Chemical recycling of epoxy-anhydride fiber-reinforced composites
Topic(s) : Special Sessions
Co-authors :
Eleonora MANARIN (ITALY), Oussama BOUMEZGANE , Gianmarco GRIFFINI (ITALY), Stefano TURRIAbstract :
Anhydride-cured epoxy resins are widely used in engineering fields as matrices for reinforced thermoset composites. However, being thermoset materials poses a significant challenge for their disposal, thus the identification of sustainable recycling methods for End-of-Life composites is an impelling challenge to solve. Within this framework, the present research focuses on chemical recycling of epoxy composites through catalyst assisted depolymerization1,2 under atmospheric pressure and moderate temperature by using bio-based and biodegradable solvents. The approach exploits the selective cleavage of ester bonds by transesterification-exchange reaction in hydroxylated bioderivable and biodegradable solvents.
An anhydride-cured epoxy resin is formulated using bisphenol-A-diglycidyl ether (DGEBA) and hexahydro-4-methylphthalic anhydride (HHMPA). Two epoxy/anhydride molar ratio are chosen (1:1 and 2:1). Unidirectional carbon fibers (CF) are used as reinforcement. 1,4-butandiol (BD) and diethylene glycol monobutyl ether (DGBE) are employed as solvents and triazabicyclodecene (TBD) as transesterification catalyst. Solvolysis is performed on 20x50x2 mm samples at 180 °C with a solid-to-solvent ratio of 10%wt and catalyst-to-solvent ratio of 3.5%wt.
The anhydride–cured epoxy matrices are depolymerized into soluble oligomers containing anhydride and ester linkages by catalyst–alcohol transesterification. A dependence of the dissolution kinetic on the composition (i.e., Tg and crosslinking density) is highlighted (Table 1).
Table 1. Conditions for solvolysis varying epoxy-anhydride molar ratio and solvent
TABLE 1
The purity of recycled fibers (rCF) compared to virgin ones is verified by means of SEM (Figure 1) and TGA. Both analyses highlight high purity of the recycled fibers, potentially reusable for second generation composite materials without additional sizing.
FIGURE 1
Figure 1. SEM images of the recycled CF (rCF) with respect to the virgin after the solvolysis of the epoxy matrices (ratio 1:1 or 2:1) in different solvents (DGBE or BD)
This research presents a promising approach towards the recycling of thermoset materials and their composites. The implementation of catalyst-assisted solvolysis methods under mild conditions and atmospheric pressure of reinforced composites yields to valuable organic products as well as clean and potentially reusable fibers, fulfilling the principles of circular economy and opening new pathways for future chemical-treatments of composite wastes.
Funded by the European Union’s Horizon Europe Research and Innovation Programme (grant Agreement no. 101058756, project: RECREATE).
An anhydride-cured epoxy resin is formulated using bisphenol-A-diglycidyl ether (DGEBA) and hexahydro-4-methylphthalic anhydride (HHMPA). Two epoxy/anhydride molar ratio are chosen (1:1 and 2:1). Unidirectional carbon fibers (CF) are used as reinforcement. 1,4-butandiol (BD) and diethylene glycol monobutyl ether (DGBE) are employed as solvents and triazabicyclodecene (TBD) as transesterification catalyst. Solvolysis is performed on 20x50x2 mm samples at 180 °C with a solid-to-solvent ratio of 10%wt and catalyst-to-solvent ratio of 3.5%wt.
The anhydride–cured epoxy matrices are depolymerized into soluble oligomers containing anhydride and ester linkages by catalyst–alcohol transesterification. A dependence of the dissolution kinetic on the composition (i.e., Tg and crosslinking density) is highlighted (Table 1).
Table 1. Conditions for solvolysis varying epoxy-anhydride molar ratio and solvent
TABLE 1
The purity of recycled fibers (rCF) compared to virgin ones is verified by means of SEM (Figure 1) and TGA. Both analyses highlight high purity of the recycled fibers, potentially reusable for second generation composite materials without additional sizing.
FIGURE 1
Figure 1. SEM images of the recycled CF (rCF) with respect to the virgin after the solvolysis of the epoxy matrices (ratio 1:1 or 2:1) in different solvents (DGBE or BD)
This research presents a promising approach towards the recycling of thermoset materials and their composites. The implementation of catalyst-assisted solvolysis methods under mild conditions and atmospheric pressure of reinforced composites yields to valuable organic products as well as clean and potentially reusable fibers, fulfilling the principles of circular economy and opening new pathways for future chemical-treatments of composite wastes.
Funded by the European Union’s Horizon Europe Research and Innovation Programme (grant Agreement no. 101058756, project: RECREATE).