(59h) A Facile Approach to Fabrication and Characterization of an Eco-Friendly Zein-Laponite Nanocomposite with Improved Mechanical, Thermal, Barrier and Surface Property

Tahrima B. Rouf, Jozef L. Kokini
Department of Food Science, Purdue University, West Lafayette, IN-47907

Email: trouf@purdue.edu

Zein, a major by-product of ethanol production from maize, is a bio-renewable resource, with unique amphiphilic and film forming properties [1]. It has been extensively investigated as one of the excellent candidates for eco-friendly polymers for several applications [2–4]. It has the ability to change its conformation and physical properties from flexible films to providing tough, glossy, and hydrophobic materials [5, 6]. Since it was first commercialized [7], zein was the material of interest in several industries including adhesives, coatings, printings, fibers, and packaging films and plastics [5]. However, the brittleness of the standalone zein film requires it to be functionalized with different additives like plasticizers and filler agents [3, 8, 9]. The objective of this study was to functionalize zein, by using a, synthetic layered silicate nanoclay called laponite and characterize the resulting product, for providing an understanding of the effect of laponite nanofiller in the mechanical, thermal, barrier and surface properties of the biopolymer.

Investigated zein biopolymer was functionalized with 1%, 3%, 5 wt% and 10% laponite nanoclay using solvent casting method, where 70% ethanol was used as a solvent and glycerol as a plasticizer. The dispersion of layered laponite nanoparticles in zein matrix was examined using Transmission Electron microscopy (TEM), which showed that up to 5% addition of laponite, some intercalation and exfoliation of the nanofiller was visible, but at 10% loading some aggregates started to form. The surface properties of the zein-laponite nanocomposite films were examined using atomic force microscopy (AFM) and water contact angle measurement (WCA). AFM results showed that zein-laponite nanocomposites had reduced surface roughness compared to control zein films, which could be attributed to the uniform dispersion of laponite throughout zein matrix. The WCA measurements showed that addition of laponite did not significantly change the hydrophobic properties of zein. Chemistry of bond formation in zein-laponite nanocomposite was investigated using, Fourier transform infrared spectroscopy (FTIR). FTIR spectra of pristine laponite shows characteristic peaks at 3649 cm^-1 (attributed to the -OH stretch of the lattice hydroxyl groups), 3450 cm^-1 (attributed to OH stretching from free H₂0), 1636cm^-1 (OH bending) and 1011 cm^-1 (attributed to Si-O stretching)[10]. A comparison of the FTIR spectra of pristine laponite and 5 different zein-laponite nanocomposites show a new peak at 1047cm^-1 for Z-1% Lap, Z-3% Lap, Z-5% Lap and Z-10% is visible, which is very similar to characteristic laponite peak at 1011 cm^-1 (Si-O). This peak formation and gradual increase in its intensity, with gradual increase in filler concentration indicated that laponite has been distributed uniformly throughout zein matrix. The mechanical properties had been investigated using texture analyzer, which showed significant improvement in the young’s modulus and tensile strength, with increasing filler concentration. Similarly, water vapor permeability tests have shown decrease in permeability with increasing laponite concentration. This means successful filler dispersion throughout the matrix, created a tortuous path which obstructed the escape of water vapor molecules and increased the barrier property. However, Dynamic Scanning Calorimetry (DSC) showed that laponite did not have any effect on the glass transition temperature of zein.

In summary, this research comprises a detailed examination of the effect of nanofillers on the properties of zein biopolymers and aims at providing a complete picture of the properties of nanocomposites, with an ultimate goal to find new application for agro based food grade materials which are environmentally friendly, low-cost, renewable and abundantly available in nature.

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