Thermal and Barrier Characterisation of Polyethylene Film as Food Packaging Material

Srećko Valić1,2, Sunčica Ostojić1, Mia Kurek3, Damir Klepac1, Kata Galić3

1 University 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

valic@irb.hr

Objective influence of the ethanol model solution on the thermal (glass transition, Tg, temperature, melting point, Tm, degree of crystallinity, c) and barrier (water vapour transmition rate-WVTR and gas permeability) of polyethylene and polypropylene films

Mrkić, S., Galić, K., Ivanković, M., Hamin, S., Ciković, N., Gas transport and thermal characterization of mono- and di-polyethylene films used for food packaging. J. Appl. Polym. Sci. 99 (2006) 1590-1599.

Feldman, D., Polymer Barrier Films. J. Polym. Environ. 9 (2002) 49-55.

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.

Sample preparation

References

Conclusions

Results

differential scanning calorimetry (DSC)gravimetric determination of WVTRthe mean values of three independent measurements were calculated for DSC and gravimetric measurementsconductivity and pH measurements of ethanol model solution

Methods

c - degree of crystallinity (%)

ΔHf - heat of fusion (J g-1)

ΔHf,th - theoretical heat of fusion of 100% crystalline polymer (J g-1)

,

100%fc

f th

H

H

Table 1. Gass transition temperature and degree of crystallinity determined by DSC for the samples with different exposure conditions

Polyethylene film (PE) – thickness 75m

Ethanol – 15 vol.% water solution

Materials

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 ( ), 22 ºC ( ), 40 ºC ( )and b) 28 days at 4 ºC ( ), 22 ºC ( ), 40 ºC ( ).

EXPOSURE CONDITIONS AND DSC RESULTS SAMPLE T / ºC Time / day Tg / C c / %

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

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.

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.

Figure 3. Results of WVTR measurements, for PE film, in a function of exposure temperature for different exposure times

Figure 4. Results of WVTR measurements for PE film, in a function of exposure time for different exposure temperatures

-4

-3

-2

-1

0

1

4 °C 22 °C 40 °C

T/°C

WV

TR

/ (

g/m

2 day

)

4th day 26th day

-4

-3

-2

-1

0

1

4 26

Exposure time / day

WV

TR

/ (g

/m2 d

ay)

4 °C 22 °C 40 °C

-1.059

0.2172

23.05 22.36

50.1 48.4

106 107

-20

0

20

40

60

80

100

120

value/a.u.

parameter

initial state -1.059 23.05 50.1 106

final state 0.2172 22.36 48.4 107

WVTR / (g/m2day)

Xc / % Tg / °C Tm / °C