Transcript Slide 1

Thermal and Barrier Characterisation
of Polyethylene Film as Food Packaging Material
Srećko Valić1,2, Sunčica Ostojić1, Mia Kurek3, Damir Klepac1, Kata Galić3
of Rijeka, School of Medicine, Braće Branchetta 20, HR-51000 Rijeka, Croatia
2 Rudjer Bošković Institute, Bijenička 54, HR-10000 Zagreb, Croatia
3 University of Zagreb, Faculty of Food Technology and Biotechnology, Pierottijeva 6, HR-10000 Zagreb, Croatia
1 University
[email protected]
Objective
Results
influence of the ethanol model solution on
the
thermal
(glass
transition,
Tg,
temperature, melting point, Tm, degree of
crystallinity, cc) and barrier (water vapour
transmition
rate-WVTR
and
gas
permeability)
of
polyethylene
and
polypropylene films
Materials
Polyethylene film (PE) – thickness 75mm
Ethanol – 15 vol.% water solution
Sample preparation
Samples were exposed to model solution; the
time and temperature of exposure were varied:
Temperature of exposure: 4 ºC, 22 ºC and 40 ºC
Time of exposure: 2 days and 28 days
Figure 1. DSC thermogram of PE films exposed to model solution during a) 2 days at 4 ºC (
and b) 28 days at 4 ºC ( ), 22 ºC ( ), 40 ºC ( ).
Table 1. Gass transition temperature and degree of crystallinity
determined by DSC for the samples with different exposure conditions
EXPOSURE CONDITIONS AND DSC RESULTS
SAMPLE
T / ºC
Time / day
Tg / C
cc / %
PE-4-2
4
2
50
23,05
PE-4-28
4
28
49
22,36
PE-22-2
22
2
50
22,83
PE-22-28
22
28
50
22,33
PE-40-2
40
2
51
23,10
PE-40-28
40
28
55
20,29
), 22 ºC (
), 40 ºC (
Hf
cc 
 100%
Hf ,th
cc - degree of crystallinity (%)
ΔHf - heat of fusion (J g-1)
ΔHf,th - theoretical heat of fusion of
100% crystalline polymer (J g-1)
Methods
106 107
120
differential scanning calorimetry (DSC)
gravimetric determination of WVTR
the mean values of three independent
measurements were calculated for DSC
and gravimetric measurements
conductivity and pH measurements of
ethanol model solution
100
80
Figure 2. Comparison of some parameters
measured for PE-LD. Initial and final states
were: 4 days and 26 days, respectively, for
WVTR and 2 days and 28 days, respectively,
for Tg, Tm and crystallinity measurements.
50.1 48.4
60
value/a.u.
40
23.05 22.36
20
0.2172
0
-20
-1.059
WVTR /
(g/m2day)
Xc / %
Tg / °C
Tm / °C
initial state
-1.059
23.05
50.1
106
final state
0.2172
22.36
48.4
107
parameter
Feldman, D., Polymer Barrier Films. J.
Polym. Environ. 9 (2002) 49-55.
1
0
-1
4 °C
22 °C
40 °C
-2
-3
-4
T/°C
Hu, Y., Topolkaraev, V., Hiltner, A., Baer, E.,
Measurement of water vaportransmission
rate
in
highly
permeable
films.
J.Appl.Polym.Sci. 81 (2001) 1624-1633.
4th day
26th day
WVTR / (g/m 2 day)
Mrkić, S., Galić, K., Ivanković, M., Hamin, S.,
Ciković, N., Gas transport and thermal
characterization
of
monoand
dipolyethylene films used for food packaging.
J. Appl. Polym. Sci. 99 (2006) 1590-1599.
WVTR / (g/m 2 day )
References
1
0
-1
4
26
-2
-3
-4
Exposure tim e / day
4 °C
Figure 3. Results of WVTR measurements, for
PE film, in a function of exposure temperature
for different exposure times
22 °C
40 °C
Figure 4. Results of WVTR measurements for PE
film, in a function of exposure time for different
exposure temperatures
Conclusions
Short exposure time does not lead to any significant changes in thermal behaviour of PE films.
Longer exposure times, particularly at higher temperatures, lead to the shift in glass transition temperature toward higher values and to the
lowering of crystalline phase fraction.
The described effects of model solution on PE induce changes in barrier properties, water vapour transmition rate and gas permeability which
may have a negative influence on the quality of packed food products.
)