High Curing Temperature Research Articles

Activated Phenyl Ester Vitrimers.

Aromatic esters are amongst the oldest known chemical motifs that allow for thermal (re)processing of thermosetting polymers. Moreover, phenyl esters are generally known as activated esters that do not require a catalyst to undergo acyl transfer reactions. Even though dynamic aromatic esters find applications in commercialized thermoset formulations, all-aromatic esters have found limited use so far in the design of covalent adaptable networks (CAN) as a result of their high glass transition temperature (Tg)and specific curing process. Here, a strategy to include partly aromatic esters as dynamic cross-links inside low Tg (-40°C) thermosetting formulations, using aliphatic esters derived from para-hydroxybenzoic acid, which serves as a highly activated phenol or as a reactive "phenylogous anhydride" is reported. A small molecule study shows that the activated phenyl ester bonds can readily exchange with free phenol moieties at 200°C under catalyst-free conditions, while the addition of a catalyst allows for a faster exchange. Robust and hydrophobic polymer networks are conveniently prepared via rapid thiol-ene UV-curing of unsaturated phenol esters. The obtained networks show high thermal stability (350°C), fast processability, good water resistance, and low creep up to 120°C, thus showing good promise as a platform for CAN.

Assessment of the biological durability of oil palm trunk modified with 1,3-dimethylol-4,5-dihydroxy-ethyleneurea (DMDHEU) following subsequent curing at elevated temperatures

The biological durability of oil palm trunk modified with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) was tested after subsequent curing at elevated temperatures. The resistance against mold, decay fungi, and subterranean termites was examined. Dimethylol dihydroxyethyleneurea-modified OPT demonstrated improved resistance against mold and decay fungi; however, the effect was lesser on subterranean termite attacks. Oil palm trunk modified with 34% DMDHEU and cured at 160 °C exhibited the most effective reduction in mass loss due to biological degradation compared to the untreated controls. High curing temperature (> 180 °C) caused cracks and ruptured the cell walls, exposing the untreated zone of the OPT to biological attack. As a non-biocidal wood modification, homogeneous dispersion of DMDHEU with adequate concentration and curing temperature is important to fully prevent OPT degradation by wood-destroying fungi and termites. These results provide valuable information for technologists to enhance or streamline the experimental design of combined modification with DMDHEU and thermal treatment, supporting their practical goals. It is recommended to continue research on the leaching of DMDHEU-modified OPT to understand the prevailing effect of DMDHEU on the biological durability of OPT, whether it is due to cross-linking or filler dispersion.

Investigating UV light and ziram catalyst as alternative activators for sulfur-promoted benzoxazine curing

High-temperature curing is a major limitation for the widespread use of benzoxazine resins. This study explores two strategies to reduce curing temperatures using minimal sulfur content (1–5 wt%): ziram catalysis and light activation. Both approaches effectively promoted curing at lower temperatures compared to traditional methods. The ziram-activated system achieved an activation energy as low as 83 kJ/mol, while the UV-activated system reached 63 kJ/mol. Furthermore, the UV-activated sulfur system exhibited improved thermal stability, particularly for cresol-based benzoxazines. The curing processes of monomers with catalysts were traced using various techniques, including nuclear magnetic resonance (NMR), Fourier-transform infrared (FT-IR), along with differential scanning calorimetry (DSC).

Multidisciplinary space shield origami composite: Incorporating cosmic radiation shielding, space debris impact protection, solar radiative heat shielding, and atomic oxygen erosion resistance

Origami composites have been extensively utilized in space structures with constrained payload volumes due to their capability to efficiently transform compact structures into larger surface area or volume configurations. The proposed origami composite incorporates hydrogen-rich benzoxazine polymers known for their high radiation shielding capability and ultra-high-molecular-weight polyethylene fibers known for their high ballistic performance, radiation shielding capability, and flexibility. The proposed origami composite and manufacturing method can enhance bonding strength by achieving precise origami shapes and utilizing the same matrix for both flexible and rigid components. Membrane sheets are manufactured at a low curing temperature to provide flexibility, while rigid facets are separately manufactured at a high curing temperature to increase rigidity. The integration of a polyimide protection layer significantly enhances space environment resistance and reduces mass loss due to atomic oxygen erosion. Despite a slight decrease in ballistic performance after exposure to space conditions, the proposed origami composite maintains superior ballistic performance compared to conventional space materials and conventional origami composites. Compared to existing origami composites or conventional space materials, the proposed origami composite exhibited superior radiation shielding performance. The laminated structure of the proposed origami composite can offer some solar radiation shielding capability. The proposed origami composite offers a multifunctional origami solution as a membrane-space shield material, fulfilling requirements for high ballistic performance, cosmic radiation shielding, solar radiative heat shielding, and space environmental resistance.

Synchronous hot-pressed metakaolin-fly ash based geopolymer: Compressive strength and hydration products

The dense structure of geopolymers typically requires long curing times, resulting in excessively lengthy production cycles for related products. To address this issue, synchronous hot-pressed curing technology is employed to accelerate the preparation of geopolymers. A comparative experiment was contrived to analyze the impacts of high-temperature curing and synchronous hot-pressed curing of metakaolin-fly ash geopolymer, examining how the silicon-aluminum ratio, alkali equivalent, and curing time influence the compressive strength and hydration products of synchronous hot-pressed cured metakaolin-fly ash geopolymer (SHPMFG) through orthogonal experiments. The outcome indicate that the compressive strength of SHPMFG test specimens can reach 80 % of their final strength within 20 min, with a more complete hydration reaction observed in SHPMFG, resulting in a denser microstructure. The alkali equivalent emerged as the dominant factor affecting SHPMFG strength, with a sample exhibiting a denser matrix structure and lower porosity achieving a maximum compressive strength of 95.33 MPa at 28 days when the alkali equivalent was 8 wt%, the silica-to-alumina ratio was 2.0, and the curing time was 30 min.

Flexural toughness and stress-strain relationship of different types of steel fiber reinforced shotcrete in high geothermal environment

The shape of steel fiber plays a pivotal role in determining the mechanical properties of concrete. In this paper, the impacts of end-hooked, wavy and ultra-fine steel fibers (all with a doping amount of 1.0 %) on the compressive strength, flexural strength, flexural toughness, and strain-strain relationship of shotcrete under curing conditions of 20 ℃, 40 ℃, and 60 ℃ are studied. Furthermore, the flexural toughness of steel fiber shotcrete is evaluated using the energy absorption method, and a constitutive model for steel fiber shotcrete was established based on meso-damage mechanics theory. The results indicate that curing temperatures below 40 ℃ are conducive to enhancing the compressive strength, flexural strength, and flexural toughness of steel fiber shotcrete, while curing temperatures above 60 ℃ are unfavorable for the development of strength and toughness in steel fiber shotcrete. Regardless of the type of steel fiber, its incorporation can alleviate the negative impact of high-temperature curing on the strength and toughness of shotcrete. Under high-temperature curing conditions, the influence of end-hooked steel fibers on the strength of shotcrete is superior to that of corrugated and ultrafine steel fibers, while ultrafine steel fibers are beneficial for improving the flexural toughness of shotcrete. The slope, peak stress, and peak strain of the stress-strain curves of shotcrete cured at 40 ℃ and 60 ℃ with the addition of the three types of steel fibers are greater than those of concrete without steel fibers. Furthermore, the descending segment of the curve is wider and smoother, with a larger surrounding area, demonstrating good toughness, deformability, and ductility. The end-hooked steel fibers and ultrafine steel fibers exhibit superior performance in enhancing the toughness and ductility of shotcrete under high-temperature curing conditions compared to wavy steel fibers. Based on meso-damage theory, the impacts of curing temperature and steel fiber types on the constitutive model of shotcrete under axial compression were established, and the model parameters were discussed. The research results can provide theoretical support for the durability design of tunnel linings in high ground temperature environments.

Influence of Graphene Nanoplatelets and Post-Curing Conditions on the Mechanical and Viscoelastic Properties of Stereolithography 3D-Printed Nanocomposites.

This study presents an innovative approach to improving the mechanical and viscoelastic properties of 3D-printed stereolithography (SLA) nanocomposites by incorporating graphene nanoplatelets (xGNP) into photopolymer matrices. Utilizing an SLA 3D printer, photopolymer formulations with xGNP concentrations of up to 0.25 wt% were successfully produced. Post-print curing was carried out using two different methods: ultraviolet (UV) curing and high-temperature curing at 160 °C. Mechanical characterization using nanoindentation showed a significant increase in elastic modulus by 104% and an increase in hardness by 85% for nanocomposites containing 0.25 wt% xGNP. Furthermore, dynamic mechanical analysis (DMA) revealed a 39% improvement in storage modulus for samples without post-curing and an improvement of approximately 30% for samples subjected to high-temperature curing. These significant improvements highlight xGNP's potential to not only increase the performance of SLA 3D-printed components but also streamline the manufacturing process by reducing or eliminating energy-intensive post-curing steps. This innovative integration of graphene nanoplatelets paves the way for the production of high-performance, functional 3D-printed products and offers significant advances for various industries with a high impact. The results highlight the transformative role of nanomaterials in additive manufacturing and position this work at the forefront of materials science and 3D printing technology.

Multiscale model for concrete cured under geothermal environment: Theoretical analysis and experimental validation

Concrete poured as linings of geothermal tunnel would deviate normal curing condition. A multiscale model based on continuum micromechanics, accounting for temperature-dependent factors, is established from the cement paste level to the concrete level. This model predicts the physical properties and compressive strength of concrete and is validated against measured strength, which incorporates the impact of high-temperature curing on the hydration degree, density of C-S-H, and chemical shrinkage of cement. Evolutions of the average hydration degree and compressive strength of concrete were experimentally investigated to this end, and then simulated with multiscale approach. The specimens were subjected to curing temperature 20°C, 40°C, 60°C, and 80°C for first 7 days while maintaining constant relative humidity of 100 %, and then water curing at 20°C for the rest days till tests. The high-temperature curing accelerates the hydration process, but the variance in hydration degree between standard temperature (20°C) and high-temperature conditions diminishes with prolonged water curing. An enhancement in compressive strength is also observed in the early stages of high-temperature curing, succeeded by a decline compared with standard curing after the 50th curing day. Quantitative analysis reveals that volume fractions of hydrates and porosity subjected to high-temperature curing show a substantial increase in the first 7 curing days, and the denser layer of hydration products formed on cement slows down the hydration in later curing ages. The complex evolution of strength in concrete undergoing high-temperature curing is influenced by temporal consideration (the hydration degree) and spatial considerations (the density of C-S-H and the chemical shrinkage of cement). The surge in hydration significantly contributes to strength promotion in early stages. However, the pivotal factor leading to strength deterioration is the increase of porosity when the difference in the hydration degree is less than 0.065.

Synthesis and characterization of bioplastics based on silyated starch and acrylated epoxidized soybean oil

In the study, the bioplastics were prepared by coupling silylated starch with acrylated epoxidized soybean oil (AESO) at various curing temperatures. 3-aminopropyltriethoxy silane (APTES) was grafted onto starch by the condensation between Si-OH and C-OH. As demonstrated by FTIR and silica content analysis, starch was successfully modified by APTES. The compatibility between silylated starch and AESO was weak as observed by FESEM. The appearance of C-N bonds confirmed the reaction between AESO and silylated starch. An apparent increase of tensile strength from 8.03 MPa to 14.12 MPa was discovered when the bioplastics were cured from 80 °C to 120 °C. Opacity of the bioplastics was enhanced remarkably by AESO due to the incompatibility of silylated starch and AESO. Water resistance test showed that the bioplastics were less sensitive to water after the addition of AESO. The bioplastics maintained good biodegradability after the introduction of AESO. However, increasing the curing temperatures of the bioplastics yielded weak effects on the water resistance and enzymatic degradation of the bioplastics. The bioplastics with excellent mechanical and water-resistant properties were synthesized via the incorporation of AESO under high-temperature curing. The property changes are highly desirable for packaging applications.

A tough, strong, and fast-curing phenolic resin enabled by dopamine-grafted chitosan and polyethyleneimine-functionalized graphene

Phenolic resins are widely used for outdoor and structural wood-based panels; however, they are challenged by high curing temperatures, low curing rates, and high brittleness. Inspired by lobster epidermis hardening, a tough, strong, and fast-curing phenolic resin (named DCS/PG/PF) was proposed herein. In this approach, dopamine-grafted chitosan (DCS) and polyethyleneimine-functionalized graphene (PEI@G) were incorporated into neat phenol formaldehyde (PF) resin. The gel time and maximum curing temperature of DCS/PG/PF resin were considerably reduced from 445 s and 147.8 °C for the neat PF resin to 317 s and 127.8 °C, respectively. This was attributed to the oxidative crosslinking of catechol moieties in DCS and amino groups in PEI@G within the naturally alkaline environment of phenolic resins in addition to the high reactivity between catechol moieties and PF chains as well as between amino and PF chains. The prepared resin demonstrated a dry bonding strength of 2.56 MPa, wet bonding strength of 1.81 MPa, and debonding work of 0.714 J, exhibiting a considerable increase of 16.9 %, 52.1 %, and 95.1 %, respectively, compared with those of the PF resin. These improvements were attributed to the dense organic–inorganic hybrid crosslinking network formed in the DCS/PG/PF. Furthermore, the DCS/PG/PF resin exhibited enhanced thermal stability.

Study on the thermo-mechanical properties of adaptive thermal control anchoring materials in high-geothermal tunnels

The heat conduction of the rock in high-geothermal tunnels can damage the grout during the initial hardening process, which directly affects the effectiveness of the anchoring support of the surrounding rock. This paper proposed the incorporation of phase change materials in grout to provide the new modified grouting material with the ability to control temperature by exploiting the phase change absorption and exothermic properties of the material. The changes in thermomechanical parameters of anchoring grout containing microencapsulated phase change material (m-PCM) under high geothermal environment were investigated. The influences of m-PCM content on the temperature control effect and mechanical properties of modified grout under different high geothermal environments were explored through macro-mechanical, micro-structural, and thermo-physical property tests on the specimens. The results indicated that m-PCM can effectively control the early hydration temperature of the grout in a high temperature environment, which can slow down the rate of change of the hydration temperature and reduce the peak temperature. The temperature control performance of modified grouts improved as the phase-change content increased, but the mechanical properties showed a significant decline after the initial increase. The results of the scanning electron microscope (SEM) analysis indicated that the high curing temperature had a negative impact on the internal structural integrity of the grout. The addition of a small amount of m-PCM reduced the fractal dimension and irregularity of the pore space in the grouting material, ultimately improving the strength of the grout body. The addition of a certain amount of m-PCM could significantly reduce the thermal conductivity of the grout, with the thermal conductivity of the specimens decreasing as the temperature increased. These study results provided valuable experimental data and theoretical support for the design of cement-based grouting materials in high-geothermal tunnels.

Fast-Hardening Production of High-Strength BOFS Aggregates by High-Temperature Carbonation Curing

Fast-Hardening Production of High-Strength BOFS Aggregates by High-Temperature Carbonation Curing

Preparation of low‐temperature curing single‐component epoxy adhesives with sedimentation coated accelerators

AbstractSingle‐component epoxy adhesives are widely used in various fields due to their simple operation process and excellent bonding properties. However, the excessively high curing temperature of the traditional single‐component epoxy adhesives may easily damage the electronic devices, limiting their further application. Hence, it is of great significance to develop the low‐temperature‐curing single‐component epoxy adhesives. However, the room temperature storage stability of low‐temperature curing system is generally poor. This work selected epoxy resin (EPON‐828), pentaerythritol tetra (3‐mercaptopropionate) (PETMP), 1‐benzylimidazole (1‐BMZ), and stabilizer (salicylic acid) as materials to prepare low‐temperature curing single‐component epoxy adhesives. In order to improve the storage stability of the system, polycarbonate (PCM‐A‐37) with low molecular weight was employed to coat the accelerator 1‐BMZ by physical sedimentation. The results showed that the room temperature storage period of the system reached 140 h, which was 2.18 times longer than before coating, and the curing temperature of 75°C was determined through DSC curves fitting. The epoxy adhesives have been completely cured at 75°C for 5 h, and shear strength reached 10.20 ± 0.51 MPa, which was not significantly different from that of the system with uncoated accelerators. We believe our paradigm can provide a feasible approach for preparing low‐temperature curing single‐component epoxy adhesives, and has reference significance for the preparation of single‐component adhesives in other systems, too.

On the surface roughness properties of fly ash-based geopolymer mortars with teff straw ash from the image analysis viewpoint

Fly ash (FA)-based geopolymer mortar is being considered for sustainability since it enjoys peculiar properties such as high mechanical properties and environmental benefits. However, the high curing temperatures of FA-based geopolymer mortar play a complex role in its outstanding mechanical behaviour thereby requiring other precursors, such as teff straw ash (TSA). In this study, we develop surface roughness properties of FA-based geopolymer mortars with TSA, where the ambient temperature is used for curing. The surface roughness characteristics of the FA-based geopolymer mortars with TSA exploit the surface roughness simulations from Gwyddion and the approach is demonstrated here in the contexts of spatial, hybrid and amplitude roughness parameters. The results show that some roughness parameters, including Ra and Rq values for FA-based geopolymer mortars with TSA, exhibit significant decreasing trends as the TSA contents increase. However, in comparison with the CA specimens (ambient temperature curing) and CE specimens (elevated temperature curing), the trends among the majority of the roughness parameters for FA-based geopolymer mortars with TSA turn out not to be very good probably due to changes in the internal structures of the mortars. Moreover, without the kurtosis values (Rku) of less than 3, it is easy to demonstrate that all the profiles of the investigated specimens reflect sharp valleys and peaks. The findings of surface roughness properties allow one to grasp the roughness parameters of FA-based geopolymer mortars with TSA. The approach for generating surface roughness properties of FA-based geopolymer mortars with TSA offers significant quantitative and qualitative information required for the bonding of mortar layers.

Curing-dependent behaviors of sustainable alkali-activated fiber reinforced composite: Temperature and humidity effects

Despite alkali-activated fiber reinforced composite (AAFRC) attracting increasing attention due to the advantages of low-carbon and superior tensile performance, the curing-dependent behaviors in practical environments are lack of knowledge. This paper aims to fill this gap by comparably investigating the macro-mechanical properties and pore structures of AAFRC under the different temperatures of −5, 20, and 60 °C and humidities of 60 % and 95 % RH. The loss on ignition, scanning electronic microscope (SEM), and fourier transform infrared spectroscopy (FT-IR) tests were performed to decouple the influence mechanisms. The results showed that the high-temperature curing slightly decreased the tensile and compressive strength but increased the tensile strain capacity with the main reason of decreasing the matrix toughness by forming more micro-cracks. The low-temperature curing deteriorated both the strength and tensile strain capacity by hindering its geopolymerization reaction. A decrease in humidity during the curing process was unconducive to the mechanical strength and slightly affect the tensile strain capacity of AAFRC, which resulted from the loss of water impeded its reaction to proceed. The normalized energy consumption and carbon emission of the AAFRC cured under the standard curing decreased by 22.6 % and 70.2 % than the classic engineered cementitious composite (ECC-M45), respectively, showing great sustainability.

Study on the Binding Behavior of Chloride Ion and Ettringite in Nano-Metakaolin Cement by Seawater Mixing and Curing Temperatures.

Mixing cement with seawater will cause the hydration process of cement to be different from that of ordinary cement, which will significantly affect cement's mechanical properties and durability. This article investigates the effects of chloride ion concentration, curing temperature, and nano-metakaolin content on the evolution process of Friedel's salts and ettringite (AFt) crystals in cement pastes. The study was conducted using X-ray diffraction (XRD), thermal analysis (TG), scanning electron microscopy (SEM), and mercury-intrusion porosimetry (MIP). The results show that chlorine salt can increase the production of Friedel's salt and ettringite, and the delayed AFt production increases by up to 27.95% after the addition of chlorine salt, which has an adverse effect on cement-based materials. Increasing the curing temperature and increasing the nano-metakaolin dosage increased the generation of Friedel's salt and decreased the delayed AFt generation, which resulted in a decrease in the length and diameter of the AFt crystals. After 28 days of high-temperature curing and the addition of nano-metakaolin, Friedel's salt production increased by 13.40% and 14.34%, respectively, and ettringite production decreased by 9.68% and 7.93%, respectively. Increasing the curing temperature and adding nano-metakaolin can reduce the adverse effect of delayed ettringite increases due to chloride ion binding.

Experimental investigation of the temperature-dependent dissolution process of aluminosilicate glass and low-calcium supplementary cementitious materials under alkaline conditions

High-temperature curing is commonly employed to promote the pozzolanic activity of supplementary cementitious materials (SCMs) in cementitious systems. Herein, the temperature-dependent dissolution processes of low-calcium SCMs and synthesised aluminosilicate glass were examined at pH 13 for cementitious systems. The dissolution rate and thermal activation energy (TAE) were estimated using nonlinear fitting and the Arrhenius equation. Experimental and analytical findings demonstrated that the TAEs of investigated SCMs and aluminosilicate glasses were temperature-dependent, decreasing with increasing temperature. Moreover, the TAE of aluminosilicate glasses increased with increasing Al/Si ratio, mainly due to the higher TAE of Al2O3 compared to SiO2. In addition, the TAE of fly ash was higher than that of investigated glass, largely because the Si and Al coordination numbers increased with decreasing cooling rates, according to molecular dynamics analysis. The topological TAE derived from molecular dynamics analysis is a promising parameter for estimating the TAE of aluminosilicate glass.

A study on the sulfate erosion deterioration law and damage model of shotcrete in high geothermal tunnels

AbstractWhen building a tunnel in an environment rich in high‐temperature hot water, it is particularly necessary to pay attention to the influence of sulfate ions in underground hot water on tunnel shotcrete. In order to study the sulfate erosion mechanism and mechanical properties of shotcrete in a real high‐temperature hot water environment, this study was carried out by setting the curing temperature (20, 40, 60, and 80°C), humidity (55% RH, 95% RH), and erosion age (0, 15, 30, 60, and 90 d) as the test influencing factors; a full combination of dry‐wet cycle test was carried out, and the specimens under different conditions were analyzed macroscopically and microscopically. The results show that with the increase of the number of dry‐wet cycles, the quality of shotcrete increases first and then decreases, and the mechanical properties gradually decrease. In the early stage of erosion, the erosion product is mainly ettringite, and the macroscopic damage is aggregate spalling. In the later stage of erosion, the erosion product is mainly gypsum, and the macroscopic damage is expansion damage. Compared with standard curing, a certain degree of high temperature curing has little effect on the sulfate attack resistance of shotcrete, but when the curing temperature exceeds 60°C, the concrete is seriously damaged. Finally, by constructing the damage model of sulfate attack shotcrete, the variation of compressive strength of shotcrete with age after sulfate attack under different curing conditions was successfully predicted.

Ion transportation properties of cement-based material under standard curing and steam curing

In coastal and saline environments, the infiltration of chloride and sulfate ions into cementitious materials can result in erosion and deterioration. This research focuses on the impact of temperature-related curing methods on the ion transport properties and microstructure of these materials. The results show the curing method does not alter the hydration products of cementitious materials. High-temperature curing reduces the content of ettringite, resulting in decreased Friedel's salt and gypsum after chloride ion corrosion. Meanwhile, high-temperature curing reduces the content of Ca(OH)2 and SiO2, decreasing the content of gypsum after sulfate ion erosion. It indicates that high-temperature curing reduces the binding capacity of both chloride ions and sulfate ions. Besides, high-temperature steam curing deteriorates the pore structure compared to standard curing. As a result, the resistance of concrete to ion corrosion is reduced under high-temperature steam curing. Besides, the surface ion concentration and binding capacity of chloride ions and sulfate ions both increase with the duration of erosion. Under the same erosion age, the binding capacity of sulfate ions is significantly higher than that of chloride ions. This research provides new insights into the transport characteristics of eroding ions under high-temperature steam curing.

Short- and long-term mechanical performances of damaged porous asphalt mixture treated with asphalt emulsion

Porous asphalt (PA) pavement usually has a short service life due to the ravelling distress. Spraying surface treatment (ST) asphalt emulsion could alleviate it. However, the effects of ST on the short- and long-term mechanical performances of PA mixture are unclear. Therefore, this study used repeated axial load test, indirect tensile fatigue test and indirect tensile cracking test to evaluate the rutting, fatigue and cracking resistances of damaged PA under different curing durations, respectively. Two curing temperatures, 25 and 60°C, were considered here. Results showed that the mechanical properties of ST treated PA were significantly improved in short-term. The durability of mechanical properties is good based on long-term observation data. The rutting resistance of treated PA was not compromised if the application rate of ST is well controlled. A high curing temperature could expedite recovery efficiency of damaged PA, but it was accompanied by faster aging, which cannot be ignored.