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TOLEDO (SPAIN)

EFFECTS OF ADDITIVES ON THE CHEMICAL RECYCLING OF AMINE AND
ANHYDRIDE CURED EPOXY RESIN IN SUBCRITICAL WATER
J. Liu1, Y. Liu1, Z.W. Jiang1 and T. Tang1
1 State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy ofSciences, Changchun, PR Chinae-mail: liujie@ciac.jl.cn

Abstract
Epoxy resin is most commonly used in producing fiber reinforced polymer composites and printed circuit boards due to its
chemical resistance, heat resistance and good mechanical properties, but it is difficult to recycle this kind of materials.
Sub- and supercritical water have been an attractive solvent for the chemical recycling of epoxy resin because they arecheap, non-toxic and nonflammable. However, the decomposition efficiency is required further increasing. In this study,
different additives were added into subcritical water to increase the decomposition efficiency of amine and anhydride
cured epoxy resin. Phenol and KOH were observed to show a synergetic effect in decomposing amine cured epoxy resin.
The resin decomposition efficiency reaches a maximum at a weight ratio of KOH/phenol=1/10. KOH is more effective
than phenol for decomposing the anhydride cured epoxy resin. Ethanolamine is also an effective additive fordecomposing this kind of epoxy resin. Alkaline conditions are found to be favorable to the cleavage of ester linkages. On
the above basis, a method is established to recover carbon fibers with no tensile strength loss from a carbon fiber
reinforced epoxy resin composite.

Keywords: Epoxy resin, subcritical water, amine, anhydride.

1. Introduction
Epoxy resin is most commonly used in producing fiber
reinforced polymer composites and printed circuit boards
due to its chemical resistance, heat resistance and goodmechanical properties, but it is difficult to recycle this kindof materials [1]. In recent years, Sub- and supercriticalwater has been an attractive solvent for the chemical
recycling of epoxy resin materials because it is cheap,
non-toxic and nonflammable [2]. However, exploring newreaction system is necessary to improve thedecomposition efficiency and lower the cost of facility andoperation.

respectively. It is noted that adding phenol and KOH
simultaneously led to the complete decomposition of theresin under the above conditions. This phenomenon
indicates that phenol and KOH have some synergistic
effect on the decomposition of DDM cured epoxy resin.

2. Materials and Methods
4, 4'-diaminodiphenylmethane (DDM) and methyltetrahydrophthalic anhydride (MeTHPA) cured epoxy
resins were prepared by mixing diglycidyl ether ofbisphenol A with corresponding curing agent,respectively. The cured resin was decomposed in a nonstirred batch autoclave reactor. The decomposition
products were characterized by FTIR and GC-MS.

3. Results and Discussion
Fig. 1 shows the decomposition rate of the DDM cured
epoxy resin in subcritical water with different additives.
As shown in Fig. 1, 12.6 wt% of DDM cured resin wasdecomposed in water at 315 oC for 30 min. The
decomposed resin percentage increased to 15.2 and40.3 wt% when phenol and KOH were added into water,interiores libro.indd 125

Fig. 1. Decomposition rate of the DDM cured epoxy resin
in different reaction system.
Fig. 2 shows the effect of the content of phenol on thedecomposition rate of the DDM cured epoxy resin inwater at 315 oC for 30 min at a fixed weigh ratio of
KOH/H2O=1/100. It can be observed from Fig. 2 that thepresence of a small quantity of phenol (1 g and 2.5 g)decreased the decomposed resin percentage comparing
with the case only adding KOH. When the quantity of

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6th International Symposium on Feedstock Recycling of Polymeric Materials

phenol increased, more cured resins were decomposed.
The decomposed resin percentage reached a maximum
at a KOH/phenol weight ratio of 1/10.

Fig. 4. FT-IR spectra of MeTHPA cured epoxy resin andits decomposed products.

4. Conclusions
Fig. 2. Effect of the phenol content on the decomposition
rate of the DDM cured epoxy resin in subcritical waterwith fixed KOH.

Various additives were used in subcritical water toimprove the decomposition rate of the amine andanhydride cured epoxy resins. A combined effect ofphenol and KOH was found for the decomposition ofDDM cured resin. The resin decomposition efficiency
reaches a maximum at a weight ratio of KOH/phenol=1/10. Among the additives used in this work, the mostefficient one in promoting decomposition of anhydride
cured resin was alkaline materials, which in favor ofcleaving ester bond in the resin network.

References

Fig. 3. Effect of the reaction temperature on thedecompoition rate of the MeTHPA cured resin withdifferent additives in subcritical water.

[1] S.J. Pickering. Recycling technologies for thermoset
composite materials-current status. Composites: Part A
37 (2006) 1206–1215.
[2] M. Goto. Chemical recycling of plastics using suband supercritical fluids. J. of Supercritical Fluids 47 (2009)
500–507.

Fig. 3 shows the effect of the reaction temperature on
the decomposition rate of the MeTHPA cured resin withdifferent additives in subcritical water for 30 min. As canbe seen in Fig. 3, higher decomposition rate wasobserved in the presence of alkaline materials such as
KOH and ethanolamine. The combined phenol and KOH
did not take the effect similar to DDM cured systems.
Fig. 4 shows the FT-IR spectra of MeTHPA cured
epoxy resin and decomposed products in subcriticalwater with and without ethanolamine. The peak at about
1730 cm-1, which is attributed to ester bond, shifted to1645 cm-1 (attributed to amide group) after subcriticalwater treatment in the presence of ethanolamine,
indicating that amino group of the ethanolamine attacked
the ester bond and formed amide.

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