Preparation and characterization of biodegradable cassava starch thin films for potential food packaging applications

Acid hydrolysis is a key chemical treatment process that can significantly improve the functional and structural properties of starch without altering its granular morphology. In this study, the effect of acid hydrolysis on the structural, thermal, and chemical properties of cassava starch was investigated using an optimum concentration of 2.2 M hydrochloric (HCl) acid with varying hydrolysis times (30, 60 and 90 min). The acid hydrolyzed cassava starch was characterized using X-ray diffractometry, 13C nuclear magnetic resonance (13C-NMR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry  (DSC), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. The results of XRD and 13C-NMR studies showed improved relative crystallinity for the films prepared from acid hydrolyzed starch. FTIR and TGA analyses revealed that the moisture absorbance of cassava starch decreased significantly due to acid hydrolysis. The acid hydrolyzed starch granules showed a 32% reduction of moisture content than the native starch granules. The thin films prepared from the acid hydrolyzed films exhibited a maximum of ~ 40% and 20% reduction of water absorption than the native cassava starch films after 2 h and 24 h. The acid hydrolysis significantly impacted the mechanical properties of the films. Enhanced tensile strengths were observed with increasing hydrolysis time, reaching a maximum tensile strength of 5.7 MPa. The acid hydrolyzed films displayed a 23% reduction of elongation compared to the native cassava starch films. Increased tensile strength, lower water absorption, biodegradability, non-toxicity, low cost, and good thermal stability make the acid hydrolyzed cassava starch beneficial for potential food packaging applications.