Abstract
Herein, a solvent-based green recycling procedure is reported for recycling thermoset epoxy resins (TERs) and carbon fiber reinforced epoxy composites (CFRECs) employing ionic liquids (ILs) and alcohols under mild conditions. With melting points less than 100 °C, ILs are defined as organic salts, typically composed of bulky cations with organic or inorganic counteranions. As a result of their unique physical properties such as low vapor pressure, relatively high thermal stability, and multifunctional tunability, these solvents are often classified as “green solvents” as compared to traditional organic solvents. In this study, swelling and dissolution of TER are evaluated in the presence of pure alkyl-methyl-imidazolium ILs, alcohols, and various mixtures of these co-solvents to determine their swelling and depolymerization capacity at mild temperatures in the absence of catalysts. In these studies, three ILs with different alkyl lengths were evaluated: 1-butyl-3-methyl imidazolium chloride ([BMIm][Cl]), 1-hexyl-3-methyl imidazolium bromide ([HMIm][Br]), and 1-octyl-3-methyl imidazolium bromide ([OMIm][Br]) along with two alcohols: ethylene glycol (EG) and glycerol (Gly). The highest swelling capacity of TER at 150 °C was achieved by a combination of [BMIm][Cl] and EG. In addition, swelling and dissolution of TER were evaluated in the presence of several anion variants of 1-butyl-3-methyl-imidazolium ILs with EG. Complete dissolution of both TERs and CFRECs was achieved in 150 min (2.5 h) at 150 °C under atmospheric pressure. Finally, recovery and reuse of the recycled monomer after dissolution were examined. Recovered epoxy monomers employed to synthesize a recycled TER exhibited similar mechanical properties to the parent TER. In addition, it was demonstrated that carbon fibers could be successfully recovered from CFREC using the recycling method detailed in this manuscript.
Highlights
Synthesized epoxy resin was characterized through use of various analytical techniques such as FT-IR, differential scanning calorimetry (DSC), and TGA
The recovered monomer from the depolymerized resin was obtained through precipitation and was employed for the synthesis of a recycled Thermoset epoxy resins (TERs)
Mechanical properties of recycled TER and carbon fiber reinforced epoxy composites (CFRECs) were similar to those of the parent TER and CFREC, indicating that the recovered materials could be employed in the synthesis of new TER and CFREC
Summary
The projected revenue from these types of materials has high potential, there is a high cost associated with common epoxy matrix and, with newly manufactured carbon fibers.[9] the major consumption of these types of epoxy materials as well as the final manufactured products generates enormous waste, and most of these unwanted products are discarded into landfills.[10,11] global consumption of such materials presents a major environmental concern and recovering these high-cost materials from waste would represent considerable economic benefit.[12−14] For these reasons, different recycling methods have been investigated and employed to decrease waste associated with these types of materials.[10,15]. Both methodologies present certain disadvantages, including higher consumption of energy, Received: July 22, 2021 Accepted: September 23, 2021 Published: October 11, 2021
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