Studies On The Process And Properties Of Zein Film Made By Extrusion

Corn was the largest and most important agricultural commodity in China. Starch processing was the most important use of corn, the annual output of which exceeded 10 million tons. Zein was extracted from waste of starch processing, and the yield of zein from corn was about 15% of corn, if it can be utilized, the additional value of starch would be increased greatly. Zein was the main protein contented in the corn and account for 60% or more of total endospermic proteins. It was composed of rod-like protein molecules and its molecular weight ranges from 25000Da to 45000Da. Zein had good film forming properties due to the disulfide bonds among protein molecular in zein. Some of its characters have been understood along with relating developments and studies, such as gas-resisting, oil-resisting, fragrance-holding, humidity and degradability. So, it had significant meaning for the byproducts of starch industry.This paper studied the processing of the casting method of producing zein films. The process was: dissolved the zein in 80% aqueous ethanol at 60℃, cast the solution on the OHP films, and dried it in nature environment to form the zein film. After analyzing through the results of the properties of zein film such as mechanical properties, water vapor permeability, water absorption index, air permeability, thermal characteristics and the scanning electron micrographs, the best addition quantity of glycerol was 20%.In this paper, the extruding method was studied to prepare zein film to settle out the problem of unable to realize the production of zein film in industry by the casting method. Properties such as mechanical properties, water resistance and other factors of zein film added with two kinds of plasticizers were studied. The extruded processing of zein films was: the mass ratio of zein/ethanol was 2:1, then added 20% of glycerol, carefully mixed, kneaded the mixture at 75℃for 15min by the kneader, cooled the products of pretreatment to the room temperature, then extruded it to 0.20 m film in single-screw extruder at 40r/min and 40～45℃.The study also found out that the zein which was treated by the higher concentration ethanol solution could improve greatly the water resistant of the zein film extruded. So the concentration of aqueous ethanol which be used in the process was 90%. In addition, it was observed that was the surface morphology of the film uniform by scanning electron microscopy (SEM), and the zein molecules formed a network structure by observation under atom force microscopy (AFM).