Epoxy/imidazolium‐based ionic liquid systems: The effect of the hardener on the curing behavior, thermal stability, and microwave absorbing properties

Thermal and Electrochemical Properties of Ionic Liquids Bearing Allyl Group with Sulfonate-Based Anions-Application Potential in Epoxy Resin Curing Process

Sulfonate-based ionic liquids (ILs) with allyl-containing cations have been previously obtained by us, however, the present study aims to investigate the thermal, electrochemical and curing properties of these ILs. To determine the temperature range in which ionic liquid maintains a liquid state, thermal properties must be examined using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Melting, cold crystallization and glass transition temperatures are discussed, as well as decomposition temperatures for imidazolium- and pyridinium-based ionic liquids. The conductivity and electrochemical stability ranges were studied in order to investigate their potential applicability as electrolytes. Finally, the potential of triflate-based ILs as polymerization initiators for epoxy resins was proven.

Formaldehyde-Free Resins for the Wood-Based Panel Industry: Alternatives to Formaldehyde and Novel Hardeners

Due to its carcinogenic properties, the presence of formaldehyde in resins and other industrial products has been a subject of great concern in recent years. The presented review focuses on modern alternatives for the production of wood-based panels; i.e., substitutes for formaldehyde in the production of amino and phenolic resins, as well as novel hardeners for formaldehyde-free wood adhesives. Solutions in which formaldehyde in completely replaced are presented in this review. Recent advances indicate that it is possible to develop new formaldehyde-free systems of resins with compatible hardeners. The formaldehyde substitutes that have primarily been tested are glyoxal, glutaraldehyde, furfural, 5-hydroxymethylfurfural, and dimethoxyethanal. The use of such substitutes eliminates the problem of free formaldehyde emission originating from the resin used in the production of wood-based panels. However, these alternatives are mostly characterized by worse reactivity, and, as a result, the use of formaldehyde-free resins may affect the mechanical and strength properties of wood-based panels. Nonetheless, there are still many substantial challenges for the complete replacement of formaldehyde and further research is needed, especially in the field of transferring the technology to industrial practice.

New Imidazolium Ionic Liquids from Recycled Polyethylene Terephthalate Waste for Curing Epoxy Resins as Organic Coatings of Steel

Imidazolium ionic liquid (IIL) was prepared from aminolysis of polyethylene terephthalate (PET) waste with pentaethylenehexamine (PEHA) to apply as hardener of epoxy resin. Its purified chemical structures, thermal stability, and thermal characteristics were identified as well as amino phthalamide aminolyzed products. The thermal, thermomechanical, and mechanical properties of the cured epoxy resins with different weight percentages of IIL were investigated to optimize the best weight ratio to obtain homogeneous networks. The adhesion, durability, and corrosion resistance of the cured epoxy resins on the steel surfaces were tested to confirm that the best weight ratio of epoxy: IL was 2:1. This ratio achieved higher adhesion strength and salt spray resistance to seawater extended to 1500 h.

Processing of Functional Composite Resins Using Deep Eutectic Solvent

Deep eutectic solvents (DESs)—a promising class of alternatives to conventional ionic liquids (ILs) that have freezing points lower than the individual components—are typically formed from two or more components through hydrogen bond interactions. Due to the remarkable advantages of biocompatibility, economical feasibility and environmental hospitality, DESs show great potentials for green production and manufacturing. In terms of the processing of functional composite resins, DESs have been applied for property modifications, recyclability enhancement and functionality endowment. In this review, the applications of DESs in the processing of multiple functional composite resins such as epoxy, phenolic, acrylic, polyester and imprinted resins, are covered. Functional composite resins processed with DESs have attracted much attention of researchers in both academic and industrial communities. The tailored properties of DESs for the design of functional composite resins—as well as the effects of hydrogen bond on the current polymeric systems—are highlighted. In addition to the review of current works, the future perspectives of applying DESs in the processing of functional composite resins are also presented.

Impact of Imidazolium-Based Ionic Liquids on the Curing Kinetics and Physicochemical Properties of Nascent Epoxy Resins

We investigated the influence of anion type (salicylate, [(MOB)MIm][Sal], vs chloride, [(MOB)MIm][Cl]) of imidazolium-based ionic liquid (IL) and its content on the curing kinetics of bisphenol A diglicydyl ether (DGEBA of molecular weight M n = 340 g/mol). Further physicochemical properties (i.e., glass transition temperature, T g, and conductivity, σdc) of produced polymers were investigated. The polymerization of the studied systems was examined at various molar ratios (1:1, 10:1, and 20:1) at different reaction temperatures (T reaction = 353-383 K) by using differential scanning calorimetry (DSC). Interestingly, both DGEBA/IL compositions studied herein revealed significantly different reaction kinetics and yielded materials of completely distinct physical properties. Surprisingly, in contrast to [(MOB)MIm][Cl], for the low concentration of [(MOB)MIm][Sal] in the reaction mixture, an additional step in the kinetic curves, likely due to the combined enhanced initiation activity of anion (salicylate)-cation (imidazolium-based), was noted. To thoroughly analyze the kinetics of all studied systems, including the two-step kinetics of DGEBA/[(MOB)MIm][Sal], we applied a new approach that relies on the combination of the two phenomenological Avrami equations. Analysis of the determined constant rates revealed that the reaction occurring in the presence of the salicylate anion is characterized by higher activation energy with respect to those with the chloride. Moreover, DGEBA/[(MOB)MIm][Sal] cured materials have higher T g in comparison to DGEBA polymerized with [(MOB)MIm][Cl] independent of the IL concentration. This fact might indicate that, most likely, the products of hardening are highly cross-linked (high T g) or oligomeric linear polymers (low T g) in the former and latter cases, respectively. Such a change in the chemical structure of the polymer is also reflected in the dc conductivity measured at the glass transition temperature, which is much higher for DGEBA cured with [(MOB)MIm][Cl]. Herein, we have clearly demonstrated that the type of anion has a crucial impact on the polymerization mechanism, kinetics, and properties of produced materials.