Preparation of Polylactic Acid/Modified Natto Composite Films and Property Evaluation

The polyglutamate-coated natto (PGM-natto) was synthesized in situ by treating bleached natto with methanol by using H₂SO₄ as a catalyst to convert polyglutamic acid (γPGA) on the surface into polyglutamate. The PGM-natto was analyzed with attenuated total reflectance Fourier transform infrared (ATR-FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) techniques to confirm that polyglutamate was on the natto surface and to observe changes in its thermal properties. The PGM-natto flake was compounded with PLA in a twin-screw extruder to obtain PLA/PGM-natto composite masterbatch for further fabrication into films using a cast and sheet extruder. The composite films showed a noticeable increase in mechanical properties. The results showed that the PLA/PGM-natto composite film with 1 wt % PGM-natto had a big improvement in mechanical properties (tensile strength, Young's modulus, and % E at break) by 98%, meaning it became stiffer and more flexible because of the good bonding and reinforcing particles. Adding more PGM-natto (3 and 5 wt %) led to a gradual decline in the mechanical properties because of a common issue with how the particles are distributable when there is too much added. Additionally, the modification of surface and bulk hydrophilicity enhanced the printability and oxygen barrier performance of the acrylic inks. These properties are required in the field of active and environmentally friendly packing applications.