Submitted to: Polymer Degradation and Stability
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2012
Publication Date: 12/27/2012
Citation: Selling, G.W., Utt, K.D. 2012. Effect of multiple extrusion passes on zein. Polymer Degradation and Stability. 98(1):184-189.
Interpretive Summary: This research examines how zein, the major protein in corn (a potential major co-product of bioethanol production), is affected by recycling through an extruder. Traditional plastics are produced using extruders. Extrusion processing utilizes high temperatures and high mixing to provide the desired product. This production technique provides relatively low equipment cost, high throughput and low chemical waste. The ability to process zein on an extruder is very important to allow zein to take the place of petroleum based materials. There is some information on how to process zein on an extruder, but there still is much to learn. One of the attractive benefits of extrusion processing of traditional plastics (e.g. polyethylene) is the ability to recycle the plastic in order to make useful products. The impact that recycling has on zein is not known. To study this, zein was processed on an extruder so that it was passed up to seven times through it. It was found that while measurable changes do occur, they are relatively small. In applications where physical properties, such as strength, are most important zein is very amenable to recycling through an extruder. This information will be beneficial to manufacturers involved in the production of ethanol from corn as well as those companies interested in producing biobased (zein) articles using extrusion processing.
Technical Abstract: Zein was repeatedly processed up to seven times using a single screw extruder at a temperature of 145 °C and at approximately 15 grams per minute to determine the extent of degradation that occurs with multiple extrusion passes. SDS-PAGE shows that with the second pass, and each additional pass, the amount of high molecular weight material increases. Given that a reducing agent cleaves most of these branches, then these cross-links are predominantly due to disulfide bond formation. Examination of the secondary structure of the protein using far-UV CD illustrated that after the third pass there was a significant reduction in the amount of alpha-helix and beta-sheet content. Examining the near-UV CD spectra, which reflects changes in protein tertiary structure, illustrates significant changes in structure after the first and second pass through the extruder. IR and NMR spectroscopy displayed little differences with multiple passes through the extruder. Examining color using the delta epsilon scale, displays a change in color after four extrusion passes. The physical properties are very similar with statistical differences being observed only in modulus. While some changes in zein properties can be observed with multiple extrusion passes, if physical properties are of the highest importance, than zein can be processed at least seven times and still provide a quality material.