Abstract We examined an improved preparation method
of recycled unsaturated polyester resin from recovered
monomeric materials obtained from the depolymerization
of fi ber-reinforced plastics (FRPs). The formation of unsat-
urated polyester progressed smoothly in the presence of
catalytic amounts of Ca(OAc)

2

and Ti(OBu)

4

. The quality

of the resin was estimated by the durometer hardness test.
The strength test of FRP board prepared from recycled
resin showed suffi cient hardness for practical use (about
94% of the tensile strength of new resin). We examined the
recycled resin by using it to mold successfully an actual test
product.

Key words Chemical recycling · Recycled resins · Hardness
test · Acid catalysts · Unsaturated polyester

Introduction

Waste fi ber-reinforced plastic (FRP) has been causing
serious environmental problems. Appropriate and conve-
nient disposal of waste FRP is very diffi cult due to its
mechanical strength and chemical stability. As a result,
most waste FRP is either incinerated or disposed off in
landfi lls. FRP is made from carbon sources that are primar-
ily derived from petroleum. Therefore, from the perspec-
tive of carbon source conservation, suitable recycling of
waste FRP is strongly desired. However, waste FRP con-
tains a thermosetting resin whose material recycling is not
easy. In addition, the glass fi bers present in FRP cause
serious problems in incinerators when being thermally
treated for energy recycling. Chemical recycling is a process
in which waste FRP yields monomeric materials that are

recycled as feedstock. This is regarded as the only proce-
dure likely to improve the prospect for proper recycling of
FRP.

1

There have been several reports on the chemical

recycling of FRP; most of them use the glass fi bers or part
of the resin.

2–14

Recently, we reported a novel solubilization

of waste FRP under supercritical methanol conditions in the
presence of 4-dimethylaminopyridine (DMAP). In this
process, the ingredients of FRP, i.e., monomer derivative,
linker, glass fi ber, and calcium carbonate, were separated
in a simple operation.

15

From the recovered monomeric

material and glass fi ber, the possibility of the formation
of recycled plastic was examined.

16,17

However, further

improvements in the formation of recycled resin are neces-
sary to make our method practical and widely applicable.
This article reports an improved formation of recycled resin
as well as on the mechanical strength of an FRP test product
prepared using this resin.

Experimental

Depolymerization of FRP and preparation of recycled
monomer derivatives were performed in a 30-l pilot plant
autoclave following the previously reported procedure.

18

The dimethyl phthalate contents were evaluated by Gas
Chromatography analysis.

Formation of new resins in the presence of Ti(OBu)

4

– a

typical procedure. Dimethyl phthalate (100 g, 0.51 mol)
and propylene glycol (82.3 g, 1.08 mol) were poured into a
1-l separable fl ask and Ca(OAc)

2

(0.647 g, 3.6 mmol) and

Ti(OBu)

4

(0.172 g, 0.51 mmol) were then added. The

mixture was heated at 210°C for 3 h, during which about
27 g of MeOH was distilled out from the mixture. Maleic
anhydride (55.6 g, 0.57 mol) was added to the hot mixture
and the resulting reaction mixture was heated at 220°C for
an additional 3 h. The mixture was then cooled for 2 h.
Styrene monomer (145 g) was added to the mixture and the
entire resin was poured into a plastic beaker (500 ml).
Radical initiator (organic peroxide) and accelerator (cobalt

J Mater Cycles Waste Manag (2010) 12:271–274

© Springer 2010

DOI 10.1007/s10163-010-0296-7

Kazuo Yamada · Fumiaki Tomonaga · Akio Kamimura

Improved preparation of recycled polymers in chemical recycling of fi ber-
reinforced plastics and molding of test product using recycled polymers

K. Yamada · A. Kamimura (*)
Department of Applied Molecular Bioscience, Graduate School of
Medicine, Yamaguchi University, Ube 755-8611, Japan
Tel.

+

81-836-85-9231; Fax

+

81-836-85-9201

e-mail: [e-mail]

K. Yamada · F. Tomonaga
Yamaguchi Prefectural Industrial Technology Institute, Ube, Japan

Received: October 12, 2009 / Accepted: March 16, 2010

ORIGINAL ARTICLE

272

naphthenate) were added to the mixture, which yielded an
unsaturated polyester polymer plate. The quality of the
resin was estimated by the durometer hardness of the cured
product.

Preparation of recycled resins on a larger scale – typical
procedure. Reagent grade dimethyl phthalate (1.70 kg,
8.75 mol) and propylene glycol (1.524 kg, 20 mol) were
mixed, and to the mixture, recovered dimethyl phthalate
(57% purity, 3.2 kg, 9.4 mol), Ti(OBu)

4

(1 g), and Ca(OAc)

2

(5.7 g) were added. The mixture was heated at 200°C to
remove MeOH (545

g). Maleic anhydride (1.957

kg,

20.0 mol) was then added to the hot mixture and heated at
200°C for several hours to remove MeOH and water. This
crude polyester was cooled and transferred to an appropriate
vessel. Styrene (5.12 kg) and radical initiator were added to
start the radical polymerization. After curing, 7.73 kg of
recycled unsaturated polyester resin was obtained.

Molding of FRP board

FRP board was molded using a hand lay-up molding
method. Six 450-g/m

3

glass fi ber strand mats were set into

a stainless mold (150 mm

×

160 mm

×

5 mm cavity) that was

coated with mold lubricant. These mats were then
impregnated with the resin. The mold was pressed by a
metal plate and allowed to stand at 35°C in a thermostatically
controlled oven.

Strength test of FRP

Test pieces of the molded FRP board were examined at
25°C and 55% humidity. Tensile and bending strength were
tested according to the Japanese Industrial Standards (JIS)
K7113 and K7013. Charpy impact tests were performed
according to JIS K7061 in the fl atwise direction. Barcol
hardness was examined by Type A of JIS K7060.

Results and discussion

Waste FRP was depolymerized under standard conditions
(Scheme 1). We avoided using DMAP as a catalyst to facili-
tate the later polymerization reactions using recovered
materials, as has been discussed previously.

18

When resin was synthesized from the recycled monomer

under standard conditions, there was a problem with insuf-
fi cient hardness after curing. We attributed this to an insuf-
fi cient progress of the ester exchange reaction during
polyester formation. In fact, the amounts of MeOH distilled
out during the conventional esterifi cation reaction were
estimated to be less than the calculated amounts. Since the
recovered material usually contains undesirable impurities
that may negatively affect the Lewis acidity of Ca(OAc)

2

,

the rate of the ester exchange reaction decreased. To
increase the reaction rate, a stronger Lewis acid seemed
appropriate. Titanium alkoxide is known as moderately
strong Lewis acid and its acidity can be considered to be
higher than that of Ca(OAc)

2

. We examined commercially

available Ti(OBu)

4

to be used as a co-catalyst for the reac-

tion. The reaction was optimized using freshly purchased
dimethyl phthalate for these experiments (Scheme 2). As
expected, when a mixture of Ti(OBu)

4

and Ca(OAc)

2

was

added to the reaction, the amounts of MeOH that were
distilled out increased and the formation of the polyester
was accelerated. The results are summarized in Table 1.

In Table 1, certain combinations of catalysts did not

improve the transesterifi cation. We marked such entries,
where less than 70% of MeOH distilled out during the reac-
tion, with an x. In contrast, resins were successfully formed
in those reactions where more than 70% of MeOH was
distilled out. The durometer hardness of these products is
summarized in Table 1. It should be noted that most of the
resins formed under these conditions were suffi ciently hard
and of good quality because their durometer hardness
values exceeded 80. Thus, the addition of Ti(OBu)

4

enabled

acceleration of the reaction and promoted better resin for-
mation. The best hardness was observed in the resin formed
when 0.72 mol% of Ca(OAc)

2

and 0.1 mol% of Ti(OBu)

4

FRP
flakes

supercritical MeOH
275 °C

MeOH-soluble oil

insoluble inorganic residue

+

Scheme 1. Depolymerization of waste fi ber-reinforced plastic (FRP)

CO

2

Me

CO

2

Me

OH

OH

+

Ca(OAc)

2

Ti(OBu)

4

O

O

O

+

styrene
radical initiator

unsaturated
polyester

Scheme 2. Optimization of the resin formation from dimethyl phthalate and glycol

Table 1. Durometer hardness of polymer

Ca(OAc)

2

(mol% vs DMP)

Ti(OBu)

4

(mol% vs DMP)

0.00

0.05

0.10

0.15

0.20

0.25

0

×

×

0.18

×

×

0.36

×

83

86

0.54

×

86

86

86

0.72

87

0.9

×

86

87

Durometer hardness (HDD) of cured product using new resin was 88
DMP, dimethyl phthlate;

×

, transesterifi cation was not improved

273

were used. We applied these conditions to the large-scale
preparation of recycled resin as the optimum reaction
conditions.

We next performed strength tests on recycled FRP pre-

pared from the recovered materials. The outline of the pro-
cedure is summarized in Scheme 3. Three types of FRPs
were formed by our method; the molding conditions used
are summarized in Table 2. Type A FRP was made with
new resin and was used as a control; types B and C were
recycled resins prepared from recovered materials. Type C
was made from 100% recycled material and type B was
made from an equal (50:50) blend of new and recovered
materials. We performed several tests with the three types
of FRPs and the results are shown in Figs. 1–3.

Figure 1 represents the results of the Barcol hardness

tests on the FRPs. As the contents of recovered materials
increased, the hardness decreased slightly. However, the
decrease in hardness was only about 2% and so this may
not be considered as a serious defect. The mechanical
strengths of the FRPs were then determined (Fig. 2). As
shown in Fig. 2, the tensile strengths were approximately
the same for both the new and recycled resins. It is interest-

ing to note that the bending strengths for the recycled resin
were slightly higher than those for the new resin.

Figure 3 represents the results for the Charpy impact test

on the resins. It was again observed that FRPs B and C
molded using recovered materials were stronger than the
newly formed FRP A. These unexpectedly superior quali-
ties of recycled FRP are probably due to their increased
softness as compared to the newly formed FRP. Thus, the
impurities in the recovered materials made the recycled
resins softer than the newly formed resins. This was due to
incomplete polymerization. The softness provided slightly
better results for the bending test and impact strength. In
the bending test, tensile stress occurs on the outside of the
bent section, and when transformation of the stretched
resin exceeds the limit, failure occurs. Since the soft resin
followed this transformation more closely, its bending

Recovered material

+

CO

2

Me

CO

2

Me

OH

OH

+

O

O

O

+

Ca(OAc)

2

Ti(OBu)

4

styrene
radical initiator

recycled FRP

glass fiber mat

Scheme 3. The formation of recycled FRP

Table 2. Conditions for the formation of recycled fi ber-reinforced
plastic (FRP)

TYPE

Resin used

Glass fi ber content

(wt% vs total amount)

(wt% vs FRP)

A

New resin 100

38

B

New 50

+

recycled 50

39

C

Recycled resin 100

39

40

42

44

46

48

A

B

C

Barcol hardness (HBI-A)

Fig. 1. Barcol hardness of recycled fi ber-reinforced plastic (FRP)

0

50

100

150

200

250

A

B

C

Tensile

Bending

Strength(MPa)

Fig. 2. Mechanical strength of recycled FRP

0

20

40

60

80

100

120

140

A

B

C

Charpy impact strength (kJ/m2)

Fig. 3. Charpy impact test on recycled FRP

274

strength became stronger. In the impact test, the resin trans-
formation in a larger area caused absorption of more
energy. Hence, the quality of the recycled FRP was deemed
satisfactory.

Finally, we performed resin production on a large scale

and used it to prepare a test product. We chose the lid of a
composter in which food garbage is recycled into compost
as the test product. A total of 20 wt% of recycled resin was
used for the production of the material. The production
went smoothly, and the test product was prepared success-
fully. Figure 4 shows the product. The test product exhib-
ited suffi cient strength and had no problems when an adult
(about 70 kg) stepped on the product. This product was
used in the fi eld for 8 months without any problems.

In conclusion, we developed an improved method for the

preparation of unsaturated polyester, with which we suc-
cessfully prepared recycled plastics on a large scale. Use of
Ti(OBu)

4

effectively catalyzed the resin formation and

shortened the reaction time. The obtained recycled plastic
was of better quality compared to new plastics. We con-
cluded that the successful formation of a recycled test
product will open a new avenue for chemical recycling of
FRP.

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