Effect of plasticizer and storage conditions on thermomechanical properties of albumen/tragacanth based bioplastics

• Tragacanth gum in egg white albumen based bioplastics enhances their water uptake.
• Higher glycerol content in albumen based bioplastics increases their water uptake.
• Higher glycerol content results in lower flexural moduli albumen based bioplastics.
• Tensile properties of albumen bioplastics decrease when glycerol content is higher.
• Control of relative humidity promotes water migration in the bioplastic formulation.

The effects of composition of the plasticizer fraction and storage conditions on the physical and thermomechanical properties of egg albumen/tragacanth gum based bioplastics were studied. Thus, glycerol (G) and water (W) were used as plasticizers at different G/W ratios (1:0, 3:1, 1:1, 1:3, 0:1), keeping the biopolymer fraction always at 60% (w/w). Tragacanth gum was included in the formulation for its well-known hydrophilic character, as possible future applications of these bioplastics may be moisture dependent (e.g. modified atmosphere packaging). Moreover, properties of bioplastics stored at room temperature under no control of relative humidity were different of those obtained when bioplastics were equilibrated a 53% relative humidity (RH) atmosphere. This is reflected in the DMTA and tensile tests results, for which water loss in the samples with the highest water contents (1:3, 0:1) involves very significant increases in viscoelastic moduli and tensile strength when equilibrated at 53% RH. Glycerol presence when no RH control was taken promotes water uptake, probably due to an interaction between both plasticizers, which eventually lead to a greater plastic region in the tensile tests.

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