Individual partner report
ENVIROPAK
Third year report
Partner no: 2
Partner name: Istituto per i Materiali Compositi e Biomedici (IMCB-CNR)
Structure
1.
Activities
a.
Work package no: 4
i.
Progress: extrusion of zein proteins without the use of a premixing phase
was performed and was optimized. Both hydrophilic and hydrophobic
plasticizers were used. Kafirin films were produced with an internal
mixer and with several plasticizers. The effect of processing conditions
and material compositions on the final properties were investigated.
ii.
Film blowing of plasticized zein was investigated and optimized.
iii. Problems: films blowing was performed on zein due to the limited
amount of extracted kafirin
2.
Deliverables
Deliverable
Number Title
D19
3.
Report on definition of methods
to produce thermoplastic films
Date
Status
Month 32
Complete
Partner
responsible
2
Exchanges and training
4.
Materials and methods
4.1 Materials
 Zein protein was purchased from Aldrich.
 Kafirin was supplied by the group from CSIR, Pretoria (batches 2 and 4).
 Plasticizers investigated were lactic acid, PEG400, oleic acid and stearic
acid.
4.2 Extrusion
Plasticized zein was produced by using a lab-scale extruder. The extruder was
a conical counter rotating with screw diameter from 35 to 25 mm and 400 mm
lenght. Zein and PEG (at constant composition of 25%wt of plasticizer) were
manually mixed before feeding into the extruder. The temperature of the two final
zones of the extruder was changed from 65 to 85°C. The feeding zone was cooled
to avoid zein/PEG mixture to stack to the screws. The screw speed was changed
from 20 to 120 to analyze the effects of residence time and of mechanical shear
on the final properties of the plasticized zein. The total mass flow was varied
according to the screw speed from 5 g/min (at 20 rpm) to 30 g/min (at 120 rpm).
1
Individual partner report
ENVIROPAK
Third year report
4.3 Mixing
Kafirin proteins from the two batches were mixed with a suitable plasticizer in a
beaker, and then the mixer (HAAKE Rheocord mod. 9000) was used to prepare a
homogenuous mixture. The temperature was changed from 30 to 70°C and the
screw speed varied from 50 to 100 rpm.
4.4 Film preparation
A COLLIN P300P press was used to prepare the plasticized biofilms. Samples
were heated at the temperature employed during mixing and extrusion, and
pressed at 3.0 MPa for 3 minutes, then cooled to 30 °C under the pressure.
Thermoplastic zein, prepared at 80°C and 80 rpm and containing 25% of
PEG400 was used to fed a lab scale film blowing equipment. The optimum
temperature along the extruder were 70, 85, 85, 100°C. The temperature at the die
was 105°C.
4.5 Tensile test
Tensile testing of the plasticized films was carried out by using an Instron
machine model 4204. Five trials for each sample were tested at a constant speed
(1mm/min for the zein films and 10mm/min for the kafirin films). These samples
had a dog bone shape with 22 mm as gage length and were conditioned at
50%RH and at 25±3°C for 48h.
4.6 Permeability of plasticized films
Water permeability of extruded zein films was measured by a permeabilimeter
Permatran (Mocon, Model W 3/31, Neuwied, Germany). Samples were tested at
25°C, by changing water activities from 0.35 to 0.85. Dry nitrogen was used as
carrier, with a 100 sccm/min flux speed. Oxygen permeability was measured by a
OxTran (Mocon, Model 2/20, Neuwied, Germany), with a nitrogen flux speed of 10
sccm/min.
5.
Results and discussion
5.1 Zein extrusion
Zein/plasticizer composition was directly fed into the extruder, without first
solubilizing the zein protein in water/ethanol solution, as described in the literature.
Plasticized zein mixtures were extruded at different temperature and speed of
rotation, at fixed feed rate. Table 1 reports the effect of screw speed on the tensile
behaviour of extruded films, at constant temperature of 80°C and feed rate of
2.5g/min.
Table 1: results of the tensile testing on extruded zein
Screw speed (rpm)
E (MPa)
R (MPa)
R (mm/mm)
40
134.6±22.8
2.28±0.08
0.81±0.18
80
110.6±12.5
1.66±0.38
1.25±0.22
120
66.0±11.3
0.83±0.08
1.93±0.44
The effect of temperature is described in Figures1-3.
2
Individual partner report
ENVIROPAK
Third year report
1400
1200
1000
800
600
70°C
75°C
80°C
400
200
0
20
40
60
80
100
120
140
160
screw speed (rpm)
Figure 1. Effect of temperature and screw speed on the elastic modulus of extruded zein
20
70°C
75°C
80°C
15
10
5
0
0
20
40
60
80
100
120
140
screw speed (rpm)
Figure 2. Effect of temperature and screw speed on the tensile strenght of extruded zein
70°C
75°C
80°C
0,25
0,2
0,15
0,1
0,05
0
0
20
40
60
80
100
120
140
screw speed (rpm)
Figure 3. Effect of temperature and screw speed on the strain at break of extruded zein
Extruded materials at 80°C are, at all screw speeds, more rigid and stiff, while,
as a counterpart, are less deformable.
The type of plasticizer strongly affect the mechanical properties of the extruded
zein. Table 2 summarizes the results. Stearic acid led to improved stiffness and
elasticity of plasticized zein films, with a decrease of the deformation at break.
3
Individual partner report
ENVIROPAK
Third year report
Table 2: results of the tensile testing on extruded zein
Plasticizer
E (MPa)
R (MPa)
R (mm/mm)
type
PEG 400
8.060.48
0.110.0015
516.8445.16
Stearic acid
17.916.33
0.0230.016
130262.285
Figure 4 reports the results of water permeability tests performed on plasticized
zein.
3.00E-07
Extruded 20 rpm
Extruded 40 rpm
Water Permeability
2.50E-07
Extruded 80 rpm
Extruded 120 rpm
2.00E-07
Casting - PEG
1.50E-07
1.00E-07
5.00E-08
0.00E+00
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
Water activity
Figure 4. Results of the water permeability tests. The data are in g*cm/(cm2*s*atm)
Figure 5 reports the results of oxygen permeability tests performed on
plasticized zein.
1.20E-06
Extruded 20 rpm
Extruded 40 rpm
Oxygen Permeability
1.00E-06
Extruded 80 rpm
Extruded 120 rpm
Casting - PEG
8.00E-07
6.00E-07
4.00E-07
2.00E-07
0.00E+00
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
Water activity
Figure 5. Results of the oxygen permeability tests. Data are in cm3*m/(m2*s*atm)
Both water and oxygen permeabilities were scarcely affected by the process
variables and by the type of plasticization process (in the figures, a film produced
by casting is compared to the extruded films).
5.1 Kafirin films
Figure 6 reports the effects of temperature on the tensile response of kafirin
plasticized with PEG400 at 50rpm and 10min, at indicated temperatures.
4
Individual partner report
ENVIROPAK
Third year report
5
4
3
2
30°C
38°C
45°C
1
0
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Strain (mm/mm)
Figure 6. Stress-strain curves for thermoplasticized kafirin
An optimum temperature of 38°C was selected, as also reported in Table 3.
Table 3: results of the tensile testing on kafirin films, effect of mixing
temperature
T
E (MPa)
R (MPa)
R (mm/mm)
30°C
3.310.43
0.690.12
157.7440.14
38°C
4.770.44
0.680.13
172.3313.11
45°C
2.970.56
0.720.12
107.9612.02
The effect of plasticizer type is described by Figure 7 and Table 4:
4
3,5
Acido lattico
PEG 400
3
2,5
2
1,5
1
0,5
0
0
0,5
1
1,5
Strain (mm/mm)
Figure 7. Effect of plasticizer type on the tensile behaviour of kafirin films
In this case, lactic acid led to more deformable materials, while the PEG400
plasticized films were more rigid.
Table 4: results of the tensile testing on kafirin films, effect of plasticizer type
Plasticizer
E (MPa)
R (MPa)
R (mm/mm)
type
PEG 400
2.970.56
0.720.12
107.9612.02
Lactic acid
1.480.11
1.170.25
38.546.37
5
Individual partner report
ENVIROPAK
Third year report
Films blowing
a)
b)
c)
Figure 8: Film blowing of thermoplastic protein
6
Individual partner report
ENVIROPAK
Third year report
Pictures in figure 8 show the film bubble during film blowing process of
thermoplastic zein. The technology consist in extruding a cilinder of small diameter
that, before solidification, is blown with pressurized air. The pressure inside the
bubble determines the increase of the bubble and a strong decrease of thickness.
The bubble is closed at the top by the action of two rolls and, in this way, the gas
is kept inside the bubble. During the process the film is cooled and it solidify before
reaching the two rolls.
The material is subject to elongational flow in both longitudinal and radial
directions (biaxial elongational flow). For this reason the material must posses
suitable rheological properties and in particular a suitable melt strength. This
features can be optimized by a proper combination of the material composition
(type and % of plasticizer), termoplasticization conditions, moisture content, films
blowing parameters. The final thickness of the blown films was about 80m.
6 Conclusions
Plasticization of zein and kafirin proteins was extensively conducted and the
effects of the process parameters and plasticizer content on the mechanical
properties of the films were evaluated. The film of both zein and kafirin were
greatly affected by the plasticizer type, being it hydrophilic or hydrophobic.
Permeabilities to water and oxygen were measured and revealed a minor effect of
the processing variables. Films with thermoplastic zein were successfully prepared
by using a film blowing technique with thermoplastic zein containing 25% of
PEG400 as plasticizer.
Statistics report
(For EU statistics)
Number of
Totals
communications in conferences
communications in media
publications in refereed journals
articles/books
other publications
2
1
PhDs
Mscs
visiting scientists
exchanges (> 3 months)
1
2
1
2
patent application patents granted
companies created
prototypes/products developed
norms/standards developed
softwares/codes developed
production processes
5
3
7
Individual partner report
ENVIROPAK
Third year report
industrial contacts (yes/no)
financial contribution by industry (yes/no)
large industry partners (yes/no)
SME industry partners (yes/no)
yes
8