ROLE
ROLE OF
OF STRUCTURE
STRUCTURE AND
AND CRYSTALLINITY
CRYSTALLINITY OF
OF SYNTHETIC
SYNTHETIC ALIPHATIC
ALIPHATIC COPOLYESTERS
COPOLYESTERS
ON
ON THEIR
THEIR ENZYMATIC
ENZYMATIC DEGRADATION
DEGRADATION
Paola Rizzarelli**, Giorgio Montaudo*
**Istituto CNR per la Chimica e la Tecnologia dei Materiali Polimerici (ICTMP)
Viale Andrea Doria 6 - 95125 Catania, Italy.
*Dipartimento di Scienze Chimiche, Università di Catania
Viale Andrea Doria 6 - 95125 Catania, Italy.
STRUCTURE and PROPERTIES of the POLYESTERS ANALYSED
Table 1
In recent years, biodegradable polymers have
n°
received much attention and aliphatic polyesters
Samplea
are among the most interesting candidates for
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
biodegradable fibres, films, sheets and bottles.
The rates of enzymatic hydrolysis of polyesters
are in general influenced by a wide variety of
parameters including molar mass, segmental
mobility,
chemical
and
stereochemical
structure1-6, surface area, morphology and
crystallinity7-9.
Crystallinity
Chemical
Structure
Segmental
Mobility
series
of
28000
95400
17800
33600
10500
36150
32600
53400
21900
48300
24000
51700
85000
47800
51800
56700
39700
high
molar
OLIGOMERS
+
1,4-butanediol
values,
chemical
structure
O
O
O
O
to
reaction
increase
in
was
the
the
found
polymer
O
diol
excess was justified by the
n
observation that during the reaction the
O
m
1,4-butanediol
materials showing good filmability. The
O
poly(butylenesuccinate-co-butyleneadipate)
diol was partially removed from the
O
OC H 2 C H 2 CH 2 C H2 O C C H 2 C H 2 C H2 C H 2 C H2 C H 2 C H2 C H 2 C
P(BSu-co-BSe)
process
viscosity and consequently to obtain
O C H2 C H2 C H2 C H2 O C CH2 CH 2 CH 2 CH 2 C
O
O CH 2 CH 2 C H2 C H2 OC C H2 C H 2 C
of
essential
n
m
P(BSu-co-BAd)
polycondensation
polymerisation
O
poly(butylenesebacate)
O C H2 C H2 C H2 C H2 O C CH 2 C H 2 C
flask by the nitrogen stream and by the
n
poly(butylenesuccinate-co-butylenesebacate)
vacuum, restraining the polymerisation
reaction from going ahead.
ENZYMATIC DEGRADATION
FILMS
DIMENSIONS: 20 x 7,5 mm2
AREA: 3 cm2
BIODEGRADATION DEGREE
INITIAL WEIGHT: 20 - 30 mg
THICKNESS: 150 - 200 µm
WEIGHT LOSS
NORMALISED BY INITIAL
SAMPLE SURFACE AREA11
TEMPERATURE: 37 °C
BUFFER: Potassium phosphate (0.1 M)
pH: 7.4
ENZYME
——[-O(CH2)4OCO-(CH2)2-CO-]n—— [-O(CH2)4OCO-(CH2)4,8-CO-]m—— + CH3 OH↑
and
excess
n
poly(butyleneadipate)
PBSe
the
shown in Scheme 1. The use of 10 %
O C H2 C H2 C H2 C H2 OC C H2 CH 2 C H 2 C H 2 CH 2 C H2 CH 2 C H2 C
240 °C, 1h, 1 Torr
acids in order to explore the influence of molar
using
O
O
PBAd
220 °C, 1h, 1 Torr
and
dimethylesters of succinic, adipic and sebacic
mass
poly(butylenesuccinate)
n
O C H2 C H2 C H2 C H2 O CC H 2 CH 2 CH 2 CH 2 C
CH3OH↑
butylenesebacate)s were synthesized by melt
from
PBSu
180 °C, 3 h, N2
Ti (OBu)4
mass
polyesters (Tab. 1) were synthesised by
O
OC H 2 C H 2 C H 2 C H2 O C C H2 C H2 C
n CH3 OCO-(CH 2)2-COOCH3 + m CH3OCO-(CH2)4,8 -COOCH3 + (m + n +10%) HO(CH2)4 OH
poly(butylenesuccinate-co-
polycondensation
O
Scheme 1
poly(butylenesuccinate-co-butyleneadipate)s
and
49700
188800
31500
61400
23500
101500
55800
104000
37000
89500
39500
108800
210000
107000
150800
120000
79900
Tm e Tge Crystallinityf
(°C) (°C)
(%)
114
/
34
116 -33
32
65
/
56
65
-55
39
63
/
/
64
-53
36
106 -42
35
83
-53
17
48
-51
13
56
-53
26
63
/
/
64
-52
35
88
-32
22
80
-45
17
58
-52
11
39
-52
23
48
-53
35
HOMO- and CO-POLYESTERS SYNTHESIS
Configuration
Hydrophilic/
Hydrophobic
Balance
In this work, high molar mass aliphatic
SEC
Mnd
Mwd
a) PBSu = poly(butylenesuccinate); PBSe = poly(butylenesebacate); PBAd = poly(butyleneadipate);
P(BSu-co-BSe) = poly(butylenesuccinate-co-butylenesebacate); P(BSu-co-BAd) = poly(butylenesuccinate-co-butyleneadipate).
b) Carried out in CDCl3
c) Determined in CHCl3 , 30°C.
d) Number-average and weight-average molar masses determined using the calibration curve obtained with PS standards in CHCl3
e) Determined by DSC.
f) Determined using the Vonk’s method10.
Composition
Morphology
A
Molar
Mass
PBSu
PBSu
PBSe
PBSe
PBAd
PBAd
P(BSu-co-BSe)
P(BSu-co-BSe)
P(BSu-co-BSe)
P(BSu-co-BSe)
P(BSu-co-BSe)
P(BSu-co-BSe)
P(BSu-co-BAd)
P(BSu-co-BAd)
P(BSu-co-BAd)
P(BSu-co-BAd)
P(BSu-co-BAd)
Synthesis Compositionb ηsp /cc
1
Method
H-NMR
(dl/g)
I
0.56
II
1.60
I
0.43
II
0.74
I
0.30
II
1.08
I
90/10
0.50
II
70/30
0.95
I
50/50
0.42
II
30/70
0.85
I
10/90
0.39
II
10/90
1.26
II
80/20
2.03
II
70/30
0.91
II
50/50
1.04
II
30/70
1.00
II
20/80
0.77
LIPASE from MUCOR MIEHEI
CONCENTRATION: 100 µg/mL
crystallinity upon their enzymatic degradation.
3
30
2
20
1
10
Figure
Figure 11
0
100
90
80
70
60
50
40
30
BSu Content (mol %)
20
10
30
)
2
3
25
2
2
20
Figure
Figure 22
0
0
100
90
80
BSu Content (mol %)
70
60
50
40
30
20
10
0
P(BSu-co-BAd) 70/30
1
1
15
10
0
w e i g h t l o ss ( m g / c m
4
P(BSu-co-BSe) 70/30
3
4
No rm a l i se d
Mw
37000
35
Crystallinity index (%)
5
4
5
Normalised weight loss (mg/cm2)
Mn
21900
40
6
Mw
89500
50
NORMALISED WEIGHT LOSS in P(BSu-co-BSe) 70/30 and
P(BSu-co-BAd) 70/30 films versus EXPOSURE TIME (20h intervals)
to ENZYMATIC SOLUTION of LIPASE from MUCOR MIEHEI.
40
7
Mn
48300
Normalised weight loss (mg/cm2)
Crystallinity index (%)
60
X-RAY CRYSTALLINITY INDEX and NORMALISED WEIGHT LOSS
in P(BSu-co-BAd) FILMS after ENZYMATIC ATTACK
by LIPASE from MUCOR MIEHEI versus BSu CONTENT
Figure
Figure 3a
3a
0
In Fig. 1 are plotted the degree of X-ray crystallinity
The degree of X-ray crystallinity of P(BSu-co-BAd) copolymer films
The normalised weight loss of P(BSu-
and the normalised weight loss, after enzymatic attack
is plotted in Fig. 2 versus their BSu content. As expected, the
co-BSe) 70/30 and of P(BSu-co-BAd)
by Lipase from Mucor Miehei, of
copolyester films show a minimum crystallinity index. In the
70/30 is plotted in Fig. 3a as a function
copolymer films versus their BSu content.
meantime, the normalised weight loss after enzymatic attack by
of exposure time to enzymatic solution
The normalised weight loss after enzymatic attack by
Lipase
20
30
of Lipase from Mucor Miehei. These
in d e x
Lipase from Mucor Miehei (Fig. 1) shows a maximum
biodegradation degree at 50 mol % of BSu units for the P(BSu-co-
samples have just the same crystallinity
biodegradation degree at 70 mol % of BSu units, even
BAd)
indexes (Fig. 3b).
if this sample has a higher crystallinity index and a
biodegradation. Nevertheless, the degree of crystallinity can’t be
P(BSu-co-BSe) 70/30 shows a higher
higher molar mass than P(BSu-co-BSe) 50/50 sample.
considered the only factor
slope with respect to P(BSu-co-BAd)
Mucor
copolymers.
Miehei
(Fig.
Consequently
2)
shows
crystallinity
a
affects
their
affecting the enzymatic degradation
Increasing BSe content, for P(BSu-co-BSe) 10/90,
behaviour of P(BSu-co-BAd) copolymers. The inspection of the
70/30 and consequently P(BSu-co-BSe)
biodegradation degree decreases but it is however
data in Fig. 2 in fact reveals that the enzymatic biodegradation
70/30 is degraded faster by Lipase from
higher than P(BSu-co-BSe) 70/30 sample that shows a
curve is not symmetric. It is evident in Fig. 2 that the P(BSu-co-
Mucor Miehei, this indicating that
higher
PBSe
BAd) 70/30 sample has a crystallinity index lower than P(BSu-co-
sebacate units induce a higher degree
homopolymer, that has the highest crystallinity index,
BAd) 20/80 and PBAd but it is less susceptible to enzymatic attack,
of
shows a biodegradation degree higher than that of
this points out that adipate units induce a higher degree of
copolyesters.
P(BSu-co-BSe) 70/30 sample.
biodegradability in these copolyesters.
crystallinity
index.
Furthermore
The results indicate that molar mass values show no significant influence on the enzymatic degradation
degree for the polyesters films investigated. The independence of biodegradation degree from variations
in molar mass could point out that the lipase used is an endo-type enzyme that randomly splits ester
bonds in the polymer chain.
Furthermore, it was observed that undoubtedly changes in the degree of crystallinity affects polyesters
biodegradation but polymer chain structure appears to be an important factor that strongly influences
the activity of the lipase from Mucor Miehei in P(BSu-co-BSe) and in P(BSu-co-BAd) copolymers. In
particular, sebacate units appear to induce a higher degree of biodegradability.
biodegradability
in
50
60
70
80
90
100
50
maximum
from
Time (h)
40
60
C r y s t a llin it y
P(BSu-co-BSe)
10
(% )
X-RAY CRYSTALLINITY INDEX and NORMALISED WEIGHT LOSS
in P(BSu-co-BSe) FILMS after ENZYMATIC ATTACK
by LIPASE from MUCOR MIEHEI versus BSu CONTENT
40
P(BSu-co-BSe)
30
20
10
100
P(BSu-co-BAd)
90
Figure
Figure 3b
3b
80
70
60
50
40
30
BSu Content (mol %)
these
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20
10
0