Permeability of Organic Vapours through PLA

The transport of organic compound in PLA has been the subject of only a few studies, but is of importance in food packaging applications. Ethylene, 

The transport coefficients of ethyl acetate, an aroma booster found in a large variety of aroma formulations, have been calculated from sorption of ethyl acetate in PLA experiments. The ethyl acetate permeability of PLA is 5.34 x 10 kg.m.m. s Pa at 30°C and 0.3 activity. It is higher than the one of PET but lower than those of PP and LDPE. However, the ethyl acetate solubility coefficient in PLA, equal to 6.17 xlfi kg.m. Pa at 30°C and 0.3 activity, is higher than the other polymers [140]. This result is comparable to the value reported by Colomines et al. for an amorphous PLA with 99% L-lactide content at 25°C and 0.5 activity [125]. Moreover, increasing the crystallinity of PDLLA provokes a decrease of the ethyl acetate solubility coefficient at 0.5 and 0.9 activity [125]. 

The permeability of hmonene through PLA, has been estimated by Auras et al. [140]. at a maximal value of 9.96 xlO kg.m.m. s lPa at 45°C and with a limonene partial pressure of 258 Pa. The permeabihty value of this more hydro-phobic molecule is lower than that of ethyl acetate in PLA and is lower than those measured for PET, PP and LDPE [140]. Haugaard et al. have confirmed the low limonene sorption in PLA by comparison with the one in HDPE [141]. 

The study of scalping aroma compounds by PLA during high pressure treatment highlighted the lower PLA uptake of organic molecules compared to the one in LDPE. Indeed, ethyl hexanoate and limonene are more sorbed in the more apolar matrix, LDPE, than in PLA. On the contrary, the more polar molecules, 2-hexanone and ethyl butanoate, are more sorbed by the more polar polymer matrix, PLA [142]. 

Consequently, it appears that the L/D ratio of PLA influences the gas permeability but no conclusion can be reached regarding the water vapour transport in this pol)uner. Moreover, generally speaking, the crystallization of the PLA matrix makes it possible to decrease the gas permeability and the organic compound sorption in PLA. However, no agreement has been formed regarding the influence of crystallinity degree on water vapour transport in PLA due to the variety of PLA composition (L-lactic acid content) and measurement systems. 

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