Eco-friendly fabrication and characterization of mechanically strong, thermally stable, largely impermeable and biodegradable Zein-Graphene Oxide Nanocomposites

摘要

Synthetic polymers are polluting the environment at an alarming rate. It has been reported that the “Great pacific ocean garbage patch”, which was twice the size of Texas [1], is now thrice the size of France and consists of 79,000 tons of plastic waste [2]. As an eco-friendly alternative, natural polymers have received tremendous attention, due to their nontoxicity, biodegradability, biocompatibility, low cost, non-dependence on petroleum sources, and availability from renewable resources. Zein, the most abundant protein of corn, is a byproduct of ethanol production and is one of the most commonly used plant-based proteins. Due to its unique hydrophobic film forming properties, low cost, abundance and lack of essential amino acids for human consumption, zein is often used in non-food applications [3]. Zein has found application in drug delivery [4-6], coating material for tablets, nanoparticles and nanofibers [7, 8], high strength adhesives [9] and packaging materials [10, 11]. Typically standalone zein proteins often require some chemical or physical modifications, like addition of plasticizers, crosslinker or reinforcing nanofillers to have comparable properties to those of synthetic polymers [10-12]. The objectives of this study were to successfully fabricate zein-graphene oxide (Z-GO) nanocomposite films and characterize the obtained product, for offering an in-depth insight regarding the effect of graphene oxide (GO) nanofiller in the mechanical, thermal, barrier and surface properties of zein. Graphene oxide (GO), is a reinforcing nanomaterial made of single or few layers of carbon atoms, that has reportedly increased mechanical, thermal, barrier, electrical properties of different plant based biopolymers [13]. GO nanosheets were prepared using Tour’s method. Z- GO nanocomposites were fabricated using solvent casting technique, by applying GO in concentrations of 0%, 1%, 3%, and 5%, where 70% ethanol was used as a solvent, oleic acid used as a plasticizer and monoglyceride as an emulsifier. The prepared GO nanosheets and the Z-GO nanocomposite films were characterized using TEM, AFM, FT-Raman, FTIR, TGA, as well as mechanical property and water vapor permeability measurements. The TEM of the prepared GO nanosheets showed wrinkled morphology, which resembles crumpled silk veil waves [14] and the transparency of the GO sheets indicated exfoliation to few layer structured graphene material. This effect resulted in obtaining higher surface area and further increased the possibility of achieving good biopolymer/filler interface.