Melt reaction of zein with glyoxal to improve tensile strength and reduce solubility

Glyoxal, in the presence of base, has been used to crosslink zein in a melt process involving reaction in a melt state combined with compression molding. The resulting zein articles had improved tensile strength, increasing from 34.3 to 40.6 MPa, when the amount of glyoxal was 6% by zein weight. Reduced solubility in solvents, such as acetic acid, was achieved with glyoxal amounts as low as 1%. Derivitization of zein by glyoxal required the presence of base. As little as 0.00019 mmol of NaOH per gram of zein when using 6% glyoxal gave reduced solubility. Other bases such as KOH and Ca(OH) 2 also gave reduced solubility. However, these bases did not yield improvements in tensile strength. Decreases in melt temperature and processing time caused a corresponding decrease in tensile strength, but had little effect on solubility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008