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PROCESSING OF BIODEGRADABLE BLENDS
ALEXY Pavol
Slovak University of Technology in Bratislava Faculty of Chemical and Food Technology
Institute of Polymer Material
Processing properties of chosen biodegradable polymers
Polymer Properties during melt processing
PVA
-high sensitivity to thermal degradation during melt processing - high viscosity of melt -good film forming properties in film blowing technology
PCL
-good thermal stability during melt processing -low viscosity of melt -slow crystallization
PHA
-very sensitive to thermal degradation -molecular weight and viscosity of melt decreas very fast during melt processing -final thin wall products are very brittle
PLA
-good thermal stability during processing in the melt -high sensitivity to moisture during melt processing -good film forming properties -physical ageing , high brittleness of thin wall products
STARCH -high sensitivity to thermal degradation -high viscosity of TPS
These properties affect:
Processing properties
Viscosity at given temperature and shear rate
Sensitivity to degradation under processing condition
Mechanical properties of melt
Morphology of polymer blend
Processing stability of polymer or polymer blend
Final properties of products (mainly mechanical)
Usually : -thermal analysis (DSC, TG, DTA)
-re-extrusion and MFI measurement
Processing stability of biopolymers – testing method
Processing stability of biopolymers and oscillation rheometry
Two basic possibilities of oscillation test mode: Frequency sweep Strain sweep
t
t
Shear rate increases with increasing of deformation
angle at constant frequency
Shear rate increases with increasing deformation
frequency at constant angle
Testing of processing stability using oscillation rheometry
0
500
1000
1500
2000
2500
3000
3500
4000
0 10 20 30 40 50
h* [
Pa.s
]
[1/s]
a) PLA, T = 190°C
Frequency sweep Strain sweep
0
200
400
600
800
1000
1200
0 10 20 30 40 50
h* [
Pa.s
]
[1/s]
b) PHB, T = 190°C
Frequency sweep Strain sweep
0
400
800
1200
1600
2000
0 10 20 30 40 50
h* [
Pa.s
]
[1/s]
c) PCL, T = 190°C
Frequency sweep Strain sweep
Testing of processing stability using oscillation rheometry
Degradation test at constant strain and constant frequency
0
1000
2000
3000
4000
5000
0 10 20 30
h*(
t) [
Pa
.s]
time [min]
PLA
PLA, 170 PLA, 180 PLA, 190
PLA, 200 PLA, 210
0
0,2
0,4
0,6
0,8
1
1,2
0 10 20 30
h*(
t)re
l
time [min]
PLA
PLA, 170 PLA, 180 PLA, 190PLA, 200 PLA, 210
Testing of processing stability using oscillation rheometry
Degradation test at constant strain and constant frequency
0
0,2
0,4
0,6
0,8
1
1,2
0 5 10 15 20 25
h*
rel
(t)
t [min]
T = 210°C
PLA PHB PE PP
20000
25000
30000
35000
40000
45000
50000
55000
0 200 400 600 800
MV [
g.m
ol-
1]
h*(t) [Pa.s]
0
0,2
0,4
0,6
0,8
1
1,2
0 2 4 6 8 10
h*
rel (t
)
time [min]
Testing of processing stability using oscillation rheometry
Effect of moisture on processing stability of PLA
0
50000
100000
150000
200000
250000
300000
350000
400000
0 0,2 0,4 0,6 0,8
Mv [
g.m
ol-
1]
Water content [%]
0.00%
0.05%
0.38%
0.65%
Testing of processing stability using oscillation rheometry
Effect of stabilizers on processing stability of PLA
0
0,2
0,4
0,6
0,8
1
1,2
1,4
0 5 10 15 20 25
h *
rel
(t)
time [min]
T = 170°C
PLA
PLA+S1
PLA+S2
Viscosity relations versus morphology of blends
10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103
103
102
101
100
10-1
Ca kr
it
m1/m2
dispergation
without dispergation s
RCa
.
Viscosity relations versus morphology of blends
Plasticizer content increasing
PLA/TPS blends containing various amount of plasticizer for starch (90%of starch)
Viscosity relations versus morphology of blends
PLA/TPS with regulator of starch viscosity at 50% of starch content
Effect of TPS viscosity modification on mechanical properties
0,00
10,00
20,00
30,00
40,00
50,00
0 0,2 0,4 0,6 0,8 1 1,2
y
[MP
a]
modifier conc. [wt.%] PLA/TPS/M
0
10
20
30
0 0,2 0,4 0,6 0,8 1 1,2
b [
MP
a]
modifier conc. [wt.%] PLA/TPS/M
0
50
100
150
200
250
300
0 0,2 0,4 0,6 0,8 1 1,2
e b [
%]
modifier conc. [wt.%] PLA/TPS/M
Conclusion
New method for processing stability of biodegradable polymers was described based on oscillation rheometry
Oscillation rheometry is suitable also for evaluation of efficiency of stabilisers for biodegradable polymers
Type of created morphology of biodegradable blend is strongly deterimined by processing conditions, mainly by viscosity ratio between blended polymers
In special cases of processing conditions the oriented structures can be created. This leads to reinforced sturctures with enhanced mechanical properties which cannot by
achieved by individual polymeric components of the blend.
Aknowledgement
Prof. Ivan Chodák, DrSc. Prof. Dušan Bakoš, DrSc. Prof. Ivan Hudec, PhD and my PhD. Students: Mirolava Mikušová Katarína Tomanová Michal Mihalík Roderik Plavec
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