Thermal and Barrier Characterisation of Polyethylene F ilm as Food Packaging Material

1. 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 ( ). 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 2Rudjer Bošković Institute, Bijenička 54, HR-10000 Zagreb, Croatia 3University of Zagreb,Faculty of Food Technology and Biotechnology, Pierottijeva 6, HR-10000 Zagreb, Croatia valic@irb.hr 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 Table 1.Gass transition temperature and degree of crystallinity determined by DSC for the samples with different exposure conditions 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 • 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 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. References • 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. Figure 3.Results of WVTR measurements, for PE film, in a function of exposure temperature for different exposure times Figure 4.Results of WVTR measurementsfor 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.