Chemical recycling of unsaturated polyester resin and its composites via selective cleavage of the ester bond

Article abstract of DOI:10.1039/c5gc01048a

An efficient strategy has been developed for chemical recycling of unsaturated polyester resin (UPR) and its glass fibre reinforced polymer composites (GFRP) by selectively cleaving C-O bonds using the AlCl₃/CH₃COOH system. AlCl₃ promotes acyl exchange reaction between CH₃COOH and UPR. This process facilitates recovery of valuable oligomers and monomers from UPR, and glass fibres from GFRP.

Full text of DOI:10.1039/c5gc01048a

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Chemical Recycling of Unsaturated Polyester Resin and Its
Composites via Selective Cleavage of ester Bond
Yuqi Wang,a,b Xiaojing Cui,a Qiqi Yang ,c Tiansheng Deng,*a Yingxiong Wang,a Yongxing Yang,a Shiyu
Jia,a Zhangfeng Qina and Xianglin Hou*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
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An efficient strategy has been developed for chemical to comminute the scrap material for reuse as fillers or partial
recycling of unsaturated polyester resin (UPR) and its glass fibre reinforcement in new composite material. This method consumes a
reinforced polymer composites (GFRP) by selectively cleaving C-O large amount of mechanical energy, and the length of recovered GF
bonds using AlCl3/CH3COOH system. AlCl3 promotes acyl exchange is drastically declined which limits the reuse of recovered GF.8, 9 In
reaction between CH3COOH and UPR. This process facilitates the thermal process, high temperatures are demanding to
recovery of valuable oligomers and monomers from UPR, and decompose the scrap material. However, small molecules would
glass fibres from GFRP.
inevitably produce in this process, most of which are toxic gases.10-
12
The recovery of valuable units from end-of-life polymeric
materials has become an important issue in view of sustainable
chemistry and environmental protection.1 Unsaturated polyester
resin (UPR) and its composites, for example, glass fibre reinforced
unsaturated polyester resin composites (GFRP), have been widely
applied in the aeronautical, automotive, construction industries,
new energy and transport fields.2 With the large number
applications of UPR and its composites, the waste UPR and
composites including off-cuts during manufacture, unused prepreg
and end-of-life components have caused a great trouble on the
environment.3 Developing an effective recycling method for waste
UPR and its composites becomes an urgent issue that needs to be
addressed. However, as a thermoset resin, UPR and its composites
are thermal and chemical stable because of their strengthful three-
dimensional network structure.4 At the beginning, landfill and
incineration were adopted to deal with thermosetting resin and
Compared to mechanical and thermal methods, chemical
recycling is more promising because it can obtain glass fibre,
monomers and their derivatives from end-of-life thermoset resin
and its composites. Major efforts in chemical recycling strategy are
concentrated on the depolymerisation of the resin matrix for
liberation of glass fibres by solvolysis, including hydrolysis (using
water),13 alcoholysis (using alcohols), aminolysis (using ammonia)
and acid digestion (using acid). During the solvolysis process, either
sub- or supercritical conditions with high temperature and high
pressure are normally required to gain fast dissolution and high
efficiency.14, 15 For example, supercritical water was reported as the
solvent to degrade epoxy resin or UPR;16-20 numerous studies
demonstrated that the decomposition of epoxy resin or UPR can be
achieved in supercritical alcohols.21-25 In the examples of acid
digestion of resin, atmospheric conditions were normally applied
but the separation was troublesome.26, 27 In addition to solvolysis,
the degradation of UPR was reported by using strong oxidants such
6
their composites.5, However, simple treatment of the scrap
thermosetting resins and composites would cause a great waste of
valuable materials. Current recycling strategies for UPR and its
composites mainly includes mechanical, thermal and chemical
methods.7 Mechanical recycling technique involves grinding process
28-30
31-33
as hydrogen peroxide
and ionic liquid.
However, high
temperature, long reaction times, strong corrosive solvent (e.g.,
nitric acid), or rigorous conditions (e.g., supercritical fluid) are
usually required to cleave the chemical bonds of UPR. More
importantly, such cleavage of chemical bonds is non-selective,
which inevitably produces small toxic molecules, introduces a
complex distribution of products and causes a serious damage in
the strength of GF.
a.The Biorefinery Research and Engineering Center, Institute of Coal Chemistry,
Chinese Academy of Sciences, 27 South Taoyuan Road, Taiyuan, 030001, People’s
Republic of China.
b.University of Chinese Academy of Sciences, Beijing, 100049, People’s Republic of
China.
Ideally, it is desirable to decompose UPR and to recycle GF by
selective cleavage of specific bonds of resin. The complexity in
products and emission of toxic gases in such case would be
minimized. Noticeably, UPR is mainly built up by C-C, C-H and C-O
bonds (as shown in scheme 1). The exact name of the selected UPR
c.College of mechanics, Taiyuan University of Technology, 79 west Yingze Road,
Taiyuan, 030024, People’s Republic of China.
† Footnotes relaꢀng to the ꢀtle and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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(scheme 1) is poly-maleic anhydride-phthalic anhydride-1,2- of C-O bonds, and PET decomposed completely in these solutions.
propylene glycol cross-linked with styrene (PMPPS) which is a Surprisingly, PMPPS was stable in these solutions, and no swelling
convenient and versatile resin for general purpose. The selective of PMPPS was observed in the degradation process. This indicates
cleavage of C-O bond could not only facilitate recycling of GF, but that the metal ions in the solutions could not enter the matrix of
also favor the retaining of valuable carbon skeleton of resin and PMPPS. Hence, the swelling of PMPPS in solvent is vital for the
other chemicals. Herein, we report using AlCl3/CH3COOH as the following degradation. In other words, the solvent molecules should
degradation system to recycle thermoset resins and their enter the body of PMPPS readily to transfer active centres (the
composites under mild conditions (180 °C, 1-3 atm).
metal ions). The swelling behaviours of PMPPS were carried out in
various inorganic and organic solvents. The swelling effect of water
was the worst and the weight increase ratio of PMPPS in water is
about 1.5% and the swelling effect of alcohol is relatively low
(Figure 1). On the contrary, PMPPS swells the best in
tetrahydrofuran (THF) and its weight increase reaches more than
30%, followed by that of acetic acid (about 25%). THF are unable to
provide the terminal groups to complete the cleavage of ester
bonds in PMPPS, and it is more expensive than acetic acid. Taking
these into account, acetic acid was chosen as solvent.
The synthesis process of PMPPS is shown in SI Scheme 1 in ESI.
The major functional groups of PMPPS are ester bonds and benzene
ring. As benzene ring is very stable because of the aromatic
structure, ester bonds would be cleaved in the decomposition
process of the PMPPS. To selectively break C-O bond, a Lewis acid is
essential due to the existence of isolated electron pairs in O atom.
Thus, AlCl3 was selected as the Lewis acid catalyst for the cleavage
of C-O bond in PMPPS, and this paper focuses on understanding the
origin of the high efficiency of AlCl3/CH3COOH system for
decomposing PMPPS and its composites. In particular, the
contributions of AlCl3 and CH3COOH to the degradation reaction
were explored, from which the reaction mechanism was proposed.
35
30
25
20
15
10
5
CH3
O
C
O
C
CH3
O
O
O
O
H2
C
H2
C
H
C
O
O
C
H
O
O
C
H
O
O
C
H
O
O
O
O
CH2
CH
n
CH3
O
C
O
C
CH3
H2
C
H2
C
H
C
C
H
C
H
C
H
CH2
CH
0
Figure 1. Swelling of PMPPS in various solvents. Reaction condition:
180 oC, 6 h.
AlCl3
CH3COOH
The degradation of PMPPS was performed in acetic acid with
various metal salts as the catalyst (Table 1). AlCl3 and FeCl3 show
superior ability for decomposing PMPPS compared with other
counterparts. PMPPS swelled and decomposed completely in
AlCl3/CH3COOH and FeCl3/CH3COOH solutions. In contrast, MgCl2
and CuCl2 have little catalytic effect for breaking C-O bond of PMPPS.
The solubility of AlCl3 in acetic acid is less than 0.14 wt% at room
temperature, but it increases with improving temperatures and the
added 10 wt% AlCl3 dissolves entirely at reaction temperature (180
oC). Interestingly, after the degradation, the majority of Al was
deposited from the solution when the reactor was cooled down to
room temperature. This process facilitated the separation of
products from the reaction system. However, this process was not
observed for FeCl3/CH3COOH system as the solubility of FeCl3 can
reaches more than 20 wt% in acetic acid at room temperature,
bringing troubles in product separation. Hence, AlCl3/CH3COOH was
chosen as the catalytic system.
OH
OH
C
O
O
CH3 CH3
O
O
HO
OH
O
C
O
C
O
H2
C
H
C
H
C
H
H
C
C
H
+
+
nC
C
O
O
C
O
H3C
C
H
CH2
OH
OH
Scheme 1. Degradation mechanism of PMPPS in AlCl3/CH3COOH
system.
It has been demonstrated in our previous work that the
incompletely coordinated zinc ions in concentrated ZnCl2 aqueous
solution enable the cleavage of C-O and C-N bonds in organic
polymers.34, 35 Moreover, as ester bonds can hydrolyze in water,
water may be an effective solvent for decomposing PMPPS.
Accordingly, we investigated the degradation of PMPPS in metal
chloride aqueous solutions (SI Table 1 in ESI, entries 1-5). PET was
also chosen because it is also built up by C-C and C-O bonds (SI table
1 in ESI, entries 6-12). ZnCl2 and AlCl3 are effective in the cleavage
The effect of anions on the catalytic behaviours of Al ions was
explored. Al2(SO4)3 and Al(CH3COO)3 have no catalytic effect, while
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Al(NO3)3 shows much lower efficiency towards the degradation of
PMPPS than AlCl3. As active centers, the distribution of metal ions in
resin plays a crucial role for the degradation reaction. The mass
transfer behaviours of metal ions were investigated with acetic acid
as solvent. As the swelling of PMPPS was nearly complete at 3 hours
(SI Figure 1 in ESI), the reaction time in the mass transfer
experiments was fixed at 3 hours. The ICP results indicate that the
metal cations in all metal chlorides including AlCl3, ZnCl2, MgCl2,
FeCl3 and CuCl2 can enter the PMPPS body (Table 2, entries 1-5),
whereas it is troublesome for Al2(SO4)3 and Al(CH3COO)3 to enter
the interior of resin (Table 2, entries 1, 6-8). This result indicates
that the incapability of Al(CH3COO)3 and Al2(SO4)3 for decomposing
PMPPS is caused by the steric hindrance of CH3COO- and SO42-. The
[a] reaction condition: acetic acid as solvent, 10 wt%, 180 °C, 3 h.
The degradation process of PMPPS in AlCl3/CH3COOH system
was also investigated by FT-IR (Figure 2). For original PMPPS, the
peaks appeared at 1600 cm-1, 1581 cm-1, 1493 cm-1 and 1453 cm-1
are assigned to the C=C stretching vibration in benzene ring, while
the peaks at 1728 cm-1 and 1286 cm-1 are characteristic absorptions
of C=O and C-O stretching vibrations in ester bonds. The IR
spectroscopy of swollen PMPPS is similar to original PMPPS,
indicating that during the swelling process, AlCl3/CH3COOH system
has no effect on the cleavage of ester bond (see SI Figure 2 in ESI).
2-
radii of SO4 and CH3COO- are larger than that of Cl-. As a result, it
would be highly problematic for Al3+ ions to enter the matrix of
PMPPS when the paring anions are SO42- or CH3COO-.
C=C
(a)
C=O
C-O
Table 1. The degradation of PMPPS in various catalyst systems. [a]
(b)
[b]
Entry
Catalyst
Rd
(c)
(d)
C=O
C-C(=O)-O-C(=O)-C
1
2
3
4
5
6
7
8
AlCl3
100
ZnCl2
71.34
5.99
MgCl2
C-O
1200
C=O
1600
FeCl3
100
2000
1800
1400
1000
800
600
Wavenumber/cm-1
CuCl2
6.29
Al2(SO4)3
Al(NO3)3
Al(CH3COO)3
swollen
29.43
swollen
Figure 2. FT-IR spectra of PMPPS and its degradation products: (a)
PMPPS, (b) product 1, (c) product 2, (d) product 3.
After the degradation, the degradation products in the
reaction mixture were collected and weighted (see SI Figure 3 and
SI Table 2 in ESI), and their compositions were analyzed by FT-IR
(Figure 2), ICP (Table 3), gel permeation chromatography (GPC) (SI
Table 3 in ESI) and NMR (Figure 3 ,SI Figure 4 and SI Figure 5 in ESI).
As indicated by ICP, product 1 is the Al catalyst. In the IR
spectroscopy of product 1, the peaks at 1579 cm-1 and 1477 cm-1
are the characteristic peaks of Al(CH3COO)3. The NMR spectroscopy
of product 1 has two peaks, one around 179 ppm belongs to C=O,
and the other at 25 ppm is assigned to CH3. Thereby, the main
component of product 1 is Al(CH3COO)3. This result indicates that
AlCl3 changed into Al(CH3COO)3 after the degradation. Product 2 is
organic compound, as implied by ICP. In the IR spectroscopy, peaks
that are assigned to benzene ring and ester bond existed in product
2; additionally, there exists peaks for C=O (1780 cm-1 and 1856 cm-1)
and C-C(=O)-O-C(=O)-C (948 cm-1 and 915 cm-1) stretching
vibrations in cyclic anhydride. The existence of C=O (at 172 ppm),
benzene ring (at 128 ppm), 1,2-propylene glycol (at 68 ppm) and
maleic anhydride (at 42 ppm) in product 2 are also ascertained by
NMR. Besides, the number-average molecular weight of product 2,
as indicated by GPC, is 12891 g·mol-1 and its polydispersity is 1.79
(SI Table 3 in ESI). These results indicate that the main components
of product 2 are polyaddition products of maleic anhydride and
styrene. Further degradation of product 2 was also carried out in
[a] reaction condition: acetic acid as solvent; the weight ratio of
catalyst: 10 wt%; temperature: 180 oC; time: 12 h. [b] Rd:
degradation ratio.
Table 2. The distribution of cation in PMPPS on different reaction
condition by ICP.[a]
Entry
Catalyst
Content of canion/wt%
1
2
3
4
5
6
7
8
AlCl3
0.20
ZnCl2
0.71
MgCl2
0.12
FeCl2
0.74
CuCl2
0.13
Al2(SO4)3
Al(NO3)3
Al(CH3COO)3
0.0017
0.10
0.0001
o
AlCl3/CH3COOH system at 180 C for 12 h. FT-IR Results show that
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no ester bond was found, and only anhydride (1784 cm-1) and concentration of 1,2-propylene glycol diacetate may be due to that
carboxyl (1713 cm-1) existed (SI Figure 6 in ESI). For product 3, the 1,2-propylene glycol diacetate is not stable in the degradation
C=O stretching vibration in aryl conjugate acid appears at 1686 cm-1, system. To validate this hypothesis, 1,2-propylene glycol diacetate
while the peak at 1281 cm-1 is assigned to C-O stretching vibration. was added into the 10 wt% AlCl3/CH3COOH system. The GC signal
In the NMR graph of product 3, besides the C=O bond structure (at for 1,2-propylene glycol diacetate decreased drastically after
172 ppm), benzene ring of phthalic acid was observed (at 132 ppm) reacting at 180 oC for 2 hours (see SI Figure 7(b) and 7(c) in ESI). As
as the value of chemical shift moves to low-field due to the effect of the reaction time in the degradation reactions is 12 hours, the
carbonyl group. Hence, product 3 is mainly phthalic acid. Therefore, majority of the formed 1,2-propylene glycol diacetate transformed.
it is verified that the AlCl3/CH3COOH system enables the selective This accounts for the observed low concentration of 1,2-propylene
cleavage of C-O bond in ester group of in PMPPS, leaving the carbon glycol diacetate.
skeleton intact (see scheme 1). The weight of recycled polyaddition
products of maleic anhydride and styrene (product 2), and phthalic
Al3+
Al3+
Al3+
acid (product 3) accounts for 91.93 wt% of original PMPPS,
indicating the high recovery yield of the AlCl3/CH3COOH system (see
SI Figure 3 and SI Table 2 in ESI).
Al3+
O
O
O
O
O
O
O
O
R2
R2
R2
+
R2
R1
R1
HO
O
O
R2
R1
O
O
R1
O
O
R1
O
O
+
CH3
CH3
O
AlCl3
CH3
CH3
CH3
O
O
Table 3. Elemental analysis of PMPPS and degradation products.
Scheme 2. The possible reaction mechanism for decomposing
sample
Carbon
content
/wt%
Hydrogen
content
/wt%
Oxygen
content
/wt%
Aluminium
content
/wt%
PMPPS in AlCl3/CH3COOH system.
It can be deduced from the distributions of degradation
products that acyl exchange reaction occurred between PMPPS and
acetic acid, that is, an acidolysis of the polyester bonds of PMPPS by
carboxyl group of solvent molecule. This process led to the
formation of phthalic acid and 1,2-propylene glycol diacetate. But
for acyl exchange reaction, while there are many examples using
enzyme catalysts36, 37, the studies using metal ions catalyst systems
are, to date, not reported. IR characterization was explored to
understand the role of AlCl3 in the degradation reaction (SI Figure 8
and SI Figure 9 in ESI). No shifts in the peak positions of -C(=O)-O-
bond was observed for acetic acid after adding AlCl3 (SI Figure 8 in
ESI). Ethyl acetate was chosen as the model molecule for PMPPS
because it also has ester bond. Interestingly, the peak of C=O in
ester group of ethyl acetate appears at 1744 cm-1, while it appears
at 1698 cm-1 with the presence of AlCl3 (SI Figure 9). This red shift
indicates clearly the catalytic effect of AlCl3 on C=O bond. In
particular, the active Al ions coordinate with oxygen atoms of C=O
bonds, leading to weakness in the strength of (C=O)-O bonds. The
NMR results are consistent with FT-IR (SI Figure 10, 11, 12 and 13 in
ESI). The addition of AlCl3 directly leads to the decrease of signals of
carbonyl and methylene of ethyl acetate (SI Figure 12). Moreover,
different mole ratio of aluminum chloride and ethyl acetate were
investigated using NMR spectra (SI Figure 14 and 15). The changes
of the signals of methyl connected with carbonyl and methylene
connected with oxygen are obvious, which indicate that the Al ion
attack the ester bond (SI Figure 15). In addition, we noticed that the
signal of H of carboxyl in acetic acid disappeared when AlCl3 was
added, as indicated by the 1H-NMR spectrum (SI Figure 11). This
result indicates that the addition of Al ions promotes the
dissociation of acetic acid. The formed CH3COO- ions would be
more active than acetic acid molecules towards acyl exchange
reaction. Combined with the above results, the possible reaction
mechanism for decomposing PMPPS is illustrated in Scheme 2. Al
ion attacks oxygen atom of C=O in ester group of PMPPS, leading to
the formation of carbenium ion; the acyl exchange reaction takes
PMPPS
68.53
6.09
4.83
6.62
4.80
25.38
33.57
16.40
36.87
0.00
14.14
0.05
3.95
product 1 19.19
product 2 73.77
product 3 38.96
(a)
(b)
(c)
(d)
200
150
100
50
0
Chemical shift/ppm
Figure 3. Solid state 13C-NMR graphs of PMPPS and its degradation
products: (a) PMPPS, (b) product 1, (c) product 2, (d) product 3.
The compositions of degradation products are illustrated in
scheme 1 based on the above characterizations. Specifically, part of
the C-O bond in ester group of PMPPS were cleaved by
AlCl3/CH3COOH system, leading to the formation of polyaddition
products of maleic anhydride and styrene, phthalic acid and 1,2-
propylene glycol diacetate. It is noticed that although 1,2-propylene
glycol diacetate was detected by GC, its content in the degradation
products was trace (see SI Figure 7(a) in ESI). This unexpected low
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place between acetate ions and ester bond of PMPPS, resulting in
the cleavage of C-O bonds of PMPPS. To verify this hypothesis, ethyl
butyrate was chosen as the model for PMPPS, and the reaction was
performed in 10 wt% AlCl3/CH3COOH system at 180 oC. As expected,
ethyl acetate was produced with the diminishing of ethyl butyrate
(SI Figure 16 and SI Table 4 in ESI). The formation of ethyl acetate
ascertains the above hypothesis, that is, Al ions catalyze the acyl
exchange reaction between acetate ions and ester bond of PMPPS.
Therefore, the high efficiency of AlCl3/CH3COOH system for
decomposing PMPPS originates from not only the catalytic effect of
AlCl3, but also the participation of acetic acid in the reaction.
8
10
10
10
10
10
160
180
180
180
180
12
9
swollen
100
9
10
11
12
8
63.94
23.44
1.27
7
6
[a] AlCl3 as catalyst. [b] Rd: degradation ratio.
The effects of AlCl3 concentration and conditions on the
degradation behaviors of PMPPS were investigated (Table 4, entries
1-5). The PMPPS decomposed completely in 12 h with the AlCl3
concentration no less than 10%. The degradation behaviors of
PMPPS in 7 wt% and 10 wt% AlCl3/CH3COOH system were
further investigated at 180 oC. The results are as shown in SI
Figure 17, SI Table 5 and SI Table 6 in the supporting information.
The results clearly show that the degradation of PMPPS in 7 wt%
AlCl3/CH3COOH delayed about 5 hours compared with 10 wt%
AlCl3/CH3COOH. The rational reason can be explained by the
variation in the mass transfer rates of Al ions. It needs a period of
time for enough Al ions in CH3COOH to enter the matrix of UPR
and decompose UPR. More time would be needed for 7 wt%
AlCl3/CH3COOH to reach required Al concentration to decompose
PMPPS, in comparison with 10 wt% AlCl3/CH3COOH. The
aluminum contents in residual UPR in 7 wt% and 10 wt%
AlCl3/CH3COOH systems were detected during the degradation
process. As shown in SI Table 5 and SI Table 6, it took 12 hours
for the aluminum content in residual UPR to reach 0.3095 wt% in
7 wt% AlCl3/CH3COOH system, whereas it needed 6 hours for 10
wt% AlCl3/CH3COOH system to reach similar Al content. The
PMPPS can decompose into monomers and their derivatives
completely in 10 wt% AlCl3/CH3COOH when the reaction
temperature increases to 180 oC (Table 4, entries 1 and 6-8). The
decomposition time has a significant effect on the degradation
process of PMPPS because the mass transfer, that is the diffusion of
active centers (catalyst) into the matrix of PMPPS, is a dynamic-
controlled process. It took 9 hours to degrade PMPPS completely.
Thus, 12 h was selected to guarantee the complete degradation of
PMPPS (Table 4, 9-12).
Figure 4. SEM graphs of: (a) Virgin GF, (b) Recycled GF from GFRP.
The degradation of GFRP was carried out in the same condition
with that of PMPPS (10 wt% AlCl3/CH3COOH system, 180 oC, 9 h).
Glass fiber (GF) was recycled from GFRP (SI Figure 18 in ESI). SEM
results demonstrated that the recovered GFs were as clean and
smooth as virgin GFs (Figure 4). The monofilament tensile strength
of virgin glass fiber is 1783 MPa, while that of recycled glass fiber is
1719 MPa. The tensile strengths of the recovered GFs maintained
more than 96% of original one (SI Figure 19 in ESI). These results
indicate the effectiveness of AlCl3/CH3COOH degradation system on
recycling valuable GFs from their composites.
Table 4. The degradation of PMPPS in different conditions. [a]
Conclusions
[b]
Entry
Percentage/
wt%
Temp./
°C
Time/h
Rd
We reported a green and effective method for decomposing
UPR and its composites waste (GFRP) by AlCl3/CH3COOH system.
AlCl3/CH3COOH system enables the selective cleavage of C-O bond
in ester chains of UPR, leaving the carbon skeleton intact. This
process facilitates not only the recovery of valuable carbon skeleton
of UPR and other chemicals, but also favors recycling of GF from
GFRP. More than 91 wt% of monomers and oligomers can be
recycled from UPR.
1
2
3
4
5
6
7
10
7
180
180
180
180
180
190
170
12
12
12
12
12
12
12
100
9.92
5
swollen
swollen
swollen
100
3
1
In the degradation process, AlCl3 interacts with C=O bond in
ester chain of UPR, leading to the formation of carbenium ions. This
process promotes acyl exchange reaction between acetic acid and
10
10
5.11
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DOI: 10.1039/C5GC01048A
COMMUNICATION
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Green Chemistry
View Article Online
DOI: 10.1039/C5GC01048A
Graphical abstract
Chemical Recycling of Unsaturated Polyester Resin and Its
Composites via Selective Cleavage of ester Bond
Yuqi Wang,a,b Xiaojing Cui,a Qiqi Yang,c Tiansheng Deng,*a Yingxiong Wang,a Yongxing Yang,a Shiyu
Jia,a Zhangfeng Qina and Xianglin Hou*a
CH3
H2
O
C
O
C
CH3
O
O
O
O
H2
C
H
O
O
C
C
O
O
C
C
H
O
O
C
H
O
O
O
H
O
C
O
C
CH2
O
O
CH3CH3
O
O
CH
n
O
O
AlCl3/CH3COOH
O
C
C
O
C
O
H2
C
H
C
H
C
H
C
H
C
+
+
C
CH3
H2
O
C
O
C
CH3
O
n
H
H2
C
H
O
C
O
C
O
C
C
C
C
C O
H
H3
C
H
CH2
H
H
CH2
CH
O
unsaturated polyester resin
Al3+
Al3+
O
O
O
Al3+
R2
R2
R1
R1
O
O
O
O
O
R2
O
CH3
R1
CH3
O
Unsaturated polyester resin (UPR) is recycled by AlCl3/CH3COOH degradation system via
selectively cleaving ester bond.