Effects of different plasticizers on the physicochemical properties of cellulose nanocrystals-reinforced corn starch films

This study reports biodegradable films composed of corn starch and cellulose nanocrystals (CNC) for food packaging applications. The films were developed using 5% (w/w) CNC and three different plasticizers (glycerol, sorbitol, polyethylene glycol (PEG)), the content of which was based on the dry mass of starch. The CNCs were obtained via ultrafine grinding of a suspension containing 5 wt.% microcrystalline cellulose. After producing the starch films by casting, they were subjected to thickness tests, scanning electron microscopy (SEM), contact angle and tensile strength analyses, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, and differential scanning calorimetry. The micrographs showed that all films exhibited surfaces without roughness, pores, or cracks. The thermal tests indicated that the sample containing 40% (w/w) glycerol and 5% (w/w) CNC had a thermal degradation temperature of 237.7 °C, implying greater thermal stability. Mechanical tests showed that compared to the film with 40% (w/w) glycerol, the 50% (w/w) glycerol-incorporated film exhibited a lower tensile strength at break (approximately 3.28 MPa) and an increased B-type crystallinity. Furthermore, it was revealed that the starch films incorporated with 40% (w/w) glycerol and 5% (w/w) CNC had improved properties while preserving their chemical structure. These results indicate that balancing the levels of plasticizers in our corn starch/CNC-based films is crucial for ensuring their optimal performance and stability as packaging materials. (author)