Oxygen barrier, protein-based materials

The gas barrier properties (O2, CO2 and ethylene) of protein-based materials are highly attractive since they are minimal under low RH conditions. Oxygen permeability (around 1 amol/m/s/Pa) is comparable to ethylene vinyl alcohol (EVOH) properties (0.2 amol/m/s/Pa) and much lower than the properties of LDPE (1,000 amol/m/s/Pa) [61] (Table 11.12). The O2 permeability of protein films is about 10-fold higher that EVOH-based films, mainly due to the high plasticiser content of protein-based films. 

The barrier properties of protein materials depend on the nature and density of the macro-molecular network, and more particularly on the proportion and distribution of non-polar amino acids relative to polar amino acids [9,251. The protein composition and structural organisation of the network enables some chemical groups to remain free, which means that they are sites of potential interactions with permeating molecules. Generally for protein-based materials, most free hydrophilic groups are able to interact with water vapour and to permit water transfer phenomena, to the detriment of hydrophobic gas transfers, (e.g., nitrogen, oxygen). 

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