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An investigation of the relationship between the microstructure parameters and thermomechanical properties of epoxy resin can provide a scientific basis for the optimization of epoxy systems. In this paper, the thermomechanical properties of diglycidyl ether of bisphenol A (DGEBA)/methyl tetrahydrophthalic anhydride (MTHPA) and DGEBA/nadic anhydride (NA) were calculated and tested by the method of molecular dynamics (MD) simulation combined with experimental verification. The effects of anhydride curing agents on the thermomechanical properties of epoxy resin were investigated. The results of the simulation and experiment showed that the thermomechanical parameters (glass transition temperature (Tg) and Young’s modulus) of the DGEBA/NA system were higher than those of the DGEBA/MTHPA system. The simulation results had a good agreement with the experimental data, which verified the accuracy of the crosslinking model of epoxy resin cured with anhydride curing agents. The microstructure parameters of the anhydride-epoxy system were analyzed by MD simulation, including bond-length distribution, synergy rotational energy barrier, cohesive energy density (CED) and fraction free volume (FFV). The results indicated that the bond-length distribution of the MTHPA and NA was the same except for C–C bonds. Compared with the DGEBA/MTHPA system, the DGEBA/NA system had a higher synergy rotational energy barrier and CED, and lower FFV. It can be seen that the slight change of curing agent structure has a significant effect on the synergy rotational energy barrier, CED and FFV, thus affecting the Tg and modulus of the system.

Poly(2‐oxazoline)‐imidazole (POZ‐Im) polymers were synthesized by one‐pot termination of 2‐ethyl, 2‐propyl‐, and 2‐phenyl‐2‐oxazoline homopolymers with imidazole and evaluated as thermal latent curing agents (TLCs) for one‐component epoxy resins (OCERs). 1H NMR, FTIR, and MALDI‐TOF confirmed successful synthesis of polymers. The polymers were amorphous, exhibiting glass transition temperatures of 43°C (PEOZ‐Im), 24°C (PPrOZ‐Im), and 91°C (PPhOZ‐Im) and showed thermal stability with onset degradation at 364°C–375°C. When incorporated into DGEBA at a fixed 5 phr Im‐to‐epoxy ratio, their miscibility and curing performance varied with side‐chain chemistry. PPhOZ‐Im was fully miscible, PPrOZ‐Im was partially miscible, and PEOZ‐Im formed fine dispersed domains. Dynamic DSC revealed left‐limit temperatures of 91.75°C (PEOZ‐Im), 94.22°C (PPhOZ‐Im), and 103.28°C (PPrOZ‐Im). Rheological analysis showed that PPrOZ‐Im/DGEBA exhibited the longest gelation time, followed by PEOZ‐Im/DGEBA and PPhOZ‐Im/DGEBA. Shelf‐life estimations based on viscosity doubling times and Arrhenius extrapolation indicated stability of 88 days (PPrOZ‐Im/DGEBA), 34 days (PEOZ‐Im/DGEBA), and 32 days (PPhOZ‐Im/DGEBA) at −20°C. These results demonstrate that POZ‐Im polymers provide tunable latency and curing behavior suitable for advanced composite applications. Imidazole‐terminated poly(2‐oxazoline) polymers were developed as thermal latent curing agents for one‐component epoxy resins (OCERs). Side‐chain chemistry governed polymers' hydrophobicity, glass transition temperature, and miscibility with DGEBA, thus controlling curing kinetics. All OCERs exhibited latency up to 60°C, while PPrOZ‐Im based OCERs showed the longest storage stability, with an estimated shelf life of 88 days at −20°C storage.

Recently, biobased high-performance vitrimers have been developed due to the lacking of raw materials from petroleum resources that can be processable as like thermoplastic to meet the urgent demand for sustainable development. Herein, the fully biobased imine curing agent (VBI-HMDA) was synthesized from bio-resources vanillin and hexamethylenediamine and its chemical structure was ensured in detail through FTIR, 1 H-NMR and 13 C-NMR before being cross-linked by commercially available Diglycidyl ether of Bisphenol-F (DGEBF). Cyclic 4-methyl-1,3-cyclohexendiamine (HTDA) was used as a co-curing agent with VBI-HMDA at different weight ratios in terms of improving the properties of cured thermoset. The curing behaviors, mechanical, thermal and self-healing performance of the cured thermosets were investigated by DSC, strength tester, DMA and TGA analyzer. However, the viscosity and activation energy of curing are decreased as the weight ratio of HTDA increases, while flexible properties and T g values are increased gradually. In addition, the heat-resistant temperature ( T s ) and char residue at 700 °C of the cured thermosets also decreased. Overall results of 50% containing HMDA sample S03 exhibited the utmost thermomechanical performances as well as admirable self-healing ability and processability. Moreover, the recycling property of S03 is over 74%, T g of reprocessed S03 is still as high as 99 °C and it is entirely solvent resistant at room temperature. This result suggests the optimizing mechanical and thermomechanical properties of cured thermosets with potential recyclability were efficiently controlled by adjusting the co-curing agent ratio.

In this work, a flame retardant curing agent (DOPO-MAC) composed of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO and methyl acrylamide (MAC) was synthesized successfully, and the structure of the compound was characterized by FT-IR and 1H-NMR. The non-isothermal kinetics of the epoxy resin/DOPO-MAC system with 1% phosphorus was studied by non-isothermal DSC method. The activation energy of the reaction (Ea), about 46 kJ/mol, was calculated by Kissinger and Ozawa method, indicating that the curing reaction was easy to carry out. The flame retardancy of the epoxy resin system was analyzed by vertical combustion test (UL94) and limiting oxygen index (LOI) test. The results showed that epoxy resin (EP) with 1% phosphorus successfully passed a UL-94 V-0 rating, and the LOI value increased along with the increasing of phosphorus content. It confirmed that DOPO-MAC possessed excellent flame retardance and higher curing reactivity. Moreover, the thermal stability of EP materials was also investigated by TGA. With the DOPO-MAC added, the residual mass of EP materials increased remarkably although the initial decomposition temperature decreased slightly.

Using formaldehyde and urea as raw materials, a stable urea–formaldehyde resin (UF) is synthesized by the “alkali-acid-alkali” method. Unlike most thermosetting resins, UF often shows the appearance of crystal domains. In order to understand the relationship between the crystal and morphology of UF resin, analysis was carried out with the help of polarizing microscopy (POM), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). The changes of two kinds of UF resins with molar ratios (F/U) of 1.4 and 1.0 before and after curing and under the influence of different curing agents and additives were studied. SEM results showed that the UF resins with low F/U (1.0) show spherical or flat structures before and after curing, and the diameter of the spherical structure increases with the increase of the content of curing agent, while in the UF resin with high F/U (1.4) it is difficult to observe the above phenomenon. At the same time, the possible accumulation mode of UF colloidal particles in the process of aggregation is explained, and the curing agent obviously promotes the development of the crystal structure, which may be the reason for the emergence of a large number of spherical particles. XRD results showed that the resin with low F/U has higher crystallinity than the resin with high F/U, indicating that the former shows more crystallization regions, while the latter shows more amorphous structure, and the crystallinity increases with the increase of the curing agent content, but the position of the crystallization peak does not change with the type of curing agent and the amount of curing agent. Observation of the selected area electron diffraction (SAED) pattern obtained by TEM shows that the cured low F/U (1.0) resin has a polycrystalline structure and a body-centered cubic unit cell. FT-IR results showed that the linear segment, branched structure, hydroxymethyl and methylene structure changes in UF affect the formation of crystal structure. This study also shows the possible contribution of hydroxymethylated species to the formation of crystals.

Hexavalent chromium Cr (VI) pollution is prevalent at decommissioned industrial sites and poses a serious risk to the surrounding ecosystem and human health. In this study, we presented a novel heavy metal-contaminated soil curing agent derived from industrial slag (slag and desulfurization gypsum) for the treatment and remediation of Cr (VI)-contaminated soil. This curing agent was used to treat Cr (VI)-contaminated soil at pollution control (78 mg/kg), light contamination (380 mg/kg), and heavy contamination (1000 mg/kg) levels. The migratory properties of Cr (VI) in the cured contaminated soil were evaluated using toxic leaching and soil column tests. The mechanical strength and hydraulic conductivity of the cured contaminated soil were obtained using unconfined compressive, direct shear, and penetration tests. The mineralogical composition, chemical characteristics, and micromorphological features of the cured soils were analyzed using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The unconfined compressive strength and shear strength parameters (c and φ, respectively) increased significantly as the curing agent dosage was increased, whereas the Cr (VI) leaching concentration and hydraulic conductivity decreased. However, with an increase in Cr (VI) contamination, the cured soil metrics demonstrated the opposite trend. Most of the chromate (CrO42−) ions were encapsulated in hydration gelation products, such as C-S(A)-H and C-A-H. A small portion of Cr (VI) was reduced to Cr (III) or sequestered in the curing agent via charge adsorption. These test results demonstrated the multiple advantageous properties, including environmental safety, high strength, and low permeability, of this novel heavy metal curing agent derived from industrial waste.

This study aims to reveal the effects of flexible chain lengths on rosin-based epoxy resin’s properties. Two rosin-based epoxy monomers with varying chain lengths were synthesized: AR-EGDE (derived from ethylene glycol diglycidyl ether-modified acrylic acid rosin) and ARE (derived from acrylic acid rosin and epichlorohydrin). Diethylenetriamine (DETA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA) with different flexible chain lengths were used as curing agents. The adhesion, impact, pencil hardness, flexibility, water and heat resistance, and weatherability of the epoxy resins were systematically examined. It was found that when the flexible chains of rosin-based epoxy monomers were grown from ARE to AR-EGDE, due to the increased space of rosin-based fused rings, the toughness, adhesion, and water resistance of the rosin-based epoxy resins were enhanced, while the pencil hardness and heat resistance decreased. However, when the flexible chains of curing agents were lengthened, the resin’s performance did not change significantly because the space between the fused rings changed little. This indicates that the properties of the rosin-based resins can only be altered when the introduced flexible chain increases the space between the fused rings. The study also compared rosin-based resins to E20, a commercial petroleum-based epoxy of the bisphenol A type. The rosin-based resins demonstrated superior adhesion, water resistance, and weatherability compared to the E20 resins, indicating the remarkable durability of the rosin-based resin.

Epoxy is extensively used for anti-corrosion coatings on metallic materials. Conventional epoxy coatings have a permanent crosslink network that is unable to repair itself when cracks and damages occur on the coating layer. This study aims to develop self-healing epoxy vitrimer/carbon nanotube (CNTs) nanocomposite for coating. Two bio-based curing agents viz., cashew nut shell liquid (CNSL) and citric acid (CA) were employed to create covalent adaptable networks. The 0–0.5 wt% CNTs were also incorporated into epoxy/CNSL/CA matrix (V-CNT0-0.5). Based on the results of our study, thermomechanical properties of V-CNT nanocomposites increased with increasing CNTs content. The bond exchange reaction of esterification was thermally activated by near infrared (NIR) light. The V-CNT0.5 showed the highest self-healing efficiency in Shore D hardness of 97.34%. The corrosion resistance of coated steel with V-CNT0 and V-CNT0.5 were observed after immersing the samples in 3.5 wt% NaCl for 7 days. The corrosion rate of coated steel with V-CNT0.5 decreased from 9.53 × 102 MPY to 3.12 × 10–5 MPY whereas an increase in protection efficiency of 99.99% was observed. By taking advantages of the superior self-healing and anti-corrosion properties, V-CNT0.5 could prove to be a desirable organic anti-corrosion coating material.

In order to solve the shortcomings of the traditional curing agent in the treatment of composite heavy-metal-contaminated soil with the solidification and stabilization method, a new type of cementing material A was used as a curing agent, and the Pb, Cd, Cu composite heavy-metal-contaminated soil was artificially prepared to carry out an experimental study on solidification and stabilization (SS) restoration by the mechanical properties test, leaching performance test, and microscopic test. The results show that in the range of test dosage, with the increase in the curing agent content, the unconfined compressive strength of the solidified body increased, and the resistance to deformation was enhanced. From the perspective of leaching characteristics, the new curing agent A had an excellent curing effect on the composite heavy-metal-contaminated soil. To achieve safe disposal, a curing agent content of 10% applies only for the soil heavily contaminated by heavy metals. The curing agent A could significantly reduce the content of acid-extractable heavy metals after solidifying the heavy metal Pb, Cd, and Cu composite contaminated soil and effectively converted it into a residue state. The solidified phase contained hydrated products such as calcium silicate hydrate (CSH) and ettringite (AFt). These hydrated products can inhibit the leaching performance of heavy metal ions through adsorption, encapsulation, and ion exchange. The study provides a feasible method and reference for the solidification, restoration, and resource utilization of heavy-metal-contaminated soil in the subgrade.

To address the engineering problems of high cement content, high brittleness, and weak frost resistance of cement-improved loess in the seasonal frozen soil area of Northwest China, F1 ion curing agent (F1) and cement composite improved loess (FCIL) were used in this paper. Through unconfined compressive (UC) strength tests, consolidated undrained (CU) triaxial shear tests, and microscopic pore characteristics analysis, the mechanical properties, freeze–thaw cycle deterioration law, and microscopic pore structure of FCIL were studied. The effects of cement content (Cc), F1 dosage (CF), number of freeze–thaw cycles (NF-T), and confining pressure (σ3) on the strength, deformation behavior, and pore characteristics of FCIL were analyzed. The synergistic improvement mechanism of FCIL, as well as the freeze–thaw damage mechanism, was elucidated. The results show that Cc is the primary factor controlling the strength of improved loess. The incorporation of F1 can further increase UCS and markedly enhance the failure strain (εf), thereby achieving simultaneous improvements in strength and ductility. An appropriate mix proportion was identified as CF = 0.2 L/m3 and Cc = 6%. After 7 d curing, FCIL exhibited a UCS of 1.35 MPa, a cohesion (c) of 205 kPa, an internal friction angle (φ) of 36.2°, and εf 1.8 times that of loess improved with Cc = 6% cement alone. CU triaxial shear tests indicate that, under all tested conditions, the stress–strain responses of FCIL exhibit σ3-sensitive strain-softening behavior. As Cc and σ3 increase, triaxial peak strength (qmax) and secant modulus (E50) increase significantly. Compared with natural loess (NL), FCIL shows a markedly lower porosity (n), a substantial increase in the proportion of micropores, and reductions in medium and small pores. After multiple freeze–thaw cycles, the evolution of the pore structure is effectively restrained. This indicates that the combined use of F1 and cement promotes the formation of a dense layered stacking structure, significantly improves the microscopic pore-size distribution, and enhances the mechanical performance of loess under freeze–thaw environments.