Characterization of the morphology and thermal properties of Zein Prolamine nanostructures obtained by electrospinning

Abstract

Zein is a "yellowish" colored maize storage prolamine that shows great interest in a number of industrial applications such as food, food coating and food packaging. Nanofibers generated by electrospinning from solution exhibit an array of unique features and properties that distinguish them from other 1-D nanostructures fabricated using other nanotechnology techniques. This paper presents a complete study reporting on the effect of changing a number of unprecedented process parameters such as polymer concentration, solvent content, flow-rate, applied voltage, needle tip-to-collector distance and pH in order to control fiber size and end morphology. The results indicated that modifying the process parameters led to "white" colored zein fiber networks with fiber diameters ranging from less than a 100 nm (smaller nanometric morphologies ever reported for zein) to above 1 μm. Sample morphologies as determined by SEM and AFM tended to exhibit tubular-like shapes but more complex fiber morphologies such as nanobeads were also observed. Acidifying the alcohol zein solution yielded ribbon like morphologies which exhibited higher glass transition temperature than zein fibers obtained from pure alcohol solutions. On the contrary, alkaline solutions of zein yielded low solution viscosity and hence a faulty electrospinning experience. Fiber networks were seen to have increased thermal properties compared to solvent cast films due to probably their particular molecular structure and a high solvent removing efficiency. Finally, ATR-FTIR spectroscopy nicely showed that the zein secondary structure, particularly the α-helix length, is different depending on the electrospinning conditions applied and that this must influence the observed end properties of the protein fiber networks. © 2007 Elsevier Ltd. All rights reserved.