Glycerin-plasticized soy protein films were produced by casting heated alkaline (pH 8.5) protein solutions. Acetic anhydride, succinic anhydride, calcium cations, and formaldehyde were added to the film-forming solutions and their effects on film water solubility (WS), tensile strength (TS), puncture strength (PS), water vapor permeability (WVP), and oxygen permeability (OP) were determined. Acylation with acetic and succinic anhydrides increased film WS without affecting other film properties. Treatment with calcium cations increased TS and PS by 96 and 43%, respectively, but did not change film barrier properties. Formaldehyde resulted in larger than two-fold increases in TS and PS, while reducing WS and WVP. As a trade-off, formaldehyde treated films were more permeable to oxygen.
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Ghorpade et al. (1995) studied this question.