This study developed oil palm trunk starch (OPTS) films using glycerol as a plasticizer at ratios of 10, 20, and 30% (v/w, starch basis), modified with citric acid-epoxidized palm oil (CEPO) oligomers via the solution casting technique to improve mechanical properties and water resistance. FTIR results confirmed that CEPO formed strong intermolecular hydrogen bonds between glycerol and OPTS in the plastic films. The addition of glycerol altered the X-ray diffraction patterns, as indicated by changes in peak intensity and position, which were influenced by CEPO cross-linking.

SEM micrographs showed that higher glycerol content in CEPO resulted in smoother film surfaces. The compatibility between starch and glycerol increased the melting point (Tm) due to good density, while CEPO cross-linking further enhanced Tm. Conversely, the tensile strength and modulus of elasticity of OPTS films with higher glycerol concentrations significantly decreased, from 7.71 to 4.03 MPa and from 42.54 to 34.98 MPa, respectively, while elongation at break increased from 18.07 to 49.37%. The water resistance and biodegradability of the bioplastics improved with increasing glycerol concentration.

This study proposes a simple and effective modification technique using CEPO oligomers and glycerol variations to produce bioplastics with superior and eco-friendly properties.