Chemistry Reference
In-Depth Information
serious physical aging during application. Moreover, PLA is a much more expensive
material than the common industrial polymers.
Many efforts have been made to develop PLA/starch blends to reduce total raw
materials cost and enhance their degradability. The major problem of this blend system
is the poor interfacial interaction between hydrophilic starch granules and hydropho-
bic PLA. Mechanical properties of blends of PLA and starch using conventional pro-
cesses are very poor because of incompatibility. In order to improve the compatibility
between hydrophilic starch granules and hydrophobic PLA, glycerol, formamide, and
water are used alone or combined as plasticizers to enhance the dispersion and the
interfacial affi nity in TPS/PLA blends. In the presence of water and other plasticizers
including glycerol, sorbitol, urea, and formamide, the strong intermolecular and intra-
molecular hydrogen bonds in starch can be weakened.
To improve the compatibility between PLA and starch, suitable compatibilizer
should be added.
Besides, gelatinization of starch is also a good method to enhance the interfacial
affi nity. Starch is gelatinized to disintegrate granules and overcome the strong interac-
tion of starch molecules in the presence of water and other plasticizers, which leads to
well dispersion. The glass transition temperature and mechanical properties of TPS/
PLA blend depend on its composition and the content of plasticizer as well (Table 3.1),
indicating the compatibility between PLA and TPS is low but some degree of interac-
tion is formed.
Table 3.1.
Thermal and mechanical properties of thermoplastic starch/polylactide (TPS/PLA) blends.
Content of TPS [wt%]
T
g
[°C]
Tensile Strength [MPa] Elongation at Break [%]
PLA
TPS
100 (TPS1)
a
-
10
3.4
152.0
90 (TPS1)
47
NF
b
2.9
48.8
75 (TPS1)
100 (TPS2)
a
53
-
NF
43
4.8
19.5
5.7
2.8
90 (TPS2)
NF
NF
14.1
1.3
0.9
9.4
a
the content
of glycerol and water in TPS1 and PTS2 are 18 and 12, 10 and 16 wt% respectively
b
Tg value is not found in the literature
75 (TPS2)
0
NF
58
NF
-
12.0
68.4
The PCL is another important member of synthetic biodegradable polymer family. It
is linear, hydrophobic, partially crystalline polyester, and can be slowly degraded by
microbes. Blends between starch and PCL have been well documented in the litera-
tures. The weakness of pure starch materials including low resilience, high moisture
sensitivity, and high shrinkage has been overcome by adding PCL to starch matrix even
at low PCL concentration. Blending with PCL, the impact resistance and the dimen-
sional stability of native starch is improved signifi cantly. The glass transition temperature
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