Synthesis and properties of bioplastics from corn starch and citric acid-epoxidized soybean oil oligomers

Citric acid-epoxidized soybean oil oligomers (CESO) were prepared and utilized to improve the properties of corn starch-based bioplastics. CESO were synthesized by controlling the stoichiometric ratio of acid equivalent weight and epoxy equivalent weight at 3:1. Starch-based bioplastics with satisfactory properties were fabricated through solution casting. Analysis including FTIR, molecular distribution, and polydispersity index validated the ring opening polymerization of ESO and CA. The hydrogen bond and crosslinking interactions between CESO and starch were evidenced by the FTIR. SEM micrographs suggested that CESO exhibited better compatibility with starch than ESO. X-ray diffraction patterns of the bioplastics were changed apparently by CESO due to the crosslinking interaction. Swelling degree and opacity of the bioplastics reduced significantly after the introduction of CESO, while tensile strength increased remarkably from 5.62 to 6.93 MPa (p < 0.05). The bioplastic with 4 wt% CESO revealed the most comprehensive properties. Higher content of CESO (16 wt%) displayed poor interaction with starch and led to deteriorated properties of the bioplastics. The synthesized bioplastics exhibited enormous potential to partially replace petroleum-based plastics for various applications such as packaging.