriptive statistics were used to evaluate frequency and percentage reports; these were calculated with their respective 95% confidence intervals. The outliers were identified using the IQR (interquartile range) and Mahalanobis calculation, depending on the conditions. The χAll data are available in the main text or the supplementary materials.


During the experiments for the coupling effect of the wet–thermal and chloride salt environment, an environment simulation test chamber was utilized to simulate the wet–thermal and chloride salt environment, in which the parameters of relative humidity, temperature, mass fraction of NaCl solution and action time were set as 100%, 45 °C, 5% and 60 d, respectively. The content of nano-SiO2 (NS) particles added in geopolymer concrete (GPC) were 0, 0.5%, 1.0%, 1.5% and 2.0%. The result indicated that the mechanical properties of NS reinforced GPC decreased under the coupling effect of the wet–thermal and chloride salt environment compared to the control group in the natural environment. When the NS content was 1.5%, the cube and splitting tensile strength, elastic modulus and impact toughness of GPC under the coupling environment of wet–thermal and chloride salt were decreased by 9.7%, 9.8%, 19.2% and 44.4%, respectively, relative to that of the GPC under the natural environment. The addition of NS improved the mechanical properties of GPC under the coupling effect of the wet–thermal and chloride salt environment. Compared to the control group without NS, the maximum increment in cube compressive strength, splitting tensile strength and elastic modulus of NS–GPC under the coupling effect of the wet–thermal and chloride salt environment due to the incorporation of NS reached 25.8%, 9.6% and 17.2%, respectively. Specifically, 1.5% content of NS increased the impact toughness, impact numbers of initial crack and the ultimate failure of GPC by 122.3%, 109% and 109.5%, respectively.In this study, the mechanical behaviors of nano-SiO Besidesmissions . Geopolymissions ,5. Low-cmissions ,7. Compamissions ,9,10. Semissions ,13,14,15Geopolymer concrete (GPC) has the advantages of environmental protection and energy savings, as well as mechanical properties close to or better than OPC concrete (OPCC) ,18,19,20Due to the superfine size, large specific surface and high reactivity of nanoparticles, the addition of nanomaterials can greatly enhance the mechanical performances and durability of GPC. Some academics have carried out much research on improving the quality of concrete by introducing admixture and low-dose nanomaterials instead of binder materials in concrete mixtures, achieving important results ,31. Li e2, nano-CaCO3, nano-Al2O3, carbon nanofibers and so on [2 (NS) has attracted more attention due to its larger specific surface area and higher reactivity. The volcanic ash reaction of NS can accelerate the dissolution of tricalcium silicate to form hydrated calcium silicate [The most commonly used nanoparticles in engineering primarily involve nano-SiOnd so on ,35,36. Csilicate . Severalsilicate ,39. Liu silicate ,41 invessilicate ,43,44,45silicate . MoreoveWith the scale of hydraulic structures and marine structures in coastal areas becoming larger and more complex, the service environment of marine structures is also becoming more severe. Generally, the phenomena of high humidity, high temperature and high chloride concentration exist in many coastal areas. The strength and durability of many structures are seriously threatened under the coupling effect of a wet–thermal and chloride salt environment. There are various corrosive substances in the marine environment such as chloride ion, magnesium ion and sulfate radicals. Chloride ion erosion is the main reason for the durability damage of structures ,48,49. CFor the concrete structures served under the coupling effect of a wet–thermal and chloride salt environment, the mechanical properties of compressive strength, tensile strength, elastic modulus and impact resistance are significant enough to ensure the safety of the structures. Specifically, the strength and elastic modulus of the concrete must meet the requirements of the bearing capacity and deformation resistance of structures. However, there are still few studies on GPC in complex conditions, especially the coupling effect of a wet–thermal and chloride salt environment. Therefore, in this study, the effect of NS content on the mechanical properties of GPC under the coupling effect of a wet–thermal and chloride salt environment were investigated via a number of tests, and the corresponding influence law and the corresponding mechanism were revealed. Based on several researchers, the FA–MK combination, as an aluminosilicate precursor for the synthesis of a geopolymer, results in GPC possessing excellent mechanical behaviors ,13,14,15In this work, MK and FA were chosen as the geopolymer precursors, and the chemical compositions and physical properties of the MK and FA are presented in In this experiment, the mix proportion of NS-GPC was based on the Chinese Standard (JGJ 55-2011) . The watThe uniform dispersion of NS is critical to obtaining concrete with good mechanical properties . FirstlyTo investigate the mechanical properties of NS-GPC under the coupling effect of a wet–thermal and chloride salt environment, the effective way is to simulate the environment with high humidity, high temperature and salt content in the environment simulation test chamber, and then place the specimens in the test chamber to conduct the degradation test. By increasing the humidity, the temperature and the salt content, the effect of a wet–thermal and chloride salt coupling environment on NS–GPC was enhanced, and the accelerated test was then achieved. The overall appearance and internal structure of the environmental simulation test chamber are shown in Water is the carrier for the diffusion of chloride ions in NS–GPC, and therefore the influence of environmental humidity on the diffusion of chloride ions should be considered. The diffusion velocity of chloride ions will decrease and the effect of the acceleration test will not be achieved if the relative humidity in NS–GPC is too low. Furthermore, the average relative humidity in coastal cities in July is between 76% and 89% . Hence, The environment temperature is important for the diffusion of chloride ions in a solution. As the temperature grows, the solubility of inorganic salts will increase, and the water molecules will become more active with the increased diffusion velocity of chloride ions. Therefore, it is necessary to raise the test temperature appropriately. In this experiment, the calculation of the optimal test temperature was carried out according to the relationship between the diffusion coefficient of chloride ions and temperature given by Nernst–Einstein in order to accelerate the test . FinallyAccording to the Chinese Standard (GB/T 2423.17-2008)  and otheReferring to the current environmental coupling simulation test  and comb3 cube specimens from each mixture were cast. The tests were performed using an electron-hydraulic servo pressure testing device with a maximum range of 2000 kN. The loading rates for cube compressive and splitting tensile tests were set at 0.5 MPa/s and 0.07 MPa/s, respectively. The test device is shown in The cube compressive and splitting tensile strength of NS–GPC were measured following the Chinese Standard (GB/T50081-2019) . Three 13 prisms were prepared for each mix proportion of the axial compressive and elastic modulus test to acquire accurate values. The average value of the three prisms was taken as the result. According to the recent test [cE is elastic modulus (MPa); aF is the load under one-third of axial compressive strength (N); F0 is the beginning load under 0.5 MPa (N); A is the bearing area (mm2); L is the measuring range (mm); and Δn is the mean value of deformation on both sides of the prism at the last loading from F0 to aF (mm).Referring to the Chinese Standard (GB/T50081-2019) , the elaent test , the com3 cube specimens were prepared for each group. First, the sample was put in the testing device, and then the hammer with an elevation of 1000 mm was dropped. One impact procedure was set as a cycle. The cracking and failure on the surfaces of specimens were recorded after each impact. Impact numbers of initial crack and ultimate failure in the specimen were set as N1 and N2, respectively. The difference value of N2-N1 was used to describe the impact toughness of NS–GPC. A total of five specimens were tested in each working condition, the maximum and minimum values were eliminated and the average value was used as the final result.The impact resistance test of NS–GPC was performed on a drop hammer test machine. 3 were dried in a furnace at 60 °C and sprayed with gold before the test. The development and phase changes of the microcracks were observed by SEM at various magnifications.The microstructure of NS–GPC under the coupling effect of a wet–thermal and chloride salt environment was investigated using a KYKY-EM6200 scanning electron microscope (SEM). After the strength determination of each specimen, pieces of less than 1 cmCube compressive strength is the most commonly used compressive strength to evaluate the compressive properties of concrete. According to the related results, the addition of NS can improve the compressive strength of traditional cement concrete and geopolymer composites through the effect of the secondary hydration and the effect of filling NS particles ,31. Howe2, which leads to more aluminosilicate gels in mortar as a complement to the Si-O bonds [The major reasons for the improved properties of concrete are the nano-filling effect and pozzolanic reaction of NS particles . Besides-O bonds . Through-O bonds ,67. TherFor the concrete structures under the coupling effect of a wet–thermal and chloride salt environment, many concrete components will be subjected to the action of tensile stress. The direct tensile test is the best method to evaluate tensile properties of concrete composites. However, it is very difficult to carry out a test of direct tensile due to the high requirements needed of the test apparatus. As a result, the splitting tensile strength test is often applied. As mentioned previously, growth in the splitting tensile strength of GPC was caused by NS resulting from the mechanisms of the seeding effect, filling effect, and chemical reactions with FA . MoreoveFor the traditional cement concrete materials, elastic modulus is usually used to evaluate the deformation resistance of the concrete. The effect of addition of admixtures on elastic modulus depends on the effect on compressive strength. The addition of NS particles often increases the elastic modulus of cement concrete based on the related results . Since the elastic modulus is so important for the deformation resistance of the concrete, the influence of NS on elastic modulus of GPC under the coupling effect of a wet–thermal and chloride salt environment should be discussed. According to the erosion mechanism of inorganic salt on concrete and the weathering mechanism of geopolymer , chloridIn this experiment, the environment with high humidity, high temperature and salt content accelerated the physical corrosion action of chloride ions and water on GPC. In this study, the changes in mechanical properties of GPC under the coupling environment of wet–thermal and chloride salt are presented in (1)NS can effectively enhance the cube compressive strength of GPC under the coupling effect of a wet–thermal and chloride salt environment. The cube compressive strength of NS–GPC exhibited a developmental tendency to increase primarily and decrease later as the growth of NS substitute rate. Specifically, when the NS content was 1.5%, the cube compressive strength achieved an optimal value of 46.95 MPa, which was a rise of 25.8% compared to that of the control group without NS.(2)The addition of NS improved the splitting tensile strength of GPC under the coupling effect of a wet–thermal and chloride salt environment. When NS content increased from 0.5% to 2.0%, the splitting tensile strength of NS–GPC under the coupling effect of a wet–thermal and chloride salt environment presented a changing law of increasing primarily and decreasing later as the NS content increased. Distinctly, the splitting tensile strength of NS–GPC reached an optimal value of 3.30 MPa, which was an enhancement of 9.6% compared to that of the control group without NS.(3)It can be concluded through experiments that 1.5% is an optimal NS content for reinforcement in the elastic modulus of GPC under the coupling effect of a wet–thermal and chloride salt environment. Additionally, the elastic modulus of GPC exhibited a tendency of increasing primarily and decreasing later as the rise of NS content. An excess of NS will adversely affect the stability of the network structure at the molecular level, resulting in a decrease of the elastic modulus of GPC.(4)NS distinctly improved the impact resistance of GPC under the coupling effect of a wet–thermal and chloride salt environment. When the NS content was increased from 0.5% to 2.0%, impact toughness, impact numbers of initial crack and ultimate failure of GPC under the coupling effect of a wet–thermal and chloride salt environment exhibited a tendency of increasing primarily and declining later. Moreover, the SEM test results revealed that the incorporation of NS particles can effectively fulfill the pores and tiny cracks in GPC and make the internal structure of concrete more compact, allowing for more of the impact energy to be absorbed by GPC materials.(5)Compared to the control group in the natural environment, the mechanical properties of NS–GPC decreased under the coupling effect of a wet–thermal and chloride salt environment. Experimental results indicated that NS had an inhibitory influence on the decline of the elastic modulus and the impact toughness of GPC; however, NS contents had almost no obvious influence on the decline of the cube compressive and splitting tensile strength of GPC. In general, it can be concluded that NS can actively resist the severe environmental impact on GPC.In this study, simulation tests of the coupling effect of a wet–thermal and chloride salt environment were carried out. The effect of NS content on the mechanical behaviors—including cube compressive and splitting tensile strength, elastic modulus and the impact resistance of GPC after being subjected to the coupling effect of a wet–thermal and chloride salt environment—was investigated. The primary conclusions can be summarized as follows:


The pathogenesis of the development of chronic lung diseases assumes the participation of systemic inflammation factors, as well as hormone-like substances produced by adipose tissue. The aim of this study was to evaluate the associations of certain adipokines/cytokines and chronic bronchitis against the background of abdominal obesity in young people. The study included 1415 people aged 25−44. In total, 115 people were selected by the random numbers method, who were divided into two subgroups: those with chronic bronchitis and abdominal obesity and those with chronic bronchitis without abdominal obesity. A control group of patients with comparable gender and age was also selected. In the group of patients with chronic bronchitis, adiponectin, TNFa and GIP levels were 1.4 times higher. The levels of C-peptide, MCP-1 and PP in the group of chronic bronchitis were 1.3 times higher compared to the control. Adipsin, lipocalin-2, IL-6 and resistin were significantly higher in the group with chronic bronchitis. Glucagon, amylin and ghrelin were 2.2, 2.3 and 3.2 times lower, respectively, in the group of patients with chronic bronchitis. Against the background of abdominal obesity, the probability of having chronic bronchitis increased with an increase in the level of lipocalin-2 and GIP and TNFa. Chronic bronchitis (CB) is a disease determined as the presence of cough and sputum production for at least 3 months in each of two consecutive years when other respiratory or cardiac causes of chronic productive cough are excluded. The pathomorphological basis of CB is epithelial metaplasia, accompanied by excessive mucus secretion in response to chronic inflammation of the respiratory tract . The relIn addition to the mechanical effect of abdominal obesity on the bronchopulmonary system, the pathogenesis of chronic lung disease development assumes the participation of systemic inflammation factors, as well as hormone-like substances produced by adipose tissue . AdiposeOne study reported that patients with a high body mass index (BMI) suffer from chronic cough more often than other patients . A cohorThe aim of this study was to evaluate the associations of some adipokines and CB against the background of AO in young people.A population survey of the Novosibirsk population aged 25–44 years was conducted on the basis of NIITPM—a branch of ICIG SB RAS—in 2013–2016. The study was supported by the grant of the Russian Science Foundation No. 21-15-00022.To build a population sample, the base of the Territorial Compulsory Health Insurance Fund for Persons aged 25−44 was used for one of the districts of Novosibirsk, typical in industrial, social, population-demographic, transport structures and the level of migration of the population. A random representative sample of 2500 people was formed using a random number generator. Young age groups are known to be among the most rigid in terms of response; therefore, methods of phased epidemiological stimulation were applied: mail invitations, phone calls and information messages in the media. In total, 1512 people were examined at the screening; the response was 60.5%. After excluding pregnant women and women on maternity leave from the study, 1415 people were included in the study, including 670 men (47.3%) and 745 women (52.7%). The average age of the surveyed was 37.3  years. Informed consent was obtained from all persons for the examination and processing of personal data.Chronic bronchitis (CB), according to the clinical recommendations of the Russian Respiratory Society of 2021, was established on the basis of anamnesis: the presence of cough and sputum production for at least 3 months in each of two consecutive years in the absence of other pathology of the bronchopulmonary system , causing “cough history”. Abdominal obesity (AO) was determined based on waist circumference > 80 cm in women and > 94 cm in men , where Me is the median and 25 and 75 are the first and third quartiles in the case of categorical variables in the form of absolute and relative values: n (%). The nonparametric Mann–Whitney U-test was used to compare two independent samples. Pearson’s chi-squared criterion was used to compare the fractions. Associations were evaluated using multiple logistic regression analysis performed under the following conditions: the dependent variable is dichotomous: the presence/absence of CB; the independence of observations; the absence of multicollinearity, i.e., situations where independent variables strongly correlate with each other (r > 0.7); linear dependence between each independent variable and the logarithm of the odds ratio (logarithmic coefficients); the independence of residuals. The results of multiple logistic regression analysis were presented as OR and 95% CI for OR. The critical significance level of the null hypothesis (p = 0.0001).At the first stage of our study, the clinical and anamnestic data of patients with CB and the control group were analyzed. Patients with CB had a higher heart rate (HR) and BMI and higher values of waist circumference (WC) and hip circumference (HC) than patients without CB. In addition, patients with CB spent less time per week on physical activity (PA) . Additiop = 0.003), DAD was 1.3 times higher  and the triglyceride level was 1.4 times higher  compared with patients without AO.In the group of patients with CB, SAD was 1.1 times higher in the subgroup with AO  in the group with AO. Higher lipid values were also registered  141.5  vs. 88.5  mg/dL, p = 0.0001) and blood glucose  in the subgroup with AO than that without it.The control group also had higher rates of SAD and DAD , lipocalin-2 (1.9 times), IL-6 (2.5 times) and resistin (4.2 times) were significantly higher in the CK group. Additionally, the three studied molecules showed lower values compared to the control group. Glucagon was 2.2 times lower in the group of patients with CB, amylin 2.3 times and ghrelin 3.2 times. .When assessing the concentrations of the studied molecules in the subgroups with AO, we revealed that with a combination of CB and AO, the level of insulin was 1.4 times higher, the level of PAI-1 was 1.5 times higher, the level of C-peptide was 2 times higher and the level of leptin was almost 3 times higher compared to the subgroup with CB and without AO.In turn, the control group with AO also had higher levels of insulin, PAI-1, C-peptide and leptin , as well as higher values of IL-6 and TNFa compared with those without AO .The results of subsequent logistic regression analysis  of the association of adipokines with the chance of having CB in all young people included in the study are presented in Against the background of AO, the chance of having CB increased with an increase in the level of lipocalin-2 by 1 mcg/mL and an increase in the level of GIP by 1 pg/mL by 1% and 4.6%, respectively. It was also found that the chance of having CB with an increase in the level of TNFa by 1 pg/mL increases almost two times, but only a statistical trend has been achieved. It is worth noting that smoking included in the model increased the chance of having CB by almost seven times .The relationship between the presence of abdominal obesity and impaired respiratory function has been traced since early childhood and is most often associated with the development of bronchoobstructive syndrome . Among c2). In general, in the study, patients with low BMI and COPD had worse respiratory function and more frequent exacerbations of chronic bronchitis than patients with a BMI of ≥25 kg/m2 [The literature mainly presents data on the effect of abdominal obesity on the course of chronic obstructive pulmonary disease (COPD), when the changes become irreversible. In one study, it was shown that with the development of chronic bronchitis against the background of COPD, patients are less likely to register an increase in BMI, but at the same time, body weight deficiency is much more common , the results obtained can be used to develop new approaches to the diagnosis and treatment of patients with CB, which can significantly reduce the complications of this disease, as well as the early disability of people of working age.