Curing System Research Articles

Strain-induced crystallization behavior and tensile properties of natural rubber with different vulcanization bond types

The crosslinking network structure is a crucial factor influencing the properties of natural rubber. Therefore, investigating the impact of different vulcanization bond types on the strain-induced crystallization behavior and properties of natural rubber can provide a theoretical foundation for producing high-performance natural rubber. In this study, diverse curing systems were employed to produce vulcanized natural rubbers with varying crosslink types. The crosslinking network structures of the vulcanized rubbers were analyzed using the tube model theory. Additionally, the effects of vulcanization bonds on strain-induced crystallization behavior and tensile properties were examined through in-situ X-ray diffraction and a tensile testing machine. The results revealed that the vulcanizate with monosulfidic bonds, formed under the effective vulcanization (EV) system, primarily comprised chemical crosslinking networks, resulting in a high tensile modulus, low elongation at break, and low tensile strength. Conversely, the vulcanizate under the conventional vulcanization (CV) system exhibited a distinct entanglement network impact compared to the chemical crosslinking network, resulting in a smaller tensile modulus but the highest elongation at break and the largest tensile strength. These differences stemmed from the distinct roles of vulcanization bonds within the crosslinking network. Specifically, the relatively short monosulfidic bond quickly reached the critical degree of orientation for crystallization during stretching, leading to higher crystallinity under the same strain. However, its shorter length caused earlier fracture during stretching, resulting in network heterogeneity, reduced elongation at break, and lower tensile strength. On the other hand, the longer polysulfidic bond underwent fracture recombination during stretching, with slower orientation and delayed crystallization. Nonetheless, this recombination improved network uniformity and integrity due to stress dissipation from the initial fracture, enhancing crystallinity, elongation at break, and tensile strength. This study elucidated the influence of vulcanization crosslinking on the tensile properties of vulcanizates.

Ultra-high molecular weight EPDM composites via crossover curing agents: Stabilized crosslink network structure and performance properties

This study investigates the impact of various crosslinking systems, such as those based on sulfur, peroxide, and their hybrid combinations, on the thermal degradation characteristics of ethylene propylene diene rubber (EPDM). During aerobic degradation, polymer networks undergo reversible physical and irreversible chemical changes. There are two kinds of irreversible chemical changes that may occur: chain scission reactions and crosslinking events. The impact of these reactions on the characteristics of the elastomer is antagonistic. When measuring the properties of an elastomer as it ages, most standard characterization techniques reveal the aggregate impact of two reactions. This work employs a straightforward approach based on compression set measurements to distinguish between the scission and crosslinking events that occur during thermal aging. This work has analyzed hybrid crosslinked materials using this method and demonstrated their remarkable thermal stability, as evidenced by their ability to maintain equilibrium between scission and crosslinking reactions. The stability of performance characteristics, such as tensile strength and crosslink density, in hybrid-cured samples during thermal aging supports the aforementioned. Furthermore, the investigation also delves into the potential of hybrid curing systems using crossover curing agents instead of coagents, which are multifunctional additives, to augment the durability of performance characteristics over an extended period of thermal aging.

An Influential Remedy in Controlling of COVID-19 based on Predictive Models of Machine Learning: A Novel Spec

Coronavirus (COVID-19) is a highly potent virus that infects healthy living cells. COVID-19 the virus, makes copies in the organs of the body that replicate itself, leading to the death of some healthy people’s cells and as a result, weakening the immune system. In the soft tissue, it greatly affects the respiratory tract and leads to pneumonia, organ failure, and death, reaching its final stages. This paper focuses on the early detection of COVID-19 patients based on the good symptoms of the disease. In this paper, the COVID-19 Remedies (CURE) program is proposed on a machine-based basis, reading speculation models for the treatment of COVID-19 patients. With test results, performance analysis of The CURE system is being tested in a Python environment that is tested using the Kaggle database of Johns Hopkins University.

The effect of composite curing agent ratio on the photooxidative aging behavior of epoxy asphalt based on molecular dynamics simulation

In order to explore the effect of composite curing agent ratio on the photooxidative aging behavior of epoxy asphalt with an acidic composite curing system, three curing agent ratios of epoxy asphalt were prepared to obtain different cross-linking network densities. The prepared epoxy asphalt was subjected to photooxidation aging for 240 h at 60 ℃. Fourier transform infrared (FTIR) and elemental analysis tests were conducted to determine the evolution of chemical components during photooxidative aging. Based on the chemical components before and after aging, molecular models of photooxidation aged epoxy asphalt with different curing agent ratios were constructed. The mean square displacement (MSD) of oxygen atoms and the oxygen uptake of each component were calculated to study the diffusion behavior of oxygen atoms and the oxidation degree of each component under various cross-linking networks. Glass transition temperature (Tg) and interaction energy were determined to characterize the thermodynamic properties and interaction between asphalt phase and epoxy resin phase of epoxy asphalt before and after aging. The radial distribution function (RDF) was determined to simulate the distribution of asphaltene and epoxy resin crosslinked networks in different cross-linking networks. The results show that the formation of carbonyl groups, alcohol hydroxyl groups, and the fracture of methylene groups was observed during the photooxidative aging process of epoxy asphalt. The rise in the proportion of anhydride curing agents improved the stability of the chemical components in epoxy asphalt under photooxidation aging. High cross-linking density and methylene fracture weakened the diffusion ability of oxygen atoms in epoxy asphalt due to a reduction in free volume. In addition, photooxidation aging had a negative impact on the low-temperature performance and interaction between asphalt phase and epoxy resin phase of epoxy asphalt. However, a high content of acid anhydride alleviated the damage of photooxidation aging to low-temperature performance. Photooxidation aging developed the polar functional groups of epoxy asphalt, promoting the stacking of asphaltene under a high content of dicarboxylic acid curing agent, while breaking the stacking of asphaltene under a high content of acid anhydride curing agent.

Research on the formulation and performance of high-strength resin matrix T1 for wet winding

Aiming at the higher requirements on the performance of composite materials put forward by new specialized equipment, the development of new high-performance winding resin is carried out. First, basing on the epoxy curing system, the selection of the main resin has been completed, we select the appropriate curing agent according to the characteristics of the screened trifunctional glycidylamine epoxy resin and trifunctional alicyclic epoxy resin, the ratio is calculated and optimised, the curing system is established, and the design of the resin formulation system is completed. Second, according to the nature of the resin curing system, the toughening method is screened, and the synergistic enhancement of heat resistance and toughness of the resin is accomplished through the core-shell nano-toughening method. Finally, the glass transition temperature of the new high-performance winding resin T1 is 165.12°C, and the fracture toughness of the resin KIC can reach 1.74MPa-m1/2, and the annular tensile strength of the T1 resin-based T700 carbon fibre composites can reach 3500MPa, which meets the requirements of the design indexes of specialized equipment.

Study on properties of basalt fiber reinforcing reactive powder concrete under different curing conditions

The influence of basalt fiber (BF) on the mechanical properties of reactive powder concrete (RPC) under different curing systems was studied. Three curing systems were adopted: natural curing (NC), standard curing (SC) and combined curing (CC). The design formulas for compressive and splitting tensile strength of basalt fiber reactive powder concrete (BFRPC) were established. The hydration process and strength changes of BFRPC under different systems were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The test results showed that the CC was better than the SC and slightly better than the NC, while the hydration of the CC was insufficient in the later stage, and the growth rate was significantly lower than the SC or NC. BF showed good compatibility with the matrix and was closely bonded. BF with proper content and the matrix were pressed together to improve the mechanical properties of BFRPC, while an excess of BF content would cause weakened areas and reduce strength. In comparison to plain RPC (with BF content of 0 %), the maximum increase rates of 28-day compressive strength of BFRPC under NC, SC and CC systems were 22.8 %, 18.4 % and 8.9 %, respectively. As for 28-day splitting tensile strength, the maximum increase rates became 74.5 %, 66.5 % and 49.67 %, respectively. Considering the economy and practicability of the actual project, the strength prediction formula of BFRPC was put forward to facilitate its popularization and application.

Adhesives Based on Poly(glycidyl methacrylate‐co‐butyl acrylate) with Controlled Structure: Curing Behavior and Adhesion Properties on Metal Substrates

AbstractThe adhesion properties of poly(glycidyl methacrylate (GMA)‐co‐butyl acrylate (BA)) statistical copolymers, synthesized by atom transfer radical polymerization (ATRP), are investigated employing three different curing agents or hardeners, such as diethanolamine (DEA), dicyandiamide (DICY), and 2‐cyanoacetamide (2‐CA) on copper, iron, brass, aluminum, and titanium metal surfaces. This work describes the treatment of the different surfaces, establishes the optimal curing conditions from differential scanning calorimetry (DSC) analysis of these novel adhesive systems, and evaluates the results of the single‐lap shear test for metal joints. Thus, by dynamic DSC measurements of the mixtures, a low curing temperature of 90 °C is defined when DEA is used as a curative; while systems based on DICY and 2‐CA require temperatures of 150 °C and 160 °C, respectively. In addition, the curing process of this controlled acrylic copolymer with DICY exhibits a singular behavior, possibly due to the curing reaction mechanism, where multiple epoxy‐amine ring‐opening polyaddition reactions take place between DICY's active hydrogens and epoxy groups of poly(GMA‐co‐BA). This latter curing system shows the highest adhesion features with lap‐shear strength at room temperature of 15.5 MPa, using copper as metallic substrate; however, the best results are obtained using 2‐CA as curing agent with aluminum and iron.

An Introduced RNA-Only Approach for Plasmid Curing via the CRISPR-Cpf1 System in Saccharomyces cerevisiae.

The CRISPR-Cas system has been widely used for genome editing due to its convenience, simplicity and flexibility. Using a plasmid-carrying Cas protein and crRNA or sgRNA expression cassettes is an efficient strategy in the CRISPR-Cas genome editing system. However, the plasmid remains in the cells after genome editing. Development of general plasmid-curing strategies is necessary. Based on our previous CRISPR-Cpf1 genome-editing system in Saccharomyces cerevisiae, the crRNA, designed for the replication origin of the CRISPR-Cpf1 plasmid, and the ssDNA, as a template for homologous recombination, were introduced for plasmid curing. The efficiency of the plasmid curing was 96 ± 4%. In addition, we further simplified the plasmid curing system by transforming only one crRNA into S. cerevisiae, and the curing efficiency was about 70%. In summary, we have developed a CRISPR-mediated plasmid-curing system. The RNA-only plasmid curing system is fast and easy. This plasmid curing strategy can be applied in broad hosts by designing crRNA specific for the replication origin of the plasmid. The plasmid curing system via CRISPR-Cas editing technology can be applied to produce traceless products without foreign genes and to perform iterative processes in multiple rounds of genome editing.

Development of compressive strength prediction platform for concrete materials based on machine learning techniques

With the continuous development of artificial intelligence, machine learning (ML), as an important branch, is used to promote the digitalization of concrete. Considering that the verification of the strength corresponding to the concrete mixture requires strict curing system and cycle, high cost and low efficiency, ML technology is employed to predict the 28-day compressive strength of ordinary concrete for the support of engineering practices. The aim is to develop an efficient platform for predicting the compressive strength of concrete materials. Ridge Regression (RR), Least Absolute Shrinkage and Selection Operator (Lasso), Elastic Net Regression (EnR), Support Vector Regression (SVR) and K-Nearest Neighbor (KNN) are established, of which efficiency and accuracy are analyzed and calculated in detail. Then, integrated algorithms, namely Gradient Boosting Decision Tree (GBDT), eXtreme Gradient Boosting (XGBoost) and Random Forest (RF), are used to improve the prediction accuracy of a single machine learning algorithm. Finally, Grid Search (GS) optimization algorithm is used to further improve the generalization performance of the model. The results show that the R2 in training set of the single models is about 0.8, which is obviously lower than that of ensemble models (>0.95). It is encouraging that after conducting grid search optimization, the prediction accuracy of ML models can be improved obviously, of which R2 increasing by around 15%. In addition, the GS-XGBoost model achieved the most excellent prediction accuracy and generalization performance, with R2 values of over 99% in both the training and test sets. Finally, based on the results obtained, a software platform with a convenient graphical user interface (GUI) has been developed, which can greatly improve the efficiency of material design and testing required by researchers and engineers.

Effect of the Presence of a Silane Coupling Agent on Reaction Kinetics of Cationic Thermopolymerization of Epoxy Resin Adhesive

The effect of the presence of a silane coupling agent containing different functional groups on the reaction kinetics and physical properties of epoxy resin generated via cationic thermopolymerization was investigated. The kinetics of cationic polymerization of epoxy resin was studied using a nonisothermal DSC method. The polymerization is propagated by activated chain end (ACE) and activated monomer (AM) processes. With an increase in silane content, the ACE apparent activation energy first decreased and then increased, while the AM apparent activation energy increased. Moreover, the shear strength, coefficient of linear thermal expansion, gelation time, environmental testing of damp heat, and steady state with varied contents of silane coupling agents were evaluated. The results indicated that the presence of a silane coupling agent has more adhesion and lower water absorption than pure EP. The coefficient of linear thermal expansion and gelation time increased with the increase in silane content, while the water absorption decreased with the increase in silane content. Comparing the overall performance of three silane coupling agents used in the research, the curing system obtained by blending with vinyltrimethoxysliane (VTS) is a much better option for practical application as an adhesive.

Molecular dynamics and experiment on ultraviolet-thermal curing abrasive tools for polishing microstructures

To achieve efficient polishing of the microstructure array, a preparation method of the UV-thermal curing abrasive tools with diamond was proposed. The properties of the UV-thermal curing system were studied using molecular dynamics (MD) and experiments. The time, frequency, and pressure parameters of the UV-thermal curing abrasive tool were optimized by polishing the copper plate. MD simulation results show that increasing the temperature to 340 K can improve the blending compatibility. With the increase of the bisphenol A acrylate, the tensile property enhances from 16.38 MPa to 42.98 MPa, and the size shrinkage and mass loss weaken. The addition of diamond particles improves the anti-friction coefficient. Finally, the microstructure is polished twice under the polishing pressure of 300 N and 200 N, resulting in a roughness of Ra61nm on the upper surface and Ra105nm on the lower surface. This study can be used to guide the preparation and application of UV-thermal curing abrasive tools for polishing microstructure.

Influence of the Technological Mode of Mixing and Curing System on the Properties of Compositions Based on Nitrile Rubber and Ultrahigh Molecular Weight Polyethylene

Influence of the Technological Mode of Mixing and Curing System on the Properties of Compositions Based on Nitrile Rubber and Ultrahigh Molecular Weight Polyethylene

Integrating Curing Experience and Fluctuating Leaf Quality in an Intelligent End-Cloud Collaboration

Automated tobacco curing systems have been widely deployed to meet the demand of large-scale production of high-quality tobacco. Existing tobacco curing systems control the process based on a fixed standard curing curve to increase the production of high-quality tobacco and reduce the cost. However, it is difficult to adapt the standard curing curve to the various qualities of tobacco leaves and different experience of operators. In this paper, we propose an end-cloud collaborative intelligent curing technique which can continuously extract and integrate curing experience by using clustering and regression analysis method. At the terminal, we use a microcontroller to receive sensor data collected and exchange the information with servers through a 4G communication module. On the server side, we use a clustering-based method to separate the data of high-quality tobacco, and use regression analysis and kalman filtering for data fusion. Compared with the existing automatic curing method, our proposed method can continuously extract curing experience and optimize curing curves.

Study on Capillary Water Absorption of Waterborne-Polyurethane-Modified Recycled Coarse Aggregate Concrete.

The reuse of construction and demolition waste as a substitute for natural coarse aggregate in the production of recycled concrete has been widely used. In order to study the capillary water absorption performance of waterborne-polyurethane-modified recycled aggregate concrete (WPUMRC), the effects of different curing systems, polymer-cement ratios, and waterborne polyurethane addition methods on the cumulative water absorption and the rate of capillary water absorption of WPUMRC were analyzed, and through MIP tests, the micro modification mechanism of waterborne polyurethane in recycled concrete was analyzed. The results indicate that the optimal curing system for both DC (waterborne polyurethane is added separately from water) and HC (waterborne polyurethane is mixed with some effective water and then added) is the 14 d standard curing-14 d indoor natural drying curing system. Waterborne polyurethane can fill the pores and micro-cracks inside WPUMRC or interweave with the hydration products of cement to form a spatial network structure, reducing the porosity, and thereby improving the capillary water absorption performance of WPUMRC. Based on the MIP test results, the grey correlation method was used to establish the relationship between capillary water absorption and the pore structure of WPUMRC under the optimal curing system. In addition, the prediction model of capillary water absorption in recycled concrete was established according to the test results, which can be used to predict WPUMRC's capillary water absorption performance.

Computational Study on Radical-Mediated Thiol-Epoxy Reactions.

Radical-mediated thiol-epoxy reactions were elucidated for analyzing the overlap problem of the thiol-ene/thiol-epoxy systems using computational approaches. Nine epoxy model molecules were evaluated to mimic the chemical structures and reactivity of some industrial epoxy molecules. Modeling reaction mechanisms was conducted through density functional theory (DFT) calculations using the M06-2X/6-31+G(d,p) level at 1.0 atm and 298.15 K. An analog thiol-ene mechanism was proposed for radical-mediated thiol-epoxide reactions. Unlike the thiol-ene reactions, the addition reaction to epoxides is relatively slow (rate constants <10-4 M-1 s-1). However, the chain transfer, which paves the way for the overlapping of dual curing systems, is quite fast (rate constants >101 M-1 s-1). High stability of thiyl radicals, epoxy ring strain, and the instability of formed alkoxy radical from addition reaction were emphasized as the main driving forces for the reaction energetics and kinetics. Control of temperature and using certain thiols are strongly recommended to avoid curing step overlap based on the findings in this study.

Adult mortality trends in Matlab, Bangladesh: an analysis of cause-specific risks

ObjectiveWith socioeconomic development, improvement in preventing and curing infectious diseases, and increased exposure to non-communicable diseases (NCDs) risk factors (eg, overweight/obesity, sedentary lifestyle), the majority of adult deaths in Bangladesh...

Research on the Flexural Performance of Steel Pipe Steel Slag Powder Ultra-High-Performance Concrete Components.

In order to study the flexural performance of the combined structure of steel-pipe and steel slag powder ultra-high-performance concrete (UHPC), nine round steel-pipe beams filled with steel slag powder UHPC of different types were fabricated according to the orthogonal test method with the steel pipe type, coarse aggregate content, steel fiber admixture, and curing system as parameters. The broken ring morphology, deformation characteristics, deflection distribution, and flexural bearing capacity of the steel-pipe-UHPC beams were analyzed via a pure bending test and a finite element simulation. The results show that the damage morphology of the round steel-tube-UHPC beams prepared by using steel slag powder UHPC as the inner filling material was "bow damage" under the pure bending load, and the load capacity was higher. When the cross-sectional deflection reached L/30, the external load was still not reduced, and the steel-tube-steel-slag powder-UHPC beam had a better plastic deformation capacity and a later flexural bearing capacity. The type of steel tube had a significant influence on the flexural bearing capacity of the steel-tube-UHPC beam, and the larger the diameter of the steel tube section and the thicker the tube wall, the higher its flexural bearing capacity. The calculated ultimate flexural bearing capacity by the finite element software and the test results had a stable error between 5.6% and 11.2%, which indicates that the model was reasonably established. The research results can provide a reference for the application of steel pipe UHPC engineering.

Performance study of an epoxy–polythiol curing system for local insulating spraying based on the imbalance stoichiometric ratio

An epoxy–polythiol coating on a cross arm is an effective method to enhance the dielectric strength of air gaps in transmission line towers and reduce the occurrence of bird-related faults. However, epoxy–polythiol dual-component raw materials could not achieve the prescribed stoichiometric ratio of 1:1, affecting the protective performance of the formed insulation layer. This study characterizes the cured systems of epoxy–polythiol with imbalance stoichiometry using Fourier-transform infrared spectroscopy and scanning electron microscopy. Tests were conducted to analyze parameters of the epoxy–polythiol curing system, including breakdown strength, cure time, thermal conductivity, water absorption rate, and mechanical properties. Results demonstrate that nonstoichiometric conditions reduce the curing time, breakdown strength, thermal conductivity, and water absorption of the epoxy–polythiol curing system. However, a slight increase in the equivalent amount of the curing agent improves the mechanical properties of the cured products.

Strength formation mechanism and curing system optimization of low-carbon cementitious materials prepared by synergistic activation of multiple alkaline solid wastes

Lack of proper disposal of carbide slag (CS), soda residue (SR), and red mud (RM), which are alkaline solid wastes released from the production of acetylene, soda ash, and alumina, respectively, adversely affects the environment. This study synthesized a new low-carbon cementitious material using CS-SR-RM-fly ash (FA) as raw material and optimized its curing method.The influence of raw material composition and various curing systems on the mechanical properties and microstructure of specimens was analyzed using compressive strength, chloride ion consolidation, XRD, FTIR, and SEM-EDS. The optimum ratio of CS:SR:RM:FA was determined to be 2:1:4:3, and the compressive strength of 3/28 d at room temperature (RT) sealed curing reached 10.7/22.1 MPa. The alkaline environment created by CS-SR-RM facilitated the decomposition of active components in FA and RM, contributing to the formation of a stable three-dimensional network comprising N-A-S-H gel, C-(A)-S-H gel, and Friedel's salt crystal product. High-temperature (HT) curing at 80 °C for 8 h significantly enhanced early strength, with strength growth rates of up to 147.7/29.9% compared with RT sealed curing at 3/28 d. HT curing promoted the rapid and steady growth of hydration products, resulting in increased structural compactness and improved strength. The present study offers suggestions for reducing the environmental pollution caused by alkaline solid waste and developing new resource utilization means.

Biodegradation of natural rubber latex films by highlighting the crosslinked bond

Natural rubber latex (NRL) films are used to manufacture single-use items such as condoms, blood transfusion tubes, and gloves. Natural rubber is a biopolymer, but the vulcanization process that imparts resilience and elasticity makes it difficult to degrade, resulting in an amount of waste that takes too long to biodegrade in the environment. This study evaluated the effect of crosslink bonds on the biodegradation of NRL films containing two accelerators, zinc diethyldithiocarbamate (ZDEC) and tetramethylthiuram disulfide (TMTD), in various sulfur-based curing systems. The NRL films were buried for up to 180 days and their physical, chemical, and mechanical properties were examined to determine biodegradability. Microorganism colonies were visible using scanning electron microscopy (SEM), and functional group alterations detected using Fourier transform-infrared spectroscopy (FTIR) indicated chain scission. The sample 0.6/0, followed by 1.2/0, showed a more pronounced Tonset decrease at 60 and 90 days of soil burial. At 180 days, there is no difference among the samples since all of them showed decreases in Tonset and Tmax of about 70 °C and 10 °C, respectively. Tensile strength of all samples decreased over time, but only the 0.6/0 NRL film had a decrease higher than 50% at 30 days. Additionally, lower mono- and disulfide bond concentrations result in greater tensile strength loss. Results indicated that NRL latex films with lower crosslink density and higher polysulfide bond content exhibited significant reductions in mechanical properties, indicating that these factors contribute to biodegradability.