2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

Zein is a hygroscopic protein and will gain or lose moisture to reach equilibrium with ambient air. Cast films of zein are brittle at room conditions so plasticizers are added to make them more flexible. The amount of water absorbed or lost in the film is known to be affected by the relative humidity of the ambient air. However, little is known about the affect plasticizers have on water absorption in zein films. Zein films were plasticized with either glycerol, triethylene glycol (TEG), dibutyl tartrate (DB), levulinic acid, polyethylene glycol or no plasticizer (NP). Mechanical properties and moisture content (MC) of the films were measured after one week of storage at 3, 20, 50, 70, and 93% relative humidity (RH). There were large differences in the amount of water absorbed by the films, depending on the plasticizer used. At 3% RH, all films contained low amounts of water. Films with NP contained 2.44% water. Films with DB contained 3.1% water, and films with TEG contained 4.8% water. At 50% RH, the absorbed water in the film was 7.1% for NP, 4.6 for DB, and 8.1 for TEG. At high RH the differences were even greater. At 93% RH, the absorbed water in the film was 20.7% for NP, 16% for DB, and 40% for TEG. Films containing levulinic acid absorbed enough water upon storage at 93% RH to liquify. Plasticizers that are hygroscopic themselves tend to enhance film flexibility at low RH, but produce films that are too soft at high RH. For zein to have greater acceptance as films, plasticizers need to be found which don't aggravate the problem of water absorption.