The latent curing of epoxy resins has long been constrained by the inherent dilemma between easy deactivation at room temperature and the demand for rapid curing at elevated temperatures, severely limiting their large-scale applications. Herein, we innovatively constructed a Mn 2+ -based metal–organic framework (Mn-NPA) using sodium nitroterephthalate as the organic ligand, and utilized it as a host matrix to encapsulate 2-methylimidazole (2MI) with a loading ratio of 35 wt%, yielding a latent curing agent denoted as 2MI@Mn-NPA. This material demonstrated excellent thermal stability, releasing the curing agent at 170°C. Remarkably, the epoxy system exhibited a shelf life of 78 days at ambient temperature, compared to only 3.33 h for the pristine E-51 resin. The exceptional storage stability stems from the spatial confinement effect of the Mn-NPA framework, which suppresses the room-temperature activity of 2 MI; upon heating, the active species are liberated, thereby realizing an “ambient-inert, thermally activated” characteristic. Combining excellent storage stability with superior processing convenience.
Phthalonitrile (PN) resin has attracted significant attention due to its exceptional thermal stability and mechanical properties. However, the requirement for elevated curing temperatures remains a critical challenge for their widespread practical applications. In this study, phthalonitrile containing branched cyanine (BPN) was blended with silicon-containing arylacetylene (PSA) to investigate their synergistic curing effects. The 10 wt% PSA formulation offers an optimal trade-off, demonstrating that moderate PSA loading synergistically enhances both processability and thermal stability without compromising high-temperature mechanical robustness: a reduction of the initial curing temperature from 234.3 degrees C to 198.7 degrees C and a decrease in the melting point from 161.6 degrees C to 147.4 degrees C. Conversely, the processing window expanded from 41.3 degrees C to 54.7 degrees C. Furthermore, the system exhibited enhanced thermal stability, evidenced by an increase in the 5% weight loss temperature (T d5 ) from 530.33 degrees C to 552.38 degrees C and a rise in the char yield from 75.73% to 80.13%. No distinct glass transition was detected below 400 degrees C, indicating a substantial improvement in both the processability and thermal stability of the blend system. Although the incorporation of PSA resulted in a slight reduction in the mechanical properties of BPN, the blends retained excellent mechanical performance at elevated temperatures, surpassing the room-temperature properties of PSA. The findings significantly enhance the industrial viability of phthalonitrile-based materials, effectively paving the way for their large-scale deployment in high-performance sectors.
The tribological characteristic of polymer matrix composites is profoundly affected by microstructural alterations that occur during the curing and post-curing phases. This study investigates effect of post-curing on the wear resistance and frictional characteristics of epoxy composites reinforced with MWCNTs-B 4 C and graphene- B 4 C. Wear testing was performed under two distinct load conditions, with the results being analyzed, wear rate, and wear depth over time. Introduction of hybrid nanofillers provides a synergistic reinforcement effect, whereas post-curing promotes the interaction between the matrix and filler, as well as increases the crosslinking density that leads to good tribological properties. Furthermore, field emission scanning electron microscopy (FESEM) was employed to analyze the wear-tested composite samples. The results shown that composites without post-curing exhibit high wear due to weak crosslinking and poor filler–matrix interaction. The wear improves slightly by doing post-curing at 80°C which hardens the matrix. However, the best improvement is realized in 100°C post-curing whereby all the composites with MWCNTs + B 4 C as reinforcements show considerable improvements on wear rate and weight loss.
A novel renewable bis-benzoxazine has been created using a Vanillin-based dimer, furfurylamine and paraformaldehyde through a Mannich reaction. The Molecular structure of the synthesized bis-benzoxazine monomer was analyzed using Nuclear Magnetic Resonance spectroscopy and Fourier Transform infrared spectroscopy. The curing behavior of the bis-benzoxazine was evaluated by Differential Scanning Calorimetry and in situ FT-IR. The curing reaction exhibited a peak temperature of 228°C and a relatively low heat of reaction at 85 J/g. The thermal stability of the resulting polybenzoxazine was examined using thermogravimetric Analysis (TGA), which indicated a low degradation rate between 300°C and 800°C, along with a high char yield at 800°C. Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) analysis revealed that the primary pyrolysis products of polybenzoxazine were phenol and furan derivatives.
In this study, poly(furfuryl alcohol) (PFA) was chemically modified by Diels-Alder addition of maleic anhydride (MA; 1, 2, 3, 5, and 15 phr) to increase carbonyl functionality and enable ambient-temperature curing with an amine hardener. Modified PFA (mPFA) samples were cured with a polyamine (HY) and, because carbonyl content alone was insufficient to achieve satisfactory mechanical performance, blended with a commercial epoxy (Araldite LY 5052) at varying weight ratios (10-50 phr). The modification reaction and curing kinetics were followed by FTIR and chemorheology; chemical structure was confirmed by H-1/(CNMR)-C-13. Hardness, tensile (ASTM D638 type V), DMTA and TGA characterized the cured networks. FTIR and rheology showed that 1-3 phr MA produces effective modification and that 30 phr HY is sufficient for ambient curing. Incorporation of 50 phr epoxy substantially improved mechanical and thermal performance: PFA-50 exhibited hardness 253 +/- 2 cycles, tensile strength 7.58 +/- 0.38 MPa, Young's modulus 71.01 +/- 1.19 MPa and Tg 57.48 degrees C, while the best-performing MA-modified formulation (PFA/2MA-50) reached hardness 309 +/- 2 cycles, tensile strength 10.19 +/- 0.54 MPa, Young's modulus 126.9 +/- 2.22 MPa and T-g 66.94 degrees C. TGA showed increased char yield for PFA/2MA-50 (15.7 wt.% at 800 degrees C) versus epoxy alone (9.7 wt.%). DFT calculations (B3LYP/6-31G (d,p), implicit DMF) support amide formation as a favorable curing pathway for MA-modified segments and are consistent with ATR-FTIR assignments. The combined MA modification and epoxy integration yields ambient-curing, mechanically robust PFA-based networks with improved thermal stability, making them promising binders for intumescent coatings.
A series of s-triazine-based homopolyesters was synthesized via polycondensation of a 4,6-bis-(N-(4-(benzoylchloride)amino))-2-(N-benzyl-piperazin-1-yl)-1,3,5-triazine (monomer) with various aliphatic and aromatic diols. The structures were confirmed using FT-IR and 1H NMR spectroscopy. Physicochemical characterization revealed that polyesters containing aromatic moieties exhibited higher density, intrinsic viscosity, and improved thermal stability compared to those derived from aliphatic diols. Solubility studies indicated enhanced dissolution behaviour in polar aprotic solvents at elevated temperatures. Thermogravimetric analysis demonstrated significant thermal resistance, particularly for bisphenol-based systems. The thermal degradation kinetics were evaluated using Coats-Redfern, Horowitz-Metzger, Broido, and Chan methods, showing consistent trends with variations attributed to model assumptions. The overall degradation trends remained consistent. The combined physicochemical and thermal characteristics suggest that these s-triazine-based homopolyesters may be promising candidates for advanced materials requiring thermal resistance and structural stability.
The rapid advancement of aerospace and wind power industries necessitates epoxy resin matrices with simultaneous high strength and high toughness. However, conventional modification methods struggle to mitigate the trade-off between strength and toughness in epoxy resins, rendering the development of epoxy resins with both high strength and high toughness a persistent challenge. In this study, two Xylok epoxy resins (X-PPEP and X-BPEP) were synthesized utilizing para-xylene dimethyl ester (PXDM) and 4,4 '-bis(methoxymethyl)biphenyl (BMMB) as raw materials, respectively. Subsequently, with 4,4 '-diaminodiphenylmethane (DDM) serving as the curing agent, the properties of the corresponding castings and composites were investigated. The results reveal that the crosslinked networks of X-PPEP/DDM and X-BPEP/DDM exhibit highly rigid backbones and substantial free volume fraction, thereby endowing them with exceptional mechanical properties. Specifically, the tensile strength and elongation at break of both systems exceeded 90 MPa and 7%. The impact strength of X-BPEP/DDM reached 49.72 kJ/m(2). Furthermore, the glass fiber-reinforced composites based on these resins also exhibited excellent mechanical properties. These findings provide a viable strategy for fabricating epoxy resins with balanced strength and toughness, highlighting the significant application potential of X-PPEP and X-BPEP in high-performance sectors such as aerospace and wind power generation.
A new diether-diamine monomer, 1,1-bis [4-(4-aminophenoxy)-3-methylphenyl]cyclopentane (BAMPC), containing a cardo cyclopentane unit and a pendant methyl substituent, was synthesized through a multistep procedure. The structure of the methyl-substituted diether-diamine monomer was confirmed using FT-IR, 1H NMR, 13C NMR, and mass spectrometry. Polycondensation of BAMPC with aromatic dialdehydes, including terephthalaldehyde and isophthalaldehyde, produced a series of co-poly (azomethine-ether)s incorporating cardo cyclopentane units in the polymer backbone. The influence of the cardo cyclopentane structure and pendant methyl group on the solubility and thermal stability of the resulting co-poly (azomethine-ether)s was examined. The polymers exhibited glass transition temperatures (Tg) in the range of 165-178 degrees C and thermal degradation temperatures (Td) between 456 and 486 degrees C, indicating thermal stability. The polyazomethines were soluble in polar aprotic solvents such as DMF, NMP, DMAc, and DMSO at ambient temperature or upon heating. X-ray diffraction analysis indicated that SPAM-2, SPAM-3, SPAM-4, and SPAM-5 exhibited amorphous characteristics with a broad diffraction peak around 2 theta approximate to 20 degrees, whereas SPAM-1 showed semicrystalline behaviour. The inherent viscosities of the co-poly (azomethine-ether)s ranged from 0.20 to 0.39 dL g-1.
Phthalonitrile (PN) resins exhibit outstanding thermal and mechanical properties but suffer from intrinsically high melting temperatures and sluggish curing kinetics, which severely restrict their processability and manufacturability. In this work, a eutectic blending strategy based on ternary PN monomers was employed to markedly depress the melting temperature, enabling mild and controllable melt prepolymerization with a diamine curing agent. This approach produced a low-melting phthalonitrile prepolymer (MPPh) exhibiting a viscosity below 1 Pa & centerdot;s at 88 degrees C, providing a stable melt-processing window. DSC and FTIR analyses revealed that the prepolymerization predominantly proceeded through linear chain growth via amino-nitrile addition reactions. To address the inherently low curing reactivity of MPPh, 3-aminophenylacetylene (APA) was introduced as a reactive diluent to activate the curing process and further tailor the rheological behavior. The modified resin (MP-m) demonstrated significantly enhanced curing efficiency and a reduced viscosity below 1 Pa & centerdot;s at 66 degrees C, excellent isothermal stability, and pronounced shear-thinning behavior. The cured MP-m resin retained excellent thermal stability and mechanical performance. These findings provide a simple and solvent-free strategy for the preparation of low-melting-point phthalonitrile, broadening the practical application potential of PN resins in high-temperature composite manufacturing.
In this study, a novel flame retardant designated as SFD, which contains phosphorus (P), nitrogen (N), and sulfur (S), was successfully synthesized via a one-pot method utilizing 2-aminobenzothiazole, furfural, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) as raw materials. This flame retardant was subsequently incorporated as an additive into epoxy resin (EP), with various formulations prepared using dicyandiamide (DDM) as the curing agent. The epoxy formulations containing only 3 wt% of SFD exhibited an improved Limiting Oxygen Index (LOI) of 34% and achieved UL-94 V-0 ratings. The Peak Heat Release Rate (PHRR), Total Heat Release (THR), and Total Smoke Production (TSP) for the EP/SFD composites were reduced by 28.0%, 30.1%, and 30.0%, respectively, in comparison to pure EP. Mechanical property assessments of the SFD/EP composites indicated that the incorporation of SFD had minimal impact on the mechanical properties of EP; thus, SFD can enhance the flame retardancy of EP without compromising its mechanical integrity. Analysis of the flame retardant mechanism revealed a significant P-N synergistic effect between the benzothiazole moiety and the phosphorus heterophenanthrene moiety present in SFD. The addition of SFD effectively mitigates heat release and smoke production during combustion processes involving EP while demonstrating excellent flame-retardant characteristics along with smoke suppression capabilities; furthermore, it promotes carbon layer formation. This research presents a straightforward strategy for synthesizing a multi-element synergistic flame retardant system that holds promise for application across a broad spectrum of thermoset plastics.
The permanently crosslinked networks of conventional thermosetting epoxy resins endow glass fiber-reinforced polymer (GFRP) composites with excellent mechanical performance and enable their widespread application in aerospace, automotive, and other fields, but make efficient recycling extremely challenging. In this study, dynamic boronate ester (B-O-C) bonds were introduced as reversible crosslinking units to replace traditional irreversible covalent linkages, enabling the construction of recyclable thermosetting epoxy materials. A concise and effective strategy was developed to construct reversible boronate ester networks within epoxy resins. A hydroxyl-rich linear prepolymer was prepared via aniline-initiated chain extension of bisphenol A-based epoxy resin and was crosslinked with tripropyl borate under catalyst-free conditions, yielding a recyclable epoxy vitrimer (EAT) with high mechanical performance and room-temperature degradability. Owing to the rapid alcoholysis kinetics of B-O-C bonds, the cured EAT thermosets and their GFRP composites could be completely depolymerized in pure methanol within 2 h, enabling clean separation and recovery of the resin and glass fibers. XPS analysis suggested that excess boron-containing groups may react in situ with silanol groups on the glass fiber surface, likely giving rise to Si-O-B interfacial linkages, which may contribute to the excellent mechanical properties of the composites. Reprocessed materials fabricated from recovered resin and fibers retained more than 80% of their original mechanical performance after one recycling cycle. This work provides an efficient and feasible route for achieving closed-loop chemical recycling of high-performance GFRP under mild conditions.
The inherent brittleness of epoxy (EP) has long imposed limitations on its utilization within advanced field. This study synthesized a novel high-performance soluble polymer with a tetramethyl biphenyl structure (named tetramethyl biphenyl poly arylene ether ketone, S-TBPAEK) as a toughening agent for preparing EP composites. The aromatic structure in S-TBPAEK enhanced the heat resistance of composites, while its unique tetramethyl structure promoted excellent compatibility with EP. Additionally, it was observed that when S-TBPAEK content reached 12.5 phr, the impact strength of composite was significantly increased by 170 %. Additionally, the mechanical properties of the composite, such as flexural strength and tensile strength, have been enhanced by approximately 43.7 % and 55.8 % respectively. Finally, the fracture surfaces of the composites were analyzed using SEM to investigate the fracture mechanism. The results revealed that the fracture behavior of impact, flexural and tensile specimens transitioned from brittle to ductile fracture. The phenomenon suggested that the S-TBPAEK/EP composite absorbed more energy during fracturing process, thereby enhancing its toughness. In summary, S-TBPAEK shows great promise as a toughening agent for epoxy composites, offering new insights into the field of epoxy toughening.
This study establishes a systematic mechanistic framework for phthalonitrile resins containing polyimide skeletons (PIPN) to address their narrow processing window and unclear thermo-mechanical regulation. Six PIPN model compound with varied dianhydride structures PM (PMDA), BP(BPDA), F (6FDA), ABP(ABPDA), K(BTDA), E (BPADA) were designed and synthesized. Through integrated multiscale simulations and experimental characterization, a comprehensive "structure-weak interactions-packing order-molecular mobility-energetics-macroscopic properties" correlation model was constructed for the first time. Molecular backbone rigidity, symmetry and planarity govern the performance: fully rigid PM-PIPN exhibited strongest pi-pi stacking and electrostatic interactions, yielding the highest melting point (390 degrees C) and superior predicted modulus. Conversely, flexible segments (E-PIPN) or sterically hindered groups (F-PIPN) systematically weakened intermolecular interactions, reducing both melting point and modulus while increasing Poisson's ratio. Electrostatic potential analysis, weak interaction visualization (IRI), mean square displacement (MSD) and cohesive energy density calculations synergistically revealed the regulation mechanisms from electronic, spatial, dynamic and energetic perspectives. This mechanistic framework provides theoretical foundations for rational molecular design of high-performance PIPN resins.
Epoxy resin adhesives are widely used in structural repair; however, their high cross-linking density often results in limited toughness and interfacial durability. Given the high surface energy and presence of hydroxyl groups, nanoparticles are prone to aggregation via strong intermolecular interactions. In this study, a silane-assisted dispersion strategy was proposed to enhance the toughness of polyether-type polyurethane/epoxy resins by adding ZrO2 nanoparticles. Silane coupling agent (KH550) was employed to chemically modify the surface of ZrO2, and ultrasonic treatment was applied to improve nanoparticle dispersion within the PU/EP matrix. The repair performance of the composites was evaluated through the compressive and flexural bond strength tests. The results indicate that KH550-modified ZrO2 (KH550-ZrO2) can enhance the mechanical properties and adhesive strength of PU/EP interpenetrating network (IPN) composites, increasing the dry and wet bonding strengths to 6.52 MPa and 5.47 MPa, respectively. The tensile and compressive strengths of the composites reached maximum values of 71.12 MPa and 79.57 MPa at 0.8 wt% KH550-ZrO2.This study provides an effective strategy for enhancing the mechanical performance of ZrO2-reinforced PU/EP IPNs.
Epoxy resin, as a critical thermosetting polymer, is widely used in electronic encapsulation and various applications due to its excellent mechanical and electrical insulating properties. However, the permanent three-dimensional cross-linked network formed upon curing renders the material diffulting in resource waste and posing challenges to sustainable development. To address this limitation, the present study employs a curing agent containing dynamic disulfide bonds-2-aminophenyl disulfide (2-AFD)-to cure bisphenol A diglycidyl ether (DGEBA), thereby establishing a cross-linked network embedded with dynamic disulfide bonds. Given the limited density of dynamic bonds achievable solely through curing agents, which results in suboptimal property retention after thermal reprocessing, this study further developed a vanillin-based epoxy resin (VOEP) incorporating dynamic imine bonds, with vanillin (VAN) employed as the primary precursor. By progressively replacing DGEBA with VOEP, the concentration of dynamic bonds within the cross-linked network is increased, significantly improving the property retention after hot-press recycling. Experimental results show that when the VOEP mass fraction reaches 60 wt%, the resulting epoxy resin exhibits outstanding overall performance: the power frequency breakdown strength reaches 61.64 kV/mm, the tensile strength is 58.25 MPa, and high thermal stability is maintained. Moreover, the material demonstrates remarkable reprocessability, with power frequency breakdown strength and tensile strength retention rates reaching 89.01% and 86.54%, respectively, after physical hot-press recycling. This exceptional recyclability provides a novel strategy and valuable reference for the green and sustainable advancement of epoxy resins in the field of electrical engineering.
Today's ammunition comprises sparingly about 30 wt% of payloads like RDX-based explosive meanwhile, the bulk of the mass consists of structural materials such as metals (e.g., steel and aluminum), which do not contribute energetically. This highlights a significant potential for the improvement of reactive structural materials (RSMs). This class of advanced materials is designed to serve dual purposes: providing structural integrity and releasing chemical energy upon activation. Rigid polymers with glass transition temperature (Tg) higher than the operating temperatures are thought as a new emerging candidate to replace the heavy and metal-based materials (e. g., alloys, thermites). According to this vision, we report the synthesis and characterization of resorcinol-based benzoxazine (Re-Bz) energetic polymer utilizing resorcinol as a renewable material. The assessment of the energetic properties was reported as well. Overall, the newly developed polymer showed promising energetic performances with deflagration temperatures of about 270-275 degrees C, where the combustion heat released during the deflagration was found to be 20.15 kJ & centerdot;g-1. The thermal analysis results highlighted that these polymers can be effectively used as reactive structure materials (RSMs) owing to their combination of rigidity above operational temperatures and remarkable energetic performances.
The tribological characteristic of polymer matrix composites is profoundly affected by microstructural alterations that occur during the curing and post-curing phases. This study investigates effect of post-curing on the wear resistance and frictional characteristics of epoxy composites reinforced with MWCNTs-B4C and graphene- B4C. Wear testing was performed under two distinct load conditions, with the results being analyzed, wear rate, and wear depth over time. Introduction of hybrid nanofillers provides a synergistic reinforcement effect, whereas post-curing promotes the interaction between the matrix and filler, as well as increases the crosslinking density that leads to good tribological properties. Furthermore, field emission scanning electron microscopy (FESEM) was employed to analyze the wear-tested composite samples. The results shown that composites without post-curing exhibit high wear due to weak crosslinking and poor filler-matrix interaction. The wear improves slightly by doing post-curing at 80 degrees C which hardens the matrix. However, the best improvement is realized in 100 degrees C post-curing whereby all the composites with MWCNTs + B4C as reinforcements show considerable improvements on wear rate and weight loss.
In this study, two types of epoxy networks based on diglycidyl ether of bisphenol A (DGEBA) were prepared using 4,4 '-diaminodiphenyl sulfone (DDS) and isophorone diamine (IPD) as curing agents. The modified epoxy networks were subjected to thermal treatment to improve their hardness and structural integrity. Various characterization techniques, including absorption spectroscopy, photoluminescence (PL), infrared spectroscopy (IR), open-aperture Z-scan measurements, field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD), were employed to evaluate the effects of GO-NH incorporation. Open aperture Z-scan experiment was carried out using a violet semiconductor laser with continues wave (CW) beam and the wavelength of 405 nm. Also, the incorporation of piperazine-functionalized graphene oxide (GO-NH) at 0.5 wt% into the DGEBA/IPD system was investigated in order to study the effect of GO-NH on optical properties. The results showed that reverse saturable absorption (RSA) is the dominant nonlinear optical mechanism in the systems. DGEBA/DDS shows stronger RSA in comparison of DGEBA/IPD system. Notably, the addition of GO-NH led to a significant increase in the nonlinear absorption of DGEBA/IPD, indicating enhanced polarization and improved electronic interactions within the epoxy matrix. These findings suggest epoxy systems as suitable materials in optical and photonic applications.
Phthalocyanines (Pc) complexes are versatile, highly conjugated planar macrocycles known for robust thermal stability and tunable electronic properties, making them valuable in catalysis, sensing, and energy applications. Herein, we report the synthesis of novel chromium(II) and iron(II) phthalocyanines bearing peripheral 2-mercaptobenzothiazole (2-MBT) substituents. The 2-MBT groups introduce sulfur- and nitrogen-containing aromatic thiolate functionality to the macrocycle periphery, aimed at extending pi-conjugation and modulating the electronic structure of the phthalocyanine core. This functionalization strategy is expected to tailor the optical and redox characteristics of the complexes. Structural characterization via elemental analysis, Fourier-transform infrared (FT-IR), ultraviolet-visible (UV-Vis), and 1HNMR spectroscopy confirmed successful formation of the macrocyclic complexes. Notably, the disappearance of the phthalonitrile C equivalent to N stretching band in FT-IR indicated complete cyclotetramerization into the MPc framework. The UV-Vis spectra exhibited characteristic Q-bands at 683 nm and B-bands at 300-350 nm, consistent with pi-pi* transitions of the conjugated ring. Thermogravimetric analysis revealed that both complexes remain highly thermally stable up to 250 degrees C before undergoing stepwise exothermic decomposition. Electrochemical studies cyclic voltammetry and square-wave voltammetry in dimethylformamide, showed multiple quasi-reversible redox processes associated with both the phthalocyanine pi-system and the central metal ions. These findings demonstrate that the 2-MBT-functionalized phthalocyanines are thermally robust and redox-active, with promising potential for electrocatalysis and catalysis.
Epoxy resin (EP) is valued for its adhesion and chemical stability, yet its inherent brittleness and flammability limit advanced applications. To address this, a novel reactive ionic liquid flame retardant, [PMoam]Ps, was developed as a co-curing agent. It integrates into the EP network, significantly enhancing flame retardancy. The modified composite achieves a limiting oxygen index (LOI) of 29.3%, a UL-94 V-0 rating, and shows reductions in peak heat release rate (PHRR) and total heat release (THR) of 35.8% and 38.6%, respectively. Simultaneously, the ionic liquid acts as an internal plasticizer, markedly improving mechanical performance. Compared to neat EP, the composite exhibits increases of 46.1% in tensile strength, 57.4% in flexural modulus, and 87.7% in impact strength. This work provides a promising strategy for developing high-performance epoxy composites with balanced flame retardancy and mechanical properties.
