Development of bio-nanocomposite films with enhanced mechanical and barrier properties using extrusion processing

Recently, a new class of materials represented by bio-nanocomposites (biopolymer matrix reinforced with nanoparticles) has proven to be a promising option in improving mechanical and barrier properties of biopolymers derived from renewable sources. Therefore, the current study was undertaken with the main objective of developing bio-nanocomposite films based on soy protein isolate (SPI) and montmorillonite (MMT) with enhanced mechanical and barrier properties by melt intercalation using extrusion processing. Effects of extrusion processing parameters (screw speed and barrel temperature distribution) and type (natural and modified) and content (0--15%) of MMT on the structure (degree of intercalation and exfoliation) and properties (mechanical, dynamic mechanical, thermal stability, and water vapor permeability) of SPI-MMT bio-nanocomposites were studied.;The arrangement of MMT in the bio-nanocomposite matrix ranged from exfoliated to intercalated depending on the type (natural and modified) and content of MMT. The results showed that extrusion of SPI and MMTs resulted in bio-nanocomposites with exfoliated structures at lower MMT content (5%) for natural (Cloisite Na+) as well as modified MMTs (Cloisite 20A and Cloisite 30B). At higher MMT content (15%), structure of bio-nanocomposites ranged from intercalated for Cloisite Na+ and Cloisite 20A to disordered intercalated for Cloisite 30B.;Higher screw speed and barrel temperature resulted in films with improved mechanical and dynamic mechanical properties. Higher screw speed also resulted in films with lower water vapor permeability (WVP). However, the effect of barrel temperature distribution on WVP was insignificant. There was a significant improvement in mechanical and dynamic mechanical properties, thermal stability, and WVP of the films with the addition of natural and modified MMTs. At a MMT content of 5%, bio-nanocomposite films based on modified MMTs had better mechanical, dynamic mechanical, and water barrier properties as compared to those based on natural MMT. However, films based on modified MMTs were thermally less stable at temperatures higher than 500°C as compared to films based on natural MMT.;This study shows the potential of films based on SPI and Cloisite 30B to replace some of the existing plastics such as LDPE and PVDC. However, much higher WVP values of these films as compared to those of LDPE and PVDC might limit the application of these bio-nanocomposite films to packaging of high moisture foods such as fresh fruits and vegetables. Further research is required to improve the properties of these SPI-MMT bio-nanocomposite films for commercial application.