Chemistry Reference
In-Depth Information
Table 7.4 Mechanical properties of various plastics.
Plastic type
s
u
/MPa
E/MPa
%El
Reference
Thermoplastic:
PP
27
1300
200-700
74
PS
48
3400
3
28
HDPE-extrusion
16.5
155
220
29
HDPE-injection molding
21
340
100
74
PE
20-30
700
20-100
74
PVC
48
3400
200
74
Thermoset:
Urea Formaldehyde,
cellulose filled
38-90
7000-10000
1
74
Epoxy resin, glass filler
68-2000
20 000
4
74
Phenol formaldehyde,
mica filled
38-50
17 000-35 000
0.5
74
Biodegradable:
PLA
60-70
500-570
9-15
29
7.6 Poly(lactic acid)/Citrate Glyceride Blends
PLA can be mixed with various fillers and ingredients to obtain composite
blends with novel mechanical or bio-degradable properties, or to reduce the
cost.
27,46,62
Blending PLA with thermoplastic starch has become widespread
in the bio-plastic community during the last 10 years.
13,42,62,65,66
Citric acid
esters in PLA blends serve as plasticizers.
67
Since the cost of the CAG is
considerably less than PLA, we conducted a study to evaluate the mechanical
properties of PLA-CAG composites. A 1 : 1 molar ratio of citric acid to glycerol
polyester was prepared by microwaving heating as previous described.
27,28,46
The CAG polyester was then further cured for 48 h at 100 1C and ground into
a powder with a Wiley mill employing a 1 mm screen. Ground CAG powder
was mixed with PLA at various concentrations (10-70%) and extruded
through with a single-screw extruder (C. W. Brabender, South Hackensack,
NJ) at four temperatures (150, 170, 170 and 150 1C) from the feed throat to
the die. A 3 : 1 high shear mixing zone screw was employed with a hangar-type
die (254 mm
1.5 mm opening) at 150 1C. Ribbons were ground in a Wiley
mill through a 3 mm screen and reintroduced into the extruder to facilitate
homogenous blending of the CAG polyester in the PLA matrix. PLA-CAG
mixtures containing 60 and 70% CAG could not be extruded as ribbons with
this die, and had to be removed in order to obtain these blended concen-
trations which were subsequently ground. Ribbons of PLA-CAG blends con-
taining 10, 20, 30, 40 and 50% CAG (i.e., PLA-10CAG, PLA-20CAG, PLA-30-CAG,
PLA-40CAG, and PLA-50CAG) were stamped into ASTM D638-99 Type V tensile
bars (60 mm
10 mm). Blends of PLA-CAG containing 60 and 70% CAG (i.e.,
PLA-60CAG and PLA-70CAG) were compression molded in a Model C Carver
hydraulic press at 180 1C under a pressure of 90 MPa per mold for 20 min.
The mechanical values of all tensile bars were evaluated using the Instron
Model 1122 universal testing machine at testing speed of 5 mm min
1
.
