Abstract
In the present study the effects of the addition of montmorillonite (MMT) nanoplatelets on whey protein isolate (WPI)-based nanocomposite films and coatings were investigated. The main objective was the development of WPI-based MMT-nanocomposites with enhanced barrier and mechanical properties. WPI-based nanocomposite cast-films and coatings were prepared by dispersing 0 % (reference sample), 3 %, 6 %, 9 % (w/w protein) MMT, or, depending on the protein concentration, also 12 % and 15 % (w/w protein) MMT into native WPI-based dispersions, followed by subsequent denaturation during the drying and curing process. The natural MMT nanofillers could be randomly dispersed into film-forming WPI-based nanodispersions, displaying good compatibility with the hydrophilic biopolymer matrix. As a result, by addition of 15 % (w/w protein) MMT into 10 % (w/w dispersion) WPI-based cast-films or coatings, the oxygen permeability (OP) was reduced by 91 % for glycerol-plasticized and 84 % for sorbitol-plasticized coatings, water vapor transmission rate (WVTR) was reduced by 58 % for sorbitol-plasticized cast-films. Due to the addition of MMT- nanofillers the Young’s modulus and tensile strength improved by 315 % and 129 %, respectively, whereas elongation at break declined by 77 % for glycerol-plasticized cast-films. In addition, comparison of plasticizer type revealed that sorbitol-plasticized cast-films were generally stiffer and stronger, but less flexible compared glycerol-plasticized cast-films. Viscosity measurements demonstrated good processability and suitability for up-scaled industrial processes of native WPI-based nanocomposite dispersions, even at high nanofiller-loadings. These results suggest that the addition of natural MMT- nanofillers into native WPI-based matrices to form nanocomposite films and coatings holds great potential to replace well-established, fossil-based packaging materials for at least certain applications such as oxygen barriers as part of multilayer flexible packaging films.
Highlights
Edible films and coatings based on whey proteins show great potential to replace fossil-based plastics in certain applications, e.g., for oxygen-sensitive products, making whey proteins one of the most promising biopolymers in the field of packaging
The application of nanocomposites, which has proved to be a suitable strategy to overcome drawbacks derived from the neat polymeric matrix in the area of synthetic polymers in recent years (Giannelis, 1996; Sinha Ray and Okamoto, 2003; Kim et al, 2010; Huang et al, 2015), has led to considerable interest in nanocomposites based on biopolymer matrices (Alexandre and Dubois, 2000; Sorrentino et al, 2007; Paul and Robeson, 2008; Mittal, 2009)
Occurring inorganic MMT nanoplatelets were successfully dispersed in whey protein isolate (WPI)-based matrices
Summary
Edible films and coatings based on whey proteins show great potential to replace fossil-based plastics in certain applications, e.g., for oxygen-sensitive products, making whey proteins one of the most promising biopolymers in the field of packaging. Among the most commonly used layered silicates is natural montmorillonite (MMT) nanoplatelets (Alexandre and Dubois, 2000; Dean et al, 2007; Almasi et al, 2010), as they are commercially available at relatively low cost, environmentally friendly, and approved for food packaging applications (Sorrentino et al, 2007) They are plate-like nanoparticles with physical dimensions of about 100 nm in diameter and 1 nm in thickness (Paul and Robeson, 2008; Mittal, 2009). A higher degree of filler exfoliation is more likely to be achieved, which likewise leads to larger interfacial regions between the matrix and the nanofiller (Arora and Padua, 2010)
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