Curing Agents For Epoxy Resins Research Articles

Poly(2-alkyl/aryl-2-oxazoline)-Imidazole Complexes as Thermal Latent Curing Agents for Epoxy Resins.

One-component epoxy resins (OCERs) with improved stability (shelf life) and controlled curing temperatures were prepared using epoxy resins and polyoxazoline-imidazole (POZ-Im) based thermal latent curing agents (TLCs). POZ homopolymers with molar masses of 1000, 2000, and 5000 g/mol were obtained via cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline, 2-propyl-2-oxazoline, 2-pentyl-2-oxazoline, and 2-phenyl-2-oxazoline. TLCs were prepared by physically entrapping imidazole, the curing agent, in the POZ matrix at the homopolymer/Im (HP/Im) ratios of 1:1 and 5:1 and characterized by FTIR and TGA. TLCs were then mixed with bisphenol A diglycidyl ether (DGEBA) to obtain OCERs with Im concentrations of 1, 3, and 5 wt %. Dynamic DSC tests were performed to determine the effect of the pendant group and molar mass of POZ, the POZ/Im ratio, and Im concentration on the curing behavior of the OCERs, whereas isothermal DSC tests were carried out to examine their thermal stability and optimal curing temperatures. Optical microscopy was performed to study the compatibility of the TLCs with DGEBA. This study showed that the dispersion quality of TLCs is highly associated with the compatibility of POZs and DGEBA, which affected the release of Im, thus left limit temperatures of curing. In addition, higher left limit temperatures were obtained when the POZ/Im ratio increased. Isothermal DSC results conformed to the improved stability and better thermal latency of the samples with a POZ/Im ratio of 5:1. Moreover, the higher left limit temperatures were obtained with the lowest molar mass of POZ due to the better interaction between the -OH end group of POZ and Im. The shelf life of PEOZ 1K-Im 5:1 1% OCER was predicted at -20, 0, and 20 °C, with an estimated 15.3 days at 20 °C using isothermal DSC and rheology at 50, 60, and 70 °C. Overall, this research contributes to the development of OCERs by introducing POZ-Im complexes as novel TLCs. The findings shed light on the importance of compatibility in achieving optimal dispersion and release of Im and the role of the POZ/Im ratio and POZ molar mass in controlling left limit temperatures, ultimately influencing the curing behavior of OCERs.

Preparation, physicochemical analyses, and comparative evaluation studies of deep eutectic solvents (DES) from non-conventional precursor materials applied as catalytic curing agents for epoxy resin

Curing agents for epoxy resins play a significant role in initiating crosslinking reactions resulting in the hardened and durable material with enhanced properties as per end-user applications. The industrial world still lacks efficient, environmentally friendly, and cheap curing agents for epoxy resins. Here, we report the development of deep eutectic solvents (DESs) based on N, N’-Bis(2-aminoethyl)ethane-1,2-diamine (commonly known as triethylenetetramine, TETA) as hydrogen bond donor (HBD), and salicylic acid (SA) and choline chloride (CC) as hydrogen bond acceptor (HBA). The formulated DESs are suggested to be relatively safe, affordable, and eco-friendly and the active groups in the DESs are capable of initiating crosslinking reactions. The physical stability of the formulated deep eutectic solvents was examined by polarizing optical microscopic (POM) analysis, which confirmed the absence of any crystals or residues. The purity was ensured by 13C nmr spectroscopy. Additionally, supportive evidence for the hydrogen bond formation between the constituents was gained from the outcomes of FTIR, 1H nmr, and mass spectrometry. Deep depression in melting points was confirmed from DSC studies, and TGA suggested better thermal stability for DESs than its constituents. Density functional theory (DFT) at B3LYP6-31G* of Gaussian computational framework was applied to energetically optimize the isolated structure and determine the bond lengths in angstroms. The structural characteristics and nonbonding interactions of DESs were investigated by the same. In addition, the density and rheological characteristics were assessed for the ideal utilization of the formulated DESs as epoxy resin curing agents. The detailed comparative studies demonstrated the advantages of deep eutectic solvents over conventional curing agents. The efficacy of the formulations as a curing agent was primarily confirmed from FTIR analysis and the curing behavior was investigated by DSC studies.

Amino Acids as Bio-Based Curing Agents for Epoxy Resin: Correlation of Network Structure and Mechanical Properties.

Bio-based alternatives for petroleum-based thermosets are crucial for implementing sustainable practices in fiber-reinforced polymer composites. Therefore, the mechanical properties of diglycidyl ether of bisphenol a (DGEBA) cured with either l-arginine, l-citrulline, γ-aminobutyric acid, l-glutamine, l-tryptophan, or l-tyrosine were investigated to determine the potential of amino acids as bio-based curing agents for epoxy resins. Depending on the curing agent, the glass transition temperature, Young’s modulus, tensile strength, and critical stress intensity factor range from 98.1 ∘C to 188.3 ∘C, 2.6 GPa to 3.5 GPa, 39.4 MPa to 46.4 MPa, and 0.48 MPam0.5 to 1.34 MPam0.5, respectively. This shows that amino acids as curing agents for epoxy resins result in thermosets with a wide range of thermo-mechanical properties and that the choice of curing agent has significant influence on the thermoset’s properties. After collecting the results of dynamic mechanical analysis (DMA), tensile, flexural, compression, and compact tension tests, the functionality f, cross-link density νC, glass transition temperature Tg, Young’s modulus ET, compression yield strength σCy, critical stress intensity factor in mode I KIC, fracture energy GIC, and diameter of the plastic zone dp are correlated with one another to analyze their inter-dependencies. Here, the cross-link density correlates strongly positively with Tg, ET, and σCy, and strongly negatively with KIC, GIC, and dp. This shows that the cross-link density of DGEBA cured with amino acids has a crucial influence on their thermo-mechanical properties and that the thermosets considered may either be stiff and strong or tough, but hardly both at the same time.

L-Arginine as Bio-Based Curing Agent for Epoxy Resins: Temperature-Dependence of Mechanical Properties.

The precise characterization of new bio-based thermosets is imperative for the correct assessment of their potential as matrix material in fiber-reinforced polymer composites. Therefore, the mechanical properties of diglycidyl ether of bisphenol a (DGEBA) cured with l-arginine were investigated to determine whether the bio-based thermoset possesses the required mechanical properties for application as a matrix material. The cured thermoset is called Argopox. The mixture of amino acid and epoxy resin was prepared via three-roll milling and cured in the presence of an urea-based accelerator. The tensile, compression, flexural and toughness properties of Argopox were characterized at T=−40 ∘C, 22 ∘C and 80 ∘C to determine the temperature-dependence of the thermoset’s mechanical properties in its service temperature range. The glass transition temperature Tg was analyzed via dynamic mechanical analysis (DMA) and is approximately 119 ∘C. The tensile, compression and flexural strength at 22 ∘C are about 56 MPa, 98 MPa and 85 MPa, respectively. The critical stress intensity factor KIC and fracture energy GIC at 22 ∘C are roughly 1.1 MPam0.5 and 510 Jm−, respectively. Consequently, Argopox possesses mechanical properties that reach performance levels similar to that of materials which are already used as matrix for fiber reinforced composites.

L-Arginine as a Bio-Based Curing Agent for Epoxy Resins: Glass Transition Temperature, Rheology and Latency

The need for sustainable practices in the processing chain of fiber-reinforced thermosets has led to the development of bio-based epoxy resins and curing agents. As a contribution to sustainable composites, this study focuses on the glass transition temperature (), viscosity and latency of diglycidyl ether of bisphenol a (DGEBA) cured with l-arginine in the presence of a urea-based accelerator. These characteristics are decisive features for application as a matrix in fiber-reinforced polymer composites produced via prepreg technology in which low viscosity and sufficient latency, meaning low reactivity of the one-component system, are necessary. The homogeneous mixture of amino acid and epoxy resin was prepared via three-roll milling. Two formulations, Argopox-1 with 1 accelerator and Argopox-2.5 with accelerator, were prepared and parts of each formulation were stored at 22 °C and −18 °C, respectively. Both formulations were tested via differential scanning calorimetry (DSC) and small amplitude oscillatory shear rheology (SAOS) after 0 d, 30 d, 60 d, 90 d and 180 d of storage to determine the influence of accelerator weight fraction, storage temperature and storage period on the glass transition temperature of the uncured resin system , and their viscosity. The of the thermosets is about 100 °C. The DSC and SAOS measurements show that the of Argopox-1 shifts about 5 °C in 60 d, while its viscosity is still low enough to be processed in a prepreg production line. Furthermore, Argopox-1 is storable for at least 180 d at −18 °C without significant changes in its and viscosity. Consequently, Argopox-1 possesses a sufficiently high and adequate latency, as well as a low viscosity for application as prepreg matrix material.

Thermally Responsive Imidazole-Based Diels–Alder Microbeads as a Latent Curing Agent for Epoxy Resins

Thermally Responsive Imidazole-Based Diels–Alder Microbeads as a Latent Curing Agent for Epoxy Resins

Isophorone Diamine—A Curing Agent for Epoxy Resins: Production, Application, Prospects. A Review

Isophorone Diamine—A Curing Agent for Epoxy Resins: Production, Application, Prospects. A Review

Preparation and Performance Test of Modified Aromatic Amine Epoxy Resin Curing Agent

Preparation and Performance Test of Modified Aromatic Amine Epoxy Resin Curing Agent

A Study on the Synthesis, Curing Behavior and Flame Retardance of a Novel Flame Retardant Curing Agent for Epoxy Resin.

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.

Structure and Properties of Imidazolium Salt-based Ionic Liquid as a Functional Curing Agent for Epoxy Resin, Part I

Structure and Properties of Imidazolium Salt-based Ionic Liquid as a Functional Curing Agent for Epoxy Resin, Part I

Structure and Properties of Imidazolium salt-based Ionic Liquid as a Functional Curing Agent for Epoxy Resin, Part II

Structure and Properties of Imidazolium salt-based Ionic Liquid as a Functional Curing Agent for Epoxy Resin, Part II

Mono N-Alkylated DABCO-Based Ionic Liquids and Their Application as Latent Curing Agents for Epoxy Resins

Mono N-Alkylated DABCO-Based Ionic Liquids and Their Application as Latent Curing Agents for Epoxy Resins

Synthesis and characterization of a chalcone-derived epoxy containing pyrazoline ring with excellent flame resistance

Traditional epoxy resins are made by the reaction of petroleum-based bisphenol A and epichlorohydrin. The disadvantages of these petroleum-based epoxy including certain biological toxicity and flammability. To solve these problems, we first synthesized a diphenol compound 3,5-(4-hydroxyphenyl)-2-pyrazoline (TPP), which was prepared by condensation reaction of bio-based chalcone with hydrazine hydrate to replace standard petroleum-based bisphenol A. Then it was condensed with epichlorohydrin under alkaline condition to form a fully aromatic pyrazoline ring epoxy (TPP-EP). For further research, we use 4,4′-diaminodiphenylmethane (DDM) as the curing agent. When compared with bisphenol A epoxy resin (DGEBA/DDM), TPP-EP/DDM possessed a higher glass transition temperature (233°C vs. 176°C), and even showed that the residual carbon (in N2) and the storage modulus (at 30°C) increased by 201% and 74%, respectively. What’s more, TPP-EP/DDM system also had good inherent flame retardancy. The limiting oxygen index of TPP-EP/DDM was 33.1, reaching the V-0 level tested by UL-94. From the cone test, the THR, p-HRR, p-SPR and TSP values of TPP-EP/DDM systems also showed different degrees of reduction. Since TPP-EP contained tertiary amine active groups that could be used as a kind of catalytic curing agents for epoxy resins, thus the compound had certain self-curing properties. This work was of great significance for the synthesis of pyrazoline bio-based environmentally friendly flame-retardant epoxy resin.

A Novel Phosphorus-Containing Pyrazolyl Derivative as a Flame-Retardant Curing Agent for Epoxy Resins with Excellent Flame Retardance, High Transparency and Enhanced Toughness

A Novel Phosphorus-Containing Pyrazolyl Derivative as a Flame-Retardant Curing Agent for Epoxy Resins with Excellent Flame Retardance, High Transparency and Enhanced Toughness

Structure and Properties of Photo Cationic Polymerization Initiator as a Latent Curing Agent for Epoxy Resin, Part II

Structure and Properties of Photo Cationic Polymerization Initiator as a Latent Curing Agent for Epoxy Resin, Part II

Structure and Properties of Photo Cationic Polymerization Initiator as a Latent Curing Agent for Epoxy Resin, Part I

Structure and Properties of Photo Cationic Polymerization Initiator as a Latent Curing Agent for Epoxy Resin, Part I

Preparation of Latent Curing Agent for Epoxy Resin by Encapsulation Technology

The microcapsule-type curing agents DDM-PMMA and IZ-PU were prepared by solvent evaporation method and interfacial polymerization method, respectively. The surface morphology of the two microcapsules was characterized by SEM. The coating efficiency and latency were analyzed by DSC analysis of the one-component adhesive composed of the microcapsule-type curing agent and epoxy resin. Two encapsulation methods were compared in terms of hydrophilicity or lipophilicity of the core material, formation time of the microcapsules, coating efficiency and latency of the microcapsules.

Structure and Properties of Thermal Cationic Polymerization Initiator as a Latent Curing Agent for Epoxy Resin

Structure and Properties of Thermal Cationic Polymerization Initiator as a Latent Curing Agent for Epoxy Resin

Preparation of a Novel Phosphorus-Nitrogen Containing Novolac Curing Agent for Epoxy Resin and flame-retardancy of its cured epoxy resin

ABSTRACTIn this study, DICY (dicyandiamide)-containing novolac (NN) was first prepared, and then DOPO (9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) was introduced to react with the unsaturated bonds from DICY to obtain a novel phosphorus-nitrogen-containing novolac resin (PNN), which was used as a curing agent for epoxy resins. The curing condition was confirmed by a non-isothermal curing kinetics study. The thermal stability and flame retardancy of the cured epoxy resin system were studied by thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, UL-94 test and cone calorimeter. The morphology of the burned chard residues was observed by Scanning electron microscopy (SEM). The results show that epoxy resin cured by the prepared PNN curing system presents excellent flame retardancy. The cured resin system, which contains only 1.31wt% phosphorus and 2.48wt% nitrogen, can achieve UL 94 V-0 rating.

Functional dendritic curing agent for epoxy resin: Processing, mechanical performance and curing/toughening mechanism

A functional curing agent was synthesized with imidazole blocked 2,4-tolulene diisocyanate (TDI) by using dendritic polyester polyol as branching unit and toughening segment, which toughening and curing the bisphenol A type epoxy resin (E−44). The effect of dendritic polyester polyol content on the morphology of fracture surface and properties of the cured epoxy resin was investigated, which results in the multiple curing mechanism for the curing process. With the increasing of dendritic polyester polyol content, the surface fracture of the cured epoxy turns to more ductile. The mechanical properties from tensile shear and impact strength tests showed that 1% of dendritic polyester polyol (the molar percentage of isocyanate) was the optimum content to get cured epoxy with desired tensile shear strength and impact strength. The curing and toughening mechanism was proposed based on the experimental results.